Quiz - Amino Acids, Peptides, Proteins | Amino Acids, Peptides and Proteins
Which of the following statements about amino acids is incorrect?
Amino acids are both basic and acidic
Amino acids have only two chemical functions: a carboxylic acid group and an amino group
α-amino acids are the most common amino acids in nature
α-carbon has generally a S configuration
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)?
NH3+-CHR-COOH
NH3+-CHR-COO-
NH2-CHR-COO-
NH2-CHR-COOH
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)?
2.3
6.0
9.7
12.0
Isoelectric pH (or isoelectric point pI):
At pH > pI, the population of amino acids with neutral R groups in solution will have:
A net positive charge
A net negative charge
No charged groups
No net charge
Which of the following structures describes the overall 3D folding of a polypeptide?
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
Plypeptides 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?
Amide bonds in polypeptides are called peptide bonds
Polypeptides are hydrolyzed in acidic condition to form amino acids
Polypeptides are characterized by their sequence of amino acid from the carboxy end (left) to the amino end (right)
Polypeptides synthesis is the coupling between an amino-protected amino acid and a carboxy-protected amino acid
Polypeptides are characterized by their sequence of amino acid from the amino end (left) to the carboxy end (right)