The Portion of DNA which contains information for an entire polypeptide is called Cistron.

Explanation:

A cistron is defined as a portion of DNA that contains the information for the synthesis of a single polypeptide chain. It is also known as a gene. A gene is a functional unit of DNA that encodes a specific protein or RNA molecule.

The cistron consists of three types of nucleotide sequences:

1. Coding sequence: It is the sequence of nucleotides that contains the information for the synthesis of a specific polypeptide chain.

2. Regulatory sequence: It is the sequence of nucleotides that controls the expression of the coding sequence.

3. Terminator sequence: It is the sequence of nucleotides that signals the end of the coding sequence.

The cistron is transcribed into mRNA, which is then translated into a polypeptide chain. The sequence of amino acids in the polypeptide chain is determined by the sequence of nucleotides in the coding sequence of the cistron.

In prokaryotes, cistrons are often organized into operons, which are clusters of genes that are transcribed together and share a common regulatory sequence. In eukaryotes, cistrons are usually separated by non-coding sequences and regulatory elements.

In conclusion, the cistron is a fundamental unit of genetic information that contains the instructions for the synthesis of a single polypeptide chain.

A cistron is an alternative term to a gene.The word cistron is used to emphasize that genes exhibit a specific behavior in a cis-trans test; distinct positions (or loci) within a genome are cistronic.