Protein: Structure and Function Flashcards
1
Q
Building blocks of protein
A
Amino acids
2
Q
All 20 common amino acids are alpha-amino acids. T/F
A
T
3
Q
How many amino acids are commonly found in proteins?
A
20
4
Q
All the common amino acids are chiral molecules except for which amino acid?
A
Glycine
5
Q
What differentiates amino acids from each other?
A
R side chains
6
Q
Parts of an amino acid
A
Alpha-carbon, hydrogen atom, carboxyl group, amino group and R side chain
7
Q
Amino acid residues in protein molecules are exclusively D stereoisomers. T/F
A
F
They are L stereoisomers. D-amino acid residues have only been found in a few, generally small peptides.
8
Q
Which amino acid has the simplest structure?
A
Glycine
9
Q
Which of the common 20 amino acids are negatively charged or acidic?
A
Asp (D), Glu (E)
10
Q
Which of the common 20 amino acids are positively charged or basic?
A
Arg (R), Lys (K), His (H)
11
Q
Which of the common 20 amino acids are non-polar, allphatic?
A
Gly (G), Ala (A), Pro (P), Val (V), Leu (L), Iso (I), Met (M), Cys (C)
12
Q
Which of the common 20 amino acids are aromatic?
A
Phe (F), Tyr (Y), Try (W)
13
Q
Which of the common 20 amino acids are polar?
A
Asn (N), Gln (Q), Ser (S), Thr (T)
14
Q
Which of the common 20 amino acids are sulfur-containing?
A
Met (M), Cys (C)
15
Q
Amino acid with distinctive cyclic structure that contributes to rigidity of protein
A
Pro (P)
16
Q
Aromatic R groups are relatively polar. T/F
A
F
They are relatively nonpolar.
17
Q
Which aromatic amino acids are more polar than the others?
A
Tyr (Y) and Try (W) are significantly more polar than Phe (F)
18
Q
Gln
A
Glutamine
19
Q
Glu
A
Glutamate
20
Q
Asp
A
Aspartate
21
Q
Asn
A
Asparagine
22
Q
Arg
A
Arginine
23
Q
L
A
Leucine
24
Q
K
A
Lycine
25
Thr
Threonine
26
Try
Tryptophan
27
Tyr
Tyrosine
28
D
Aspartate
29
E
Glutamate
30
G
Glycine
31
N
Asparagine
32
P
Proline
33
Q
Glutamine
34
R
Arginine
35
T
Threonine
36
Y
Tyrosine
37
Which of the common 20 amino acids have a second carboxyl group?
Asp (D), Glu (E)
38
Which amino acid contains a hydroxyl group in its side chain?
A. Lysine
B. Glycine
C. Serine
D. Aspartic acid
C
39
Which amino acid can form disulfide bonds?
A. Cystine
B. Cysteine
C. Methionine
D. Proline
B
40
Which is a cyclic amino acid that provides rigidity in a polypeptide?
A. Serine
B. Proline
C. Isoleucine
D. Methionine
B
41
Which of the following molecules would be MOST EASILY separated from the rest in an electric field?
A. Isoleucine
B. Lysine
C. Alanine
D. Glycine
B
42
The following are hydrophilic / water soluble amino acids except:
a. Serine
b. Alanine
c. Glutamate
d. Arginine
B
43
Provides chemical individuality or distinction
C
44
Provides Hydrogen for Hydrogen bonding
D
45
Accepts a proton like a base
A
46
The chiral center
E
47
A water-soluble globular protein function as a transporter of lipophilic substance in the blood. Which among the choices below would likely be the component in the center of said globular protein rather than on the surface?
A. An arginine side chain
B. A lysine side chain
C. A phenylalanine side chain
D. A phosphate group covalently linked to a serine side chain
E. An oligosaccharide covalently linked to asparagines side chain
C
48
A genetic expert wants to improve the endurance of athletes by increasing the hemoglobin concentration in the erythrocytes. This however will entail increasing the water solubility of hemoglobin. Through genetic engineering, which of the following amino acid changes on the surface of the hemoglobin is most likely to increase its water solubility?
A. Arginine to Lysine
B. Leucine to Phenylalanine
C. Glutamine to Serine
D. Alanine to Asparaginine
E. Serine to Alanine
D
49
What is a zwitterion?
A dipolar ion that can act as either an acid or base
50
A zwitterion is amphoteric. T/F
T
51
Substances exhibiting both acidic and basic nature
Amphoteric
52
Substances which have both hydrophobic and hydrophilic ends
Amphiphilic
53
What is the simplest and smallest amino acid that does not have the D and L forms?
a) valine
b) leucine
c) glycine
d) alanine
C
54
Which one of the following correctly pairs an amino acid with a valid chemical characteristic?
A. Glutamine: contains a hydroxyl group in its side chain
B. Serine: can form disulfide bonds
C. Cysteine: Contains the smallest side chain
D. Isoleucine: nearly always found buried in the center of proteins
E. Glycine: Contains an amide group in its side chain
D
55
Which one of the following statements concerning glutamine is correct?
A. Contains three titratable groups
B. Is classified as an acidic amino acid
C. Contains an amide group
D. Has E as its one-letter symbol
E. Migrates to the cathode (negative electrode) during electrophoresis at pH 7.0
C
56
What holds together a chain of amino acids?
Peptide bonds
57
How are peptide bonds formed?
Through dehydration wherein the carboxyl group of an amino acid and the alpha-amino group of another amino acid loses elements of water
58
Why can't polypeptide chains rotate freely?
The partial double bonds make the molecule rigid
59
What is the primary structure of protein?
Amino acid sequence
60
What are protein's regular secondary structure?
α helix, β sheets
61
What bonds stabilizes the secondary structure of proteins?
H-bonds
62
Which of the following amino acids cannot undergo post-translational hydroxylation?
A. Lysine
B. Proline
C. Serine
D. Both A and C
C
63
Structural commonalities in all amino acids except:
A. Alpha carbon
B. Amino group
C. Carboxyl group
D. Methyl group
D
64
Which amino acid forms desmosin crosslinks in elastin?
A. Lysine
B. Glutamine
C. Alanine
D. Proline
A
65
Which of the following are the most important determinants of the electrophoretic mobility of amino acids?
A. Temperature and pressure
B. Buffer concentration and net charge
C. Net charge and molecular weight
D. Molecular weight and buffer concentration
C
66
Which of the following statements does NOT describe beta-keratin?
A. Assumes a “beta-pleated sheet” (zigzag) configuration
B. All H bonds are interchain rather than intrachain
C. Flexible, non-stretchable, and insoluble in water
D. Oriented in parallel direction for stability
E. R groups are mostly glycine and alanine
D
67
Peptide bonds are broken by conditions that denature proteins, such as heating or high concentrations
of urea. T/F
F
68
Prolonged exposure to a strong acid or base at elevated
temperatures can break peptide bonds. T/F
T
69
What BEST describes an amide plane?
a. 3-dimensional
b. An imaginary rotating plane made possible
by the peptide bond
c. A rigid, non-rotating plane provided by
the partial double character of the peptide
bond
d. A triangular plane
C
70
The secondary structure of keratins
α helix
71
Hydrogen bonds are individually
weak, but they collectively serve to stabilize the helix. T/F
T
72
Each turn of an α-helix contains how many amino acids?
3.6
73
What describes the hydrogen bond in secondary protein structure?
a. Between oxygen of the amino group of one amino acid and hydrogen of the carboxylic group of another
b. Between the oxygen of the carboxylic group of one amino acid and hydrogen of amino group of another
c. Stronger than peptide bond
d. Interchain and intrachain
B
74
Which factor/s will render the alpha-keratin resistant to water dissolution?
A. The amino acid protruding externally in the helix are big and have polar side chains
B. The amino acids in the interior of the helix are small and non-polar
C. The amino acids in the exterior of the helix are non-polar.
D. The presence of a lot of disulfide bonds
E. The participation of all amino acids in the formation of hydrogen bonds
C
75
Which of the following statements does NOT describe collagen?
A. High tensile strength and non-stretchable
B. Left-handed strands that are tightly intertwined
C. Found predominantly in tendon, hide, cartilage, and inner skin
D. Abundance of proline and hydroxyproline
E. Contains a lot of lysine, forming desmosine
E
76
Which of the following statements does not describe elastin?
A. Found predominantly in large arteries, alveoli sac and epiglottis
B. Rich in lysine
C. Abundance of proline and hydroxyproline
D. Desmosine provides stretchability of the protein
E. R-groups are nonpolar and small
C
77
Binds irreversibly with oxygen
A. Myoglobin
B. Hemoglobin
C. Both
D. Neither
D
78
Exhibit(s) an allosteric functional property
## Footnote
A. Myoglobin
B. Hemoglobin
C. Both
D. Neither
B
79
Release(s) oxygen only at a very low pO2
A. Myoglobin
B. Hemoglobin
C. Both
D. Neither
A
80
Has iron in ferrous form
A. Myoglobin
B. Hemoglobin
C. Both
D. Neither
C
81
What primarily stabilizes the tertiary structure of protein?
a. Hydrogen bonds
b. Hydrophobic interaction
c. Ionic interaction
d. Disulfide bonds
e. All of the above
E
82
What makes the tertiary protein structure water-soluble?
a. Hydrophobic R groups must be externally
located.
b. Hydrophilic R groups must be in the interior.
c. Exposed R groups must either be polar or
charged.
d. Must contain prosthetic group.
C
83
If protein structure is globular and water-soluble, what
then is its most probable function?
a. External protection
b. Carrier/transporter
c. Structural support
d. Ground substance
B
84
Which of the following would give Oxygen at levels of severe oxygen deprivation?
a) myoglobin
b) hemoglobin
c) Both
d) Neither
A
85
A peptide bond:
A. has a partial double-bond character.
B. is ionized at physiologic pH.
C. is cleaved by agents that denature proteins, such as
organic solvents and high concentrations of urea.
D. is stable to heating in strong acids.
E. occurs most commonly in the cis configuration.
A
Correct answer A. The peptide bond has a
double-bond character. Unlike its
α-amino and α-carboxyl
components of the peptide bond do
not accept or give off protons. The peptide bond
are not cleaved by organic solvents or urea, but
labile to strong acids. It is usually in the trans
configuration.
86
Which one of the following statements is correct?
A. The α-helix can be composed of more than
polypeptide chain.
B. β-sheets exist only in the antiparallel form.
C. β-bends often contain proline.
D. Motifs are a type of secondary structure.
E. The α-helix is stabilized primarily by ionic interactions between the side chains of amino acids.
C
β-bends often contain pro
line, which provides a kink. The α-helix differs
from the β-sheet that always involves the
coiling of a single polypeptide chain. The
sheet occurs both parallel and antiparallel
forms. Motifs are elements of tertiary structure.
The α-helix stabilized primarily by hydrogen
bonds between the -C= 0 and -NH groups of
peptide bonds.
87
Which of the following statements about protein
structure is correct?
A. Proteins consisting of one polypeptide can have
quaternary structure.
B. The formation of a disulfide bond in a protein
requires that the two participating cysteine residues
be adjacent to each other in the primary sequence
of the protein.
C. The stability of quaternary structure in proteins is
mainly a result of covalent bonds among the sub
units.
D. The denaturation of proteins always leads to irre
versible loss of secondary and tertiary structure.
E. The information required for the correct folding of a
protein is contained in the specific sequence of
amino acids along the polypeptide chain.
E
The correct folding of a protein is guided by specific interactions among the side chains of the amino acid residues of a polypeptide chain. The two cysteine residues that react to form the disulfide bond may be a great distance apart in the primary structure (or on separate polypeptides), but are brought into close
proximity by the three-dimensional folding of the
polypeptide chain. Denaturation may either be
reversible or irreversible. Quaternary structure
requires more than one polypeptide chain.
These chains associate through noncovalent
interactions.
88
How many oxygen molecule can a myoglobin bind?
One
89
Hemoglobin consists of a single polypeptide chain. T/F
F
It is myoglobin that consists of that. Hemoglobin is a tetramer, composed of more than one chains.
90
How many oxygen molecules can a hemoglobin bind?
Four
91
The interior of myoglobin consists of almost entirely nonpolar or polar molecules?
Nonpolar
92
The polar amino acids of myoglobins are located on the surface or interiorly?
Surface
93
What is heme-heme interaction?
The increase in oxygen affinity of the remaining subunits of hemoglobin caused by the binding of the first oxygen
94
The oxygen-binding curve of hemoglobin is sigmoidal curve because
A. The binding of oxygen to a heme group increases the oxygen affinities of the other heme groups
B. The heme groups of the alpha-chains have a higher oxygen affinity than the heme groups of the beta-chains
C. The distal histine allows the hemoglobin molecule to change its conformation in response to an elevated carbon dioxide concentration
D. The subunits are held in place by interchain disulfide bonds
E. The solubility of the hemoglobin changes with its state
A
95
Which one of the following statements concerning the
binding of oxygen by hemoglobin is correct?
A. The Bohr effect results in a lower affinity for oxygen at higher pH values.
B. Carbon dioxide increases the oxygen affinity of hemoglobin by binding to the amino terminal groups of the polypeptide chains.
C. The oxygen affinity of hemoglobin increases as the
percent saturation increases.
D. The hemoglobin tetramer binds four molecules of 2,3BPG.
E. Oxyhemoglobin and have the same
affinity for protons
C
The binding of oxygen at
one heme group increases the oxygen affinity of
the remaining heme groups in the same
molecule. Carbon dioxide decreases oxygen
affinity because it lowers the pH; also binding of
carbon dioxide stabilizes the taut, deoxy form.
Hemoglobin binds one molecule of 2,3-BPG.
Deoxyhemoglobin has a greater affinity for
protons and, therefore, is a weaker acid.
96
The most abundant protein in the body
Collagen
97
A typical collagen molecule is made up of how many polypeptide chains wound around one another?
Three
98
Collagen is rich in which amino acids?
Proline and glycine
99
Why is proline and glycine important in collagen?
Proline causes the "kinks" in the peptide chain, and glycine, due to its size, fits into the restricted spaces where the three chains of the helix come together.
