Chapter 4 -- The Three-Dimensional Structure of Proteins

Cys-Ala-Gly-Arg-Gln-Met

Total hydrolysis of the peptide in HCl would yield these products:
A. Ala, Arg, Cys, Gln, Gly, Met
B. Ala, Arg, 2 Cys, Gln, Gly, H2S
C. Ala, Arg, Cys, Glu, Gly, Met, NH3
D. Ala, Arg, 2 Cys, Glu, Gly, H2S, NH3
E. None of these answers is correct.

Ala, Arg, Cys, Glu, Gly, Met, NH3

Cys-Ala-Gly-Arg-Gln-Met

The amino terminal amino acid is:

Cys

Cys-Ala-Gly-Arg-Gln-Met

The carboxyl terminal end is:

met

Cys-Ala-Gly-Arg-Gln-Met

The overall, net ionic charge on this peptide at pH = 7 would be:

+1

The sequence of monomers in any polymer is this type of structure:

primary structure

Hydrogen bonds are most important in this type of structure in proteins:

secondary structure

The overall folding of a single protein subunit is called:

tertiary structure

The location of prosthetic groups is shown in this level of structure:

tertiary structure

Structures which repeat over and over in secondary structure are called:

supersecondary structure

Covalent bonds are important in all these structures, except:

quaternary structure

Disulfide bonds are most important in this type of structure:

tertiary structure

Which of the following forces are involved in maintaining the primary structure of a protein?

covalent bonds

Assuming the oligopeptide ALPHAHELICKS forms one continuous a-helix, the carbonyl oxygen of the glutamic acid residue is hydrogen bonded to the amide nitrogen of

cysteine.

What happens when a protein is denatured?

Its secondary structure is disrupted but its primary structure remains intact.

Which of the following best defines a domain?

A supersecondary region, often shared by proteins, that has a specific function.

Which of the following amino acids is unlikely to be found in an a-helix due to its cyclic structure?

proline

Which of the following statements regarding hydrogen bonding in secondary structures is true?

a-helices only use intrachain hydrogen bonds and b-sheets can use either intrachain or interchain hydrogen bonds.

Which of the following factors tend to destabilize a-helices?
A. clusters of amino acids with bulky R-groups
B. clusters of amino acids with similarly charged R-groups
C. Both of these.
D. Neither of these

Both of these.

Which of the following best describes the structure of collagen?

a triple helix

. Which of the following is true?
A. The peptide bonds in the b-sheet are extended.
B. The peptide bonds in the a-helix coil back on themselves.
C. Both a-helices and b-sheets can be found as part of tertiary structure.
D. All of these

All of these

Which of the following is often found connecting the strands of an antiparallel b-sheet?

reverse turn

Which of the following best describes a motif?

a repetitive supersecondary structure

In the b-pleated sheet conformation
A. there are hydrogen bonds perpendicular to the direction of the polypeptide chain.
B. the polypeptide chain is almost fully extended.
C. the polypeptide chains may be hydrogen bonded together in a parallel or antiparallel orientation.
D. all of these

all of these

Which of the following is the most common function for fibrous proteins?

structural roles.

In the a-helix

there are hydrogen bonds parallel to the helix axis

Which one is not an example of supersecondary structure?
A. the pyrrole ring
B. the Greek key
C. the b-meander
D. the b-barrel

the pyrrole ring

. Which of the following is true?
A. The collagen helix and the a-helix are the only types of helices in proteins.
B. Globular proteins tend to be water soluble
C. Globular and fibrous are examples of secondary structure
D. All of these

Globular proteins tend to be water soluble

As an animal ages, the amount of cross-linking of collagen in tissue

tends to increase.

Vitamin C (ascorbic acid) prevents scurvy because

it is used to hydroxylate prolines in the primary structure of collagen.

The following is true about the hydroxyproline in collagen:

Hydroxyproline requires Vitamin C for its synthesis and it holds the collagen helix together.

Fibrous proteins

can be composed of either helical or b-sheet structures.

The protein myoglobin

contains a heme group

Generally speaking, this type of protein is water-soluble:

Globular.

Domains are

independently folded regions of proteins

Two amino acids frequently found in reverse turns are

glycine and proline

Which of the following amino acid residues would most likely be found in the interior of a globular protein?

leucine

Disulfide bonds in proteins occur between the side chains of which of the following amino acid residues?

cysteine

X-ray crystallography is used to determine protein structure because

the positions of all atoms can be found by this method

The structure of myoglobin consists

almost entirely of a-helices.

The tertiary structure of a protein is usually a result of which of the following interactions?
A. intramolecular hydrogen bonding
B. electrostatic interactions
C. hydrophobic interactions
D. all of these

all of these

Heme would best be described as a

prosthetic group.

Why does myoglobin have a histidine that prevents both O2 and CO from binding perpendicularly to the heme plane?

This lessens the difference in myoglobin's affinity for CO versus O2.

In what oxidation state must the iron atom be for heme to bind oxygen?

2+, Fe(II)

Which of the following is not true?
A. The heme group of myoglobin is held in place only through non-covalent bonding.
B. The F8 histidine is important to the function of myoglobin
C. The E7 histidine is important to the function of myoglobin
D. Myoglobin and hemoglobin differ only in one amino acid

Myoglobin and hemoglobin differ only in one amino acid

Which of the following can result in protein denaturation?
A. heat
B. extremes of pH
C. detergents
D. all of the above

all of the above

The following bond forces are important in tertiary structure:
A. Disulfide bonds
B. Hydrogen bonds
C. Hydrophobic attraction
D. Both hydrogen bonds and hydrophobic attraction.
E. All of these are important in tertiary structure

All of these are important in tertiary structure

Quaternary structure is associated with

the relative orientation of one polypeptide to another polypeptide in a multisubunit protein

Which of the following forces are involved in maintaining the quaternary structure of a protein?
A. hydrogen bonds
B. ionic interactions
C. hydrophobic interactions
D. All of these

All of these

The following bond forces are important in quaternary structure:

Both hydrogen bonds and hydrophobic attraction.

. Under normal circumstances:
A. Adult Hb binds to oxygen more tightly than Mb binds.
B. Fetal Hb binds oxygen more tightly than adult Hb.
C. Adult Hb binds oxygen more tightly than either fetal Hb or Mb binds.
D. Mb has the lowest affinity for oxygen of the 3.
E. More than one of these statements is correct.

Fetal Hb binds oxygen more tightly than adult Hb.

Which of the following statements regarding hemoglobin (Hb) and myoglobin (Mb) is true?

Mb displays simple kinetics of binding while Hb displays cooperativity.

Which of the following is not a characteristic of hemoglobin?

It is an allosteric enzyme.

The Bohr effect for oxygen binding states that

as the pH goes down, Hb binds oxygen less tightly.

In allosteric interactions

changes that take place in one site of a protein cause changes at a distant site.

Hemoglobin differs from myoglobin because

it is a tetramer, whereas myoglobin is a single polypeptide chain.

Which of the following best describes what happens when hemoglobin binds bisphosphoglyceric acid (BPG)?

Binding of BPG causes oxygen to dissociate from Hb.

The binding of oxygen to hemoglobin differs from the oxygen-binding behavior of myoglobin because

oxygen binding to hemoglobin is cooperative.

In the Bohr effect the binding of oxygen to hemoglobin

is decreased by the presence of H+ and CO2

The affinity of fetal hemoglobin for oxygen

is higher than that of maternal hemoglobin

Variations in the structure of hemoglobin
A. do not always have an adverse effect on health
B. can alter the binding of heme to the protein
C. can occur on the surface of the protein
D. all of these

all of these

In sickle-cell anemia hemoglobin

groups of hemoglobin molecules aggregate with each other

Which of the following proteins is not homologous with the others?
A. myoglogin
B. a-chain of hemoglobin
C. b-chain of hemoglobin
D. collagen

collagen

What is the major force that drives nonpolar substances out of aqueous solution?

Increased entropy of solvent water molecules.

Hydrophobic interactions may occur between the R groups of which of the following amino acids?

phenylalanine and tryptophan

The information needed for the structure of a protein is contained in

primary structure

Incorrect protein folding resulting in exposure of hydrophobic regions can result in

aggregation.

Proteins that aid in the correct and timely folding of other proteins are called

chaperones.

The oxygen binding curve of which of the following is the closest to that of myoglobin?

hemoglobin that lacks BPG

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

proline