Transcript Document

1. The peptide unit is rigid and planar because:
A. The R group interferes with the rotation.
B. The carbon-nitrogen bond has partial double-bond
character.
C. The bond between the  carbon atom and the
peptide nitrogen atom is not free to rotate.
D. The secondary structure affects the strength of the
peptide
unit.
E. There is a large degree of freedom of rotation on
either side of
the peptide unit.
• 2.  helices:
•
A. Constitute a common type of secondary structure,
characterized by an almost planar, fully extended
configuration of
the polypeptide chain.
•
B. Are stabilized by hydrogen bonds between adjacent
chains.
•
C. Are always left-handed.
•
D. Exhibit a tightly coiled polypeptide main chain from
which the
R groups extend outward.
•
E. Are a major structural component of collagen.
• 3. Gel-filtration chromatography is a method for purification of
proteins which is based on:
•
A. The charge of the proteins.
•
B. The specific binding of the proteins to a certain matrix.
•
C. The capacity of the proteins to traverse a
semipermeable
membrane.
•
D. The combined effect of solubility and charge.
•
E. The size of the proteins, which determines their
migration
through a column filled with special carbohydrate
beads.
• 4. Proteins are made of a set of 20 amino acids that differ in
the size,
shape, charge and chemical nature of the R group.
Which of the following
statements is not true?
•
A. The aliphatic side chains of leucine and isoleucine are
highly
hydrophobic
•
B. Amino acids cysteine and methionine include a sulfur
atom in
their side chains.
•
C. Both cysteine and methionine can form disulfide bridges
(-S-S).
•
D. Phenylalanine, tyrosine and tryptophan have aromatic
side chains.
•
E. Amino acids at neutral pH are predominantly dipolar
ions (zwitterions).
• 5. The mean molecular weight of a
protein composed of 2,000 amino acids
is:
•
A. 220,000 kDa.
•
B. 200,000 daltons.
•
C. 2,200 kDa.
•
D. 220 kDa.
•
E. 2,000 atomic mass units.
• .
•
•
•
The term zwitterion denotes:
A. The un-ionized form of an amino acid.
B. A commonly used synonym for an amino acid.
C. The presence of single + and - charges on the
same molecule (i.e., a
dipolar ion).
•
D. The fully dissociated from of an amino acid.
•
E. The fully protonated form of an amino acid.
• .
An enzymatically-catalyzed reaction is faster than the same reaction
performed in the absence of enzyme because:
• A.
The enzyme allows the reaction to occur under standard
conditions.
• B.
The enzyme is usually a bigger molecule than the
reactants.
• C.
The enzyme lowers the free energy of activation of the
reaction.
• D.
The enzyme shifts reaction equilibrium towards the
products.
• E.
The enzyme increases the free energy of activation of
the reaction.
• The tripeptides Trp-Ala-Ser and Ser-Ala-Trp
exhibit:
•
•
•
•
•
A.
B.
C.
D.
E.
Identical amino acid sequence.
Identical N-terminal amino acid.
Identical C-terminal amino acid.
Identical amino acid sequence and composition.
Identical amino acid composition.
• . Myoglobin does not bind oxygen in a
cooperative fashion because:
• A.
The affinity of myoglobin for oxygen is very low.
• B.
Myoglobin is a monomeric protein.
• C.
The heme group is covalently bound to the polypeptide
chain.
• D.
There is no 2,3-BPG in muscles.
• E.
Myoglobin does not bind 2,3-BPG.
• Phosphorylation:
• A. Is an efficient mechanism for regulation of
enzymatic activity.
• B. Takes place both in intracellular and
extracellular (secreted) proteins.
• C. Is an irreversible process.
• D. Takes place only on tyrosine residues.
• E. Is catalyzed by phosphatases.