test 2 questions Flashcards
1) Which of the following amino acids would most likely be found on the surface of a protein? A) Aspartic acid B) Leucine C) Proline D) Valine E) Phenylalanine
A
2) Protein biosynthesis uses only L-amino acids.
Answer: TRUE
3) All amino acids have a chiral α-carbon EXCEPT ________.
Answer: glycine
4) The side chain of ________ has a pKa in the physiological pH range and is therefore often involved in proton transfer during enzymatic catalysis.
Answer: histidine
5) At physiological pH, the carboxylic acid group of an amino acid will be ________, while the amino group will be ________, yielding the zwitterion form.
Answer: deprotonated, protonated
6) At pH=0, the net charge on a polypeptide will be negative.
Answer: FALSE
7) Which of the following modified amino acids is incorporated during translation rather than being modified post-translationally? A) Phosphoserine B) Selenocysteine C) γ-carboxyglutamate D) N-ε-acetyllysine E) 4-hydroxyproline
Answer: B
8) An amide bond between the α-carboxylic acid group of one amino acid and the α-amino group on another is called a ________.
Answer: peptide bond
9) The chemical ________ can cleave amide bonds on the C-terminal side of methionine residues.
Answer: cyanogen bromide
10) Which of the following is FALSE when considering the standard genetic code?
A) Three separate codons encode translation stop signals.
B) There are 64 possible codons to represent 20 common amino acids.
C) AUG serves as the translation start codon in most cases.
D) Apart from methionine, the only other amino acid with a single codon is tryptophan.
E) Each of the three stop codons can also encode rare modified amino acids.
Answer: E
11) Which of the following statements about insulin is INCORRECT?
A) In the active form it has two polypeptide chains joined by disulphide bonds.
B) It is synthesized as a random coil single chain on membrane-bound ribosomes.
C) The leader sequence is cleaved off after membrane transport.
D) The disulphide bonds form after the final proteolytic cleavage to yield mature insulin.
E) It is stored in the pancreas in an inactive form.
Answer: D
12) Most proteins have blocked amino and carboxyl terminals.
Answer: FALSE
13) Conservative amino acid changes never affect stability or function of a protein.
Answer: FALSE
14) When referring to the amino acid sequences of proteins, sequence homology is the same as sequence similarity.
Answer: FALSE
15) Several homologous proteins can be aligned to provide a ________ sequence.
Answer: consensus
Recombinant proteins containing a ________ can be purified using immobilized metal affinity chromatography and eluted by the addition of imidazole, a low pH buffer or a buffer containing EDTA.
Answer: his-tag, or hexahistidine-tag
17) Applications of mass spectrometry include:
A) determination of the mass of a protein.
B) determining the primary structure of proteins.
C) detection of post-translational modifications on proteins.
D) A and B.
E) A, B, and C.
Answer: E
18) In size exclusion chromatography, the smallest proteins are eluted last.
Answer: TRUE
19) ________ chromatography is used to separate proteins based on their surface charge.
Answer: Ion exchange
1) In considering protein secondary structure which of the following is INCORRECT?
A) An α helix repeats after 18 residues and has 3.6 residues per turn.
B) A network of main-chain hydrogen bonds connect β strands in a β sheet.
C) The most common structures are the α helix and the β sheet.
D) The 310 helix is right-handed and often contains proline residues.
E) The β strands can be in either parallel or antiparallel configuration.
Answer: D
2) The amino acid side chain residues in an α helix point outwards away from the center of the helix.
Answer: TRUE
3) ________ between amide protons and carbonyl oxygens is necessary to stabilize a regular folding of protein secondary structure.
Answer: Hydrogen bonding
4) A ________ plot describes which structures in a polypeptide are sterically possible and which are not based on the angles of rotation about the backbone Namide —Cα and Cα-Ccarbonyl bonds.
Answer: Ramachandran
5) Which of the following statements about α-keratins is FALSE?
A) They include a major class of protein that comprises hair, fingernails and animal skin.
B) Individual molecules are α-helical.
C) There is a strip of contiguous hydrophobic surface making a shallow spiral around the helix.
D) They include a small globular regions covalently linked to the surface.
E) Pairs of α-helices twist about each other in a coiled-coil structure held together entirely by hydrophobic interactions.
Answer: E
6) The protein that makes up about a third of the total protein mass in animals is: A) β-keratin. B) collagen. C) hemoglobin. D) myoglobin. E) α-keratin.
Answer: B
7) Fibroin is a β-sheet protein, with a high proportion of glycine.
Answer: TRUE
8) Tropocollagen is a double helix of two left-handed polypeptide chains.
Answer: FALSE
9) Scurvy results in weakness in collagen fibres because the enzymes that catalyze ________ of proline and lysine residues in collagen require Vitamin C.
Answer: hydroxylation
10) Which of the following is CORRECT when considering the tertiary structure of globular proteins?
A) β sheets are usually twisted or wrapped into barrel structures.
B) Hydrophobic residues are normally on the inside and hydrophilic residues are on the outside.
C) The amino acid proline never occurs in a region where the polypeptide chain bends or turns.
D) All parts of the proteins can be classified as helix, β sheet or turns.
E) None of the above.
Answer: B
11) Proteins cannot self-assemble into a functional conformation after they have been denatured.
Answer: FALSE
12) Protein folding is a random process, whereby a vast number of possible conformations are tested to find the desired most stable state.
Answer: FALSE
13) The folded conformation of proteins can be stabilized by the binding of a metal ion or cofactor.
Answer: TRUE
14) The interactions that stabilize multisubunit complexes are different to those that stabilize tertiary structure.
Answer: FALSE
15) Protein folding is a thermodynamically favorable process under physiological conditions because:
A) there is an increase in entropy associated with protein folding.
B) there is a decrease in entropy of the solvent by burying hydrophobic groups within the molecule.
C) of the large negative enthalpy change associated with many noncovalent interactions.
D) no intermediate stage disulphide bonds form during the folding process.
E) all of the above.
Answer: C
16) The cavity in the GroEL-GroES complex from E. coli provides a favorable environment that prevents ________ and mis-folding.
Answer: aggregation
17) Bovine spongiform encephalopathy is an infectious disease caused by a prion protein, which undergoes a ________ change to become pathogenic.
Answer: conformational
18) Proteins have an asymmetrical tertiary structure, while multisubunit proteins can exhibit several types of symmetry.
Answer: TRUE
19) The functional organization of proteins where specific complexes of two or more polypeptides are formed is called ________ structure.
Answer: quaternary
20) Which technique is able to investigate secondary structural features of proteins? A) Infrared spectroscopy B) Ultraviolet spectroscopy C) Fluorescence spectroscopy D) Circular dichroism E) All of the above
Answer: E
21) ________ spectroscopy can be used to study dynamic processes in solution.
Answer: Nuclear magnetic resonance
22) SDS gel electrophoresis can be used to determine:
A) whether subunits in a protein complex are identical or not.
B) the molecular mass of a native protein complex.
C) the overall charge on a polypeptide.
D) the molecular mass of denatured protein subunits.
E) none of the above.
Answer: D
1) Which of the following is NOT true of immunoglobulin molecules?
A) They consist of four polypeptide chains held together by disulphide bridges.
B) They have two identical heavy chains and two identical light chains.
C) Antigenic determinants reside only in the variable region of the light chains.
D) Proteolytic cleavage can generate fragments containing the antigen-binding site.
E) Some are membrane bound.
Answer: C
2) The immunoglobulin domain is a stable scaffold containing two antiparallel β- sheets upon which to display hypervariable loops.
Answer: TRUE
3) The specific interaction between an antibody and antigen occurs by virtue of both shape and ________ complementarity.
Answer: charge
4) Which of the following statements is FALSE?
A) Myoglobin is a single polypeptide chain folded about a heme prosthetic group.
B) Hemoglobin is a tetramer, each of which binds a heme group.
C) In both hemoglobin and myoglobin, iron is chelated by a tetrapyrole ring system.
D) The iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen.
E) Hydrogen bonding to a histidine residue assists stabilization of the Fe2+ -O2 complex in both hemoglobin and myoglobin.
Answer: D
5) Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.
Answer: FALSE
