DNA molecules consist of chemically linked sequences of the bases adenine, guanine, cytosine, and thymine, denoted A, G, C, and T. A sequence of three bases is called a codon. A base may appear more than once in a codon.

a. How many different codons are there?

b. The bases A and G are purines, while C and T are pyrimidines. How many codons are there whose first and third bases are purines and whose second base is a pyrimidine?

c. How many codons consist of three different bases?

Answer

Step 1 of 3

There are four bases A,C,G and T

A sequence of three bases are called codon

a) The number of possible codons are 4(4)(4)=64

Step 2 of 3

b)The purines are A and G

The pyrimidines are C and T

The no. of choices for the first element of codon is 2(A and G)

The no. of choices for the second element of codon is 2(C and T)

The no. of choices for the third element of codon is 2(A and G)

The no. of codons with first and third bases are purines and second base as pyrimidines

=2(2)(2 )

=6