February 12th, 2007


Biochemistry 106: Insulin

The term mellitis (from diabetes mellitis) comes from apis melliferous which means honey. Doctors used to taste a patient's urine to assess if it contained sugar.

Insulin is a protein that is assembled as pre-pro-insulin from the mRNA. It has an N terminal leader sequence that is hydrophobic allowing transport through membranes. It has a connecting sequence in the middle that gets chopped out later. It also has cysteines which contain sulfur at several sites. When the leader sequence is cleaved off it becomes proinsulin. Then the sulfurs on the cysteines bond to each other, forming sulfhydryl bridges between two parts of the strand, soon to be known as the A strand and B strand. The sulfhydryl bonds twist the original strand into a glob, and insulin is stored this way. Insulin is activated when a connecting sequence is chopped off between the A and B chains.