Question

In 1958, Francis Crick proposed that genes and their corresponding polypeptides are "colinear." Which of the following statements concerning the concept of colinearity is incorrect?

1) Colinearity means that the linear nucleotide sequence of a given gene corresponds directly to the linear amino acid sequence in the corresponding polypeptide.
2) The number of nucleotides in a gene should be precisely proportional to the number of amino acids present in the corresponding polypeptide.
3) Colinearity generally holds true for the coding regions of prokaryotic viral genes.
4) The vast majority of eukaryotic genes also follow the concept of colinearity although the size of genes may be larger.
5) The exception to colinearity between genes and polypeptides is the presence of untranslated sequences (UTRs).

Answer 1

The incorrect statement concerning the concept of colinearity is that the vast majority of eukaryotic genes follow colinearity, whereas in reality eukaryotic genes contain introns that disrupt the DNA-to-protein sequence alignment. The colinearity only applies to the processed mRNA and the amino acid sequence of the polypeptide.

Step-by-step explanation:

The concept of colinearity refers to the hypothesis that there is a direct correspondence between the linear sequence of nucleotides in a gene and the linear sequence of amino acids in a corresponding polypeptide. The incorrect statement concerning the concept of colinearity is: "The vast majority of eukaryotic genes also follow the concept of colinearity although the size of genes may be larger." The reason this statement is incorrect is because in eukaryotes, genes often contain intervening, non-translated sequences called introns which disrupt the colinear relationship. The coding sequences called exons are interrupted by introns, hence the DNA sequence of the gene doesn't directly align with the sequence of the final protein.

In eukaryotic organisms, the genetic material required for the production of polypeptides is initially transcribed into RNA, which is then processed to remove introns (non-coding regions). This results in an mRNA that is shorter than the DNA sequence from which it was transcribed, and it is this processed mRNA that is used to synthesize corresponding polypeptides during translation. Therefore, the genetic code is initially disrupted by introns, and colinearity is only observed in the final processed mRNA sequence and the polypeptide sequence.