some of the discovery in genetics

 1)Epilepsy gene LGI2
Everyone knows that DNA is nature’s most basic building block, with many species sharing similar, if not identical, versions of the same genes. But it can be easy to forget just how universal it really is. Take epilepsy gene LGI2 for example. It was actually first discovered inLagotto Romagnolo dogs (better known as the dogs used to track down underground mushrooms known as Truffles), but has implications for better understanding childhood epilepsy.

Epilepsy is the most common neurological condition in children. The gene discovery was made by a group of researchers at the University of Helsinki led by Dr. Hannes Lohi, who says it will open up many avenues of research that will provide insight into the mechanisms underlying neurological development in the adolescent brain.

2) BOULE, the world’s most universal sexy gene
We say “sexy gene.” By that, we mean a gene specific to sex. Last year, researchers at Northwestern University Feinberg School of Medicine discovered that the gene BOULE is not only responsible for sperm production, it’s actually the first known gene to be required for sperm production in species ranging from insects to mammals.

“This is the first clear evidence that suggests our ability to produce sperm is very ancient, probably originating at the dawn of animal evolution 600 million years ago,” said Eugene Xu, who led the study. “Our findings also show that humans, despite how complex we are, across the evolutionary lines all the way to flies, which are very simple, still have one fundamental element that’s shared.”

Discovery of the gene’s linchpin role in sperm production have countless potential applications in the public health sector, including male contraception, male infertility, and even development of pesticides to fight against disease-carrying parasites.

3) SIGMAR1 mutation causes juvenile ALS
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a devastating neurodegenerative disorder characterized by the loss of motor neurons in the brain and spinal cord. When the disease begins progressing before the age of 25 — as it did in physicist Stephen Hawking — it is known as juvenile ALS.

The genetic underpinnings of ALS are poorly understood, so the discovery of genetic associations always has exciting implications for new areas of research. Just this month, researchers from the Kingdom of Saudi Arabia identified a mutation on the SIGMAR1 gene associated with the development of juvenile ALS. The gene affects a class a proteins the authors suspect is involved in motor neuron function and movement disorders, and is one that the researchers say could soon become a potential therapeutic target.

4) MYB-NFIB Fusion gene found in 100% of examined adenoid cystic carcinomas
Fusion genes are created when a chromosomal mutation causes two otherwise healthy genes to join together. For many years, it was believed that fusion genes were implicated only in blood and bone marrow cancers like leukemia, but a recent study by researchers at the Sahlgrenska Academy at the University of Gothenburg, Sweden found that the MYB-NFIB fusion gene was found in 100% of adenoid cystic carcinomas — a glandular cancer usually fond in the head, neck, and breasts.

“We suggested back in 1986 that the MYB gene might be involved in this form of cancer, but it’s only recently that we’ve had access to the tools needed to prove it,” says Göran Stenman, who led the team that made the discovery. He continues:

Now that we know what the cancer is down to, we can also develop new and more effective treatments for this often highly malignant and insidious form of cancer… One possibility might be to develop a drug that quite simply turns off this gene.

5) Mutation in the PRPS1 gene linked to a progressive hearing loss in males
Postlingual nonsyndromic hearing impairment (DFN2 for short) is a rare form of progressive deafness in males. Boys with the disease have been identified in the US, Great Britain, and China, and typically begin losing their hearing between the ages of 5 and 15 and continue to experience hearing loss over the course of their lives.

University of Miami Miller School of Medicine researcher Xue Zhong Liu led a team that recently discovered that the PRPS1 gene plays an indispensable role in the development and maintenance of the middle ear. “PRPS1 is an interesting example of a human disease gene in which gain of function or loss of function mutations cause several different and distinct hereditary disorders,” said Liu.

The fact that PRPS1 is only the second identified gene associated with NFD2 makes it a groundbreaking discovery, but its role in the development of the middle ear makes it even more important. Dr. James F. Battey, director of the National Institute on Deafness and Other Communication Disorders (NIDCD) said:

This discovery offers exciting therapeutic implications…not only does it give scientists a way to develop a targeted treatment for hearing loss in boys with this disorder, it may also open doors to the treatment of other types of deafness, including some forms of acquired hearing loss.

6) The discovery of mutations in MCF2L could lead to therapies for osteoarthritis sufferers
Osteoarthritis is a debilitating disease that affects upwards of 40% of people over the age of 70, and an estimated 27 million people in the US alone. Historically speaking, the complicated nature of the condition has made it especially difficult for researchers to identify what are believed to be a number of interrelated genetic causes; despite the prevalence of osteoarthritis, only two genetic links had ever been made.

But by collaborating with The 1000 Genomes Project, an international team of scientists led by researchers at The Sanger Institute was able to conduct a massive genetic screen (eventually involving over 50,000 people) to identify a third genetic link: MCF2L.

Alan Silman, the Medical Director of Arthritis Research UK, said:

Osteoarthritis is a complicated disease with many genetic causes. However, it has proved very difficult to discover the genes involved and help us to identify potential areas of treatment.

We are delighted that investigators at the Sanger Institute have been able to identify a new gene connected with this painful condition and offer new lines of research for possible treatments. We are also excited that employing the technique of using the 1000 Genomes Project data to investigate genetic associations in far greater depth could reveal even greater insights into this debilitating disease.

7) A large scale multiple sclerosis (MS) gene study doubles the number of genes known to play a role in the disease
Research published this month in the journal Nature uncovered 29 new genes that underlie the development of MS, an inflammatory disease that leads to communication issues between nerve cells in the brain and spinal cord. The impressive genetic study drew on resources from twenty-three research groups from 15 countries; according to the researchers, their findings double the number of genes implicated in the onset and progression of MS.

“We now know just how complex multiple sclerosis is,” said geneticist Jonathan Haines, director of Vanderbilt University’s Center for Human Genetic Research (CHGR) and one of the project’s head researchers. “These new genes give us many new clues as to what is happening in MS and will guide our research efforts for years to come.”

8) RGS17 could be used to identify patients who would benefit from more aggressive lung cancer screening
Despite the fact that smoking certainly contributes to the development of lung cancer, the fact remains that a significant genetic component makes lung cancer the leading cause of cancer related disease and death. Now Cancer Biologists at the University of Cincinnati showed that identifying the gene RGS17 in patients with a history of lung cancer could help improve courses of treatment for the disease.

“Understanding how the RGS17 gene impacts cancer development could change clinical diagnosis and treatment as radically as discovery of the breast cancer genes (BRCA1 and BRCA2) did,” explains Marshal Anderson, who led the study and has headed up the multi-institutional Genetic Epidemiology of Lung Cancer Consortium (GELCC) since 1997. “A proven genetic test could help us identify people at risk before the disease progresses.”

9) Massive genetic screen uncovers 5 new genes that increase the risk of developing Alzheimer’s Disease
Cardiff University’s Julie Williams recently led the world’s largest-ever genetic investigation of Alzheimer’s, screening around 20,000 people with the disease and 40,000 unaffected individuals to identify five new Alzheimer’s-linked genes, doubling the total number of genes known to increase the risk of developing Alzheimer’s.

The results of the investigation, which were published in an April issue of Nature Genetics (no subscription required) are helping researchers identify promising new avenues of research.

Williams said: “What’s exciting is the genes we now know of – the five new ones, plus those previously identified – are clustering in patterns.” She continues:

This study, plus our previous studies, means that we are beginning to piece together the pieces of the jigsaw and gain new understanding. We still have a long way to go – but the jigsaw is beginning to come together.

If we were able to remove the detrimental effects of these genes through treatments, we hope we can help reduce the proportion of people developing Alzheimer’s in the long-term.

10) International team identifies 13 new gene sites associated with heart disease
The World Health Organization estimates that heart diseases claim upwards of 17 million lives a year, making them the world’s deadliest class of diseases. Just like lung cancer, while environmental factors like smoking and drinking certainly put people at higher risk of developing cardiovascular diseases, there is believed to be a strong genetic component to them as well.

In March of this year, an international team of scientists published the results of a study that analyzed the genetic profiles of over 80,000 people, making it the largest screen for heart-disease related genes ever conducted (around ten times larger, to be exact). The study confirmed 10 of 12 previously reported heart-disease-related genes, and identified 13 new ones.

Interestingly, many of the newly identified genes have no known relation to previously identified cardiovascular risk factors like cholesterol or hypertension, which suggests that there are promising therapeutic mechanisms yet to be discovered.

“The lack of apparent association with the risk factors we know so well is the source of a lot of excitement concerning these results,” explains Dr. Sekar Kathiresan, the director of Preventive Cardiology at Massachusetts General Hospital and one of the study’s lead authors. “If these variants do not act through known mechanisms, how do they confer risk for heart disease? It suggests there are new mechanisms we don’t yet understand.”

Nanobionics supercharge photosynthesi

Nanobionic Leaf: DNA-coated carbon nanotubes (top) incorporated inside chloroplasts in the leaves of living plants (middle) boost plant photosynthesis. Leaves infiltrated with carbon nanotubes (orange) are imaged with a single particle microscope that monitors their near infrared fluorescence (bottom).

Credit: Image courtesy of Michael Strano

A new process has been developed for spontaneously incorporating and assembling carbon nanotubes (CNTs) and oxygen scavenging nanoparticles into chloroplasts, the part of plant cells that conduct photosynthesis — converting light into energy. Incorporation of CNTs enhanced electron flow associated with photosynthesis by 49% in extracted chloroplasts and by 30% in leaves of living plants, and incorporation of cerium oxide nanoparticles (nanoceria) into extracted chloroplasts significantly reduced concentrations of superoxide, a compound that is toxic to plants.

Chloroplasts alone absorb light only from the visible portion of the solar spectrum, allowing access to only about 50% of the incident solar energy radiation, and less than 10% of full sunlight saturates the capacity of the photosynthetic apparatus. This nano-bio approach is believed to increase the breadth of the solar spectrum that is used to make energy and is expected to contribute to the development of biomimetic materials with enhanced photosynthetic activity and improved stability towards oxidative degradation.

A novel nanobionic approach has been developed that imparts higher photosynthetic activity to plant leaves and extracted plant chloroplasts, the biological organelles that convert captured carbon dioxide into solar energy. While chloroplasts host all of the biochemical machinery needed for photosynthesis, little is known about how to engineer chloroplasts extracted from plants for long-term, stable solar energy harnessing. Now, researchers at the Massachusetts Institute of Technology have discovered that highly charged single-walled carbon nanotubes (CNTs) coated with DNA and chitosan (a biomolecule derived from shrimp and other crustacean shells) are able to spontaneously penetrate into chloroplasts. This new lipid exchange envelope penetration (LEEP) process for incorporating the nanostructures involves wrapping CNTs or nanoparticles with highly charged DNA or polymer molecules, enabling them to penetrate into the fatty, hydrophobic membranes that surround chloroplasts.

Incorporation of CNTs into chloroplasts extracted from plants enhanced choloroplast’s photosynthetic activity by 49% compared to the control. When these nanocomposites were incorporated into leaf chloroplasts of living plants, the electron flow associated with photosynthesis was enhanced by 30%.

These results are consistent with the idea that semiconducting carbon nanotubes are able to expand the light capture by plant materials to other parts of the solar spectrum such as the green, near infrared and ultraviolet. Another major limitation in the use of extracted chloroplasts for solar energy applications is that they easily break down due to light- and oxygen-induced damage to the photosynthetic proteins. When potent oxygen radical scavengers such as cerium oxide nanoparticles (nanoceria) were combined with a highly charged polymer (polyacrylic acid) and incorporated into extracted chloroplasts using the LEEP process, damage to the chloroplasts from superoxides and other reactive oxygen species was dramatically reduced. This nanobionics approach is expected to contribute to the development of biomimetic materials for light-harvesting and solar energy conversion, as well as biochemical detection with regenerative properties and enhanced efficiency

development of eye from stem cell

A stem-cell biologist has had an eye-opening success in his latest effort to mimic mammalian organ development in vitro. Yoshiki Sasai of the RIKEN Center for Developmental Biology (CBD) in Kobe, Japan, has grown the precursor of a human eye in the lab.

The structure, called an optic cup, is 550 micrometres in diameter and contains multiple layers of retinal cells including photoreceptors. The achievement has raised hopes that doctors may one day be able to repair damaged eyes in the clinic. But for researchers at the annual meeting of the International Society for Stem Cell Research in Yokohama, Japan, where Sasai presented the findings this week, the most exciting thing is that the optic cup developed its structure without guidance from Sasai and his team.

Dougal Waters/Getty

The human eye is a complex structure — but the cues to build it come from inside the growing cells.

“The morphology is the truly extraordinary thing,” says Austin Smith, director of the Centre for Stem Cell Research at the University of Cambridge, UK.

Until recently, stem-cell biologists had been able to grow embryonic stem-cells only into two-dimensional sheets. But over the past four years, Sasai has used mouse embryonic stem cells to grow well-organized, three-dimensional cerebral-cortex¹, pituitary-gland² and optic-cup³ tissue. His latest result marks the first time that anyone has managed a similar feat using human cells.

Familiar patterns

The various parts of the human optic cup grew in mostly the same order as those in the mouse optic cup. This reconfirms a biological lesson: the cues for this complex formation come from inside the cell, rather than relying on external triggers.

In Sasai’s experiment, retinal precursor cells spontaneously formed a ball of epithelial tissue cells and then bulged outwards to form a bubble called an eye vesicle. That pliable structure then folded back on itself to form a pouch, creating the optic cup with an outer wall (the retinal epithelium) and an inner wall comprising layers of retinal cells including photoreceptors, bipolar cells and ganglion cells. “This resolves a long debate,” says Sasai, over whether the development of the optic cup is driven by internal or external cues.

There were some subtle differences in the timing of the developmental processes of the human and mouse optic cups. But the biggest difference was the size: the human optic cup had more than twice the diameter and ten times the volume of that of the mouse. “It’s large and thick,” says Sasai. The ratios, similar to those seen in development of the structure in vivo, are significant. “The fact that size is cell-intrinsic is tremendously interesting,” says Martin Pera, a stem-cell biologist at the University of Southern California, Los Angeles.

An eye for an eye

The achievement could make a big difference in the clinic. Scientists have had increasing success in transplanting cells: last month, a group at University College London showed that a transplant of stem-cell derived photoreceptors could rescue vision in mice⁴. But the transplant involved only rod-shaped receptors, not cone-shaped ones, and would leave the recipient seeing fuzzy images. Sasai’s organically layered structure offers hope that integrated photoreceptor tissue could one day be transplanted. The developmental process could also be adapted to treat a particular disease, and stocks of tissue could be created for transplant and frozen.

Sasai emphasizes that the cells in the optic cup are “pure”, unlike those in two-dimensional aggregates, which may still contain embryonic stem cells. This reduces concerns that transplants of such cells might develop cancerous growths or fragments of unrelated tissues. “It’s like pulling an apple from a tree. You wouldn’t expect iron to be growing inside,” says Sasai. “You’d have no more reason to expect bone to be growing in these eyes.”

Masayo Takahashi, an ophthalmologist at the CBD, has already started transferring sheets of the retina from such optic cups into mice. She plans to do the same with monkeys by the end of the year. The big question is whether transplanted tissue will integrate into native tissue.

Clinicians and stem-cell biologists will also want to know just how easy it will be to repeat Sasai’s success. Some at the meeting had already tried and failed to reproduce Sasai’s mouse experiment using human cells. “We need to know how robust, how reproducible it is,” says Smith

Bumblebees differentiate flower types when arranged horizontally but not vertically

Source:

University of Queen Mary London

Summary:

It is well known that bumblebees and other pollinators can tell the difference between plants that will provide them with nectar and pollen and those that won’t. However, until now little has been known about how the arrangement of flowers affects their decision making.

Dr Stephan Wolf, co-author of the research, said: “This is a rare example of a pollinator being able to tell the difference between different flowers but simply choosing not to do so.”

Credit: Jardín Botánico de Madrid

It is well known that bumblebees and other pollinators can tell the difference between plants that will provide them with nectar and pollen and those that won’t. However, until now little has been known about how the arrangement of flowers affects their decision making Researchers from the School of Biological and Chemical Sciences at Queen Mary University of London, taught bumblebees to distinguish between two visually clearly different feeder types, one type containing food while the other did not. They found that bees were able to quickly learn the feeder types containing food when the feeders were arranged horizontally. However, the bees failed to distinguish these feeder types when these were distributed vertically on a wall and significantly more often chose the wrong feeder type.

The researchers are sure that the bees were equally able to discriminate between the two presented feeders in both arrangements but simply chose not to waste the brain power doing so on vertically arranged feeders. They believe that this is because in a meadow typically rewarding and unrewarding flowers of different species grow side-by-side and bees benefit from visiting only flowers similar to the ones that have previously rewarded them. In contrast, vertically clustered flowers, such as on flowering bushes or trees, the flowers in the arrangement are typically the same and paying close attention to the flower features may not be needed.

Dr Stephan Wolf, co-author of the research, said: “This is a rare example of a pollinator being able to tell the difference between different flowers but simply choosing not to do so.

“Further illustrating the impressive learning abilities of mini-brained bees, this study also shows that these capabilities may be applied in very surprising ways in different natural foraging situations.”

World’s first artificial enzymes created using synthetic biology

Medical Research Council (MRC) scientists have created the world’s first enzymes made from artificial genetic material. Their synthetic enzymes, which are made from molecules that do not occur anywhere in nature, are capable of triggering chemical reactions in the lab.

The research, published today in Natureopens in new window, gives new insights into the origins of life and could provide a starting point for an entirely new generation of drugs and diagnostics.

The findings build on previous workopens in new window by the team at the MRC Laboratory of Molecular Biologyopens in new window, which saw them create synthetic molecules called ‘XNAs’ that can store and pass on genetic information, in a similar way to DNA.

Using their lab-made XNAs as building blocks, the team has now created ‘XNAzymes’, which power simple reactions, such as cutting up or stitching together small chunks of RNA, just like naturally occurring enzymes.

Dr Philipp Holliger, who led the research at the MRC Laboratory of Molecular Biology, said:

“All life on earth depends on a series of chemical reactions, from digesting food to making DNA in our cells. Many of these reactions are too sluggish to happen at ambient temperatures and pressures, and require enzymes to kick-start or ‘catalyse’ the process.”

Every one of our cells contains thousands of different enzymes, many of which are proteins. But some of the key fundamental reactions necessary for life are performed by RNA, a close chemical cousin of DNA. Life itself is thought to have begun with the evolution of a self-copying RNA enzyme.

Dr Holliger explains: “Until recently, it was thought that DNA and RNA were the only molecules that could store genetic information and, together with proteins, the only biomolecules able to form enzymes. Our work suggests that, in principle, there are a number of possible alternatives to nature’s molecules that will support the catalytic processes required for life. Life’s ‘choice’ of RNA and DNA may just be an accident of prehistoric chemistry.

Dr Alex Taylor, the study’s first author in Phil Holliger’s lab at the MRC Laboratory of Molecular Biology, and a Post-doctoral Research Associate at St John’s College, Cambridge, adds: “The creation of synthetic DNA, and now enzymes, from building blocks that don’t exist in nature also raises the possibility that, if there is life on other planets, it may have sprung up from an entirely different set of molecules, and it widens the possible number of planets that might be able to host life.”

DNA and RNA are the building blocks of life, storing all of our genetic information and passing it on to future generations.

In 2012, Dr Holliger’s group showed that six alternative molecules, called XNAs, could also store genetic information and evolve through natural selection. They have now expanded on this principle to discover, for the first time, four different types of synthetic catalyst formed from these entirely unnatural building blocks.

The XNAzymes are capable of catalysing simple reactions like cutting and joining RNA strands in a test tube. One of the XNAzymes can even join XNA strands together, which represents one of the first steps to creating a living system.

Because their XNAzymes are much more stable than naturally occurring enzymes, the scientists believe they could be particularly useful in developing new therapies for a range of diseases, including cancers and viral infections, which exploit the body’s natural processes to take hold in the body.

Dr Holliger added: “Our XNAs are chemically extremely robust and, because they do not occur in nature, they are not recognised by the body’s natural degrading enzymes. This might make them an attractive candidate for long-lasting treatments that can disrupt disease-related RNAs.”

Professor Patrick Maxwell, Chair of the MRC’s Molecular and Cellular Medicine Board, said:

“Synthetic biology is delivering some truly amazing advances that promise to change the way we understand and treat disease. The UK excels in this field, and this latest advance offers the tantalising prospect of using designer biological parts as a starting point for an entirely new class of therapies and diagnostic tools that are more effective and have a longer shelf-life.”

Funders of this work included the MRC, European Science Foundationopens in new window and theBiotechnology and Biological Sciences Research Councilopens in new window.

courtesy: MRC

what is DNA?

DNA is often referred to as the “building block of life”. This is because it stores, in coded form, all the genetic information needed to create a living being.

Discovering the structure of this amazing molecule was one of the most important scientific breakthroughs of the 20th century. The first description of DNA structure was published in 1953 by James Watson and Francis Crick. Their research would earn them the 1962 Nobel Prize in Medicine and Physiology.

The Process

Within their testing labs the DNA sequence services extract the DNA from your swab. This involves breaking the cells to release tiny quantities of DNA. Once this is separated from the rest of the cell it’s washed to ensure there are no contaminants. The DNA is then kept in tubes at a temperature of -20°C.

Your genome, your complete set of genes, is extremely large. There are 3 billion bases, or chemical components, grouped into 46 chromosomes. The specialists could analyze directly from this raw DNA but, to make the process much more efficient, they concentrate on a small region of around just 200-400 bases. The Procedure continues by obtaining the DNA sequence by employing a technique known as ‘polymerase chain reaction’, or PCR for short. PCR is at the core of much molecular biological work and its inventor, Dr. Cary Mullis, received the Nobel Prize in recognition of this. PCR allows a scientist to ‘zoom in’ on a short, specific stretch of DNA and then make copies of this region.

DNA Sequence services takes a small quantity of your DNA and adds it to a tube with some chemicals that will create a PCR reaction. These include some small pieces of DNA called primers, and some copies of the sequences as well as some other key nucleotides and enzymes. This mix is loaded onto a machine where it is alternately heated and cooled 20-40 times. This helps trigger the reaction and allows multiple copies of the relevant sequence to be completed. By the time the process has been completed, the tube will contain millions of copies of the stretch of DNA we are interested in.

The next step in the process is to determine the sequence of this amplified region. DNA sequence services does this using a technique known as automated fluorescent DNA sequencing, which, they admit is a bit of a mouthful.

They then carefully analyses your DNA sequence using computer software to identify the exact base positions that hold the key to your Y chromosome’s demographic history. By deducing what sites you are either ‘derived’ or ‘ancestral’ for, they can identify how you fit into the phylogenetic tree of worldwide Homo sapiens Y chromosomes. Or, in short, where your ancestors came from!

DNA – short for DeoxyriboNucleic Acid – is found within the nucleus of most types of cells. It contains the instructions for a cell and determines how a person’s characteristics are passed from one generation to the next. Within the nucleus of a human cell, there are 23 pairs of chromosomes, making 46 chromosomes in total. Each chromosome consists of coiled chromatin which is composed of DNA wrapped around proteins called histones. The 23 pairs of chromosomes within the nucleus are like the “instruction manual” for the development of a person. Whether a person has blue eyes or brown, or whether he or she has dark or blonde hair, is determined by DNA. How can molecules (and strands of DNA are molecules) give “instructions”? To understand how this is possible, we should consider how we communicate and understand the textbooks, web sites and life’s other “instruction manuals” from which we can get information. At the most basic level we can only understand life’s “instruction manuals” if they use acode that we can
understand. In the case of this web site, the code is called English or French. Your understanding of the text you are presently reading depends upon your understanding of the individual English or French words on this page. Furthermore, words seldom convey complete or understandable information. Information is better communicated by grouping words together, and as you already know, a set of words that conveys a complete thought is a sentence. The DNA language, just like English and French, consists of words and sentences too! Each “word” is a single unit of the DNA molecule called a nucleotide. Each “sentence” is a large string of nucleotides called a gene. Let’s talk about the DNA words first.
Building Up a DNA Molecule: NucleotidesDNA “words” are small molecules called nucleotides. The human genome, made up of 23 pairs of chromosomes, consists of a total of about 3 billion nucleotides. Each nucleotide consists of a backbone and a nitrogen-containing base. The backbone serves to attach one nucleotide to another.
All nucleotides have the same backbone (which is made up of a phosphate molecule and a special sugar molecule called deoxyribose). However, a nucleotide may have any one of four possible bases: Adenine (A), Cytosine (C), Guanine (G) or Thymine (T). Because there are only 4 different types of nucleotides that can make up DNA, there are only 4 “words” in the DNA language. There is one other important aspect of nucleotides that we should discuss: Adenine (A) binds only to Thymine (T) and Cytosine (C) binds only to Guanine (G). Because of this, we say that A is complementary to T and that C is complementary to G. It is a lot easier to break up A-T and C-G bonds (which are called hydrogen bonds) than to break up the bonds that connect the nucleotide backbones together in the DNA chain (called covalent bonds). This property will become important later, when we discuss protein synthesis.
Building Up a DNA Molecule: How Nucleotides are Attached TogetherDNA molecules actually consist of two parallel chains of nucleotides. Each chain is said to be complementary to the other, because each nucleotide on one chain binds to its complementary partner on the other. It might be useful to imagine the DNA molecule as a ladder, where the two long supporting pieces are composed of the nucleotide backbones fastened together, and the rungs are the complementary A-T and G-C base pairs. So if one side of the ladder had the sequence: AATGC, the complementary side would be TTACG. In reality, the DNA ladder is twisted up into what is called a double helix conformation. Because the hydrogen bonds (connecting the G to the C, or the T to the A) are weaker than the covalent bonds connecting the individual nucleotides together, the two complementary chains which make up the twisted ladder can be easily unravelled and separated.

Genetic Engineering

Genetic engineering is the process of identifying and isolating DNA from a living or dead cell and introducing it into another living cell. Before the genetic material is introduced, it may be altered in the laboratory. When the genetic engineering process is successful, the new DNA becomes permanently incorporated into the chromosomes of the new cell, and appears in the DNA of progeny cells as well. How can scientists do genetic engineering? They use recombinant DNA technology.

Recombinant DNA Technology

The methods developed for isolating, manipulating, amplifying, cutting and splicing together identifiable sequences of DNA are collectively called recombinant DNA technology.The next three sections will introduce several recombinant DNA techniques used to locate, isolate and amplify DNA. A final section shows how other recombinant techniques can be used to introduce new DNA into cells.

Locating A Gene

Many techniques in molecular biology are used to find out where a given gene is located within the human genome. This is not an easy task, since the human genome contains thousands of genes, many of which have not yet been found or sequenced. Of particular use in this task are DNA probes.

What is a DNA Probe?

One way of finding a specific gene is through the use of a DNA probe, a relatively short single stranded DNA molecule that is complementary to a sequence on the gene of interest. In other words, if a segment of the gene of interest is known to be: AGTTCG, the complementary segment of the DNA probe would be TCAAGC, because A binds T and C binds G. (Actually, because of certain structural details about DNA molecules, the complementary sequence should actually be written as CGAACT, which is TCAAGC backwards. However, we are using the technically incorrect format here, to avoid confusion.)

An actual DNA probe would probably consist of at least a few dozen nucleotides complementary to a segment of the same length on the gene of interest. The probe is made to be radioactive, so that it can be detected easily.

Since a DNA probe will bind to single-stranded DNA, a technique called Southern Blotting can be performed which separates the double-stranded sample DNA into single strands and transfers them to a nylon membrane. When the probes are incubated with the membrane in a solution, they bind to complementary regions in the DNA and become “stuck” to the membrane. Afterwards, the membrane is put into contact with a sheet of photographic film that is sensitive to radioactive emission. Only those sections of the sample where the gene is located shows up as a dark spot on the paper, because these are the only sections bound to a radioactive probe.

DNA probes have several applications in molecular biology, including genetic methods of disease prediction and diagnosis , where probes that identify gene sequences known to be responsible for diseases are used. DNA probes can also be used in DNA fingerprinting , a technique often employed by forensic scientists to determine whether DNA found at a crime scene matches a suspect’s DNA.

How are DNA Probes Constructed?

A DNA probe can be constructed even before the gene sequence itself is known! The way that this is done is by working backwards from the gene’sprotein product. Recall in our discussion of how proteins are made , we said that a gene is transcribed into messenger RNA (mRNA), based on simple rules of complementary nucleotide bases. The mRNA is then transported out of the nucleus and is used as a template for the assembly of a chain of amino acids, which folds into a protein.

We can isolate the protein produced by the gene we are interested in, and find out what the first 30 amino acids of the protein are. Based on this information, we can determine the first 90 nucleotides of that protein’s mRNA template (recall that each sequence of 3 nucleotides codes for one amino acid, hence the 90:30 ratio). And because the mRNA template is complementary to the gene of interest, we now know what the sequence our DNA probe should be so that it is complementary to the first 90 nucleotides of the gene of interest.

To construct the DNA probe, we use a “Gene Machine,” which is capable of synthesizing a short single-stranded DNA molecule containing the desired sequence of nucleotides in only a few hours.

Isolating A Gene

If we were interested in introducing a human gene into another cell, it would not be sufficient to merely know that gene’s location within the human genome. We would also need to isolate a copy of the gene, so that it can be inserted into the new cell.

For example, the human insulin gene must be isolated from human cells so that it can be incorporated into E. coli bacteria cells. The incorporated gene causes the bacterial cells to produce the human insulin protein, which can be administered to diabetics.

One method of isolating a gene is to work backwards from its protein product. First, at least part of the protein is sequenced, meaning that the order of the amino acids that make up the protein chain are determined. Usually, knowing the first 30 amino acids of the protein is enough. Next, based on the known amino acid sequence, and understanding the process of protein synthesis , we can predict the nucleotide sequence of part of the protein’s mRNA template.

Next, a single stranded DNA probe is constructed that is complementary to the predicted mRNA sequence. For example, if part of the predicted mRNA sequence is CUA GUA CGA, the corresponding section of the DNA probe would be: GAT CAT GCT, because G’ is complementary to C’ and A’ is complementary to T’. (Actually, because of certain structural details about DNA molecules, the complementary sequence should really be written as TCG TAC TAG, which is GAT CAT GCT backwards. However, we are using the technically incorrect format here, to avoid confusion.) The DNA probe is made to be radioactive so that it will be detectable when it binds to its DNA “mirror image.”

The single-stranded DNA probe is then incubated with a sample thought to contain the complete mRNA protein template. When we isolate the mRNA to which the DNA probe binds, we have likely found the mRNA we are looking for.

Once the mRNA strand is found, all that must be done is to work backwards we need to synthesize the DNA strand that would have served as the template for the mRNA. That is, we need to synthesize DNA from RNA. There is an enzyme that allows us to do just that called reverse transcriptase, and which is found inside certain virus particles called retroviruses. These viruses employ RNA as their genetic material and use reverse transcriptase to generate DNA once they have infected a host cell. Biotechnologists can mix reverse transcriptase with mRNAs in vitro (outside of living cells in the laboratory, usually in a small plastic tube). As a result, the DNA sequence for the gene of interest is synthesized by the enzyme, based on the mRNA strand presented. Because the DNA produced was made artificially to be complementary to the mRNA, it is called a cDNA.

Amplifying DNA: The Polymerase Chain Reaction

Often, DNA samples are in quantities that are too small to work with. Luckily, a technique invented in the 1980s called the Polymerase Chain Reaction (or PCR ), can be used to “amplify” the amounts of DNA in these samples.

The PCR machine is actually nothing more than a very precise heating and cooling device. The machine has small slots which hold small tubes containing the DNA sample and other necessary reaction ingredients. These additional ingredients include a generous supply of individual nucleotides (A’s, T’s C’s and G’s), short single-stranded DNA molecules called primers and an enzyme called Thermus aquaticus polymerase (Taq polymerase, for short). Taq polymerase is derived from bacteria that live in hot springs and are among the few enzymes that can function at very high temperatures.

The cycle begins when the machine heats the tube to a temperature somewhere around 90-95 C, pausing each double-stranded DNA molecule in the original sample to separate into two single stranded pieces.

(Recall that the hydrogen bonds that connect the two complementary strands of the DNA double helix are much weaker than the covalent bonds that connect the nucleotides together that make up each chain. The heating causes the hydrogen bonds to be broken, thus unravelling and separating the two strands, while the covalent bonds remain unaffected.)

Next, the temperature is lowered slightly, which allows the DNA primers to bind to the separated strands. The primers bind because they are complementary to certain sequences of each DNA strand which “flank” the DNA that is to be replicated in the middle. Once the primers have attached themselves to the single strands, Taq polymerase synthesizes, using the individual nucleotides floating around in the tube, a complementary strand for each original single strand. This completes the first cycle, and doubles the amount of sample DNA present in the tube.

In the next cycle, the PCR machine heats and cools as before, causing the new double-stranded DNA molecules to separate, and for new complementary strands to be synthesized by Taq polymerase.

Every time one cycle is performed, the amount of copies of the desired DNA sequence (located between the two primers) theoretically doubles. After about 30 cycles (which will typically take about 3 hours), enough DNA copies of this DNA sequence will have been made for the application of further biotechnology techniques.

The DNA Learning Centre, has developed an online video that gives a very good explanation of the PCR technique.

Introducing A Gene To A Cell

A gene, which is likely isolated in the form of a cDNA , can be introduced into a cell using a vector. A vector is a vehicle by which foreign DNA is transferred from one cell to another.

Some examples of vectors include modified viruses and plasmids.

Viruses as Vectors
Viruses are excellent vectors, because they have gained, through long periods of evolution, the ability to avoid destruction by the human immune system, and have the capacity to get their own genetic material inside specific cells. As we examined in the section describing viruses, a viral infection consists of foreign (viral) genetic material entering the cell and harnessing the cell’s nucleic acid and protein-making machinery to produce its own DNA, RNA and proteins. To use a virus as a vector, the harmful sections of its DNA are replaced with the desired cDNA to be introduced in the cell. Then, we allow the virus to infect’ our host cell and if all goes well, the cDNA enters the cell and will be used to make the desired protein.

Some viruses can produce their own DNA and incorporate it into the host cell’s genome. These RNA-based retroviruses are the most common viral vectors used in Gene Therapy, where genes with therapeutic value are inserted into the retroviruses which, upon infection, incorporate these into the genome of the recipient cell.

It should be noted that viruses that are to be used as vectors are made to be “replication defective”. In other words, the harmful parts of the viral genome that serve to produce more viral particles have been removed and replaced by a sequence that codes for the protein of interest.

Plasmids as Vectors
The way in which the human insulin cDNA is introduced into bacterial cells is through the use of a plasmid. A plasmid is simply a loop of DNA containing genes that can easily diffuse into and out of bacterial cells. Although plasmids occur naturally in certain bacteria, the plasmids used for the purpose of introducing and expressing a foreign gene into a cell have been altered to such an extent, that the sequences they contain are very different from the naturally occurring plasmids upon which they are based.

For one thing, the plasmid contains several specialized short sequences called restriction sites. Enzymes called restriction endonucleases recognize these sites and cut the plasmid DNA. For example, a restriction enzyme called EcoR1 recognizes the sequence GAATTC and cuts between the G and the first A. Notice that the complementary sequence is CTTAAG, which is GAATTC backwards! So the enzyme cuts both strands of the plasmid like so:

Notice that cutting using EcoR1 generates two “sticky ends” which are single stranded strings of nucleotides that will bind to a complementary set of single-stranded “sticky ends.” Most importantly, the plasmid is engineered so that this particular restriction sequence is present only once, meaning that EcoR1 will cut the double-stranded plasmid at only one location.

The cDNA (which contains the human insulin gene) to be inserted into the plasmid is altered depending on the restriction enzyme that was used to cut the plasmid. In keeping with our Eco R1 example, the following “sticky ends” would be needed on each end of the cDNA:

Now we incubate the altered cDNA sequence in a solution with a plasmid cut using the EcoR1 enzyme and with an enzyme that fastens DNA pieces together (called DNA ligase). This results in a closed circular plasmid which contains the cDNA, and therefore the human insulin gene.

The plasmid is subsequently incubated with bacterial cells (in the case of the insulin process, the bacteria used are a species called E. coli) under specific conditions which favour the absorption of the plasmid by the bacterial cell.

In theory, the plasmid containing the human insulin gene will enter all of the bacterial cells and all of these cells will transcribe the protein and produce human insulin, which can then be harvested and used to treat diabetic patients.

Unfortunately, not all the bacteria cells will actually absorb the plasmid. In fact, in most cases, relatively few of them will absorb it. How can biotechnologists select only those bacteria cells that have absorbed the plasmid?

The answer lies in the bacterial culture conditions and in another special modification built into genetically engineered plasmids. The bacteria, after they have been incubated in the presence of the plasmid (and some have absorbed it), are cultured in a medium that contains an antibiotic, like ampicillin. Ampicillin will kill E. Coli bacteria, unless they are protected in some way. The plasmid that the bacteria have absorbed also contains a gene that confers a resistance to ampicillin. Therefore, only those bacteria that have absorbed the plasmid will be resistant to the antibiotic and will survive. Since the plasmid also contains the gene for human insulin, we have allowed only those bacteria that may be capable of producing insulin to survive and multiply.

Article is done with the help of geogene

Latest discovery proves that babies start learning their language while still unborn.

When did you start speaking your language? At the age of 1? Researchers at the University of Wurzburg insist that we all start acquiring our mother tongues while still in the womb.

They studied 60 newborn babies, one half of those being French, and the other half being German. The findings suggest that babies were clearly imitating the pitch and the melody of their parents’ speech when crying.

Traditionally, it was thought that babies start producing sounds resembling their native-to-be languages at the age of 3 months. Researchers are assured that though being isolated from the outer world, unborn babies still can hear sounds, and imitate vocal patterns in order to establish tighter bond with their parents.

Full details of the study have been published in the recent issue of the Current Biology journal.