Deck 4: Amino Acids and the Peptide Bond

Question 1

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

A) leucine
B) phenylalanine
C) aspartate
D) asparagine
E) lysine

Answer 1

E

Question 2

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

A) serine
B) lysine
C) threonine
D) cysteine
E) aspartic acid

Answer 2

C

Question 3

All of the statements about the classification of these amino acids are correct EXCEPT:

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

Answer 3

A

Question 4

The pK_a of the cysteine side chain ____ group is 8.32, so it is about 11% deprotonated at pH ____.

A) acid, 3.2
B) amino, 8.5
C) hydroxyl, 10.2
D) sulfhydryl, 7.4
E) none of the above

Question 5

The intrinsic properties of the 20 amino acids include all EXCEPT:

A) α-Carbon is symmetric.
B) The capacity to polymerize.
C) Novel acid-base properties.
D) Varied structure and chemical functionality in side chains.
E) Chirality.

Question 6

The pK_a of the α−carboxyl group of an amino acid is ____ by the presence on the amine group.

A) greatly increased (>2 pH units)
B) greatly decreased (> 2 pH units)
C) unchanged
D) slightly increased (1-2 pH units)
E) slightly decreased (1-2 pH units)

Question 7

Glutamic acid has pK_a values of 2.2, 4.3, and 9.7. Calculate the isoelectric point for glutamic acid.

A) 3.25
B) 4.3
C) 5.4
D) 7.0
E) 8.6

Question 8

The amino acid with a side-chain pK_a near neutrality and which therefore plays an important role as proton donor and acceptor in many enzyme catalyzed reactions is:

A) histidine.
B) cysteine.
C) proline.
D) serine.
E) methionine.

Question 9

What is the pH of a serine solution in which the α−amine group (pK_a 9.2) is 33% deprotonated?

A) 8.7
B) 8.9
C) 9.0
D) 9.5
E) 9.8

Question 10

If the pI of a peptide is 4.6, ____ might be present while ____ would probably be absent.

A) Glu / Lys
B) His / Ser
C) Arg / His
D) Asp / Gly
E) Cys / Tyr

Question 11

For the peptide Ala-His-Glu-Val-Asp-Cys-Lys-Leu, what is the net charge at pH 3?

A) -1
B) 0
C) +1
D) +2
E) +3

Question 12

At which of the following pH values would histidine (pK_a values of 1.8, 6.0 and 9.2) be found with a net negative charge?

A) 1.0
B) 4.0
C) 8.0
D) 11.0
E) none of the above

Question 13

All of the amino acids EXCEPT ____ have both free α-amino and free α-carboxyl groups.

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

Question 14

All are true for stereoisomers EXCEPT:

A) A diastereomer is a nonsuperimposable non-mirror image.
B) An enantiomer is a nonsuperimposable mirror image.
C) Diastereomers have different melting points.
D) Diastereomers rotate plane polarized light in equal but opposite directions.
E) None, all are true.

Question 15

All are true statements about L-isoleucine EXCEPT:

A) Its enantiomer is named D-isoleucine.
B) L-alloleucine would be its diastereomer.
C) It contains a total of two asymmetric or chiral carbons.
D) It can also be named as (2S,3S)-isoleucine using the (R,S) system.
E) Its diastereomer would be named D-leucine.

Question 16

The difference between serine and homoserine is the same as between cysteine and homocysteine. This change from the common amino acid is:

A) one additional methylene (−CH₂−) group.
B) one additional carboxyl group.
C) two additional amine groups.
D) presence of a ring system.
E) one additional amine group.

Question 17

The amino and carboxyl groups of amino acids react in a head-to-tail fashion, eliminating water, and forming a covalent ____ linkage typically referred to as a(n) ____ bond.

A) ester, aromatic
B) anhydride, phosphoanhydride
C) amide, peptide
D) dehydration, hydrogen
E) none of the above

Question 18

Which of the following amino acids absorbs light most strongly between 250 and 300 nm?

A) His
B) Phe
C) Trp
D) Tyr
E) None of the above absorb light in this range

Question 19

Which of the peptides would absorb light at 280 nm?

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

Question 20

Which of the following is classified as a neutral polar amino acid?

A) Asp
B) Leu
C) His
D) Ser
E) Trp

Question 21

Discuss the side-chain groups of amino acids that undergo ionizations.​

Question 22

The peptide bond has partial ____ character.

A) hydrogen bond
B) double bond
C) triple bond
D) van der Waals bond
E) all of the above

Question 23

Where Cα is the α-carbon, N represents the amide nitrogen and C_o is the carbonyl carbon of amino acids in a peptide, the peptide backbone of a protein consists of the repeated sequence:

A) −C_α−N−C_o−
B) −N−C_o−C_α−
C) −N−C_α−C_o−
D) −C_o−C_α−N−
E) none of the above

Question 24

Explain the chirality of amino acid molecules.​

Question 25

Explain the classification of peptides based on the number of amino acids they contain.​

Question 26

Which of the following atoms IS NOT contained within the amide plane of the peptide backbone?

A) Cα-carbon.
B) amide nitrogen.
C) side chain carbons.
D) carbonyl carbon.
E) none, all are included.

Question 27

Discuss the principles on which methods of amino acid separation are based.​

Question 28

Which of the following IS NOT a result of resonance in peptide bonds?

A) approximately 40% double bond (coplanar) character.
B) restricted rotation in the peptide backbone at the N−Cα bond and C_α−C_o bond.
C) the coplanar six atoms of the peptide bond group of atoms.
D) a C_α−carbon that is out of the coplanar group of atoms.
E) C_o−N bond distance that is shorter than normal, but longer than C=N bonds.

Question 29

Discuss the amino acids that occur only rarely in proteins.​