Which of the following pairs is NOT the result of a geneduplication? a. -and -ch
ID: 5175 • Letter: W
Question
Which of the following pairs is NOT the result of a geneduplication?a. -and -chains of hemoglobin
b. Chymotrypsin and subtilisin
c. Any pair of paralogous proteins (paralogs)
In aligningprotein sequences, which of the following is NOT a majorconcern?
a. Maximizing the number of identical and conservativepositions
b. Introduction of sufficient gaps such that the N- andC-termini of the proteins can be aligned
c. Minimizing the number of gaps which must beintroduced
Gene duplication during the course of evolution is the mostlikely source of proteins that are classified as
a. Homologs
b. Orthologs
c. Paralogs
Explanation / Answer
The three serine proteases of the chymotrypsin-like clan thathave been studied in greatest detail are chymotrypsin, trypsin,and elastase. All three enzymes are synthesized by the pancreatic acinar cells, secreted in the small intestine, and are responsible forcatalyzing the hydrolysis of peptide bonds. All three of these enzymes aresimilar in structure, as shown through their X-ray structures. Thediffering aspect lies in the peptide bond that is being cleaved;this is called the scissilebond. The different enzymes, like most enzymes,are highly specific in the reactions they catalyze. Each of thesedigestive serine proteases targets different regions of a polypeptide chain, based upon the sidechains of the amino acid residues surrounding the site ofcleavage:
The combination of these three enzymes make an incrediblyeffective digestive team and are primarily responsible for thedigestion of proteins.
Subtilisin is a serine protease in prokaryotes. Subtilisin is evolutionaryunrelated to the chymotrypsin-clan, but shares the same catalyticmechanism utilising a catalytic triad, to create a nucleophilicserine. This is the classic example used to illustrateconvergent evolution, since the samemechanism evolved twice independently during evolution.
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a.Maximizing the number of identical and conservativepositions
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answer Paralogs
Orthologs, or orthologous genes, are genes indifferent species that are similar to each other because theyoriginated from a common ancestor. The term "ortholog" was coinedin 1970 by Walter Fitch.
The strongest evidence that two similar genes are orthologous isthe result of a phylogenetic analysis of the gene lineage. Genesthat are found within one clade areorthologs, descended from a common ancestor. Orthologs often, butnot always, have the same function.
Homologous sequences are paralogous if theywere separated by a gene duplication event: if a gene in anorganism is duplicated to occupy two different positions in thesame genome, then the two copies are paralogous.
A set of sequences that are paralogous are calledparalogs of each other. Paralogs typically havethe same or similar function, but sometimes do not: due to lack ofthe original selective pressure upon one copy of the duplicatedgene, this copy is free to mutate and acquire new functions.
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