A random-sequence polyribonucleotide produced by polynucleotide phosphorylase, w

Question

A random-sequence polyribonucleotide produced by polynucleotide phosphorylase, with CDP and ADP in a 5:1 molar ratio stimulated the incorporation of proline, histidine, threonine, glutamine, asparagine, and lysine in a cell-free translation system in the following proportions: 100, 23.4, 20, 3.3, 3.3, and 1.0, respectively.

What does this experiment reveal about the nucleotide composition of coding triplets for these six amino acids? Select all that apply.

AAA - lysine1C2A (AAC, ACA, CAA) - glutamine, histidine1C2A (AAC, ACA, CAA) - threonine, prolineCCC - lysine2C1A (CCA, CAC, ACC) - glutamine, proline2C1A (CCA, CAC, ACC) - glutamine, asparagine1C2A (AAC, ACA, CAA) - glutamine, asparagine2C1A (CCA, CAC, ACC) - histidine, threonine2C1A (CCA, CAC, ACC) - threonine, prolineCCC - prolineAAA - proline1C2A (AAC, ACA, CAA) - histidine, threonine

Explanation / Answer

Ans.

There can be 8 possible coding triplets with only CDP and ADP. those are

CCC

CCA, CAC, ACC

CAA, ACA, AAC

AAA

as CDP is 5 times more abundant than ADP thus the nucleotide composition of coding triplet for lysine must be AAA as lysine is least incorporated.

similarly, codons with two A i.e., CAA and AAC must code for glutamine and asparagine as having two A have second least possibility.

as proline is incorporated most of the time, it must be having two C in its coding triplets and two or more codons out of those 8 must be coding for proline. similarly for histidine and threonine the coding triplet must be containing two C.

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