4. Consider the codon 5 CGU 3\' that is part of mRNA molecule produced by a prot

Question

4. Consider the codon 5 CGU 3' that is part of mRNA molecule produced by a protein-coding gene. Which of the following mutational changes in the codon is likely to have the greatest effect on the function of the resulting protein? The standard genetic code table can be found on page 6 of the exam. a) 5' CAU 3 b) 5' CGG 3' c) 5' AGA 3 d) 5' CUU 3 e) All changes above are silent 5. Normal (unlabeled "N, light) DNA that is allowed to replicate for two generations in the presence of labeled ('5N, heavy) nucleotides and then subjected to CsCI Density Gradient Centrifugation such as that used by Meselson and Stahl would result in: a) two bands of DNA: one light and one medium in density b) two bands of DNA: one light and one heavy in density c) two bands of DNA: one heavy and one medium in density d) three bands of DNA: one light, one medium, and one heavy in density e) one band of DNA: medium in density

Explanation / Answer

CGU codes for arginine which is the correct code. Now upon mutations code, CGU changes into -

CAU-forms histidine

CGG- forms arginine

AGA- forms arginine

CUU-forms leucine

All changes above are not silent.

As we can see that codons CGG, AGA both codes for arginine hence mutations in them will have no effect. Now CUU forms lysine and CAU forms histidine. Because both histidine and arginine are positively charged amino acids thus they will have little similarities between them as compared to leucine. Hence the code changed to CUU will have the greatest effect of the mutation.

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