Scientists can examine the amino acid sequences of particular protein molecules found in vertebrates to determine the degree of similarity between vertebrate species. Even organisms that appear to have few physical similarities may have similar sequences of amino acids in their proteins and be closely related through evolution. The fewer the differences there are between the organisms the more closely related they are.

Cytochrome-c is a protein found in the mitochondria that is used in cellular respiration. This protein consists of a chain of 104 amino acids. The chart below shows the amino acid sequence of seven vertebrates.

Animal

Amino Acid Sequences in Cytochrome-c
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Horse gln pro phe thr thr ala lys asn lys thr lys glu glu thr leu met glu lys ala thr asn glu
Chicken gln glu phe ser thr asp lys asn lys thr gly glu asp thr leu met glu lys ala thr ser lys
Frog gln ala phe ser thr asp lys asn lys thr gly glu asp thr leu met glu ser ala cys ser lys
Human gln pro tyr ser thr ala lys asn lys ile gly glu asp thr leu met glu lys ala thr asn glu
Shark gln gln phe ser thr asp lys ser lys thr gln gln glu thr leu arg ile lys thr ala ala ser
Monkey gln pro tyr ser thr ala lys asn lys thr gly glu asp thr leu met glu lys ala thr asn glu
Rabbit gln val phe ser thr asp lys asn lys thr gly glu asp thr leu met glu lys ala thr asn glu

 

Compare the amino acid sequence of human cytochrome-c with that of the other eight vertebrates. For each vertebrate, count the number of amino acids that differ from those in the human. Click on the blanks in the table to check your answers.

Number of Amino Acid Differences
from Human Cytochrome-c

Species

Number Differences

Human

0

Horse

Chicken

Frog

Shark

Monkey

Rabbit

 

  1. Which organism is most closely related to humans?

    Interactive popup. Assistance may be required.

    Check Your Answer

    monkey Close Pop Up
  2. Which organism is least closely related to humans?

    Interactive popup. Assistance may be required.

    Check Your Answer

    shark Close Pop Up