Deck 2: Protein Composition and Structure

Question 1

_______________ is a fibrous protein and is the primary component of wool and hair.

Answer 1

$\alpha$ -Keratin

Question 2

A term that describes a molecule that contains both positive and negative charges but overall has a neutral charge is _____.

A) enantiomer
B) amino acid
C) racemate
D) zwitterion
E) amphipath

Answer 2

D

Question 3

What type of plot allows one to investigate the likely phi and psi angles of the peptide backbone?

A) Hill
B) Lineweaver-Burk
C) Hanes-Woolf
D) Ramachandran
E) Michaelis-Menten

Answer 3

D

Question 4

What is the charged group(s)present in glycine at a pH of 7?

A) -NH₃⁺
B) -COO^-
C) -NH₂⁺
D) -NH₃⁺ and -COO^-
E) All the charged groups are present.

Question 5

The ________________________ β-sheet structure occurs when the two strands are oriented in the same directions (N →
C).

Question 6

Every third residue in the protein collagen is ____________________.

Question 7

The overall three-dimensional structure of a single polypeptide is referred to as _____.

A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) both secondary structure and tertiary structure

Question 8

Key properties of proteins include

A) a wide range of functional groups.
B) an ability to possess either rigid or flexible structures as dictated by functional requirements.
C) the ability to interact with other proteins.
D) All of the answers are correct.
E) a wide range of functional groups and an ability to possess either rigid or flexible structures as dictated by functional requirements.

Question 9

Which of the following amino acids has an ionizable R-group with a pK_a near neutral pH?

A) histidine
B) serine
C) aspartic acid
D) lysine
E) tyrosine

Question 10

What level of protein structure is composed of $\alpha$ helices, $\beta$ sheets,and turns?

A) primary
B) secondary
C) tertiary
D) quaternary
E) both secondary and tertiary

Question 11

_____________________________ refers to the spatial arrangement of subunits and the nature of their interactions.

Question 12

Formation of a peptide bond produces _____ as a byproduct.

A) ammonia
B) carbon dioxide
C) water
D) H⁺
E) OH^-

Question 13

A protein is considered to be __________________ when it is converted into a randomly coiled structure without its normal activity.

Question 14

Collagen contains _____________________,a modified amino acid.

Question 15

Which of the following is most often found in proteins?

A) D-amino acids
B) L-amino acids
C) an equal amount of D- and L-amino acids
D) amino acids with the $\alpha$ -carbon exclusively having an R absolute configuration
E) amino acids with the $\alpha$ -carbon exclusively having an S absolute configuration

Question 16

Which amino acid forms disulfide bonds?

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

Question 17

Agents such as ______________________ and guanidinium chloride denature proteins by disrupting the noncovalent interactions.

Question 18

Which of the following is a function of proteins?

A) energy carrying molecules
B) catalysts
C) storage of genetic information
D) None of the answers is correct.
E) All of the answers are correct.

Question 19

Disulfide bonds in proteins can be reduced to free sulfhydryl groups by reagents such as _____________________.

Question 20

______________________ is the major fibrous protein present in skin,bone,tendon,cartilage,and teeth.

Question 21

The term "quaternary" with respect to protein structure means

A) a repeating structure stabilized by intrachain hydrogen bonds.
B) the ability to form all four kinds of noncovalent bonds.
C) a multisubunit structure.
D) a linear sequence of four amino acids.
E) None of the answers is correct.

Question 22

Which two amino acids contain a sulfur atom?

A) serine and methionine
B) serine and threonine
C) methionine and threonine
D) cysteine and methionine
E) cysteine and threonine

Question 23

What is the approximate mass of a protein containing 200 amino acids? (Assume there are no other protein modifications.)

A) 2,000
B) 11,000
C) 22,000
D) 222,000
E) None of the answers is correct.

Question 24

What are some of the modifications that proteins acquire?

A) cleavage and trimming of the protein
B) addition of carbohydrate groups
C) phosphorylation of certain groups
D) All of these are modifications proteins acquire.
E) addition of carbohydrate groups and phosphorylation of certain groups

Question 25

What structure(s)did Pauling and Corey predict in 1951?

A) α helix
B) β sheet
C) β turns
D) Pauling and Corey predicted all three of these structures.
E) α helix and β sheet

Question 26

Which of the following amino acid residues would most likely be buried in the interior of a water-soluble,globular protein?

A) Asp
B) Ser
C) Phe
D) Lys
E) Gln

Question 27

How does the protein backbone add to structural stability?

Question 28

At a pH of 12,what is the charged group(s)present in glycine?

A) -NH₃⁺
B) -COO^-
C) -NH₂⁺
D) -NH₃⁺ and -COO^-
E) All the charged groups are present.

Question 29

The configuration of most peptide bonds in a protein is _____.

A) cis
B) circular
C) parallel
D) trans
E) perpendicular

Question 30

Which of the following pairs of amino acids is positively charged at a neutral pH?

A) Lys, Arg
B) Tyr, Arg
C) Cys, Met
D) Leu, Pro
E) Asp, Glu

Question 31

Where are Ω and β turns and loops often found?

A) in a hydrophobic pocket
B) on the interior cleft
C) at the protein interface with ligand
D) on the surface of proteins
E) None of the answers is correct.

Question 32

What is the advantage of having 20 different amino acids available to form proteins?

Question 33

What is the advantage of protein interaction and assembly with other proteins?

Question 34

Why is the peptide bond planar?

A) Bulky side chains prevent free rotation around the bond.
B) It contains partial double-bond character, preventing rotation.
C) Hydrogen bonding between the NH and C=O groups limits movement.
D) All of the answers are correct.
E) None of the answers is correct.

Question 35

What do the amino acids Tyr,Asn,and Thr have in common?

A) aromatic rings
B) negatively charged at pH 7.0
C) positively charged at pH 7.0
D) double bonds in side chains
E) polar

Question 36

What are the three aromatic amino acids?

Question 37

Which individual won a Nobel Prize for his (her)landmark work in sequencing the protein insulin?

A) Pauling
B) McClintock
C) Gilbert
D) Maxam
E) Sanger

Question 38

Which amino acid side chains are capable of ionization?

Question 39

How does a protein's amino acid sequence influence the tertiary structure?

Question 40

In the following peptide,which amino acid is the N-terminus?Phe-Ala-Gly-Arg

A) Phe
B) Ala
C) Gly
D) Arg
E) Phe and Arg

Question 41

Describe some of the features of an α helix.

Question 42

In the ribonuclease experiments performed by Anfinsen,what was the significance of the presence of the reducing agent β-mercaptoethanol?

Question 43

What is the advantage of having certain areas of partially correct folded regions?

Question 44

What is the "hydrophobic effect" as it relates to protein structure?

Question 45

Why are all the theoretical combinations of phi and psi not possible?

Question 46

What does the modification involving the attachment of acetyl groups to the amino termini of proteins do?

Question 47

$\alpha$ -Keratin is referred to as a coiled-coil protein.Describe the protein structure of $\alpha$ -keratin.

Question 48

What are prions?