This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Physiology
C-peptide is seen 
Select and explain. 
A. In Pre-proinsulin, B. In Proinsulin, C. As a gastrointestinal proactive molecule, D. As a combined entity with insulin after secretion
B: In Proinsulin
Answer: B: In Proinsulin 
Explanation: Insulin * Insulin is synthesized in the rough endoplasmic reticulum of the B cells * The gene for insulin is located on the sho arm of chromosome 11 in humans. * Normally, 90-97% of the product released from the B cells is insulin along with equimolar amounts of C peptide. * C peptide can be measured by radioimmunoassay, it is an index of B cell function in patients receiving exogenous insulin. Ref:- Ganong's Review of Medical Physiology 25th ed; pg num:- 431