AP BIOLOGY

LABORATORY REVIEW

MOLECULAR BIOLOGY

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
An RNA sequence includes 15 codons. How many amino acids does this sequence have?
A
3
B
5
C
15
D
45
Explanation: 

Detailed explanation-1: -In the given mRNA sequence there are 15 nucleotide . One amino acid codes triplet three nucleotide. So, after addition of adenosine residue the total number of nucleotide is 16. So five amino acids will be coded by the mRNA sequence.

Detailed explanation-2: -A 15 nucleotide mRNA sequence could only encode up to 4 amino acids (15 nucleotides-3 nucleotide stop codon = 12 nucleotides = 4 amino acids).

Detailed explanation-3: -The three-letter nature of codons means that the four nucleotides found in mRNA-A, U, G, and C-can produce a total of 64 different combinations. Of these 64 codons, 61 represent amino acids, and the remaining three represent stop signals, which trigger the end of protein synthesis.

Detailed explanation-4: -Thus 61 codons are available for 20 amino acids, and hence the genetic code is degenerate.

Detailed explanation-5: -Because DNA consists of four different bases, and because there are three bases in a codon, and because 4 * 4 * 4 = 64, there are 64 possible patterns for a codon. Since there are only 20 possible amino acids, this means that there is some redundancy–several different codons can encode for the same amino acid.

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