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

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


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


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:


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 


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


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)


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)