Question

Nucleic acid can be synthesized only in the direction of

• A. $3-3$
• B. $3-5$
• C. $5-3$
• D. $5-5$

Answer 1

The correct option is C

$5-3$

Explanation for correct option

(C) $5-3$

1. Only in this direction of $5-3$can nucleic acid be produced.
2. The $5$′ ($5$-prime) and $3$′ ($3$-prime) ends of nucleic acids are two distinguishing features.
3. The $5$′ and $3$′ carbons on the sugar are referred to by this phrase.

Explanation for incorrect options

(A) $3-3$

1. Nucleotide triplets would not be enough to identify every amino acid.
2. The number of potential nucleotide triplets is $64$.
3. Which is significantly more than the number of amino acids.

(B) $3-5$

1. DNA replication can only proceed in the $5$' to $3$' direction
2. because DNA polymerase can only add nucleotides to the developing DNA strand's $3$' $\mathrm{OH}$ group.
3. The last deoxyribonucleotide in the developing strand's $3$′ $-\mathrm{OH}$ group is bound by the $5$′-phosphate group of the new deoxyribonucleotide.

(D) $5-5$

1. DNA polymerase lengthens the DNA strand from the RNA primer that DNA primase produces.
2. Only in the $5$' to $3$' direction does DNA synthesis take place.
3. DNA synthesis is ongoing on the leading strand.

Hence, the correct option is (C) .Nucleic acid can be synthesized only in the direction of $5-3$.