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Genetic Engineering - Gene Expression

Gene Expression:
The pattern of gene expression was proposed by Crick as the Central Dogma. Central dogma is accepted in molecular biology. The mode of gene expression is represented as below.



Gene Expression starts with transcription process followed by translation process. Translation occurs in three steps – initiation, elongation and termination.

Amino acid methionine is responsible for initiation of protein synthesis. Methionine arranged on m-RNA at a proper place and enzyme require for this is formyl-methionine-acyl-t-RNA.

After initiation process, elongation phase starts in which t-RNA carries specific amino acids and arranges them at its proper place and forms a dipeptide bond between them and polypeptide chain elongates.

At the end, the nonsense codon or termination codon helps to release the synthesized polynucleotide chain from ribosome and terminate the synthesis process. Released polynucleotide chain develops its three-dimensional shape and is now ready for its function.


Genetic Code:
The group of three nucleotides present on m-RNA constitutes the genetic code. Each genetic codon is responsible for one particular amino acid. They are universal and have the same meaning in all organisms.

UAA, UGA and UAG are termination or nonsense codon. They terminate the process of protein synthesis. Human has 64 genetic codons. Nirenberg, Khorana and Mathai have first established the genetic codons and explained as triplet in form.


Recombinant DNA technology:
Recombinant DNA (r-DNA) is a DNA formed by blending of two different fragments of genetic material derived from two different organisms. Recombinant DNA is also called as hybrid DNA. Examples of r-DNA are streptokinase, G-CSF, erythropoietin, r-Hepatitis-B vaccine, interferon etc.

Human insulin is the best example of recombinant –DNA technology. This r-DNA is introduced in to host cell with the help of vectors which can be activated to produce desire product.


Cloning:
Cloning is the non-sexual growth of cell and its mechanism is very hard. Take a donor egg, such out the nucleus (DNA) and fuse it with another cell of human being (skin cell). Then with the help of an electrical current, the reconstituted cell should begin to grow into a genetic duplicate. Some will grow, while some will die.

Cloning is helpful to those people who are suffering from very painful diseases but it may also disturb the human reproduction cycle. However, abortion and euthanasia will become tame and transparent as compared with cloning rise.


Self study:
Example-1: Which amino acid is responsible for initiation of protein synthesis?
a)  Glysine
b)  Serine

c)  Methionine
d)  Arginine

Answer: Amino acid methionine is responsible for initiation of protein synthesis.


Example-2: Genetic codon is a group of three ………………..
a)  Protein

b)  Nucleotides
c)  Fatty acids
d)  None

Answer: Genetic codon is a group of three nucleotides.


Example-3: Which of following is not a nonsense codon or termination codon?
a)  UAA
b)  UGA

c)  AGT
d)  UAG

Answer: AGT is not a nonsense codon or termination codon.


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