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.

Accepted Answer

histidine

Question 2

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

Accepted Answer

glycine

Question 3

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

Accepted Answer

Sequence homology implies a common evolutionary origin, whereas sequence similarity refers to the degree of matching between sequences, which may or may not be due to a shared ancestry.

Question 4

Most proteins have blocked amino and carboxyl terminals.

Accepted Answer

Most proteins in their native state have free amino (N-terminus) and carboxyl (C-terminus) terminals, not blocked. Blocking usually occurs during specific experimental procedures or post-translational modifications.

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.

Accepted Answer

The answer of Recombinant proteins containing a ________ can be...

Question 6

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

Accepted Answer

Conservative amino acid changes involve replacing one amino acid with another that has similar properties or structures. While these changes may not completely disrupt the structure or function of a protein, they can still affect stability and function to some extent. Therefore, the statement is false.

Question 7

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

Accepted Answer

The answer of ________ chromatography is used to separate proteins...

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.

Accepted Answer

The answer of At physiological pH, the carboxylic acid group...

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.

Accepted Answer

Mass spectrometry can be used for determining the mass of a protein (option A), determining the primary structure of proteins (option B), as well as detecting post-translational modifications on proteins (option C), making options A, B, and C all correct. Therefore, the best choice is E.

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

Accepted Answer

Selenocysteine is incorporated into proteins during translation as a result of a specific codon and tRNA. The other modified amino acids listed are typically added post-translationally.

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

Accepted Answer

Aspartic acid has a negatively charged side chain, making it hydrophilic and more likely to be found on the surface of a protein where it can interact with water molecules. Leucine, Proline, Valine, and Phenylalanine have hydrophobic side chains and would therefore be more likely to be found buried in the interior of a protein away from water molecules.

Question 12

Protein biosynthesis uses only L-amino acids.

Accepted Answer

Protein biosynthesis only uses L-amino acids, and not D-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.

Accepted Answer

The disulfide bonds in insulin form before the final proteolytic cleavage steps that yield mature insulin, not after. These bonds are crucial for the structural integrity of the insulin molecule and are formed during its precursor stages.

Question 14

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

Accepted Answer

The answer of Several homologous proteins can be aligned to...

Question 15

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

Accepted Answer

At pH=0, the environment is highly acidic, leading to the protonation of acidic and basic groups on the polypeptide. This generally results in a net positive charge, as the amino groups are protonated and the carboxyl groups are less likely to lose a proton in such an acidic environment.

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.

Accepted Answer

Each of the three stop codons do not encode any amino acids, modified or otherwise. They serve solely as translation stop signals.

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 ________.

Accepted Answer

The answer of An amide bond between the α-carboxylic acid...

Question 18

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

Accepted Answer

The answer of The chemical ________ can cleave amide bonds...

Question 19

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

Accepted Answer

Size exclusion chromatography separates proteins based on their size. The stationary phase is composed of porous beads with different pore sizes. Larger proteins are unable to penetrate the pores and are eluted first, while smaller proteins can enter the pores and take longer to be eluted. Therefore, the smallest proteins are eluted last.

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

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

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

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

Most proteins have blocked amino and carboxyl terminals.

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.

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

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

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

Applications of mass spectrometry include:

Which of the following modified amino acids is incorporated during translation rather than being modified post-translationally?

Which of the following amino acids would most likely be found on the surface of a protein?