Amino Acids & Peptides Revison Questions

Question 1

All hydrophobic amino acids (valine, leucine, isoleucine, etc.) share which of the following properties?

a. Nonpolar uncharged R group
b. Basic R groups
c. Polar uncharged R groups
d. Aromatic R groups

Answer 1

a. Nonpolar uncharged R Group

Question 2

Which of the following amino acids has a net negative charge at physiologic pH (~7.4)?

a. Lysine
b. Glutamic acid
c. Histidine
d. Lysine
e. Asparagine
f. Glutamine

Answer 2

b. Glutamic Acid

Question 3

The following amino acid causes a kink or bend in the alpha-helix

a. Ala
b. Glu
c. Pro
d. Trp

Answer 3

c. Pro

Question 4

Disulfide bonds can form between the thiol groups of which amino acid?

a. Cysteine
b. Asparagine
c. Methionine
d. Histidine
e. Glycine

Answer 4

a. Cysteine

Question 5

The amino acid glycine is a neutral amino acid. Its alpha-carboxyl group has a pKa
of 2.34 and its alpha-amino group has a pKa of 9.6. What is the pI of glycine?
a. 2.06
b. 3.63
c. 5.97
d. 7.26
e. 11.94

Answer 5

c. 5.97

Question 6

All Amino Acids are considered amphoteric. If a substance is said to be amphoteric,
what is true of this substance?
a. It can act as an acid or a base
b. It can function in both cold and warm temperature
c. It can function in high salt environments
d. It has a polar head and a non-polar region

Answer 6

a. It can act as an acid or a base

Question 7

A polypeptide with a net positive charge at physiologic pH (~7.4) most likely contains
amino acids with R groups of what type?
a. Acidic R groups
b. Aliphatic R groups
c. Aromatic R groups
d. Basic R groups

Answer 7

d. basic R groups

Question 8

How many water molecules are lost from the condensation of 100 amino acids into a
polypeptide?
a. 100
b. 102
c. 101
d. 99
e. 98

Answer 8

d. 99

Question 9

The peptide with the sequence:
Lys-Glu-Thr-Trp-Trp-Glu-Thr-Trp-Trp-Thr-Glu-Trp-Ser-Gln-Pro-Lys-Lys-Lys-Arg-Lys-Val
a. How many peptide bonds it has?

Answer 9

It as 21 AA residues, therefore it has 20 petide bonds

Question 10

The peptide with the sequence:
Lys-Glu-Thr-Trp-Trp-Glu-Thr-Trp-Trp-Thr-Glu-Trp-Ser-Gln-Pro-Lys-Lys-Lys-Arg-Lys-Val
b. What is its charge at physiological pH?

Answer 10

(3x Glu = -3; (5x Lys, 1 Arg) = +6; overall

charge is +3

Question 11

The peptide with the sequence:
Lys-Glu-Thr-Trp-Trp-Glu-Thr-Trp-Trp-Thr-Glu-Trp-Ser-Gln-Pro-Lys-Lys-Lys-Arg-Lys-Val
Can you quantify its concentration using a spectrophotometer and measuring
its A280 nm? Why?

Answer 11

Yes, because it has 5 L-Trp. Trp is an aromatic AA that

absorbs light at 280 nm.

Question 12

What accounts for peptide bond planarity within a polypeptide?

a. Partial double bond character of the peptide bond
b. The fully double bonded peptide bond
c. The Hydrogen bonding between amino acid chains and water
d. Electronegativity difference between nitrogen and carbon
e. The peptide bond is not planar, it can rotate relatively freely

Answer 12

a. partical double bond character of the peptide bond

Question 13

True or False: The pKa value of the amino group is around 2 for all amino acids.

Answer 13

False, pKa of

amino group is close to 9-10. The pKa of carboxyl groups is around 2.

Question 14

True or False:

ttere are three aromatic amino acids

Answer 14

True (Phe, Trp, Tyr)

Question 15

True or False: Amino acids are joined together with peptide bonds

Answer 15

True

Question 16

True or False: Amino acids in biological proteins are normally L-stereoisomers.

Answer 16

True. Most
amino acids in biological proteins are L-amino acids, with few exceptions that
have D-amino acids

Question 17

True or False: Glycine is an achiral amino acid

Answer 17

. True, Gly is the only achiral amino acid. To be
chiral, the Carbon alpha should bond to 4 different groups (in Gly, the Carbon
alpha is bound to 2 H)

Question 18

Which groups on a pair of amino acids must react to form a peptide bond?

a. Both amino groups
b. The amino group of one and the carboxyl group of another
c. The R-group of one and the amino group of the other
d. Two carboxyl groups

Answer 18

b. The amino group of one and the carboxyl group of another

Question 19

What is true about uncharged polar amino acids?

a. The side chains carry a net charge
b. The side chains are insoluble in water
c. The side chains form H-bonds
d. They participate in hydrophobic effect

Answer 19

c. the side chains form H-bonds

Question 20

Quaternary structure is associated with

a. The overall shape of the polypeptide chain
a. The sum of secondary and tertiary interactions
b. Simple protein with only one subunit
c. The organisation of polypeptides in a multisubunit protein.

Answer 20

c. the organisation of polypeptides in a multisubunit protein

Question 21

The tertiary structure of a protein is usually a result of which of the following

a. H-bonds
b. Electrostatic interactions
c. Hydrophobic effect
d. Disulfide bonds
e. All of these

Answer 21

e. all of these

Question 22

The α-helix and the β-pleated sheet are part of which protein structure?

a. Primary
b. Secondary
c. Tertiary
d. quaternary

Answer 22

b. secondary

Question 23

A new drug is developed to selectively cleave covalent bonds between two sulfur
atoms of non-adjacent amino acids in a polypeptide chain. Which level of protein
structure is affected by the drug?
a. Primary
b. Secondary
c. Tertiary
d. Quaternary

Answer 23

c. tertiary

Question 24

The major protein component of human hair is α-keratin. Hair ‘straighteners’ are
commonly used tools which use heat to iron hair into temporarily lying flat and
straight. What is the best biological explanation for this phenomenon?
a. Hair straighteners disrupt disulfide bridges in α-keratin
b. Hair straighteners denature proteins by disrupting the pH
c. Hair straighteners disrupt hydrogen bonds in α-keratin
d. Hair straighteners disrupt ionic bonds between α-keratin molecule

Answer 24

c. hair straighteners distrpt hydorgen bonds in a-keratin

Question 25

Which of the following properties of a protein is least likely to be affected by changes
in pH?
a. Tertiary structure
b. Primary sequence
c. Secondary structure
d. Net charge

Answer 25

b. primary sequence

Question 26

A hydrophobic amino acid such as isoleucine is most likely to be found in which of
these locations?
a. On the surface of a cytosolic protein
b. Near the core of a cytosolic protein
c. Within a transmembrane segment of a protein
d. On the cytosolic surface of a membrane protein

Answer 26

b. Near the core of a cytosolic protein

c. Within a transmembrane segment of a protein

Question 27

Which of the following properties of a protein is primarily responsible for the function
of that particular protein?
a. The affinity of that protein to nonpolar compounds
b. The molecular weight of the protein
c. The number of amino acids contained by the protein
d. The structural conformation of the protein

Answer 27

d. the structural conformation of the protein

Question 28

Where do hydrophobic amino acids cluster within a protein?

a. Away from water
b. Near water
c. The interior of a protein
d. The exterior of a protein
e. Both the interior of a protein and away from water

Answer 28

e. both the interior of a protein and away from water

Question 29

The "kinks" formed by proline residues in a chain of amino acids is an example of what
degree of amino acid structure?
a. Quaternary
b. Secondary
c. Primary
d. Tertiary

Answer 29

b. secondary