Question 1

Which of the following amino acids would generally not be found in an α-helix?

Accepted Answer

Serine (Ser) is less commonly found in α-helices due to its small side chain that contains a hydroxyl group, which can form hydrogen bonds that disrupt the helical structure.

Question 2

Tertiary structure of proteins depends on all of the following EXCEPT:

Accepted Answer

Proteins are not stable as a single-layer structure but fold into complex three-dimensional structures known as the tertiary structure, which is critical to their function. The other options are all factors that contribute to the formation of tertiary structure.

Question 3

Prolyl hydroxylase has all of the following characteristics EXCEPT:

Accepted Answer

Prolyl hydroxylase does not require citric acid. It requires α-ketoglutarate as a co-substrate, molecular oxygen as a co-factor, and Fe2+ or Fe3+ as a co-factor, which can be supplied by Fe²⁺. Prolyl hydroxylase hydroxylates proline residues in proteins, leading to the formation of hydroxyproline.

Question 4

In hemoglobin, a ____ protein, the space between the helices is filled efficiently and tightly with mostly ____ amino acid chains and with ____ side chains facing the outside of the protein structure.

Accepted Answer

Hemoglobin is a globular protein, and the space between the helices is filled efficiently and tightly with mostly hydrophobic amino acid chains and with polar side chains facing the outside of the protein structure. This structure is important for the function of hemoglobin as it allows it to bind and transport oxygen in the blood.

Question 5

The outward face of a(n) ____ consists mainly of polar and charged residues, whereas the inner face contains mostly nonpolar, hydrophobic residues.

Accepted Answer

An amphiphilic helix is composed of both hydrophobic and hydrophilic residues, which result in two distinct faces on the helix. The outward face contains mainly polar and charged residues, while the inner face consists mostly of nonpolar, hydrophobic residues.

Question 6

α-Keratin has all of the following characteristics EXCEPT:

Accepted Answer

The presence of properly placed polar amino acids does not help to solubilize α-keratin. In fact, α-keratin is insoluble in water due to the presence of hydrophobic strips on the two coiled coils.

Question 7

The unique composition of collagen is accommodated in a structure called a(n):

Accepted Answer

Collagen has a unique composition of three polypeptide chains that are tightly coiled together in a triple helix form. This is known as the collagen triple helix structure.

Question 8

____ β-sheets characteristically distribute hydrophobic side chains on both sides of the sheet, and ____ β-sheets are usually arranged with all their hydrophobic residues on one side of the sheet.

Accepted Answer

The answer of ____ β-sheets characteristically distribute hydrophobic side chains...

Question 9

Which statement is correct about the β−α−β motif?

Accepted Answer

The β−α−β motif is characterized by two parallel β-strands connected by an α-helical segment.

Question 10

Tertiary structure is defined as:

Accepted Answer

Tertiary structure refers to the three-dimensional folding of a single polypeptide chain, which is critical for the protein's function. This folding is determined by the interactions between amino acid side chains within the polypeptide chain, including hydrogen bonds, disulfide bonds, hydrophobic interactions, etc.

Option A is incorrect because this refers to the primary structure of a protein, which is simply the linear sequence of amino acids. Option C is incorrect because it describes the formation of secondary structure elements such as alpha helices or beta sheets, which are important components of tertiary structure but not sufficient to define it. Option D describes quaternary structure, which involves the association of multiple protein subunits, and is not necessary for all proteins to have a defined tertiary structure.

Question 11

Collagen has the following characteristics EXCEPT:

Accepted Answer

Modification of prolines occurs after collagen synthesis, not prior to it.

Question 12

A major stabilizing factor in the triple helix is a ____ structure such that ____ residues from the three strands stack along the center of the triple helix.

Accepted Answer

The major stabilizing factor in the triple helix is a staggered structure, where glycine (Gly) residues from the three strands stack along the center of the triple helix. Glycine is the smallest amino acid and its small side chain allows it to pack tightly in the center of the triple helix. The other options (A, B, C, and E) are incorrect because they either describe the wrong type of structure or the wrong type of residue involved in the stabilization.

Question 13

Flexible, disordered segments of proteins are commonly high in the amino acid:

Accepted Answer

The answer of Flexible, disordered segments of proteins are commonly...

Question 14

Silk fibers consist of ____ proteins consisting of alternating ____ and ____ or ____ residues.

Accepted Answer

Silk fibers are predominantly made up of fibroin, which is composed of amino acids such as glycine, alanine, and serine. The repetitive arrangement of these amino acid residues in fibroin creates a crystalline structure that imparts the unique characteristics of silk, such as its strength, flexibility, and lightness. Therefore, the best choice is E, which lists fibroin, glycine, alanine, and serine as the primary components of silk fibers.

Question 15

Why should the core of most globular and membrane proteins consist almost entirely of α-helix and β-sheets?

Accepted Answer

The highly polar N−H and C=O moieties of the peptide backbone must be neutralized in the hydrophobic core of the protein to avoid unfavorable interactions with the aqueous environment. The α-helix and β-sheet structures provide a way for the polar backbone to be neutralized while still allowing for hydrogen bonding within the protein.

Question 16

A β-barrel would most likely be composed of ____.

Accepted Answer

The answer of A β-barrel would most likely be composed...

Question 17

Which of the following would be the most rapidly occurring event giving rise to protein motion?

Accepted Answer

The tyrosine ring flip is a rapid intramolecular motion compared to other events like hinge-bending or cis-trans isomerization, which involve larger structural changes or energy barriers.

Question 18

Fibrous proteins contain polypeptide chains ____ producing long fibers or large sheets.

Accepted Answer

Fibrous proteins are characterized by their highly elongated, rod-like structures that are organized approximately parallel along a single axis. This arrangement allows for the formation of long fibers or large sheets, which is a defining feature of fibrous proteins. While some fibrous proteins may contain an abundance of aromatic or hydrophilic amino acids, this is not a universal feature of all fibrous proteins. The repeating (-a-b-c-d-)_n sequence is a characteristic of collagen, one type of fibrous protein, but not all fibrous proteins share this sequence.

Question 19

The "permanent" part of adding wave in hair is primarily due to:

Accepted Answer

Permanent wave in hair involves reducing the disulfide bonds in hair fibers using a chemical such as thioglycolic acid. This allows the hair to be reshaped and set in the desired wave pattern. Once the hair has been reshaped, the disulfide bonds are re-oxidized to reinforce the new shape, resulting in a permanent effect.

Question 20

The amino acid residue most likely to be found in a beta turn is:

Accepted Answer

Beta turns involve a reversal in the direction of the polypeptide chain, and glycine is the only amino acid with a small enough side chain to allow for the necessary conformational flexibility in the turn.

Quiz 6: Proteins: Secondary, Tertiary, and Quaternary Structure