Deck 5: Introduction to Proteins: the Primary Level of Protein Structure

Question 1

The side chain of ________ has a pKa in the physiological pH range and is therefore often involved in proton transfer during enzymatic catalysis.

Answer 1

histidine

Question 2

All amino acids have a chiral α-carbon EXCEPT ________.

Answer 2

glycine

Question 3

When referring to the amino acid sequences of proteins, sequence homology is the same as sequence similarity.

Answer 3

False

Question 4

Most proteins have blocked amino and carboxyl terminals.

Question 5

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.

Question 6

Conservative amino acid changes never affect stability or function of a protein.

Question 7

________ chromatography is used to separate proteins based on their surface charge.

Question 8

At physiological pH, the carboxylic acid group of an amino acid will be ________, while the amino group will be ________, yielding the zwitterion form.

Question 9

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.

Question 10

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

Question 11

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

Question 12

Protein biosynthesis uses only L-amino acids.

Question 13

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.

Question 14

Several homologous proteins can be aligned to provide a ________ sequence.

Question 15

At pH=0, the net charge on a polypeptide will be negative.

Question 16

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.

Question 17

An amide bond between the α-carboxylic acid group of one amino acid and the α-amino group on another is called a ________.

Question 18

The chemical ________ can cleave amide bonds on the C-terminal side of methionine residues.

Question 19

In size exclusion chromatography, the smallest proteins are eluted last.