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Biochemistry

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Purines, Pyrimidines and Nucleic Acid Metabolism

Question
22 out of 59
 

Four encode codon instead of three, number of combination of AA (AIIMS Nov 2010)



A 4
B 16
C 64
D 256

Ans. D 256

a. The Nucleotide Sequence of an mRNA Molecule Consists of a Series of Codons That Specify the Amino Acid Sequence of the Encoded Protein

b. Twenty different amino acids are required for the synthesis of the cellular complement of proteins; thus, there must be at least 20 distinct codons that make up the genetic code. Since there are only four different nucleotides in mRNA, each codon must consist of more than a single purine or pyrimidine nucleotide.

c. Codons consisting of two nucleotides each could provide for only 16 specific codons, whereas codons of three nucleotides could provide 64 specific codons. , whereas codons of four nucleotides could provide 256 specific codons.

d. It is now known that each codon consists of a sequence of three nucleotides; ie, it is a triplet code. The deciphering of the genetic code depended heavily on the chemical synthesis of nucleotide polymers, particularly triplets in repeated sequence. These synthetic triplet ribonucleotides were used to program protein synthesis, allowing investigators to deduce the genetic code.


The Genetic Code (Codon Assignments in Mammalian Messenger RNA)

First Nucleotide

Second Nucleotide

Third Nucleotide

U

C

A

G

U

Phe

Ser

Tyr

Cys

U

Phe

Ser

Tyr

Cys

C

Leu

Ser

Term

Term2

A

Leu

Ser

Term

Trp

G

C

Leu

Pro

His

Arg

U

Leu

Pro

His

Arg

C

Leu

Pro

Gln

Arg

A

Leu

Pro

Gln

Arg

G

A

Ile

Thr

Asn

Ser

U

Ile

Thr

Asn

Ser

C

Ile2

Thr

Lys

Arg2

A

Met

Thr

Lys

Arg2

G

G

Val

Ala

Asp

Gly

U

Val

Ala

Asp

Gly

C

Val

Ala

Glu

Gly

A

Val

Ala

Glu

Gly

G

Purines, Pyrimidines and Nucleic Acid Metabolism Flashcard List

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