Question

The smallest unit of DNA capable of coding for the synthesis of a polypeptide is the ___________.
A. Operon
B. Promoter
C. Cistron
D. Replicon

Answer 1

Hint: It is a transcription unit and the functional unit of inheritance is called a gene. It is an alternate name for a gene.

Complete answer:Gene is also defined as the DNA sequence coding for tRNA or rRNA molecule
1. Cistron is a segment of DNA coding for a polypeptide.
The structural gene in a transcription unit is known as monocistronic or polycistronic.
Monocistronic type is mostly seen in eukaryotes and polycistronic is most commonly seen in bacteria or prokaryotes.
2. The monocistronic structural genes (eukaryotes) have interrupted coding sequences that means the genes present in eukaryotes are split.
3. An operon is a functional unit of DNA that has a cluster of functionally-related genes that are controlled by a shared operator.
Operon has a set of multiple genes together with a promoter and an operator.
It is present in prokaryotes but absent in eukaryotes.
4. The promoter is a sequence of DNA to which a protein binds and this protein initiates transcription of a single RNA.
Promoter has a binding site for the enzymes to initiate transcription.
5. Replicon is a segment of the eukaryotic genome that contains several genes and replicates from a single origin of replication.

Therefore the correct answer is (C) Cistron.

Note: Exons are said to be the coding sequences or expressed sequences.
These are the sequences that appear in mature or processed RNA.
The exons are interrupted by sequences that do not appear in mature or processed RNA called Introns or intervening sequences.