Biochemistry

Question 1

The pH at which majority of amino acid exists in a form where it has an equal number of positive and negative charges and thus is electrically neutral is called the:
A.	pK1
B.	pK2
C.	pK1 + pK2
D.	pIE. pH

Answer 1

A zwitterion is a molecule with a positive and a negative charge in different locations yielding to a net charge of zero for the whole molecule. The pI, or the isoelectric pH is the pH at which this isoelectric/zwitterion form of the amino acid predominates.

Question 2

Glutathione is an important molecule for the clearance of free radicals in the body. It consists of only 3 amino acids. Which of the following polypeptides is the primary structure of glutathione?

A. Glutamyl – cysteinyl – glycine 
B. Glutamine – cysteinyl – glycine
C. Glutamine – threonyl – methionine 
D. Glutamine – cysteinyl – methionine 
E. None of the above

Answer 2

Remember the 3 amino acids which make up Glutathione. (Similar principle/concept to previous exam questions) The most important amino acid is cysteine which contains the active -SH group.

Question 3

Which of the following amino acid is incorrectly paired with its side chain?
A. Tyrosine – Thiol group containing
B. Tryptophan – indole group containing
C. Proline – imino group containing
D. Arginine – guandino group containing
E. Histidine – imidazole group containing

Answer 3

Tyrosine does not contain a thiol group. Tyrosine contains a phenol group.