Presentation-1......................pptx

Education

1. MUTATIONS • An error is the copying of a sequence of bases is called a mutation . • Can also occur during replication . Base error can also occur during transcription in protein synthesis .

2. These errors may have widely varying consequences : • the code for valine in mRNA can be GUA , GUG , GUC , or GUU . • In DNA , these codons correspond to GTA , GTG , GTC , and GTT .

3. • Ionizing radiation (X rays, ultraviolet light, gamma rays) can cause mutations. Furthermore, a large number of organic compounds can induce mutations by reacting with DNA. Such compounds are called mutagens. • Many com- pounds (both synthetic and natural) are mutagens, and some can cause cancer when introduced into the body. These substances are called carcinogens

4. Mutations and Biochemical Evolution We can trace the genetic relationship of different species through the variability of thee amino acid sequences in different proteins. The genes of closely related species, s u c h a s humans and apes, have very similar primary structures, prem s u m a b l y because these two species diverged on the evolutionary tree only recently.

5. An o n cogene is a gene that in one way or another participates i n t h e d e v e l o p m e n t of cancer . Cancer cells differ from normal cells in a variety of structural and metabolic ways . ONCOGENES The uncontrolled proliferation allows cells to spread, invade other tissues, and colonize t h em, in a process called metastasis T he normal EGF gene in the normal cell was tumed into an oncogene, we call it a proto - oncogene . Such conversions of a proto-onicogene to an oncogene can occur not just by viral invasion, but al s o by a mutation of the gene.

6. A Central Tumor Suppressor Protein N ot a l l cancer - c a u sing gene mut a t ions have their origin is i n o n c o r g e n e . There are some 3 6 known tumor suppressor genes , the products of which are proteins controlling cell growth. No n e of them i s m o r e important than the protein with a molar mass of 5 3 , 000, simply named p53 . In about 40% of all cance cases, the tumor contains p53 that underwent mutation. Mutated p53 protein can be found in 55% of lung cancers, about half of all colon and rectal cancers , and some 40% of lymphomas, stomach cancer, and pancreatic cancers. In addition, in one third of all soft tissue sarcomas, p53 is inactive, even though it did not undergo mutation.

7. R e combinant DNA techniques At this time, these DNA techniques are being used mostly in bacteria, plants, and test animals (such as mice), but they are slowly being applied to humans as well . One example of recombinant DNA techniques begins with certain c i r c u lar DNA molecules found in the cells of the bacterium Escherichia col i . These molecules, called plasmids .

8. The enzyme is so programmed that whenever it f i n d s t h i s specific sequence of bases in a DNA molecule, it cleaves i t as shown. Because a plasmid is c i r c u lar, cleaving it in this way produces a double stranded chain with two ends ( as shown on the figure ). These are called " sticky ends " b ecause o n o n e strand each has several free bases that are ready to pair up with a complementary section if the c an find one .

9. Gene Therapy While viruses have traditionally been seen as problems for humans, there is one field where they are now being used for go o d . Vi r u s e s can be used t o a lter somatic c e lls, where a genetic d i s e a se in tre a t e d by the introduction of a g e n e for a missing protein. This process is called gene therapy .

10. The most successful form of gene therapy to date involves the gene for adenosine deaminase ( ADA ), an enzyme involved in purine c a tabolism . If this enzyme is missing, dATP builde up in tissues, inhibiting the action of the enzyme ribonucleotide reductase. The result a deficienty of the other three deoxyribonucleoside triphosphates ( dNTPs ). The dATP (in excess) and the other three dNTPs (deficient) are precursors for DNA synthesis. This imbalance particularly affects DNA synthesis in lymphocytes , on which much of the immune response depends .

11. Individuals who are homozygous for adenosine deaminase deficiency develop severe combined immune deficiency ( SCID ), the " bubble boy " syndrome. They are prone to infection because of their highly compro m ised immune systems. The ultimate goal of the planned gene therapy is to take bone marrow cells from affected individuals, introduce the gene for adenosine d e aminase into the cells using a virus as a vector, and then reintroduce the bone marrow cells in the body, where they will produce the desired enzyme.

12. Two type of delivery methods in h u m a n gene therapy : The first, called ex vivo , is the type used to combat SCID . Ex vivo means that somatic cells are removed from the patient, altered with the gene therapy, and then returned to the patient. The most common vector for this approach is M a loney murine leukemia virus ( MMLV ).

13. shows how the virus is used for g e ne therapy. Some of the MMLV is altered to remove the gag, pol, and env genes, rendering the virus unable to replicate. These genes are replaced with an expression cassette , which contains the gene being administered, such as the ADA gene, along with a suitable promoter. This mutated virus is used to infect the packaging cell line.

14. In the second delivery method, called in vivo , the virus is used to directly infect the patient's tissues. The most common vector for this delivery is the DNA virus, adenovirus . A particular vector can be chosen based on specific receptors on the target tissue. Adenovirus has receptors in lung and liver cells, and it has been used in clinical trials for gene therapy of cystic fibrosis and ornithine transcarbamoylase deficiency .