Question

A DNA strand individually has 3 different reading frames. Why? Explain your answer.

A. multiple reading frames exist on both DNA strands

B. 3 different polypeptide sequences exist

C. multiple methionine amino acids are in a polypeptide

D. codon sequences can be read in 3 different ways

E. open reading frame can be determined by wobble

Answer 1

Codon sequence is made up of three nucleotides and therefore, a DNA strand can have three different reading frames. This can be understood by the following example-

Let there be a DNA sequence 3'AATGTCAGAA5'. So, the mRNA sequence will be 5'UUACAGUCUU3'. Now, this mRNA can be read in 3 different ways. The possible protein sequences are shown below-

Thus, there are three possible reading frames present in a DNA strand and this occurs because codon sequences can be read in three different ways. So, option D is the appropriate reason.