第四章蛋白质生化作业

Chapter 4. Amino acid and protein

1. Definitions

(1) Isoelectric point

(2) Ninhydrin reaction

(3) Tertiary structure

(4) Motif

(5) Chaperone

(6) Chromatography

(7)α-helix

(8) Protein denaturation

(9) Allosteric effect

(10) Bohr effect

(11) Molecular disease

(12) HbS

2. Mono-choice questions

(1) Two amino acids of the standard 20 contain sulfur atoms. They are:

A. cysteine and serine.

B. cysteine and threonine.

C. methionine and cysteine

D. methionine and serine

E. threonine and serine.

(2) Proline is distinct among the 20 commonly found amino acids because

A. it is a ring compound.

B. it is hydrophilic and ionic.

C. the nitrogen of the amino group is in a ring.

D. the carbon of the carboxyl group is in a ring.

E. it has little effect on protein structure.

(3) Cysteine residues play an important role in the structure of many proteins by

A. providing covalent links between parts of a protein molecule or between two different protein chains.

B. forming disulfide bonds with another amino acid.

C. linking two protein chains through hydrophobic interactions.

D. reducing two cysteine residues.

(4) Because proteins can absorb light maximally at 280 nm, they can be identified and quantified in solution by using a spectrophotometer. Which of the following is true about the absorption of light by proteins?

A. Proteins absorb infrared light.

B. All amino acids absorb light equally.

C. The greater the concentration of protein in a solution, the more 280 nm transmitted light will be detected by a spectrophotometer.

D. Absorbance of 280 nm light by proteins increases with the concentration of the protein.

(5) Which of the following amino acids has a net negative charge at pH 7.0?

A. glycine

B. threonine

C. aspartate

D. arginine

(6) The isoelectric point, or pI, of an amino acid or a protein is

A. the pH at which the amino acid or protein has no net charge.

B. zero at pH 7.0.

C. the pH at which the amino acid or protein is neither hydrophobic nor hydrophilic.

D. the measure of how hydrophobic an amino acid or protein is.

(7) A protein retained on an affinity chromatography column is usually eluted off the column by

A. gradually increasing the salt concentration of the elution buffer.

B. adding the protein's free ligand.

C. changing the pH of the elution buffer.

D. allowing the retained protein to naturally come off the column after the non-specifically bound proteins have first passed through the resin.

(8) For the study of a protein in detail, an effort is usually made to first:

A. conjugate the protein to a known molecule.

B. determine its amino acid composition.

C. determine its amino acid sequence.

D. determine its molecular weight.

E. purify the protein.

(9) In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography?

A. cytochrome c Mr = 13,000

B. immunoglobulin G Mr = 145,000

C. ribonuclease A Mr =13,700

D. RNA polymerase Mr = 450,000

E. serum albumin Mr =68,500

(10) By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:

A. determine a protein’s isoelectric point.

B. determine an enzyme’s specific activity.

C. determine the amino acid composition of the protein.