BCCB2000 Lecture 5 Questions

Question 1

The ________ is the single shape a protein adopts under physiological conditions.

Answer 1

native conformation

Question 2

Which statement is not true about the peptide bond? A. The peptide bond has partial double-bond character. B. The peptide bond is longer than the typical carbon-nitrogen bond. C. Rotation is restricted about the peptide bond. D. The carbonyl oxygen and the amide hydrogen are most often in a trans configuration with respect to one another.

Answer 2

B. The peptide bond is longer than the typical carbon-nitrogen bond.

Question 3

The native structures of proteins are more stable than non-native conformations; they occupy a low-energy well when folded. True or False?

Answer 3

True

Question 4

A polypeptide chain may have abrupt changes in direction and restriction in geometry because of the presence of: A. arginine B. glycine. C. proline D. leucine or isoleucine

Answer 4

C. proline

Question 5

In an aqueous solution, protein conformation is determined by two major factors. One is the formation of the maximum number of hydrogen bonds. The other is the: A. formation of the maximum number of hydrophilic interactions. B. maximization of ionic interactions. C. minimization of entropy by the formation of a water solvent shell around the protein. D. placement of polar amino acid residues around the exterior of the protein. E. placement of hydrophobic amino acid residues within the interior of the protein.

Answer 5

E. placement of hydrophobic amino acid residues within the interior of the protein.

Question 6

Nearly all peptide bonds are in the trans configuration because: A. cis peptide bonds are weaker. B. trans peptide bonds are stronger. C. cis peptide bonds prevent R groups from interacting. D. trans peptide bonds minimize steric hindrance of R groups.

Answer 6

D. trans peptide bonds minimize steric hindrance of R groups.

Question 7

Most proteins contain an approximately equal amount of each of the standard amino acids. True or False?

Answer 7

False

Question 8

Protein subunits in a multisubunit protein are held to each other primarily by: A. covalent bonds. B. hydrophobic interactions exclusively. C. both strong and weak interactions. D. hydrophobic and other weak interactions. E. All of the above

Answer 8

D. hydrophobic and other weak interactions.

Question 9

An octapeptide composed of four repeating glycylalanyl units has: A. two free amino and two free carboxyl groups. B. a single free amino group on an alanyl residue. C. two free carboxyl groups, both on glycyl residues. D. a single free amino group on an alanyl residue and a single free carboxyl group on a glycyl residue. E. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue.

Answer 9

E. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue.

Question 10

The reaction of two amino acids to form a dipeptide is a: A. cleavage. B. condensation. C. group transfer. D. oxidation-reduction. E. rearrangement.

Answer 10

B. condensation.

Question 11

Which is true about the side chains of residues in an α-helix? A. They extend above or below the pleats. B. They extend radially outward from the helix axis. C. They point toward the center of the helix. D. They hydrogen bond extensively with each other

Answer 11

B. They extend radially outward from the helix axis.

Question 12

In an alpha helix, the R groups on the amino acid residues: A. stack parallel within the interior of the helix. B. are mainly responsible for the hydrogen bonds that form the helix. C. extend radially outward from the helix axis. D. cause only right-handed helices to form. E. alternate between the outside and the inside of the helix.

Answer 12

C. extend radially outward from the helix axis.

Question 13

Structural proteins that typically assemble into large cables or threads to provide mechanical support to cells or organisms are classified as ________ proteins.

Answer 13

Fibrous

Question 14

The peptide alanylglutamylglycylalanylleucine has: A. five peptide bonds. B. no free carboxyl group. C. a disulfide bridge. D. four peptide bonds.. E. two free amino groups.

Answer 14

D. four peptide bonds.

Question 15

Which one of the following statements is correct? A. beta bends often contain proline B. the alpha helix is stabilized primarily bu ionic interactions between the side chains of amino acids C. The alpha helix can be composed of more than one polypeptide chain. D. domains are a type of secondary structure E. beta sheets exist only in the antiparallel form

Answer 15

A. beta bends often contain proline

Question 16

The subunits of a multisubunit proteins are always identical. True or False?

Answer 16

False

Question 17

Which represents the backbone atoms of a protein? Note: R = amino acid side chain; N = nitrogen; Cα = alpha carbon; C = carbonyl carbon A. R1R2R3R4R5 B. repeating units of N-C C. repeating units of N-Cα-C D. repeating units of Cα-C

Answer 17

C. repeating units of N-Cα-C

Question 18

Which of the following is correct with respect to the amino acid composition of proteins? A. Proteins contain at least one each of the twenty different standard amino acids. B. Proteins with different functions usually differ C. The average molecular weight of an amino acid in a protein increases with the size of the protein. D. Proteins with the same molecular weight have the same amino acid composition. E. Larger proteins have a more uniform distribution of amino acids than smaller proteins.

Answer 18

B. Proteins with different functions usually differ

Question 19

The conformation of a protein enzyme determines whether it is functional or not. True or False?

Answer 19

True

Question 20

The principle forces holding subunits of an oligomeric protein to each other are ________.

Answer 20

hydrophobic interactions

Question 21

How many monomers are there in an oligomeric protein designated αβ2γ2?

Answer 21

αβ2γ2 = (1 x α) + (2 x β) + (2 x γ) = 5 monomers

Question 22

Disulfide bridges can form in proteins ________.

Answer 22

between cysteine residues that are close in three-dimensional space, but not necessarily close in the primary structure

Question 23

Removal of water from a chemical combination of particular monomers results in the formation of a polymer molecule. True or False?

Answer 23

True

Question 24

Identify the CORRECT statement relating to the alpha helix in a protein: A. The alpha helix structure is maintained by hydrogen bonding between amino acids side chains B. The alpha helix makes up approximately the same percentage of most proteins C. The alpha helix is stabilized by hydrogen bonds between backbone amido groups and carbonyl groups of polypeptide chains D. The alpha helix includes all twenty amino acids at equal frequencies E. The alpha helix never contains proline

Answer 24

C. The alpha helix is stabilized by hydrogen bonds between backbone amido groups and carbonyl groups of polypeptide chains

Question 25

All amino acids can readily interconvert between the cis and trans forms by rotation about the peptide bond. True or False?

Answer 25

False

Question 26

Which of the following are true? A. The alpha carbon is bonded to a nitrogen and an oxygen atom B. The ball & stick and the spacefill (cpk) representations are essentially the same thing and mostly differ in the size of radius of the atoms C. The helix structure is formed from the interaction of residue side chains D. There is a 'hole' or space through the central axis of the helix such that small molecules could pass through the helix E. The side chains of the residues in the helix point outwards from the helix F. The carbonyl oxygen atoms point 'up' the axis of the helix from the N-terminal to the C-terminal. G. The helix is composed of only one type of amino acid and this is alanine H. Covalent radii are used for the atoms in both the ball & stick and spacefill representations

Answer 26

B. The ball & stick and the spacefill (cpk) representations are essentially the same thing and mostly differ in the size of radius of the atoms E. The side chains of the residues in the helix point outwards from the helix F. The carbonyl oxygen atoms point 'up' the axis of the helix from the N-terminal to the C-terminal. G. The helix is composed of only one type of amino acid and this is alanine

Question 27

To what level of structure do α-helices belong?

Answer 27

secondary

Question 28

Water can easily penetrate and even pass through the interior of a folded protein. True or False?

Answer 28

False

Question 29

Which of the following statements about proteins is false? A. Nonpolar amino acid side chains generally are arranged on the surface where they interact with water. B. Globular proteins are generally very compact. C. Proteins are sometimes conjugated with carbohydrates or fats. D. Proteins consists of amino acids linked by peptide bonds. E. Primary structure determines tertiary structure.

Answer 29

A. Nonpolar amino acid side chains generally are arranged on the surface where they interact with water.