Question 1

Structures which repeat over and over in secondary structure are called:
A) primary structure
B) domain
C) supersecondary structure
D) prosthetic group
E) All of these

Accepted Answer

Supersecondary structures refer to specific arrangements of secondary structural elements (such as alpha helices and beta sheets) that repeat over and over, forming recognizable motifs within protein structures.

Question 2

Hydrogen bonds are most important in this type of structure in proteins:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

Hydrogen bonds are crucial in stabilizing the secondary structure of proteins, particularly in the formation of alpha-helices and beta-sheets.

Question 3

The overall folding of a single protein subunit is called:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

The tertiary structure refers to the overall three-dimensional folding of a single protein molecule, which is a result of interactions among the amino acid side chains.

Question 4

Which of the following best defines a domain?
A) A supersecondary region, often shared by proteins, that has a specific function.
B) A repetitive supersecondary structure.
C) A double-layered arrangement formed so that the polar groups face the aqueous environment, while the nonpolar regions are kept away from the aqueous environment.
D) An unfolded region of a protein.

Accepted Answer

A domain in the context of protein structure refers to a distinct structural unit within a protein that can often fold independently of the rest of the protein chain and usually has a specific function. This definition aligns with choice A, indicating a region within proteins that is not only structurally distinct but also functionally significant. Choices B, C, and D describe other structural features or arrangements that do not accurately define a domain.

Question 5

Which of the following amino acid substitutions would be least likely to have a deleterious effect on protein function?
A) His changes to Asp
B) Leu changes to Ile
C) Glu changes to Gln
D) Trp changes to Gly

Accepted Answer

Leu (Leucine) and Ile (Isoleucine) are both nonpolar, hydrophobic amino acids with similar sizes and shapes, making a substitution between them less likely to disrupt protein function compared to the other options, which involve more drastic changes in charge, size, or hydrophobicity.

Question 6

A single amino substitution can give rise to a malfunctioning protein.

Accepted Answer

A single amino acid substitution can alter the protein's structure, stability, or function, potentially leading to a malfunctioning protein, as seen in diseases like sickle cell anemia.

Question 7

Exhibit 4A The following question(s) refer to this peptide:
Cys-Ala-Gly-Arg-Gln-Met
Refer to Exhibit 4A. The amino terminal amino acid is:
A) Arg
B) Cys
C) Gln
D) Met
E) None of these.

Accepted Answer

The amino terminal (N-terminal) of a peptide is the end where the amino group is not involved in a peptide bond, indicating the start of the peptide sequence. In the given peptide sequence (Cys-Ala-Gly-Arg-Gln-Met), Cys (Cysteine) is the first amino acid, making it the amino terminal amino acid.

Question 8

Which of the following statements regarding hydrogen bonding in secondary structures is true ?
A) Both α -helices and β -sheets only use intrachain hydrogen bonds.
B) Both α -helices and β -sheets only use interchain hydrogen bonds.
C) α -helices only use intrachain hydrogen bonds and β -sheets can use either intrachain or interchain hydrogen bonds.
D) α -helices can use either intrachain or interchain hydrogen bonds and β -sheets only use interchain hydrogen bonds.

Accepted Answer

α-helices are stabilized by intrachain hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid four residues away. β-sheets are stabilized by hydrogen bonds between the carbonyl oxygen of one strand and the amide hydrogen of another strand, which can be either from the same polypeptide chain (intrachain) or from different polypeptide chains (interchain).

Question 9

Exhibit 4A The following question(s) refer to this peptide:
Cys-Ala-Gly-Arg-Gln-Met
Refer to Exhibit 4A. The carboxyl terminal end is:
A) Arg
B) Cys
C) Gln
D) Met
E) None of these.

Accepted Answer

The carboxyl terminal end of a peptide is the end with the free carboxyl group (-COOH). In the given peptide sequence (Cys-Ala-Gly-Arg-Gln-Met), Met (Methionine) is the last amino acid, making it the carboxyl terminal end.

Question 10

Which of the following forces are involved in maintaining the primary structure of a protein?
A) covalent bonds
B) hydrogen bonds
C) ionic interactions
D) hydrophobic interactions

Accepted Answer

The primary structure of a protein is maintained by covalent bonds, specifically peptide bonds, which link amino acids together in a linear chain.

Question 11

Covalent bonds are important in all these structures, except:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

The answer of Covalent bonds are important in all these...

Question 12

The sequence of monomers in any polymer is this type of structure:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

The sequence of monomers in a polymer defines its primary structure, similar to how the sequence of amino acids determines the primary structure of proteins.

Question 13

Exhibit 4A The following question(s) refer to this peptide:
Cys-Ala-Gly-Arg-Gln-Met
Refer to Exhibit 4A. The overall, net ionic charge on this peptide at pH = 7 would be:
A) +2
B) +1
C) 0
D) − 1
E) − 2

Accepted Answer

At pH 7, the amino (N-terminus) and carboxyl (C-terminus) groups are ionized, giving a +1 and -1 charge, respectively. The side chains of the amino acids in the peptide also contribute to the overall charge. Cysteine (Cys) has a neutral charge at pH 7. Alanine (Ala) and Glycine (Gly) are also neutral. Arginine (Arg) has a positively charged side chain, and Glutamine (Gln) and Methionine (Met) are neutral at pH 7. Therefore, the overall charge is +1 from the N-terminus plus +1 from Arginine, minus 1 from the C-terminus, resulting in a net charge of +1.

Question 14

What happens when a protein is denatured?
A) Its secondary structure is disrupted but its primary structure remains intact.
B) Its primary structure is disrupted but its secondary structure remains intact.
C) It is broken apart into its constituent amino acids.
D) It becomes all α -helix.

Accepted Answer

Denaturation of a protein involves the disruption of its secondary, tertiary, and quaternary structures without breaking the peptide bonds that form its primary structure. The primary structure, which is the sequence of amino acids, remains intact.

Question 15

Which of the following amino acids is unlikely to be found in an α -helix?
A) phenylalanine
B) tryptophan
C) proline
D) lysine

Accepted Answer

Proline is unlikely to be found in an α-helix because its cyclic structure disrupts the regular hydrogen bonding pattern of the helix.

Question 16

Which of the following factors tend to destabilize α -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

Accepted Answer

Both clusters of amino acids with bulky R-groups and clusters of amino acids with similarly charged R-groups can destabilize α-helices. Bulky R-groups can cause steric hindrance, while similarly charged R-groups can repel each other, both disrupting the helical structure.

Question 17

The location of prosthetic groups is shown in this level of structure:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

Prosthetic groups are non-protein components that are tightly bound to proteins and are essential for their function. The location and interaction of prosthetic groups with proteins are typically defined at the tertiary structure level, where the overall 3D folding of the protein allows for the specific positioning and attachment of these groups.

Question 18

Assuming the oligopeptide ALPHAHELICKS forms one continuous α -helix, the carbonyl oxygen of the glutamic acid residue is hydrogen bonded to the amide nitrogen of
A) leucine.
B) isoleucine.
C) cysteine.
D) lysine.
E) serine.

Accepted Answer

The answer of Assuming the oligopeptide ALPHAHELICKS forms one continuous...

Question 19

Disulfide bonds are most important in this type of structure:
A) primary structure
B) secondary structure
C) tertiary structure
D) quaternary structure
E) All of these

Accepted Answer

Disulfide bonds are crucial in stabilizing the tertiary structure of proteins by forming covalent links between cysteine residues, which helps to maintain the overall 3D shape of the protein.

Question 20

Which of the following best describes the structure of collagen?
A) It is composed of a single α -helix.
B) It is a double helix.
C) It is a triple helix
D) It is composed primarily of β -sheet.

Accepted Answer

Collagen is characterized by its triple helix structure, where three polypeptide chains are wound around each other in a rope-like configuration. This structure is crucial for its biological function, providing strength and elasticity to connective tissues.

Quiz 4: The Three Dimensional Structure of Proteins

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

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

The overall folding of a single protein subunit is called:

Which of the following best defines a domain?

Which of the following amino acid substitutions would be least likely to have a deleterious effect on protein function?

A single amino substitution can give rise to a malfunctioning protein.

Exhibit 4A The following question(s) refer to this peptide: Cys-Ala-Gly-Arg-Gln-Met Refer to Exhibit 4A. The amino terminal amino acid is:

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

Exhibit 4A The following question(s) refer to this peptide: Cys-Ala-Gly-Arg-Gln-Met Refer to Exhibit 4A. The carboxyl terminal end is:

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

Covalent bonds are important in all these structures, except:

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

Exhibit 4A The following question(s) refer to this peptide: Cys-Ala-Gly-Arg-Gln-Met Refer to Exhibit 4A. The overall, net ionic charge on this peptide at pH = 7 would be:

What happens when a protein is denatured?

Which of the following amino acids is unlikely to be found in an α -helix?

Which of the following factors tend to destabilize α -helices?

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

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

Disulfide bonds are most important in this type of structure:

Which of the following best describes the structure of collagen?