Thursday, January 15, 2009
What is a Genome??
Why we study Mitochondrial??
Why is there a separate Mitochondrial Genome??
The energy-conversion process that takes place in the mitochondria takes place aerobically, in the presence of oxygen. Other energy conversion processes in the cell take place anaerobically, or without oxygen. The independent aerobic function of these organelles is thought to have evolved from bacteria that lived inside of other simple organisms in a mutually beneficial, or symbiotic, relationship, providing them with aerobic capacity. Through the process of evolution, these tiny organisms became incorporated into the cell, and their genetic systems and cellular functions became integrated to form a single functioning cellular unit. Because mitochondria have their own DNA, RNA, and ribosomes, this scenario is quite possible. This theory is also supported by the existence of a eukaryotic organism, called the amoeba, which lacks mitochondria. Therefore, amoeba must always have a symbiotic relationship with an aerobic bacterium. |
Organelle DNA
Not all genetic information is found in nuclear DNA. Both plants and animals have an organelle—a "little organ" within the cell— called the mitochondrion. Each mitochondrion has its own set of genes. Plants also have a second organelle, the chloroplast, which also has its own DNA. Cells often have multiple mitochondria, particularly cells requiring lots of energy, such as active muscle cells. This is because mitochondria are responsible for converting the energy stored in macromolecules into a form usable by the cell, namely, the adenosine triphosphate (ATP) molecule. Thus, they are often referred to as the power generators of the cell.
Unlike nuclear DNA (the DNA found within the nucleus of a cell), half of which comes from our mother and half from our father, mitochondrial DNA is only inherited from our mother. This is because mitochondria are only found in the female gametes or "eggs" of sexually reproducing animals, not in the male gamete, or sperm. Mitochondrial DNA also does not recombine; there is no shuffling of genes from one generation to the other, as there is with nuclear genes.
The four DNA bases
Each DNA base is made up of the sugar 2'-deoxyribose linked to a phosphate group and one of the four bases depicted above: adenine (top left), cytosine (top right), guanine (bottom left), and thymine (bottom right). | |
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| The DNA that constitutes a gene is a double-stranded molecule consisting of two chains running in opposite directions. The chemical nature of the bases in double-stranded DNA creates a slight twisting force that gives DNA its characteristic gently coiled structure, known as the double helix. The two strands are connected to each other by chemical pairing of each base on one strand to a specific partner on the other strand. Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Thus, A-T and G-C base pairs are said to be complementary. This complementary base pairing is what makes DNA a suitable molecule for carrying our genetic information—one strand of DNA can act as a template to direct the synthesis of a complementary strand. In this way, the information in a DNA sequence is readily copied and passed on to the next generation of cells. |
Physical structure of a Human Genome
Nuclear DNA
Inside each of our cells lies a nucleus, a membrane-bounded region that provides a sanctuary for genetic information. The nucleus contains long strands of DNA that encode this genetic information. A DNA chain is made up of four chemical bases: adenine (A) and guanine (G), which are called purines, and cytosine (C) and thymine (T), referred to as pyrimidines. Each base has a slightly different composition, or combination of oxygen, carbon, nitrogen, and hydrogen. In a DNA chain, every base is attached to a sugar molecule (deoxyribose) and a phosphate molecule, resulting in a nucleic acid or nucleotide. Individual nucleotides are linked through the phosphate group, and it is the precise order, or sequence, of nucleotides that determines the product made from that gene.
What is a Gene therapy???
A gene is a linear sequence of DNA that codes for a particular protein. On rare occasions, usually during the division of the cell, the nucleotide sequence (the order of the DNA base pairs) of a gene can get jumbled up and mutated, so that the resultant protein is faulty. Such a mutation event is the root cause of genetic diseases such as cystic fibrosis, adenosine deaminase (ADA) deficiency and sickle-cell anaemia. For example, people who suffer from cystic fibrosis produce a faulty cellular transport protein called cystic fibrosis transmembrane conductance regulator, which results in the build-up of mucous in their lungs.
The earliest applications of gene therapy were based on the principle that a disease is caused by a faulty gene (or combination of genes), and if such genes can be replaced with ‘correct’ versions, the disease might be controlled, prevented or cured. Gene therapy is being applied to many different genetic diseases, both congenital (since birth) and acquired. However, most diseases involve multiple genetic factors (they are polygenic). Until the precise involvement of different genes (their regulation and expression) in the disease process and the proteins they encode is established, gene therapy is most likely to be clinically effective as a preventative or curative treatment for single-gene defects such as ADA deficiency, familial hypercholesterolaemia. and cystic fibrosis. Several clinical trials employing gene therapy protocols have already been completed, with some success in patients who have cystic fibrosis and ADA deficiency, although the effectiveness of the protocols was not as dramatic as first envisaged, mainly owing to the inefficiency of the gene transfer vectors that were used.
Originally known as ‘genetic replacement therapy’ during the early 1980s, ‘gene therapy’ has now outgrown its original definition and is applied to all manner of protocols that involve an element of gene transfer, either in vivo or ex vivo, and not necessarily a gene that is known to cause a disease. In vivo gene transfer is the introduction of genes to cells at the site they are found in the body, for example to skin cells on an arm, or to lung epithelial cells following inhalation of the gene transfer vector. Ex vivo gene transfer is the transfer of genes into viable cells that have been temporarily removed from the patient and are then returned following treatment (e.g. bone marrow cells). Gene therapy can be subdivided into somatic cell gene transfer (that is transfer to normal diploid cells), which is the focus of this review, and germline gene transfer (transfer to haploid sperm or egg cells of the reproductive system). The ethical issues associated with germline gene therapy are far more complex than those surrounding somatic cell gene transfer, because the genes are transferred not only to treated individuals but also to their progeny. Germline gene therapy is being widely used for the production of transgenic animals for research, and increasingly for agriculture and biotechnology, but the long-term effects of each transferred gene in animals will need to be carefully monitored and analysed, as well as the significance of any residual vector DNA if applicable. The benefits that the use of germline gene therapy in humans could bring are significant. The development of serious and distressing inherited genetic diseases could be prevented before birth and eliminated in subsequent generations. However, because of the potential for abuse and eugenics, gene therapy in humans needs to be widely discussed and the associated safety issues evaluated before this approach can be used for the treatment of diseases.
Gene transfer vector
Vectors are the vehicles that are used in gene therapy to transfer the gene(s) of interest [transgene(s)] to the target cells, which will then go on to express the therapeutic protein encoded by the transgene(s). The most important factor in any gene transfer protocol., apart from the gene of interest, is the choice of vector, which can result in either success or failure. Unfortunately, there is no such thing as a ‘good universal vector’; all of the vectors that are currently available have both advantages and disadvantages. For example, one vector might be able to enter target cells very efficiently but once there invokes a strong immune response, resulting in that cell being killed by the immune system. Many factors must be taken into consideration when choosing a vector. The most import ones are: the length of time that the transgene needs to be expressed, the dividing state of the target cells, the type of target cell, the size of the transgene, the potential for an immune response against the vector to be induced, and whether this is deleterious, the ability to administer the vector more than once, the ease of production of the vector, the facilities available, safety issues and regulatory issues. Table 1 (tab001jfo) outlines the advantages, disadvantages and major differences of the gene delivery vectors that are currently in research and clinical use.
Immunosuppresives cytokiness
The delivery of genes that encode immuno-modulatory molecules to the site of the graft, or to the graft itself, has much scope for reducing the harmful local immune response against foreign tissue that occurs in acute and chronic rejection.
Cytokines are soluble mediators of the immune system, and some of them have immunosuppressive effects. The viral form of interleukin 10 (vIL-10) is a protein that is encoded by the Epstein-Barr virus; it is structurally homologous to mouse and human IL-10 but does not possess the T-cell co-stimulatory properties that IL-10 does. Thus, it is a useful tool in gene transfer to tissue where T-cell activation needs to be switched off or downregulated. DeBruyne and colleagues. have demonstrated that gene transfer of vIL-10 to a murine cardiac allograft via vasculature perfusion using DNA-liposome complexes prolonged graft survival (16 days compared with 8 days for untreated grafts). The result was attributed to the vIL-10 gene, because treatment with either an antisense plasmid to vIL-10 or a monoclonal antibody targeted against vIL-10 reversed the graft-prolongation effect. Other cytokine genes, such as transforming growth factor beta (TGF-b), have also been shown to have a significant immunosuppressive effect . This type of approach is not intended to induce immunological tolerance, but might be useful for the delivery of local immunosuppression.
Genes of interest in transplantation
MHC
The MHC is a highly conserved yet polymorphic gene locus. MHC molecules are surface proteins that present intracellularly processed peptides in a helical groove to their ligand, the T-cell receptor (TCR). Cognate interaction between an MHC molecule presenting peptide on an antigen-presenting cell and a specific TCR on a T cell can result in T-cell activation if the appropriate co-stimulatory molecules are present on the antigen-presenting cell. MHC class I molecules consist of three alpha domains and a b2 microglobulin chain, which is not encoded by the MHC gene locus. MHC class II molecules consist of two alpha domains and two beta domains. Peptides that are presented on the class I molecule are usually derived from intracellular proteins, whereas class II molecules present extracellularly derived peptides. The mechanism by which these peptides are transported to the immature MHC molecule is also very different for class I and class II MHC molecules, and has been recently reviewed in this journal (Ref. 7). The MHC is the major identification molecule that triggers allograft rejection, because it determines the difference between self (syngeneic) and non-self (allogeneic). When searching for a suitable organ donor, it is the MHC antigens that are matched between donor and recipient, to give the graft as good a chance as possible of functioning. In defined situations, this potency of the MHC has been exploited to tip the balance of the immune system from immunity to tolerance. The exposure of the recipient of a graft to donor MHC antigens before transplantation to induce tolerance was first investigated in a mouse model by Billingham and colleagues in 1953, when cells from a donor strain were introduced into a recipient mouse in utero
Three Types of Cloning
Therapeutic cloning
Adult DNA cloning
Embryo cloning
Human Cloning
Centuries ago, twins were killed because primitive people thought they were evil. Today ethicists are telling you the same about cloned children, will you let them decide for you? Reproductive cloning is giving life to a few individuals and cannot harm any one. The Hollywood stories of monstruous defects have no real scientific bases if you listen to real experts and I would be happy to demonstrate this to you. In the future, reproductive cloning will enable all of us to live eternally. This is what Rael, founder of the Raelian Movement and of Clonaid, announced 30 years ago (see www.rael.org ) and what is slowly demonstrated in more and more laboratories around the world as they are working on brain mapping and personality transfer. By declaring human cloning a crime against humanity, you will just slow down an unescapable process as sooner or later, not only will we beat most of the diseases thanks to stem cells but we will also beat death thanks to cloning and a majority of people on this planet will request it.
Advatages of Biotechnology in Agriculture
Improve yield from crops
Using the techniques of modern biotechnology, one or two genes may be transferred to a highly developed crop variety to impart a new character that would increase its yield . However, while increases in crop yield are the most obvious applications of modern biotechnology in agriculture, it is also the most difficult one. Current genetic engineering techniques work best for effects that are controlled by a single gene. Many of the genetic characteristics associated with yield (e.g., enhanced growth) are controlled by a large number of genes, each of which has a minimal effect on the overall yield . There is, therefore, much scientific work to be done in this area.
Cloning
Cloning involves the removal of the nucleus from one cell and its placement in an unfertilized egg cell whose nucleus has either been deactivated or removed.
There are two types of cloning:
1. Reproductive cloning. After a few divisions, the egg cell is placed into a uterus where it is allowed to develop into a fetus that is genetically identical to the donor of the original nucleus.
2. Therapeutic cloning.The egg is placed into a Petri dish where it develops into embryonic stem cells, which have shown potentials for treating several ailments.
Uses of Genetic testing
- Determining sex
- Carrier screening, or the identification of unaffected individuals who carry one copy of a gene for a disease that requires two copies for the disease to manifest
- Prenatal diagnostic screening
- Newborn screening
- Presymptomatic testing for predicting adult-onset disorders
- Presymptomatic testing for estimating the risk of developing adult-onset cancers
- Confirmational diagnosis of symptomatic individuals
- Forensic/identity testing
Genetics testing
Pharmaceutical Products
Most traditional pharmaceutical drugs are relatively simple molecules that have been found primarily through trial and error to treat the symptoms of a disease or illness. Biopharmaceuticals are large biological molecules known as proteins and these usually (but not always, as is the case with using insulin to treat type 1 diabetes mellitus) target the underlying mechanisms and pathways of a malady; it is a relatively young industry. They can deal with targets in humans that may not be accessible with traditional medicines. A patient typically is dosed with a small molecule via a tablet while a large molecule is typically injected.
Small molecules are manufactured by chemistry but large molecules are created by living cells such as those found in the human body: for example, bacteria cells, yeast cells, animal or plant cells.
Modern biotechnology is often associated with the use of genetically altered microorganisms such as E. coli or yeast for the production of substances like synthetic insulin or antibiotics. It can also refer to transgenic animals or transgenic plants, such as Bt corn. Genetically altered mammalian cells, such as Chinese Hamster Ovary (CHO) cells, are also used to manufacture certain pharmaceuticals. Another promising new biotechnology application is the development of plant-made pharmaceuticals.
Pharmacogenomics
Pharmacogenomics is the study of how the genetic inheritance of an individual affects his/her body’s response to drugs. It is a coined word derived from the words “pharmacology” and “genomics”. It is hence the study of the relationship between pharmaceuticals and genetics. The vision of pharmacogenomics is to be able to design and produce drugs that are adapted to each person’s genetic makeup.
Pharmacogenomics results in the following benefits:
1. Development of tailor-made medicines. Using pharmacogenomics, pharmaceutical companies can create drugs based on the proteins, enzymes and RNA molecules that are associated with specific genes and diseases. These tailor-made drugs promise not only to maximize therapeutic effects but also to decrease damage to nearby healthy cells.
2. More accurate methods of determining appropriate drug dosages. Knowing a patient’s genetics will enable doctors to determine how well his/ her body can process and metabolize a medicine. This will maximize the value of the medicine and decrease the likelihood of overdose.
3. Improvements in the drug discovery and approval process. The discovery of potential therapies will be made easier using genome targets. Genes have been associated with numerous diseases and disorders. With modern biotechnology, these genes can be used as targets for the development of effective new therapies, which could significantly shorten the drug discovery process.