University of Cape Town
Department of Molecular & Cell Biology
Course Code: MCB200F
Course Name: Intro to Biochemistry
Paper:
2 (Theory)
Date:
18 June 2002
No.of pages:
6
Marks:
120
Time: 3 Hours
Venue:
Zoo 1
- a.m.
Attachments:
2 pages & graph paper
ANSWER
ALL
THE QUESTIONS
In the interest of economy please write on both sides of the exam script
Please answer each section in a different answer book.
Section 1
Amino acids and proteins
Total marks: 32
1.
A binding site on a protein depends critically on the pK
a
of a single glutamic acid
residue.
What would the effect on the pK
a
be (increases or decreases), if the following
changes were made to this critical glutamic acid?
(a)
An arginine side-chain was brought into close proximity.
(b)
A C-terminal carboxyl group was brought into close proximity.
(c)
Moving the glutamic acid residue from the outside to the hydrophobic interior of the
protein.
[6]
2.
Given the following peptide:
Asn-Ala-Lys
(a)
Draw the complete structure of this tripeptide at pH 7.0
, with the side chains oriented
in the trans configuration (show every atom including hydrogens).
(6)
(b)
Estimate the approximate charge of this peptide at pH 7.0.
(2)
(c)
Circle any one
of the internal phi torsion angles.
(1)
[9]
3.
What role does cysteine play in stabilizing the tertiary structure of secretory proteins as
opposed to proteins found in the cytoplasm of eukaryotic cells?
(hint: intracellular
milieu of cells is highly reducing and proteases compartmentalized).
[4]
4.
Nearly every third amino acid residue in the primary structure of collagen is glycine.
Another abundant amino acid that is present is proline.
(a)
Which weak non-covalent force is mainly responsible for stabilizing the collagen triple
helix?
(1)
(b)
Name the amino acid residue that plays an important role in stabilizing the triple helix as
alluded to in (a)?
(2)
[3]
1
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5.
Determine the amino acid sequence of the following oligopeptide about which the
following data are known:
(a)
The amino acid composition is found to be (Ala, Lys, Phe, Met, Gly, Cys).
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- Fall '10
- Williams
- amino acid residue, glutamic acid residue
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