Quiz

QUIZ

1. What is the amino acid cutoff, above which a polypeptide becomes a protein?

a. 10 b. 20

c. 50 d. 100

Answer: c. A protein is a polypeptide that will be at least fifty amino acids in total length.

2. What is considered the simplest amino acid?

a. Glycine b. Lysine c. Isoleucine d. Alanine

Answer: a. Glycine is the simplest amino acid, consisting only of NH2CH2COOH, which serves to have the most basic definition of an amino acid, having an amino group and a carboxylic acid side chain.

3. What type of amino acid makes up the twenty amino acids seen in proteins?

a. All alpha amino acids b. All beta amino acids c. All gamma amino acids d. A mixture of alpha and beta amino acids

Answer: a. All amino acids seen in nature are consisted of alpha amino acids, which means that the amino group is attached to the alpha carbon or the carbon just adjacent to the carboxylic acid carbon. It means that the NH2 side chain becomes NH3+ and the COOH side chain becomes COO.

4. Which amino acid is not basic in nature?

a. Arginine b. Histidine c. Lysine d. Aspartate

Answer: d. Aspartate is a carboxylic acid amino acid, making it acidic and not basic. The rest of them have an amine side chain, making them basic in nature.

5. Which amino acid has the highest isoelectronic point?

a. Lysine b. Glycine c. Histidine d. Arginine

Answer: d. While both arginine and histidine are basic amino acids, arginine will have the greatest isoelectronic point at 10.76.

6. In the Fischer projection of a carbohydrate or amino acid, which is not true of these diagrams?

a. The most reduced form of carbon is on the top. b. The longest chain is written vertically. c. The aldehyde, ketone, or carboxylic acid is at the top. d. There can be L- or D- forms written with these diagrams.

Answer: a. What is true is that the most oxidized form of the amino acid or carbohydrate is on the top of the diagram with the longest chain written vertically and D or L forms written out.

7. In making amino acids, there can be nucleophilic substitution reactions at the chiral center, which is the alpha carbon. Which is the molecule at the alpha carbon that must be there to have the NH2 group take the place of?

a. Hydrogen b. Hydroxyl c. NO2 d. Halide

Answer: d. The alpha carbon must have a halide atom attached to it in order to act as a leaving group so that the NH2 or NH3+ side chain can be substituted there.

8. The Strecker synthesis of amino acids forms an intermediary, which is an amino nitrile. The end result is an amino acid by the addition of what to the amino nitrile molecule?

a. Ammonia b. Base c. H3O+ d. HCl

Answer: c. The amino nitrile compound has a CN side chain and an amino side chain. What needs to happen is the transformation of CN into COOH. This can only take place with heat and the addition of H3O+.

9. Which type of bonding systems is least reactive?

a. Amide bond b. RCN (cyanide bond) c. Amine bond d. Carboxylic acid bond

Answer: a. The amide bond is a relatively inactive bond because of the resonance of the CNO bonding system in an amide. This makes sense

because proteins in biological systems need to be relatively inactive when compared to other types of bonding systems.

10. What bonding does not help in the forming of the three-dimensional shape of a protein molecule?

a. Hydrophobic attractions b. Covalent bonding c. Disulfide bonding d. Hydrogen bonding attractions

Answer: b. Each of these attraction forces or bonding contributes to the three-dimensional shape of a protein except for covalent bonding between R chains. There is no covalent bonding that takes place between R chains except for disulfide bonding.