NAME:________________________________________
Amino Acid Sequences: Evidence of Evolution
Scientists have gathered a variety of evidence to support the theory of evolution: fossil record,
radioactive dating, coevolution, embryonic similarities, structural similarities, and biochemical similarities.
Similarities in structure and biochemistry provide support for Darwin’s conclusion: living organisms evolved
through gradual modification of earlier forms, that is, decent from a common ancestor.
One biochemical similarity that can be studied is the similarity in amino acid sequences in homologous
proteins of different organisms. The greater the similarity in amino acid sequences of homologous proteins the
closer the evolutionary relationship; the greater the differences the more distant the relationship. You will study
two proteins in vertebrates: hemoglobin and cytochrome c. Hemoglobin is the oxygen carrying molecules
founds in red blood cells; it is composed of several long chains. The sequence used in this lab is a portion of a
chain consisting of 146 amino acids. Cytochrome c is a respiratory enzyme found in mitochondria consisting of
104 amino acids.
Part I:
Examine Figure I, which compares portions of hemoglobin molecules in humans and five other vertebrae
animals. Hemoglobin, a protein composed of several long chains of amino acids, is the oxygen carrying
molecule in red blood cells. Only a portion of the chain is shown in Figure I.
1) Highlight the differences between humans and each of the other organisms; remember to compare
humans versus the other species; do not compare adjacent rows
Figure I
87
Human
THR
Chimp
THR
Gorilla
THR
Rhesus
GLN
Horse
ALA
Kangaroo LYS
Human
Chimp
Gorilla
Rhesus
Horse
Kangaroo
88
LEU
LEU
LEU
LEU
LEU
LEU
89
SER
SER
SER
SER
SER
SER
90
GLU
GLU
GLU
GLU
GLU
GLU
91
LEU
LEU
LEU
LEU
LEU
LEU
92
HIS
HIS
HIS
HIS
HIS
HIS
93
CYS
CYS
CYS
CYS
CYS
CYS
94
ASP
ASP
ASP
ASP
ASP
ASP
95
LYS
LYS
LYS
LYS
LYS
LYS
96
LEU
LEU
LEU
LEU
LEU
LEU
97
HIS
HIS
HIS
HIS
HIS
HIS
98
VAL
VAL
VAL
VAL
VAL
VAL
99
ASP
ASP
ASP
ASP
ASP
ASP
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
ASN
ASN
ASN
ASN
ASN
ASN
PHE
PHE
PHE
PHE
PHE
PHE
ARG
ARG
LYS
LYS
ARG
LYS
LEU
LEU
LEU
LEU
LEU
LEU
LEU
LEU
LEU
LEU
LEU
LEU
GLY
GLY
GLY
GLY
GLY
GLY
ASN
ASN
ASN
ASN
ASN
ASN
VAL
VAL
VAL
VAL
VAL
ILE
LEU
LEU
LEU
LEU
LEU
ILE
VAL
VAL
VAL
VAL
ALA
VAL
CYS
CYS
CYS
CYS
LEU
ILE
VAL
VAL
VAL
VAL
VAL
CYS
LEU
LEU
LEU
LEU
VAL
LEU
ALA
ALA
ALA
ALA
ALA
ALA
HIS
HIS
HIS
HIS
ARG
GLU
2) Compile these amino acid differences in Table below.
Table I: amino acid difference between humans/species pairs
Organisms
Number of Amino Acid
Differences
Human/ chimpanzee
0
Human/ gorilla
1
Human/ rhesus monkey
Human/ horse
Human/ kangaroo
Number Positions in which
they vary
104
100
PRO
PRO
PRO
PRO
PRO
PRO
101
GLU
GLU
GLU
GLU
GLU
GLU
NAME:________________________________________
Questions:
1) If the amino acid sequences in homologous proteins of two organisms are similar, what can you
conclude about the DNA of the two organisms?
2) In the human and gorillas there is a difference of only one amino acid in one chain of hemoglobin. Give
a possible explanation for this.
3) Using the hemoglobin data you collected, which organisms appear most closely related to humans?
Which appear to be least related? Explain you answers.
Most Closely:
How do you know?
Least Closely:
How do you know?
Part II:
Another commonly studied protein is cytochrome c. This protein, consisting of 104 amino acids, is located in
the mitochondria of cells, where it functions as a respiratory enzyme. Examine Table 2. Using cytochrome c as
a standard, the amino acid differences between humans and other organisms are shown.
Table 2
Species Pairings
Human-chimpanzee
Human-fruit fly
Human-horse
Human-pigeon
Human-rattlesnake
Human-red bread mold
Human-rhesus monkey
Human-screwworm fly
Human-snapping turtle
Human-tuna
Human-wheat
Number of Difference
0
29
12
12
14
48
1
27
15
21
43
NAME:________________________________________
Questions:
1) Using the data in Table 2 construct a bar graph below to illustrate amino acid differences between humans
and other organisms.
2) Name the pair of organisms that appear to be equally related to humans on the basis of cytochrome c
similarity. ___________________________________________________________________________
Part III:
Now we will be examining and comparing the cytochrome c in fruit flies. Below, in Table 3, the fruit fly is used
as the standard in comparing the amino acid differences in several organisms. Use the data to construct a bar
graph to illustrate the amino acid differences between fruit flies and other organisms:
Table 3
Species Pairing
Fruit fly- dogfish shark
Fruit fly-pigeon
Fruit fly-screwworm fly
Fruit fly-silkworm moth
Fruit fly-tobacco hornworm mother
Fruit fly-wheat
Number of Differences
26
25
2
15
14
47
NAME:________________________________________
Questions:
1) Use the data to construct a bar graph belpw to illustrate the amino acid differences between fruit flies
and other organisms.
2) Agree or disagree with the following statement and give reasons to support your answer.
“Fruit Flies appear to be more closely related to silkworm moths than they are screwworm flies”
3) It is generally accepted that the fewer differences found in the amino acid sequences of homologous
proteins the less time since the species diverged from the common ancestor. Biologists believe that
humans, chimpanzees and gorillas diverged from common ancestor only a few million years ago (a short
time in evolutionary history). Use your data to explain this statement.
4) If the amino acid sequences in the proteins of two organisms are similar, why will their DNA also be
similar?