Protein Structure MCQ

• Experiments on denaturation and renaturation after the reduction and reoxidation of the —S—S— bonds in the enzyme ribonuclease have shown that?

  A)folding of denatured RNase into the native, active conformation, requires the input of energy in the form of heat.

  B) native ribonuclease does not have a unique secondary and tertiary structure.

  C) the enzyme, dissolved in water, is stable relative to the mixture of amino acids whose residues are contained in RNase.

  D)the primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure

  D
• In the α helix the hydrogen bonds:

  A)are roughly parallel to the axis of the helix.

  B)are roughly perpendicular to the axis of the helix.

  C)occur mainly between electronegative atoms of the R groups.

  D)occur only between some of the amino acids of the helix.

  E)occur only near the amino and carboxyl termini of the helix.

  A
• Protein folding to a native conformation is highly dependent upon all of the following, except:

  A)rotation about the alpha-carbon, carbon bond in the backbone.

  B)the polar character of sequences of amino acids.

  C)the rotation about the peptide bond.

  D)the relative size of amino acid R-groups.

  E)the rotation about the alpha-carbon, nitrogen bond.

  C
• The configuration of most peptide bonds in a protein is _____

  trans
• The disulphide bond between two cysteine molecules:

  A)is a covalent bond formed by oxidation.

  B)is a hydrogen bond between the two sulfhydryl groups.

  C)is a peptide bond.

  D)is a weak ion-induced dipole attraction.

  E)is an ionic bond that is stable at physiological pH.

  A
• The molecular interaction called "hydrophobic effect" is best described as:

  A)caused by the induction of dipole moments in polarisable molecules.

  B)the tendency of non-polar molecules to avoid interactions with water and thus aggregate.

  C)the ability of non-polar solvents to dissolve hydrophobic compounds.

  D)the inherent attractive force between non-polar molecules.

  E)the result of the interaction between two charged molecules.

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

  tertiary structure
• The term "quaternary" with respect to protein structure means

  A)a linear sequence of four amino acids.

  B)a multisubunit structure.

  C)a repeating structure stabilised by intrachain hydrogen bonds.

  D)the ability to form all four kinds of noncovalent bonds.

  E)None of the above answers are correct.

  B
• What important function do molecular chaperones perform?

  fold proteins into a native conformation
• What level of protein structure is composed of α helices, β sheets, and turns?

  secondary
• Which amino acid forms disulphide bonds?

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

  A)aspartate

  B)glutamine

  C)lysine

  D)phenylalanine

  E)serine

  D
• Which of the following best describes the arrangement of amino acid side chains in an alpha helix?

  A)The side chains point inward toward the centre of the helix.

  B)The side chains point outward away from the helical axis.

  C)The side chains point toward the C-terminal end of the helix.

  D)The side chains point toward the N-terminal end of the helix.

  E)The side chains point toward the nearest beta-sheet.

  B
• Most proteins have a molecular mass between:

  A)10 kDa and 20 kDa

  B)10 kDa and 500 kDa

  C)10 Da and 20 Da

  D)10 Da and 500 Da

  E)10 Da and 20 kDa

  F)10 Da and 500 kDa

  B
• Which of the following best represents the backbone arrangement of two peptide bonds?

  A)Ca—N—C a—C—C a—N—C a—C

  B)C a—N—C—C—N—C a

  C)C—N—C a—C a—C—N

  D)C a—C—N—C a—C—N

  E)C a—C a—C—N—C a—C a—C

  D
• Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds?

  A)C α—C and N—C α

  B)C=O and N—C

  C)C=O and N—C α

  D)N—C α and N—C

  E)N—C and C α—C

  A