Studies of existing cells to determine the minimum number of genes for a living
ID: 184629 • Letter: S
Question
Studies of existing cells to determine the minimum number of genes for a living cell have suggested that 206 genes are sufficient. If the ratio of protein-coding genes is the same in this minimal organism as the genes of Escherichia coli (0.980), how many proteins are represented in these 206 genes? Protein-coding genes = -----------
The Escherichia coli genome contains 4377 genes and 5175720 base pairs. How many base pairs would be required to form the genome of this minimal organism if the genes are the same size as Escherichia coli genes? Base pairs =
Explanation / Answer
Please find the answers below:
Answer 1: The prokaryotes contain no introns or intervening non-coding regions in their genome, hence all the proteins are encoded from euchromatin only. Since a gene in prokaryotes encodes for a single protein due to lack of post-transcriptional and post-translational modifications, the 206 genes will encode for exactly 206 proteins. However, this does not hold true for eukaryotes where both post-transcriptional and post-translational modifications take place and hence the number of proteins encoded from a given number of genes is very high. (Check: Since the protein-coding genes ratio is 0.98, the total genes encoding for proteins would be 206*0.98 which is again close to 206, or exactly 201.)
Answer 2: According to the information, the number of genes in the organism is 4377 having 5175720 base pairs. These base pairs will form triplet codons in the number 5175720/3 or 1725240. These 1725240 codons will encode for 1725240/2 or 862620 protiens (the number is halved since a peptide bond exists only between two amino acids).
Thus, the minimum number of base pairs that are required to be present in this minimal organism would be given by:
206* Number of base pairs = 1725240 * size of gene
thus, number of base pairs = 1725240/206 or 8375 base pairs.