Tutorial Practice Questions - Week 4 Flashcards
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
a. Nonpolar uncharged R group
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
b. Glutamic acid
The following amino acid causes a kink or bend in the alpha-helix
a. Ala
b. Glu
c. Pro
d. Trp
c. Pro
Disulfide bonds can form between the thiol groups of which amino acid?
a. Cysteine
b. Asparagine
c. Methionine
d. Histidine
e. Glycine
a. Cysteine
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
c. 5.97
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
a. It can act as an acid or a base
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
d. Basic R groups
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
d. 99
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?
b. What is its charge at physiological pH?
c. Can you quantify its concentration using a spectrophotometer and measuring its A280 nm? Why?
a. It has 21 AA residues, therefore it has 20 peptide bonds
b. (3x Glu = -3; (5x Lys, 1 Arg) = +6; overall charge is +3
c. Yes, because it has 5 L-Trp. Trp is an aromatic AA that absorbs light at 280 nm.
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
a.
T/F: The pKa value of the amino group is around 2 for all amino acids.
False, pKa of amino group is close to 9-10. The pKa of carboxyl groups is around 2.
T/F: There are three aromatic amino acids.
True (Phe, Trp, Tyr)
T/F: Amino acids are joined together with peptide bonds.
True
T/F: Amino acids in biological proteins are normally L-stereoisomers.
True. Most amino acids in biological proteins are L-amino acids, with few exceptions that have D-amino acids
T/F: Glycine is an achiral amino acid.
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)
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
b.
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
c. The side chains form H-bonds
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.
c.
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
e.
The α-helix and the β-pleated sheet are part of which protein structure?
a. Primary
b. Secondary
c. Tertiary
d. quaternary
b.
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
c.
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 molecules
c.
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
b.
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
b.
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
d.
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
e.
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
b.
