Therapeutic Cloning

Therapeutic Cloning

The word cloning rings in frightening images of duplicate human beings created of the a person. When 'Dolly the sheep' was cloned in an experiment, it was subject to a lot of public outrage. The process used here was Adult DNA cloning, which is different from therapeutic cloning. In therapeutic cloning there is no sperm fertilization or uterus implantation involved. Thus, a new human being is not created, but rather an organ, a nerve tissue or skin is produced. To help people understand this process better, few therapeutic cloning facts are discussed below.

Therapeutic Cloning Facts

What is Therapeutic Cloning?
Therapeutic cloning is a method through which stem cells are created, but used only for repairing damaged tissues in the parent clone cell. These stem cells can be used to grow alternate varieties of organs such as heart, liver and kidney, which can be transplanted as an exact match. This method can create stem cells which could produce sound nerve cells for patients suffering from Parkinson's or Alzheimer's disease.

The person in search of healthy stem cells will have to offer a non-sperm and non-egg cell, from which the DNA would be taken out. This DNA will contain two replicates of each human chromosome. It will then be introduced into a donor egg, which would have its DNA and nucleus already removed. This process is known as somatic cell nuclear transfer. The newly inserted egg would now behave like it has just been fertilized, and would start to divide to form an embryo. It is from this embryo that stem cells would be taken out and refined to generate the required healthy tissue. Read more in detail on embryonic stem cell research.

Therapeutic Cloning Benefits
In case of successful embryo creation through therapeutic cloning, replacement organs can be produced and a lot of people who are suffering from this condition can be cured. Numerous lives can be saved and people can live longer as well. Several benefits with regards to this include:

* As the organ's DNA exactly matches with the person's, the fear of rejection while transplant vanishes.
* The practice of waiting for a donor to obtain the desired organ would come to a halt as the required organ can be generated at will.
* Unlike an already used organ from a donor, the new one would be brand new and without any problems which could have come with the a used organ.
* Kidney transplants will become easier as the need of a donor who would have to shorten his lifespan will erase.
* There is a possibility that therapeutic cloning can find cures for diseases which cannot be treated otherwise.
* Lives of patients in want of an organ donor will be saved.

Problems With Therapeutic Cloning
It is true that there are tremendous benefits of therapeutic cloning. This however, does not in any way dilute the various hurdles the process has to face before rendering successful. Few therapeutic cloning problems and obstacles are discussed below:

* Research on therapeutic cloning over years has been promising, but adult cells by nature do not have a wide scope of application. Stem cells from embryos have proven to have greater flexibility than adult cells.
* Through the somatic cell nuclear transfer, a new person comes to existence. When stem cells are removed from the embryo, it is killed and many people consider this as murder. Pro-life supporters are therefore in protest of therapeutic cloning.
* There are still a few defects in the process, as a few tests have shown people and animals to develop diseases or tumors post therapeutic cloning. These shortcomings need to be eliminated before approval.
* The major concern regarding therapeutic cloning is, where to get eggs from? To start this process at a wide level, millions of eggs would be needed. Removing eggs from women is painful for them and not practically feasible as well. Thus, efficient ways to produce stem cells need to be discovered before taking therapeutic cloning to the next level.

Human Cloning

Human Cloning

Cloning an organism involves replicating the DNA of that organism in a new organism that, as a result, has the same exact features and characteristics. Human Cloning would mean recreating the person that is being cloned. With the successful cloning of Dolly The Sheep, Human Cloning, long the staple of science fiction, is on the verge of becoming a reality.

How would Human Cloning work?
Human Cloning, if it is ever done, will be carried out by the same method that brought forth Dolly, Reproductive Cloning.

In Reproductive Cloning, the nucleus is removed from a body cell of the organism to be cloned and this nucleus is inserted into an enucleated egg, that is, an egg whose nucleus has previously been removed.

The egg with the new nucleus is then treated to electric or chemical treatment to simulate cell division. The resulting embryo is transferred to a host uterus to develop properly and eventually be given birth to.

The new-born organism will be a replica of the original organism, but not the exact same actually, since it will have DNA derived from both the organism as well as the egg.

Why would Human Cloning be done?
Cloning animals, especially endangered species, is one way of preserving the species from dying out entirely. But why would anyone want to clone human beings? There are enough of us already on the planet without resources enough for the well-being of all of us. So why bother to clone?

Well, one reason is pure scientific research. We've already come a long way. After Dolly, scientists have managed to clone various animals. So cloning humans seems the next logical step and a very important one it would be too.

Cloning humans could also prove a major breakthrough as far as cloning for therapeutic purposes is concerned. Cloning could be used to produce new organs for organ transplants. Since the cloned organ, produced from a body cell of the person needing the transplant, would have the same genetic code, there would be less risk of the body rejecting the new, transplanted organ. Cloning could also be used to treat Cancer, Alzheimer's and Parkinson's Diseases, and host of other illnesses.

Cloning would allow infertile couples to have their own genetic offspring or otherwise normal couples to order designer babies. It could also be used to bring back to life your dead ancestors. So if you want to give birth to your great-great-grandmother, you can. Just as long you managed to preserve some samples of her body cells.

One American couple reportedly is willing to pay $500,000 to clone their dead infant daughter.

And then there are some who would like to clone themselves and thereby achieve eternal life.

Is it ethical to go ahead and clone humans?
Well, sometimes one of a kind is more than one can tolerate. But, on the serious side, many of the leading Scientists involved in cloning research, like Ian Wilmut and Richard Gardner, have expressed serious doubts and ethical dilemmas over the cloning of human beings.

Firstly, reproductive cloning is not yet a fool-proof method. It took 272 attempts before Dolly was produced. This means 272 embryos either failed to develop properly or were discarded as defective. In other cases, if the embryos weren't miscarried, a large percentage of the animals born showed a high degree of abnormality and died quickly or had to be euthanized. Those successfully cloned have showed many health problems and none have lived to a ripe old age so far.

Now, since human beings consider themselves a class apart, obviously many moral problems would arise with treating defective human embryos or new-born, handicapped babies in the very same manner.

There is also no way of predicting what the intelligence level and capabilities of a human clone would be. What would be the psychological and societal implications for it as an individual? What kind of a life or future would it have? Since we don't know, many people consider it unethical to go ahead and clone.

But that argument doesn't hold much water with others. After all, we have no way of knowing exactly what sort of a person a normally conceived embryo will turn out to be either.

Is Human Cloning legally allowed?
Reproductive Cloning of Humans is banned is many countries around the world, including the USA and the UK, and allowed in some. Therapeutic Cloning is allowed to some degree, but there is already a clamor against it from religious and pro-life organizations, many of whom are more acquainted with its theological implications than its theoretical possibilities.

Scientists Post Lower Speed Limit for Cell-Signaling Protein Assembly

Scientists Post Lower Speed Limit for Cell-Signaling Protein Assembly

The apparently random self-assembly of molecular threads into the proteins that make the body work is far less frantic than previously thought, Michigan State University scientists say. That discovery could be a key to help unlock the nature of some diseases.

How proteins spontaneously "fold" from wiggling chains of amino acids into a wide variety of functional -- or malfunctioning -- three-dimensional molecules is one of the biggest mysteries in biochemistry.

"People thought they understood how protein diffusion worked, but now our data suggests they're wrong by a factor of 1,000," MSU physics and astronomy assistant professor Lisa Lapidus said. "Now we can start changing the models -- we've been trying to solve protein folding for 50 years, and now we're advancing our fundamental understanding of what unfolded proteins do before they fold."

The findings were published online by the science journal Proceedings of the National Academy of Sciences. Lapidus was joined in the research by University of Zurich Institute of Physical Chemistry researcher Steven Waldauer, whose recent MSU doctoral dissertation formed the basis of the study, and University of California, Davis, scientist Olgica Bakajin.

Proteins, which do most of the work in the body's cells, are chain molecules composed of amino acids. The order in which the amino acids are assembled was charted by the Human Genome Project, but the function of the protein depends on its shape, and how a protein folds is not yet understood. Much of the process is random and diffusive, like sugar moving through an unstirred cup of coffee.

Most proteins can fold in milliseconds, although there are so many possible combinations that left to chance it's physically impossible, scientists agree. So they speculate that there must be built-in folding pathways -- but those remain unproved. Now physics is helping make sense of biology, posting a lower speed limit for proteins as they spontaneously assemble into their lowest-energy, so-called natural state -- like a relaxed spring.

"In order to measure how quickly this random, unfolded state changes confirmations, we had to design an entirely new apparatus as well as design and fabricate a microfluidic chip capable of observing proteins within a fraction of a millisecond after being allowed to refold," Waldauer explained. Two lasers were employed to observe the formation of the immunoglobulin proteins.

"We found that the nature of the unfolded state is far from intuitive and that a protein will change from one random conformation to another much more slowly than previously thought," he said.

Scientists know that errors can occur in folding, and these are associated with a variety of diseases including Alzheimer's, ALS, cystic fibrosis and diabetes. Lapidus and colleagues speculate that the rate of the process could influence the outcome. Proteins that wiggle more rapidly, for example, may be more prone to sticking together and causing plaques such as those in Alzheimer's. The team's discovery may lead to new therapeutic strategies for this class of diseases.

"I believe this measurement of intramolecular diffusion is something that will be crucial for any subsequent studies of protein folding or mis-folding," Lapidus said.

RNA Offers a Safer Way to Reprogram Cells

RNA Offers a Safer Way to Reprogram Cells

In recent years, scientists have shown that they can reprogram human skin cells to an immature state that allows the cells to become any type of cell. This ability, known as pluripotency, holds the promise of treating diseases such as diabetes and Parkinson's disease by transforming the patients' own cells into replacements for the nonfunctioning tissue.

However, the techniques now used to transform cells pose some serious safety hazards. To deliver the genes necessary to reprogram cells to a pluripotent state, scientists use viruses carrying DNA, which then becomes integrated into the cell's own DNA. But this so-called DNA-based reprogramming carries the risk of disrupting the cell's genome and leading it to become cancerous.

Now, for the first time, MIT researchers have shown that they can deliver those same reprogramming genes using RNA, the genetic material that normally ferries instructions from DNA to the cell's protein-making machinery. This method could prove much safer than DNA-based reprogramming, say the researchers, Associate Professor of Electrical and Biological Engineering Mehmet Fatih Yanik and electrical engineering graduate student Matthew Angel.

Yanik and Angel describe the method, also the subject of Angel's master's thesis, in the July 23 issue of the journal PLoS ONE.

However, the researchers say they cannot yet claim to have reprogrammed the cells into a pluripotent state. To prove that, they would need to grow the cells in the lab for a longer period of time and study their ability to develop into other cell types -- a process now underway in their lab. Their key achievement is demonstrating that the genes necessary for reprogramming can be delivered with RNA.

"Before this, nobody had a way to transfect cells multiple times with protein-encoding RNA," says Yanik. (Transfection is the process of introducing DNA or RNA into a cell without using viruses to deliver them.)

In 2006, researchers at Kyoto University showed they could reprogram mouse skin cells into a pluripotent, embryonic-like state with just four genes. More recently, other scientists have achieved the same result in human cells by delivering the proteins encoded by those genes directly into mature cells, but that process is more expensive, inefficient and time-consuming than reprogramming with DNA.

Yanik and Angel decided to pursue a new alternative by transfecting cells with messenger RNA (mRNA), a short-lived molecule that carries genetic instructions copied from DNA.

However, they found that RNA transfection poses a significant challenge: When added to mature human skin cells, mRNA provokes an immune response meant to defend against viruses made of RNA. Repeated exposure to long strands of RNA leads cells to undergo cell suicide, sacrificing themselves to help prevent the rest of the body from being infected.

Yanik and Angel knew that some RNA viruses, including hepatitis C, can successfully suppress that defensive response. After reviewing studies of hepatitis C's evasive mechanisms, they did experiments showing they could shut off the response by delivering short interfering RNA (siRNA) that blocks production of several proteins key to the response.

Once the defense mechanism is shut off, mRNA carrying the genes for cell reprogramming can be safely delivered. The researchers showed that they could induce cells to produce the reprogramming proteins for more than a week, by delivering siRNA and mRNA every other day.

Key Step in Body's Ability to Make Red Blood Cells Discovered

Key Step in Body's Ability to Make Red Blood Cells Discovered

Researchers at UT Southwestern Medical Center have uncovered a key step in the creation of new red blood cells in an animal study.

They found that a tiny fragment of ribonucleic acid (RNA), a chemical cousin of DNA, prompts stem cells to mature into red blood cells. The researchers also created an artificial RNA inhibitor to block this process.

Such interventions, if fruitful in humans, might be useful against some cancers and other diseases, such as polycythemia vera, in which the body produces a life-threatening excess of blood cells. Conversely, a drug that boosts red blood cell production might be useful against anemia, blood loss or altitude sickness.

"The important finding is that this microRNA, miR-451, is a powerful natural regulator of red blood cell production," said Dr. Eric Olson, chairman of molecular biology at UT Southwestern and senior author of the study, which appears in the Aug. 1 issue of Genes & Development.

"We also showed that a man-made miR-451 inhibitor can reduce miR-451 levels in a mouse and block blood-cell production. We hope that this inhibitor and similarly functioning molecules might lead to new drugs against the fatal disease polycythemia vera, which currently has no therapies," said Dr. Olson, who directs the Nancy B. and Jake L. Hamon Center for Basic Research in Cancer and the Nearburg Family Center for Basic and Clinical Research in Pediatric Oncology.

Red blood cells, which carry oxygen throughout the body, are created in bone marrow from stem cells. The body steps up its production of red blood cells in response to stresses such as anemia, blood loss or low oxygen, but overproduction of the cells increases the risk of stroke and blood clots.

RNA molecules, found throughout cells, perform several jobs. MicroRNAs often bind to and disable other types of RNA, preventing them from carrying out their functions.

Dr. Olson and his colleagues study many different types of microRNAs to determine their functions and to find therapeutic uses of artificial microRNAs.

"miR-451 is found in great abundance in mature red blood cells, but its function was not known," said lead author David Patrick, a graduate student in molecular biology.

In the new study, the scientists created genetically engineered mice that could not make miR-451. The mice had a lowered red blood cell count and also had difficulty creating more red blood cells under conditions that usually stimulate production.

miR-451 works by interacting with another RNA involved in producing a protein called 14-3-3-zeta, which plays a role in the maturation of many types of cells, the researchers found.

The team also treated blood stem cells with an artificial RNA designed to inhibit miR-451. As a result, the number of red blood cells decreased.

Dr. Olson and his colleagues are pursuing a patent on miR-451 inhibitors and studying whether a microRNA-based drug might be useful in treating several blood-related disorders.

Other UT Southwestern researchers involved in the study were Dr. Cheng Zhang, assistant professor of physiology and developmental biology; Xiaoxia Qi, research scientist in molecular biology; and Dr. Lily Jun-Shen Huang, assistant professor of cell biology. Researchers from Texas A&M Health Science Center, Houston; Texas Heart Institute, Houston; and the University of Houston also participated.

Vascular-Targeted Photodynamic Therapy for Localized Prostate Cancer

Vascular-Targeted Photodynamic Therapy for Localized Prostate Cancer

NYU Langone Medical Center has begun a clinical trial offering vascular-targeted photodynamic therapy to patients with localized prostate cancer. This novel, minimally invasive procedure uses a light-activated drug to deliver light energy waves by way of laser fibers in order to destroy prostate cancer cells.

"This minimally invasive technique for localized prostate cancer offers the potential to destroy the cancer without making any incision or causing any potentially devastating sexual, urinary or reproductive side-effects," said Samir S. Taneja, MD, The James M. Neissa and Janet Riha Neissa Associate Professor of Urologic Oncology and director of the Division of Urologic Oncology at NYU Langone Medical Center and principal investigator for the national, multi-center clinical trial testing this technology. "This procedure only treats the cancerous part of the prostate gland, similar to how a lumpectomy might be done for breast cancer.

Photodynamic therapy is just one of the many personalized treatment options offered by the Smilow Comprehensive Prostate Cancer Center at NYU Langone Medical Center. The Center offers a wide range of the latest treatment options for prostate cancer including: open or robotic prostatectomy surgery, brachytherapy, external beam radiation therapy, cryotherapy and high-intensity focused ultrasound (HIFU), a focal therapy that uses high-energy sound waves to treat prostate cancer, now also in clinical trials at the medical center.

This Phase I/II photodynamic therapy trial is open to men diagnosed with localized prostate cancer -- determined by a needle biopsy and advanced imaging techniques -- who have chosen active surveillance, also known as "watchful-waiting. During the procedure, laser fibers are positioned over the prostate where cancer cells have been identified. Once in place, a photosensitizing drug called WST11 is administered to the patient intravenously and circulates throughout the blood stream for ten-minutes. The laser fibers are then activated to deliver a specific wavelength of light to the prostate for twenty-minutes. When the light comes into contact with the drug in circulation, the laser fibers destroy the blood vessels around the tumor shutting down the blood supply to the cancer. Patients are followed for a year after treatment with PSA tests after each visit and an MRI and needle biopsy performed at six months.

"Focal treatment of prostate cancer with techniques such as photodynamic therapy is an emerging paradigm since the over treatment of prostate cancer is a major concern for both physicians and patients," said Dr. Taneja who is also a member of the NYU Cancer Institute.

Recent European studies show photodynamic therapy successfully treats localized prostate cancer with minimal side effects. This study will investigate optimal dosage of the photosensitive drug and light-energy waves and measure outcomes of patients as well as long-term cancer control. Researchers believe the technology has the potential to treat any early stage prostate cancer as well as tumors in other organs of the body.

Cell-of-Origin for Human Prostate Cancer Identified for First Time

Cell-of-Origin for Human Prostate Cancer Identified for First Time

scientists have identified for the first time a cell-of-origin for human prostate cancer, a discovery that could result in better predictive and diagnostics tools and the development of new and more effective targeted treatments for the disease.

The researchers, from UCLA's Jonsson Comprehensive Cancer Center, proved that basal cells found in benign prostate tissue could become human prostate cancer in mice with suppressed immune systems, a finding that bucks conventional wisdom. It had been widely believed that luminal cells found in the prostate were the culprits behind prostate cancer because the resulting malignancies closely resembled luminal cells, said Dr. Owen Witte, a Jonsson Cancer Center member and director of the UCLA Broad Stem Cell Research Center.

"Certainly the dominant thought is that human prostate cancer arose from the luminal cells because the cancers had more features resembling luminal cells," said Witte, senior author of the study and a Howard Hughes Medical Institute Investigator. "But we were able to start with a basal cell and induce human prostate cancer and now, as we go forward, this gives us a place to look in understanding the sequence of genetic events that initiates prostate cancer and defining the cell signaling pathways that may be at work fueling the malignancy, helping us to potentially uncover new targets for therapy."

The study appears July 30, 2010 in the peer-reviewed journal Science.

The researchers took healthy tissue from prostate biopsies and separated the cells based on their surface marker expression into groups of luminal cells and groups of basal cells. Using viral vectors as vehicles, they then expressed altered genes known to cause cancer into both cell populations and placed the cells in mice to see which developed cancer, said Andrew Goldstein, a UCLA graduate student and first author of the study.

"Because of the widespread belief that luminal cells were the root of human prostate cancer, it would have been those cells examined and targeted to treat the disease," said Goldstein. "This study tells us that basal cells play an important role in the prostate cancer development process and should be an additional focus of targeted therapies."

In normal prostate tissue, basal cells have a more stem cell-like function, Goldstein said, meaning they proliferate more to re-grow human prostate tissue. Luminal cells don't proliferate as much, but rather produce major proteins that are important for reproduction. Something is going awry in the basal cells that results in cancer and Witte and Goldstein plan to study those cells to uncover the mechanisms that result in malignancy.

Currently, there is a dearth of knowledge about how prostate cancer develops to treat it effectively in a targeted way, as Herceptin targets an out-of-control production of growth factor receptors in breast cancer cells. The major targeted therapy used for prostate cancer is directed at the androgen receptor and it is not always effective, Witte said.

The new human-in-mouse model system developed in the study -- created by taking healthy human prostate tissue that will induce cancer once it is placed in mice instead of taking malignant tissue that is already cancerous and implanting it -- can now be used to evaluate the effectiveness of new types of therapeutics. By using defined genetic events to activate specific signaling pathways, researchers can more easily compare therapeutic efficacy. The new model, by deconstructing tissue and then reconstructing it, also will aid in analyzing how the cells change during cancer progression.

"There are very few examples of taking benign cells and turning them into cancer experimentally," Goldstein said. "We usually study cancer cell lines created from malignant tumors. This study resulted in the creation of a novel model system that is highly adaptable, such that we can test any cellular pathway and its interactions with other genes known to induce cancer, and we can start with any type of cell as long as it can be reproducibly purified."

In this system, Witte and Goldstein know the "history" of the cells that became cancer, unlike the cancer cells lines used in other work.

"We know those cells are malignant, but we don't know how they got there," Goldstein said. "By starting with healthy cells and turning them into cancer, we can study the cancer development process. If we understand where the cancer comes from, we may be able to develop better predictive and diagnostic tools. If we had better predictive tools, we could look earlier in the process of cancer development and find markers that are better than the current PSA test at catching disease early, when it is more treatable."

Rising PSA levels can indicate the presence of cancer that is already developing in the prostate. However, now that it is known that basal cells are one root of human prostate cancers, scientists can study pre-malignant basal cells and uncover what they express that the healthy ones don't, perhaps revealing a new marker for early detection, Goldstein said. Also, a therapy directed at the pre-malignant basal cells about to become malignant could provide a way to prevent the cancer before it becomes dangerous.

Adult stem cell

Adult stem cell

Adult stem cells are undifferentiated cells found throughout the body that divide to replenish dying cells and regenerate damaged tissues.

Also known as somatic stem cells, they can be found in children, as well as adults. Research into adult stem cells has been fueled by their abilities to divide or self-renew indefinitely and generate all the cell types of the organ from which they originate — potentially regenerating the entire organ from a few cells.

Unlike embryonic stem cells, the use of adult stem cells in research and therapy is not controversial because the production of adult stem cells does not require the destruction of an embryo.

Adult stem cells can be isolated from a tissue sample obtained from an adult.

They have mainly been studied in humans and model organisms such as mice and rats. The rigorous definition of a stem cell requires that it possesses two properties: Self-renewal - the ability to go through numerous cycles of cell division while maintaining the undifferentiated state. Multipotency or multidifferentiative potential - the ability to generate progeny of several distinct cell types, for example both glial cells and neurons, opposed to unipotency - restriction to a single-cell type.

Some researchers do not consider this property essential and believe that unipotent self-renewing stem cells can exist. Stem Cell Treatments Due to the ability of adult stem cells to be harvested from the patient, their therapeutic potential is the focus of much research.

Adult stem cells, similar to embryonic stem cells, have the ability to differentiate into more than one cell type, but unlike embryonic stem cells they are often restricted to certain lineages.

The ability of a stem cell of one lineage to become another lineage is called transdifferentiation.

Different types of adult stem cells are capable of transdifferentiation more than others, and for many there is no evidence of its occurrence.

Consequently, adult stem therapies require a stem cell source of the specific lineage needed and harvesting and or culturing them up to the numbers required is a challenge. Adult stem cell treatments have been used for many years to treat successfully leukemia and related bone/blood cancers through bone marrow transplants..

Cell Theory & Structure

Cell Theory & Structure
Cell theory has three basic generalizations, according to the University of California at Davis. These generalizations state that all organisms are composed of one or more cells, the cell is the smallest unit that has properties of life, and life continues as a result of division and growth of single cells.
The Facts
Cell theory is often referred to as cell doctrine. The concept that all organisms are made up of similar units called cells was originally formulated by Matthias Jakob Schleiden and Theodor Schwann in 1839. This theory was developed prior to other important theories in biology including Charles Darwin's theory of evolution in 1859.
History
In 1838, Schleiden, a botanist, and Schwann, a zoologist, had a conversation regarding their respective studies of cells. According to Charles Mallery of the Department of Biology, University of Miami, Schwann saw similarities between plant cells that Schleiden discussed and his own observations of animal tissue cells. They proceeded to Schwann's lab and wrote a book about plant and animal cells the following year.
Features
Schwann and Schleiden's conclusions regarding cells stated that cells are a unit of structure, organization and physiology in living things. Furthermore, the cell acts as both a unique entity and as a building block in organism construction, and cells result from free-cell formation that is similar to crystals. Today, biologists know that their first two statements are true, however the third it incorrect. In fact, it was Rudolph Virchow who suggested a more accurate description of cell generation by stating that "all cells only arise from pre-existing cells."
Considerations
While the three generalizations listed in the overview are the core tenets, cell theory has three other statements that add to a more complete picture of cell structure. These tenets state that cells contain hereditary information that passes on from cell to cell during cell division. Furthermore, all cells are considered of the same chemical composition and all energy flow of life (particularly metabolism and biochemical reactions) occur within the cells.
Structure
All cells are considered to have three things in common. Cells have a cell membrane that selects which materials are allowed to pass into and out of the cell. They also have cytoplasm, which is the part of the cell that is enclosed by the cell membrane, and DNA, which is the genetic material of the cell. Furthermore, cells are divided into two types, prokaryotic (simple cells like bacteria) or eukaryotic (more complex cells like plants).

Cell Theory

Cell Theory
The discovery of the cell was made possible by the invention of the microscope, which was made possible by improved lens-grinding techniques. Antoni van Leeuwenhoek (1632-1723), a Dutch tradesman, learned to grind lenses and assemble them into simple microscopes. His contemporary Robert Hooke (1635-1703) used such an instrument to observe cork cells, sketches of which appeared in his 1665 publication "Micrographia." Inspired by Hooke's work, Leeuwenhoek began making microscopic examinations of his own. In 1678, he reported to the Royal Society that he had discovered "little animals" -- bacteria and protozoa -- in various samples. The society asked Hooke to confirm Leeuwenhoek's findings, and he did.
protozoaAaron Bell/Visuals Unlimited/Getty ImagesIn 1678, Antoni van Leeuwenhook reported that he had observed "little animals" -- protozoa -- through a microscope.­
T­his paved the way for wide acceptance that a hidden world existed just beyond the limits of human vision and encouraged many scientists to take up the microscope in their investigations. One such scientist was German botanist Matthias Jakob Schleiden (1804-1881), who looked at numerous plant samples. Schleiden was the first to recognize that all plants, and all the different parts of plants, are composed of cells. While having dinner with zoologist Theodor Schwann (1810-1882), Schleiden mentioned his idea. Schwann, who came to similar conclusions while studying animal tissues, quickly saw the implications of their work. In 1839, he published "Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals," which included the first statement of the cell theory: All living things are made up of cells.
Then, in 1858, Rudolf Virchow (1821-1902) extended the work of Schleiden and Schwann by proposing that all living cells must rise from pre-existing cells. This was a radical idea at the time because most people, scientists included, believed that nonliving matter could spontaneously generate living tissue. The inexplicable appearance of maggots on a piece of meat was often given as evidence to support the concept of spontaneous generation. But a famous scientist by the name of Louis Pasteur (1822-1895) set out to disprove spontaneous generation with a now-classic experiment that both firmly established the cell theory beyond doubt and solidified the basic steps of the modern scientific method.

Brain Anatomy

Brain Anatomy
The cerebellum is the portion of the brain that is responsible for the coordination of movement. It is located just above the brainstem, beneath the occipital lobes at the base of the skull. Similar to the cerebrum, the cerebellum contains several folded bulges which add to its surface area and therefore increases the quantity of information that can be processed.
The cerebellum controls movement by processing and coordinating sensory input, then sending the information to the motor nerves. Whenever we perform a physical task, the cerebellum records the information so that we don't forget it. That is why we don't have to re-learn how to walk, run or ride a bike. Think you know all about the cerebellum and the brain? Take the Human Brain Quiz and test your knowledge of human brain anatomy.

Bacteriophage

Bacteriophage
A bacteriophage (from 'bacteria' and Greek φᾰγεῖν phagein "to eat") is any one of a number of viruses that infect bacteria. Bacteriophages are among the most common biological entities on Earth. The term is commonly used in its shortened form, phage.
Typically, bacteriophages consist of an outer protein capsid enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) long with either circular or linear arrangement. Bacteriophages are much smaller than the bacteria they destroy.
Phages are estimated to be the most widely distributed and diverse entities in the biosphere. Phages are ubiquitous and can be found in all reservoirs populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. They have been used for over 60 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe. They are seen as a possible therapy against multi drug resistant strains of many bacteria.

Diploid

Diploid
The basic set of chromosomes in an organism is called the monoploid number. This number is indicated by x. In an organism, the ploidy of cells can vary. Humans and almost all mammals, have diploid cells. The gametes or sex cells (egg and sperm) are haploid cells. In this article, we shall understand what is a diploid cell. You can read more on biology.
What is a Diploid Cell?
According to the diploid cell definition, it is an organism or cell that contains double set of chromosome (2n), one inherited from the mother and one inherited from father. Another diploid cell definition also includes an individual that contains a double set of chromosome per cell. The somatic tissues of higher plants and animals contain diploid chromosome content.
Almost all animals have diploid number of cells. All the organisms that produce sexually, have two copies of chromosomes that have different origins, that is, paternal and maternal. This help in mixing of genes that gives rise to better progeny.
There are a few species that have haplodiploid cells. Here, one sex (mostly male) contains haploid cells and the other sex (female) has diploid cells. The male have developed from unfertilized eggs and the females develop from fertilized eggs. Thus, they have a complete set of chromosome. The diploid cell example in such a case, includes insects like ants, bees and wasps, where the queen has diploid number of chromosome. You can read more on human genetics.
Another, diploid cell example is the human race. Humans contain 2 set of chromosomes in their cells. The somatic cells or non-sex cells contains 46 chromosomes each. There are 22 sets of autosomal chromosomes and 1 set of sex chromosome. This brings the total to 23 sets of chromosomes. After fertilization, the somatic cells receive 23 chromosomes from each parent making the number of chromosomes in the cell 46.

Lysosome

Lysosome
Structure
The human body comprises of about 50 to 75 trillion cells. The cell is the smallest unit of life and is often called the building block of life. A single cell is made up of many different organelles, that have specific functions, such as the nucleus, Golgi bodies, mitochondria, peroxisomes and lysosomes. In this article, we shall learn about lysosome structure, its function and its importance in the cell.
Lysosomes
Lysosomes are membrane bound organelles that are found in the cytoplasm of both plant and animal cells. The word lysosome was derived from two Greek words, 'lysis' which means destruction or dissolution and 'soma' which means 'body'. Lysosomes were discovered in 1949, by a Belgian cytologist, Christian de Duve.
Lysosome StructureLysosomes are actually membranous sacs filled with enzymes. They are found in all eukaryotic cells and act as 'garbage disposal' or the 'digester' of the cell. Lysosomes are spherical bag like structures that are bound by a single layer membrane, however, the lysosome shape and size may vary to some extent in different organisms. The lysosome size ranges between 0.1 to 1.2μm. The membrane that surrounds the lysosome, protects the rest of the cell from the hydrolytic or digestive enzymes that are contained in the lysosomes.
Lysosomes are manufactured by the Golgi apparatus, by budding, in the cell and the various digestive enzymes, that are present in the lysosomes are produced in the endoplasmic reticulum. These enzymes are then transported to the Golgi apparatus and are distributed to the lysosomes. Some examples of enzymes present in the lysosomes include nucleases, proteases, lipases and carbohydrases. These enzymes are used to dissolve nucleic acids, proteins, lipids and carbohydrates, respectively. All these enzymes are typically hydrolytic and can digest cellular macromolecules. Lysosomes are acidic, with a pH of 4.8. This acidic pH is maintained by pumping protons, from the cytosol that has a pH of 7.2. The protons are pumped across the membrane via proton pumps and chloride ion channels. The membrane thus acts as a protective barrier, that protects the cytosol and the rest of the cell from the hydrolytic enzymes within the lysosome.
Lysosome Function
Lysosomes act as disposal system of the cell. They break down complex proteins, carbohydrates, lipids and other macromolecules into simpler compounds. These simple compounds are returned to the cytoplasm and are used as new cell building materials. They are used for digestion of cellular waste products, dead cells or extracellular material such as foreign invading microbes, that pose a threat to the cell by phagocytosis process. However, phagocytosis is just one process that helps to get rid of unwanted material in the cell. Lysosomes are also involved in other digestive processes including endocytosis and autophagy. Another interesting function of the lysosomes is to repair the damage to the plasma membrane. They serve as membrane patch and help in sealing the wound in the plasma membrane. Lysosomes are also involved in programmed cell death, or autolysis, which is a catabolic process involving degradation of the cell's own components. This is the reason why lysosomes are often called as 'suicide sacs'. Read more on lysosomes function.
Lysosome Defects
Any malfunctioning of the lysosomes or any of the digestive proteins, results in lysosomal storage diseases, such as Tay-Sachs disease and Pompe's disease. These diseases are caused by defective function of the lysosomes or in absence of any of the digestive proteins or lysosomal hydrolytic enzymes.

Animal Cell

Animal Cell
Animal Cell ModelAs the name signifies, an animal cell is an advanced, eukaryotic type of cell isolated from animal species. If you have learned plant and animal cell differences, you might be already aware that the latter type is nearly circular in shape. An animal cell lacks the protective cell wall, hence the shape of the cell is framed by a plasma membrane. Inside the cell, there are various membrane bound organelles, each of which is responsible for specific functions.
Topics concerning plant cell vs animal cell and their similarities are introductory chapters in science subjects. They provide information about the types and functions of cells. However, demonstrating cell models is a better way to understand the lessons precisely and also, in an interactive manner. Thus, in biology experiments, students are often given assignments to prepare an animal cell model or diagram.
How to Make an Animal Cell Model?
Before you get involved in making an animal cell model, try to understand the anatomy and parts of a typical eukaryotic cell. A better alternative is to examine the shapes and structures of the organelles in a labeled animal cell diagram. This will help you in coming up with innovative ideas for your project. With a little creativity and forethought, you can prepare an animal cell model with less effort.
Following is a step by step procedure for building a labeled animal cell model:
Required Materials and Supplies
* Colorful animal cell picture
* Styrofoam balls
* Playdough (or modeling clay)
* Cardboard for base
* Pipe cleaners
* T - Pins
* Duct tape or regular tape
* Glue or adhesive
* Ruler
* Box cutter
* Knife and scissors
Steps for Building an Animal Cell
Step # 1
Gather the required supplies for building an animal cell model. Select a large and detailed animal cell picture with colorful parts. For the cell nucleus part, you can purchase a small ball or Styrofoam block from the garden supplier. You can make remaining cell organelles from this block or playdough.
Step # 2
It is better to make the individual organelles before and stick to the cardboard base with adhesive pr pins. Otherwise, working directly on the model will make the job more tedious and messy. Accordingly, prepare a list of the cell parts, which you are supposed to build. Remember to make appropriate sized organelles with respect to the model size.
Step # 3
Lay the cardboard base and start building an animal cell model. To create plasma membrane, you can use a large rubber band or paint with a brush. Then, stick the nucleus (round plastic ball or Styrofoam ball) in the center with the help of duct tape or glue. For chromatin structures, you can use pipe cleaners in a random manner.
Step # 4
Cut out different shapes of Styrofoam that resemble cell organelles and color each of them with different shades. With reference to the labeled animal cell diagram, attach the colored pieces to the cardboard one by one, making sure that they occupy the correct positions in the animal cell model.
Step # 5
For better understanding, prepare a key on a paper sheet and illustrate the various cell parts. Ensure that the spellings are correct and if possible, explain their main functions in one or two lines. Finally, document the steps of making animal cell model, especially if you are presenting in a science fair project.
So, isn't making animal cell model interesting? After completion of the task, you will be familiar with the functions of the organelles. You can look out for different animal cell model ideas and choose the best for your project. Be accurate with the cell shape, structure and organelles to get good scores. Next time, learn about plant cell structure and parts and portray your understandings by building a plant cell model.

Angiosperms and Gymnosperms

Angiosperms and Gymnosperms
The seed bearing plants are broadly divided into a single class known as Sprematophyta, which is further sub-divided into angiosperms and gymnosperms. The word gymnosperm is derived from Greek word gymnospermos, meaning 'naked seed'. Angiosperms and gymnosperms are both seed bearing plants. Although, differences are more distinct, the points mentioned below are some of the similarities between them.
* They are capable of producing pollen for fertilization and their fertilization is siphonogamous, i.e through a pollen tube. Gymnosperms mostly depend on wind pollination and some angiosperms are also dependent on the same agent.
* The sporophyte of angiosperms and gymnosperm is differentiated into root, stem and leaves. * Apart from primary growth, their stem undergoes expansion by secondary growth.
* Like angiosperms, gymnosperms also have vessels and companion cells. The vascular system is common for the both of them consisting of conjoint and vascular bundles (open and collateral).
* Ovules of angiosperms and gymnosperms develop into seeds. The mode of seed germination is epigeal and hypogeal or both.
* One distinct similarity is, reduced gametophytic phase of both angiosperms and gymnosperms.
* Polyembryony, a common feature of gymnosperms is also prevalent in some angiosperms and a suspensor is formed during the embryo development phase.

Kingston Computing Expert Charts Amputees' Rehabilitation

Kingston Computing Expert Charts Amputees' Rehabilitation

New Kingston University research could reduce the recovery time for lower limb amputees by helping health professionals chart patients' progress more easily. Tom Geake, from Kingston's Mobile Information and Network Technologies Research Centre, has designed a new method of interpreting results from the locomotor capabilities index, used by clinicians to assess amputees' improvement in the four-week period after they have been fitted with a socket and artificial limb.
Using the index, amputees are set goals at the start of their rehabilitation programme which are later reviewed to see how much progress has been made. Patients are assessed on 14 activities, ranging from basic tasks such as rising from a chair to more advanced tasks such as walking outside on uneven ground. Their capability is recorded on a scale of 0-3. Until now there had been no simple method for therapists to analyse the data gathered, Mr Geake said. His research has produced a new system using colour and shape on patients' charts to improve the process. "Time is scarce in the NHS, so the faster a clinician can assess a person's rehabilitation the better," Mr Geake said. "Rather than having to think about what each figure tells them, the system allows the therapist to see at a glance which goals have been reached from the colour and shape they see on the chart. They can draw conclusions more easily about the patient's progress and, if necessary, suggest changes to their individual recovery programme." Another advantage is that patients can also understand the contents. "Seeing which activities they need to concentrate on to achieve their goals helps them become more motivated - a key factor in their rehabilitation," Mr Geake said.
The research was commissioned by Dr Rajiv Hanspal, a consultant in rehabilitation medicine at the Royal National Orthopaedic Hospital. Dr Hanspal's colleague, senior physiotherapist Jennifer Fulton, and Dr David Wertheim from the University's School of Computing and Information Systems were also involved in the project.
Mr Geake presented the research at the National Scientific Meeting of the International Society for Prosthetics and Orthotics, where he was awarded the British Limbless Ex-Servicemen's Association prize. He is due to outline his findings to NHS representatives with a view to further trials of the system.

Beyond genes: Mapping the “brave new world” of the epigenome

With the human genome — the “Book of Life” — in hand, scientists are trying to fill the pages of an anthology of closely related volumes that explain how simple chemical modifications to DNA and its packaging proteins turn genes on and off in ways that impact human health. Those companion tomes involve the human “epigenome,” the topic of the cover story in the current issue of Chemical & Engineering News, ACS’ weekly newsmagazine.
C&EN contributing editor Laura Cassiday notes in the article that the basic DNA sequence in the genome remains relatively constant throughout a person’s life. Epigenomic changes, however, can cause dramatic alterations how genes work without altering the underlying gene sequence. Studies link some of those changes to aging, cancer, certain birth defects, autoimmune diseases and other health problems.
The article describes ongoing epigenomics research and notes that the field is getting a boost from the National Institutes of Health Roadmap Epigenomics Program. It will fund more than $190 million in research over the next five years to support development of new technologies for mapping the epigenome. “With a brave new world awaiting exploration beyond the genome, it’s not surprising that epigenetics has risen from near obscurity to one of the hottest fields in biology,” the article notes.

DNA

DNA

(DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.
Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts.[1] In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.
Deoxyribonucleic (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.
Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.
Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

Types of RNA

Types of RNA
Messenger RNA (mRNA) is the RNA that carries information from DNA to the ribosome, the sites of protein synthesis (translation) in the cell. The coding sequence of the mRNA determines the amino acid sequence in the protein that is produced. Many RNAs do not code for protein however (about 97% of the transcriptional output is non-protein-coding in eukaryotes ).
These so-called non-coding RNAs ("ncRNA") can be encoded by their own genes (RNA genes), but can also derive from mRNA introns. The most prominent examples of non-coding RNAs are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation. There are also non-coding RNAs involved in gene regulation, RNA processing and other roles. Certain RNAs are able to catalyse chemical reactions such as cutting and ligating other RNA molecules, and the catalysis of peptide bond formation in the ribosome;[3] these are known as ribozymes
Messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell. It is coded so that every three nucleotides (a codon) correspond to one amino acid. In eukaryotic cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it is processed to mature mRNA. This removes its introns—non-coding sections of the pre-mRNA. The mRNA is then exported from the nucleus to the cytoplasm, where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After a certain amount of time the message degrades into its component nucleotides with the assistance of ribonucleases.
Transfer RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time. rRNA is extremely abundant and makes up 80% of the 10 mg/ml RNA found in a typical eukaryotic cytoplasm.
Transfer-messenger RNA (tmRNA) is found in many bacteria and plastids. It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling.

Regulatory RNAs
Several types of RNA can downregulate gene expression by being complementary to a part of an mRNA or a gene's DNA. MicroRNAs (miRNA; 21-22 nt) are found in eukaryotes and act through RNA interference (RNAi), where an effector complex of miRNA and enzymes can break down mRNA which the miRNA is complementary to, block the mRNA from being translated, or accelerate its degradation. While small interfering RNAs (siRNA; 20-25 nt) are often produced by breakdown of viral RNA, there are also endogenous sources of siRNAs. siRNAs act through RNA interference in a fashion similar to miRNAs. Some miRNAs and siRNAs can cause genes they target to be methylated, thereby decreasing or increasing transcription of those genes. Animals have Piwi-interacting RNAs (piRNA; 29-30 nt) which are active in germline cells and are thought to be a defense against transposons and play a role in gametogenesis. Many prokaryotes have CRISPR RNAs, a regulatory system similar to RNA interference. Antisense RNAs are widespread; most downregulate a gene, but a few are activators of transcription. One way antisense RNA can act is by binding to an mRNA, forming double-stranded RNA that is enzymatically degraded. There are many long noncoding RNAs that regulate genes in eukaryotes, one such RNA is Xist which coats one X chromosome in female mammals and inactivates it.
An mRNA may contain regulatory elements itself, such as riboswitches, in the 5' untranslated region or 3' untranslated region; these cis-regulatory elements regulate the activity of that mRNA.The untranslated regions can also contain elements that regulate other genes. In RNA processingUridine to pseudouridine is a common RNA modification.
Many RNAs are involved in modifying other RNAs. Introns are spliced out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNA),or the introns can be ribozymes that are spliced by themselves.RNA can also be altered by having its nucleotides modified to other nucleotides than A, C, G and U. In eukaryotes, modifications of RNA nucleotides are generally directed by small nucleolar RNAs (snoRNA; 60-300 nt),found in the nucleolus and cajal bodies. snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA. These enzymes then perform the nucleotide modification. rRNAs and tRNAs are extensively modified, but snRNAs and mRNAs can also be the target of base modification. RNA genomes
Like DNA, RNA can carry genetic information. RNA viruses have genomes composed of RNA, and a variety of proteins encoded by that genome. The viral genome is replicated by some of those proteins, while other proteins protect the genome as the virus particle moves to a new host cell. Viroids are another group of pathogens, but they consist only of RNA, do not encode any protein and are replicated by a host plant cell's polymerase. In reverse transcription
Reverse transcribing viruses replicate their genomes by reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA. Retrotransposons also spread by copying DNA and RNA from one another, and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes. Double-stranded RNA
Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells. dsRNA forms the genetic material of some viruses (double-stranded RNA viruses). Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates.

Comparison with DNA

Comparison with DNA

RNA and DNA are both nucleic acids, but differ in three main ways. First, unlike DNA which is double-stranded, RNA is a single-stranded molecule in most of its biological roles and has a much shorter chain of nucleotides. Second, while DNA contains deoxyribose, RNA contains ribose (there is no hydroxyl group attached to the pentose ring in the 2' position in DNA). These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. Third, the complementary base to adenine is not thymine, as it is in DNA, but rather uracil, which is an unmethylated form of thymine.
Like DNA, most biologically active RNAs, including mRNA, tRNA, rRNA, snRNAs and other non-coding RNAs, contain self-complementary sequences that allow parts of the RNA to fold and pair with itself to form double helices. Structural analysis of these RNAs has revealed that they are highly structured. Unlike DNA, their structures do not consist of long double helices but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical catalysis, like enzymes. For instance, determination of the structure of the ribosome—an enzyme that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA.

Ribonucleic acid (RNA)

Ribonucleic acid (RNA)
Ribonucleic acid (RNA) is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded, while DNA is usually double-stranded; RNA nucleotides contain ribose while DNA contains deoxyribose (a type of ribose that lacks one oxygen atom); and RNA has the base uracil rather than thymine that is present in DNA. RNA is transcribed from DNA by enzymes called RNA polymerases and is generally further processed by other enzymes. RNA is central to protein synthesis. Here, a type of RNA called messenger RNA carries information from DNA to structures called ribosomes. These ribosomes are made from proteins and ribosomal RNAs, which come together to form a molecular machine that can read messenger RNAs and translate the information they carry into proteins. There are many RNAs with other roles – in particular regulating which genes are expressed, but also as the genomes of most viruses.