Quiz - Amino Acids, Peptides, Proteins | Amino Acids, Peptides and Proteins

Organic Chemistry 3 - Quiz - Amino Acids, Peptides, Proteins

1

Which of the following statements about amino acids is incorrect?

Amino acids are carboxylic acids bearing an amino group but they can have additional chemical functions

2

What is the dominant form of an amino acid in a basic aqueous solution (pH > 13)?

Amine (pKa ~ 9-10) and carboxylic acid (pKa ~ 2-3) groups ⇒ amino acids are both basic and acidic. The structure of an amino acid depends on the pH:

3

What is the isoelectric pH of glycine (pKaCOOH = 2.3; pKaNH2 = 9.7)?

Isoelectric pH (or isoelectric point pI):

pI=pKa COOH + pKa NH22=2.3 + 9.72=6.0 

4

At pH > pI, the population of amino acids with neutral R groups in solution will have:

5

Which of the following structures describes the overall 3D folding of a polypeptide?

Polypeptides are organized in 4 different structures:

- primary structure ⇒ sequence of amino acids
- secondary structure (pleated sheet + α helix) ⇒ folding of the primary structure
- tertiary structure (pleated sheet + α helix) ⇒ further folding and coiling
- quaternary structure ⇒ aggregation of several polypeptides (overall 3D folding)

6

Which of the following statements about polypeptides is incorrect?

Polypeptides are characterized by their sequence of amino acid from the amino end (left) to the carboxy end (right)