Concepts in Biochemistry, Chapter 4
1.
What determines the tertiary structure of a protein?
A.
a
-helices
B.
b
-sheets
C.
Primary structure
D.
Hydrophobic interactions
2.
Amino acids are held together in proteins by peptide bonds. Which of the following is true of a peptide bond?
A.
Planar
B.
Partial double-bond character
C.
Rigid
D.
trans
configuration
E.
All of the above
3.
Proteins have regularly repeating structures called secondary structures. One of these is an
a
-helix. Which of the following are true of an
a
-helix?
A.
H bonds between C=O of the n
th
amino acid and N-H of n+4
th
amino acid.
B.
L-amino acids favor a right-handed
a
-helix.
C.
Proline disrupts an
a
-helix
D.
An
a
-helix contains3.6 amino acid residues per turn.
E.
All of the above
4.
Another secondary structure is a
b
-sheet. Which statements are true of
b
- sheets?
A.
b
-sheets
exist in either parallel (both N
g
C) directions; not in antiparallel (one C
g
N and one N
g
C) directions.
B.
b
-sheets
contain almost no alanine or glycine residues.
C.
H bonds are formed between intrachain and interchain amino acid side chains.
D.
The size and charge of R group side chains is unimportant.
5.
Bends or loops are considered to be non-regular secondary structures because they do not repeat. Which of the following is true of bends?
A.
Bends do not reverse the direction of a polypeptide chain.
B.
Bends connect regions of
a
-helixes and
b
-sheets.
C.
Glycine and proline are absent from bends.
D.
Bends are usually found at the C terminus.
6.
Fill in each blank with the letter that matches the described secondary structure.
bbbb
___
aa___
bab___
bb___
Answer:
7.
Collagen, a major component of skin and bone, is a fibrous protein with repeating units of Pro-Gly-X or Hyp-Gly-X. Collagen has strength because the structure is:
A.
Web like
B.
Three interlaced helices forming a rope
C.
An
a
-helix
D.
A
b
-sheet
E.
A
b
-barrel
8.
Proteins must fold into their final structures to be functional. Which of the following statements are not true?
A.
Protein tertiary structure is determined by the primary sequence.
B.
Hydrophobic amino acids are buried in the interior.
C.
Structural motifs such as
aa
or
bb
act as seeds around which the rest of the protein folds.
D.
Helper proteins called chaperones may assist protein folding.
E.
Folding begins with disulfide bond formation.
9.
Hemoglobin is the O
2
carrier in the blood. It is made up of 4 polypeptide chains. Each chain contains the heme, which is a prosthetic group containing Fe held in place by 4 Nitrogen atoms. Which of the following is a true statement:
A.
O
2
binding is achieved by the heme groups of hemoglobin.
B.
A sigmoidal curve is characteristic of uncooperative binding.
C.
Allosteric interactions are driven by a difference in charge of nearby molecules.
D.
Increased O
2
binding to hemoglobin at low pH describes the Bohr effect.
E.
Sickle cell anemia has no effect on a patient's hemoglobin.
10.
Hair contains the fibrous protein
a
keratin. How does a permanent wave (perm) change the shape of hair?
A.
Hair fibers are stacked.
B.
-keratin is converted from the "soft" to "hard" form.
C.
Disulfide bonds are broken and reformed.
D.
Hair is made water-soluble.
11.
The salt-tolerant bacteria
Halobacterium halobium
contains the protein bacteriorhodopsin in its cell membrane. Bacteriorhodopsin consists of a bundle of
a
-helical rods. How does this protein allow
H. halobium
to live in water with a high salt concentration?
A.
Bacteriorhodopsin turns the cell purple.
B.
Bacteriorhodopsin acts as a proton channel in the membrane.
C.
Bacteriorhodopsin forms salt crystals.
D.
Bacteriorhodopsin acts as an O
2
carrier.
E.
All of the above
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