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Biochemistry

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Purines, Pyrimidines and Nucleic Acid Metabolism

Question
49 out of 59
 

All are true about translation in eukaryotes except (AIPG 2010)



A The mRNA is translated from 5' to 3' end

B 1st amino acid is formylated

C Capping at 5' end in mRNA is helpful in recognitiony translatory mechanism

D It requires GTP to GDP transformation

Ans. B 1st amino acid is formylated

1st amino acid is methionine in Eukaryotes and formylated methionine in prokaryotes.

Translation:

a. Occurs in cytoplasm

b. Translated from 5' to 3' end

c. In involves 5 steps:

i. Activation of amino acids

ii. Initiation

iii. Elongation

iv. Termination

v. Post translational modification

Activation:

Amino acid + tRNA + ATP Aminoacyl tRNA + AMP Amino acyl tRNA synthetase

Fidelity of translation resides in the specificity of enzyme aminoacyl tRNA synthetase.

Initiation:

In prokaryotes "shine dalgarno" is the marker

In Eukaryotes "Kozak Consensus" is the marker

In prokaryotes formylated methionine is 1st AA

In Eukaryotes methionine incorporated as 1st AA

Preinitiation complex (formed by GTP, ElF-2 and met­tRNA) binds with mRNA which is facilitated by 5' methylated cap and forms initiation complex.

"Recognition of cap on mRNA by IF-4E is the rate limiting step in translation"

Elongation:

a. Binding of New amino acyl tRNA

b. Peptide Bond formation

c. Translocation

Each peptide bond formation requires 4 high energy phosphate bonds

a. Two for initial activation

b. One for EF 1 step (GTP to GDP)

c. One for EF 2 step (GTP to GDP)

d. Termination:

When ribosome reaches the terminator codon sequence no anticodon sequence is present. The Reptidye tranfferene hydrolyses the peptide chain and it is released.

Post translational Modification:

a. Proteolytic cleavage: Removal of signal sequences

b. Modification:carboxylation, Hydroxylation etc.

c. Subunit aggregation: Ig, hemoglobin, collagen maturation.

Purines, Pyrimidines and Nucleic Acid Metabolism Flashcard List

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