Question

Assertion:  A single strand of mRNA is capable of forming a number of different polypeptide chains.

Reason: Termination codons occur in mRNA.

(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

Correct option(b) 

Explanation:

mRNA brings instructions from the DNA for the formation of a particular type of polypeptide. The instructions are present in the base sequence of its nucleotides. mRNA has methylated region at the 5' terminus. It functions as a cap for attachment with the ribosome. Cap is followed by an initiation codon (AUG) either immediately or after a small non-coding region. Then there is coding region followed by a termination codon (UAA, UAG or UGA). An mRNA may specify only a single polypeptide or a number of them. The former is called monocistronic while the latter is known as polycistronic.