Chapter 5—Proteins: Their Primary Structure and Biological Functions
MULTIPLE CHOICE
1. A gene can be defined as:
a.
the unique function that some cells have but other cells do not have.
b.
a specific segment of nucleotide bases in DNA that encode for the synthesis of a particular
protein.
c.
a single strand of DNA that is designated as the sense strand.
d.
a functional segment of a unique protein.
e.
the segment of DNA that is changed in a mutation.
2. Proteins with two different polypeptide chains are:
a.
monomeric proteins.
b.
trimeric proteins.
c.
homodimeric proteins.
d.
heterodimeric proteins.
e.
none of the above.
3. Hemoglobin is an 2, 2 ____ whereas, glutamine synthatase from E. coli is an 2 ____.
a.
-homodimer, -homomultimer
b.
-heteromultimer, -homomultimer
c.
-homomultimer, -heterodimer
d.
-heterodimer, -monomeric protein
e.
-heterodimer, -homomultimer
4. Fibrous proteins, such as collagen, have which one of the following properties?
a.
Highly soluble in water.
b.
Their hydrophilic residues are directed into the interior of the protein.
c.
Exhibit enzymatic activity.
d.
Serve structural roles in the cell.
e.
Monomeric.
5. Which of the following IS NOT a characteristic of globular proteins?
a.
Insoluble in water.
b.
Roughly spherical.
c.
Folded so that the hydrophobic amino acids are in the interior of the molecule.
d.
Hydrophobic side chains are exposed to the water.
e.
None, all are true.
6. Molecules of a given protein have all EXCEPT:
a.
a fixed amino acid composition.
b.
a defined amino acid sequence.
c.
a sequence read from C-terminal end to N-terminal end.
d.
an invariant molecular weight.
e.
a nucleotide sequence from which they are encoded.
7. Membrane proteins differ from globular proteins in that:
a.
membrane associated amino acids usually have polar side chains.
b.
membrane proteins are much more soluble in detergents than water.
c.
membrane proteins usually have more hydrophobic amino acids.
d.
globular proteins are water insoluble.
e.
All are true.
8. A common reaction of two cysteine residues in proteins results in the formation of ____.
a.
thioester bonds
b.
disulfide bonds
c.
dithiol bonds
d.
thioether bonds
e.
none of the above
9. The amino acid sequence is defined as ____ structure.
a.
primary
b.
secondary
c.
tertiary
d.
quaternary
e.
all are true
10. –Helix and -strand are components of ____ structure
a.
primary
b.
secondary
c.
tertiary
d.
quaternary
e.
all are true
11. All of the information necessary for a protein to achieve its intricate architecture is contained within its
____ structure.
a.
primary
b.
secondary
c.
tertiary
d.
quaternary
e.
all are true
12. The formation of a disulfide bond would be an example of what level of protein structure?
a.
primary
b.
secondary
c.
tertiary
d.
quaternary
e.
both c and d are correct
13. Which of the following IS NOT a characteristic of a protein’s overall conformation?
a.
The overall three-dimensional architecture of the protein.
b.
Achieved by breaking and reforming covalent bonds.
c.
Achieved by rotations about each single bond along the peptide backbone.
d.
The result of amino acid side-chain interactions.
e.
None, all are true.
14. Which of the following levels of protein structure is correctly defined?
a.
primary: interaction between subunits of a protein
b.
secondary: hydrogen bond arrangement of polar R-groups
c.
tertiary: three dimensional arrangement of all atoms in a single peptide
d.
quaternary: order of amino acid residues in the peptide chain
e.
none of the above are correct
15. Which of the following is not a commonly used technique for protein isolation and purification?
a.
gas-liquid chromatography.
b.
ion exchange chromatography.
c.
electrophoresis.
d.
solubility (“salting in” and “salting out”).
e.
affinity chromatography.
16. Even though acid hydrolysis of proteins is favored over basic hydrolysis, with acid hydrolysis ____ is
destroyed and must be estimated by other means.
a.
Lys
b.
Leu
c.
Asp
d.
Cys
e.
Trp
17. Amino acid analysis of a protein gives:
a.
the sequence of the protein.
b.
the number of residues of each amino acid in the protein.
c.
the molecular weight of the protein.
d.
the percentage or ratio of the various amino acids in the protein.
e.
an identification of the N-terminal and C-terminal amino acids.
18. The amino acid sequence is NOT:
a.
a distinctive characteristic of a polypeptide.
b.
encoded by the nucleotide sequence of DNA.
c.
a form of genetic information.
d.
read from N-terminal end to C-terminal end.
e.
constant for proteins with the same function from different organisms.
19. Edman degradation will:
a.
determine the C-terminal amino acid by using a carboxypeptidase.
b.
cleave the protein into a multitude of smaller peptides.
c.
compare overlapping sets of peptide fragments.
d.
determine the N-terminal amino acid.
e.
generate two different, but overlapping sets of peptide fragments.
20. After treating a protein with trypsin, which of the following techniques could be used to determine its
identity by peptide mass fingerprinting?
a.
NMR
b.
MALDI-TOF mass spectrometer
c.
HPLC
d.
gel electrophoresis
e.
none of the above
21. Reaction of the peptide, ala-met-lys-ser, with phenylisothiocyanate (PITC) at pH 8.0 followed by mild
acidification (first cycle of Edman method) would release:
a.
the labeled peptide ala-met-lys-ser-PTH.
b.
PTH-ala, PTH-ser, PTH-lys and PTH-met.
c.
PTH-ser and the peptide ala-met-lys.
d.
PTH-ala and the peptide met-lys-ser.
e.
All of the above.
22. What is the product formed from the acid hydrolysis of a simple amide?
a.
acid & base
b.
aldehyde & alcohol
c.
acid & amine
d.
ester & alcohol
e.
amine & aldehyde
23. Which of the following would not be a useful procedure for dissociating the subunits of a multimeric
protein in order to sequence the individual subunits?
a.
Exposure to pH extremes (ie, pH 1 or pH 13).
b.
High salt concentrations.
c.
6 N HCl at 110C for 24 hours.
d.
8 M urea.
e.
6 M guanidinium chloride.
24. Insulin is a polypeptide hormone that contains two short polypeptide chains linked by two interstrand
disulfide bonds. The most logical order of events to perform in order to sequence this protein would
be:
A.
The peptides are reduced with mercaptoethanol.
B.
The peptides are sequenced using Edman chemistry.
C.
The peptides are separated by chromatography techniques.
D.
The peptides are alkylated with iodoacetamide.
a.
A, D, C, B
b.
C, A, D, B
c.
C, B, A, D
d.
A, B, C, D
e.
A, C, D, B
25. The C-terminal residue of a polypeptide can be determined by first cleaving the polypeptide with:
a.
chymotrypsin.
b.
carboxypeptidase.
c.
trypsin.
d.
CNBr.
e.
none of the above.
26. ____ is specific in hydrolyzing only peptide bonds in which the carboxyl function is contributed by an
arginine or a lysine residue.
a.
Chymotrypsin
b.
Carboxypeptidase
c.
Trypsin
d.
CNBr
e.
None of the above.
27. The advantage of treating separate samples of a protein with two or more enzymes when sequencing a
protein is that the products are:
a.
more homogeneous.
b.
sequenceable without further chromatography.
c.
fragments with the same N- and C-terminal amino acids.
d.
fragments with sequence overlaps.
e.
all are true.
28. What is the overall net charge on the peptide lys-lys-ser-glu at pH 7.0?
a.
+2
b.
+1
c.
0
d.
−1
e.
−2
29. All of the statements about the peptide val-asp-trp–asn-ser are correct EXCEPT:
a.
This peptide would show a strong absorption band at 280 nm.
b.
Reaction with chymotrypsin would yield two peptides.
c.
To synthesize this peptide using the solid phase method of Merrifield, the amino acid
directly attached to the resin would be valine.
d.
After the second round of Edman degradation using the reagent PITC, the PTH-amino
acid residue released would be PTH-asp.
e.
The peptide would be converted to a dipeptide and a tripeptide by chymotrypsin.
30. Which of the following would be a possible amino acid sequence for an oligopeptide given the
1.
The amino acid composition is found to be [ala, lys, phe, met, cys, plus some
decomposition products].
2.
The peptide has a molecular weight around 700 Da and absorbs at 280 nm.
3.
Treatment with carboxypeptidase results in tryptophan and a peptide.
4.
CNBr treatment yields a tetrapeptide and a dipeptide.
5.
Trypsin digestion produces an amino acid and a pentapeptide with met on the amino end.
6.
Chymotrypsin digestion yields a dipeptide and a tetrapeptide.
a.
trp-lys-met-cys-met-ala
b.
lys-met-cys-phe-ala-trp
c.
trp-ala-phe-cys-met-lys
d.
lys-ala-cys-phe-met-trp
e.
lys-met-cys-ala-phe-trp
31. The preponderance of protein sequence information is now derived from:
a.
chemical sequencing (Edman method).
b.
mass spectrometry.
c.
mass spectrometry-mass spectrometry.
d.
translating the nucleotide sequence of genes into codons, and thus amino acid sequence.
e.
none of the above.
32. Homologous proteins such as hemoglobin from different organisms do NOT:
a.
have nearly identical lengths.
b.
share little sequence homology with other proteins with similar function (e.g., myoglobin).
c.
share a significant degree of sequence similarity.
d.
perform the same function in different organisms.
e.
have sequence identity in direct correlation to the relatedness of the species from which
they were derived.
33. Although they have very different functions, hen egg white lysozyme and ____ share similar sequence
homology and similar tertiary structure.
a.
trypsin
b.
-lactalbumin
c.
thrombin
d.
hemoglobin
e.
chymotrypsin
34. The diversity in hemoglobin mutants indicates that:
a.
any amino acid change is relatively important.
b.
any amino acid change is lethal to the organism.
c.
specific amino acid changes drastically alter one or more functions of a protein.
d.
any amino acid change will have the same effect on the protein function.
e.
All are true.
35. Proteins destined for an extracellular location are characteristically:
a.
phosphoproteins.
b.
glycoproteins.
c.
lipoproteins.
d.
nucleoproteins.
e.
flavoproteins.
36. Proteins that do NOT perform any obvious chemical transformation, but control the ability of other
proteins to carry out their physiological functions are:
a.
enzymes.
b.
regulatory proteins.
c.
transport proteins.
d.
storage proteins.
e.
structural proteins.
37. Hemoglobin is an example of a(n):
a.
enzyme.
b.
regulatory protein.
c.
transport protein.
d.
storage protein.
e.
structural protein.
38. Collagen is an example of a(n):
a.
enzyme.
b.
regulatory protein.
c.
transport protein.
d.
storage protein.
e.
structural protein.
39. The lac repressor is an example of a(n):
a.
enzyme.
b.
regulatory protein.
c.
transport protein.
d.
storage protein.
e.
structural protein.
40. Which of the following reagents is correctly defined?
a.
iodoacetic acid: reduces disulfide bonds
b.
guanadinium hydrochloride: disrupts ionic interactions and hydrogen bonds
c.
phenylisothiocyanate: reacts with free carboxyl groups
d.
cyanogen bromide: reacts with internal cysteine residues
e.
performic acid: reacts with free cysteine residues
41. Which of the following protease enzymes is correctly identified with its specificity?
a.
trypsin: cleaves on C-side of acidic amino acids
b.
chymotrypsin: cleaves on C-side of aliphatic amino acids
c.
staphylococcal protease: cleaves on C-side of acidic amino acids
d.
clostripain: cleaves on C-side of lysine
e.
none of the above are correct
42. Which of the following amino acids occurs most frequently in proteins?
a.
methionine
b.
alanine
c.
tryptophan
d.
tyrosine
e.
histidine
43. Which of the following mutations would probably be least likely to impact the function of the protein?
a.
Lys to Ser
b.
Ala to Asp
c.
His to Pro
d.
Val to Ile
e.
Phe to Tyr