Cytochrome-C Comparisons Lab

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Name
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Period
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Date
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Science
Cytochrome C Comparison Lab
PURPOSE: To compare the relatedness between organisms by examining the amino acid sequence in the
protein, Cytochrome C.
BACKGROUND: Genes are made of DNA and are inherited from parent to offspring. Some DNA
sequences code for mRNA which, in turn, codes for the amino acid sequence of proteins. Cytochrome C
is a protein involved in using energy in the cell. Cytochrome C is found in most, if not all, known
eukaryotes. Over time, random mutations in the DNA sequence occur. As a result, the amino acid
sequence of Cytochrome C also changes. Cells without usable Cytochrome C are unlikely to survive.
METHOD:
A . Compare the amino acid sequence of Cytochrome C in various organisms.
1.
Mark the amino acids which are different Use the example to show you how.
- - - - -
G
D V A K
G
K K T
F
V Q K
C
A Q
C H
T V E N G G K H
K
V
G P
N
L
W
G
L F G
R
K T
- G V P A
G
D V E K
G
K K I
F
V Q R
C
A Q
C H
T V E A G G K H
K
V
G P
N
L
H
G
L F G
R
K T
Note that some of the amino acids are always the same in all species, these have been shaded blue
or light gray.
2. Count and record the total number of differences.
Tuna &
24
Fly:
3. Note: Be sure to study the entire molecule.
Each protein sequence has 103-112 amino acids; the sequence extends onto two (2) lines.
4. Share your data with the rest of the class and complete Table 1.
B . Make a branching tree, or cladogram using the data in Table 1.
1. The two most closely related species have the fewest differences in amino acid sequence.
Place the two most closely related species on the two shortest branches of the tree.
2. Place the next two closest species on the next shortest branches.
3. Place the species which is the next closest on the next longest branch.
Continue until all the species have been placed.
C. Answer the
questions.
Page 1 of 4
Cytochrome Clab pt 2
kew 04/02

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