Question

Cytochrome c is an important component of the electron transport chain, a part of cellular respiration, and it is normally found in the cellular organelle, the mitochondrion. This protein has a heme prosthetic group, and the central ion of the heme gets alternately reduced and oxidized during electron transfer. Because this essential protein’s role in producing cellular energy is crucial, it has changed very little over millions of years. Protein sequencing has shown that there is a considerable amount of cytochrome c amino acid sequence homology among different species; in other words, evolutionary kinship can be assessed by measuring the similarities or differences among various species’ DNA or protein sequences.

Scientists have determined that human cytochrome c contains 104 amino acids. For each cytochrome c molecule from different organisms that has been sequenced to date, 37 of these amino acids appear in the same position in all samples of cytochrome c. This indicates that there may have been a common ancestor. On comparing the human and chimpanzee protein sequences, no sequence difference was found. When human and rhesus monkey sequences were compared, the single difference found was in one amino acid. In another comparison, human to yeast sequencing shows a difference in the 44th position. The protein sequence of cytochrome c from chimpanzees and humans is identical.

The protein sequence of cytochrome c from rhesus monkeys differs from the human sequence by one amino acid. What do these comparisons suggest?

a. Rhesus monkeys are more closely related to humans than chimpanzees.
b. Chimpanzees are more closely related to rhesus monkeys than to humans.
c. Humans are related to chimpanzees, but are not related to rhesus monkeys.
d. Chimpanzees are more closely related to humans than rhesus monkeys.

Answer 1

The identical cytochrome c sequences between humans and chimpanzees indicate they are closely related, and the one amino acid difference with rhesus monkeys implies a more distant relationship, highlighting a common ancestor.

Step-by-step explanation:

The comparisons of cytochrome c sequences among different species have significant implications for understanding evolutionary relationships. Since there is no difference between the human and chimpanzee cytochrome c sequences and only one difference between the human and rhesus monkey sequences, it can be deduced that chimpanzees are more closely related to humans than rhesus monkeys are to humans.

The fact that the sequences are highly conserved across different species with minimal differences suggests that they likely share a common ancestor. Because of the critical function of cytochrome c in the electron transport chain and cellular respiration, its protein sequence has remained remarkably stable through evolution, allowing scientists to trace these relationships.