Deck 4: Amino Acids

Question 1

Which of the following has partial double-bond character?

A)hydrogen bond
B)peptide bond
C)phosphoanhydride bond
D)van der Waals bond

Answer 1

B

Question 2

What is the pH of a serine solution in which the a-NH₃⁺ group,which has a pKₐ 9.2,is one-third dissociated?

A)8.7
B)8.9
C)9.0
D)9.5

Answer 2

B

Question 3

Which of the following does NOT react with the -SH group on cysteine?

A)N-ethylmaleimide
B)benzaldehyde
C)acrylonitrile
D)iodoacetate

Answer 3

B

Question 4

Histidine has pKₐ values of 1.8,6.0,and 9.2.At which of the following pH values would histidine be found with a net negative charge?

A)1.0
B)4.0
C)8.0
D)11.0

Question 5

Glutamic acid has pKₐ's at 2.2,4.3,and 9.7.What is the isoelectric point for glutamic acid?

A)3.25
B)4.3
C)5.4
D)7.0

Question 6

Which of the following amino acid derivatives is correctly derived from its corresponding commonly occurring amino acid?

A)GABA is a neurotransmitter derived from aspartic acid.
B)Histamine is a neurotransmitter derived from proline.
C)Epinephrine is a hormone derived from tyrosine.
D)Serotonin is a neurotransmitter derived from phenylalanine.

Question 7

Based on their properties,which amino acids are correctly classified?

A)Alanine and valine are neutral,nonpolar amino acids.
B)Aspartic acid and asparagine are acidic amino acids.
C)Serine and glutamine are polar,charged amino acids.
D)Lysine and arginine are basic,uncharged amino acids.

Question 8

Which of the following amino acids is classified as a basic amino acid?

A)leucine
B)aspartic acid
C)asparagine
D)lysine

Question 9

Which of the following results from resonance in peptide bonds?

A)a C?-carbon that is out of the coplanar group of atoms
B)unrestricted rotation in the peptide backbone at the N-C_? bond and C_?-Co bond
C)approximately 40% double-bond character
D)Co-N bond distance that is longer than normal,but shorter than C=N bonds

Question 10

What effect does the presence of the a-COO- group of an amino acid have on the pKₐ value of its a-NH₃⁺ group?

A)The pKa value increases by >2 pH units.
B)The pKa value decrease by > 2 pH units.
C)The pKa value increases by ~1.5 pH units.
D)The pKa value decrease by ~ 1.5 pH units.

Question 11

At what pH is the cysteine side-chain sulfhydryl group 11% dissociated if its pKₐ value is 8.32?

A)3.2
B)7.4
C)8.5
D)10.2

Question 12

Which of the following is a property of ninhydrin?

A)It produces a yellow product upon reaction with histidine.
B)It can be used to detect the location of amino acids following SDS-PAGE.
C)It produces a green product upon reaction with alanine.
D)It reacts with an amino acid by oxidatively deaminating its amino group.

Question 13

Which of the following amino acids has a side-chain pKₐ near neutrality and therefore plays an important role as proton donor and acceptor in many enzyme-catalyzed reactions?

A)histidine
B)cysteine
C)aspartic acid
D)arginine

Question 14

Which of the following amino acids has more than 1 chiral carbon?

A)serine
B)lysine
C)threonine
D)cysteine

Question 15

The amino and carboxyl groups of amino acids react in a head-to-tail fashion and forming a covalent linkage.What is this linkage typically referred to as?

A)an aromatic bond
B)a phosphoanhydride bond
C)a peptide bond
D)a hydrogen bond

Question 16

Which of the following amino acids most likely to be present if the pI of a peptide is 4.6?

A)glutamic acid
B)histidine
C)arginine
D)cysteine

Question 17

Which of the following tri-peptides would absorb light at 280 nm?

A)Ala-Lys-His
B)Ser-Gly-Asn
C)Ala-Ala-Trp
D)Val-Pro-Leu

Question 18

Which of the following is an intrinsic property of the commonly occurring 20 amino acids?

A)asymmetrical a-carbon
B)the inability to polymerize
C)polarity
D)non-chirality

Question 19

What type of thermodynamic reaction must be coupled to peptide bond formation in biological systems?

A)adverse
B)compatible
C)reverse
D)favourable

Question 20

Which of the following amino acids has a free a-carboxyl group but no free a-amino group?

A)aspartic acid
B)proline
C)asparagine
D)lysine

Question 21

Of the following four amino acids which one absorbs light most strongly between 250 and 300 nm?

A)histidine
B)phenylalanine
C)tryptophan
D)tyrosine

Question 22

Which of the following is a characteristic of stereoisomers?

A)A diastereomer is a non-superimposable mirror image.
B)An enantiomer is a superimposable mirror image.
C)Diastereomers rotate plane-polarized light in equal magnitude but opposite directions.
D)Diastereomers have different melting points

Question 23

Which of the following is a feature of L-isoleucine?

A)It has four stereoisomers.
B)L-allo-leucine would be its diastereomer.
C)It contains a total of 2 symmetric carbons.
D)Using the (R,S)system,it can also be named as (3S,2S)-isoleucine.