This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glycogen, Subject name: Biochemistry
Glycogenin is a protein with self-glucosylation capacity. To which amino acid of glycogenin, glucose molecules are attached? 
Select and explain. 
A. Serine, B. Threonine, C. Tyrosine, D. Hydroxylysine
C: Tyrosine
Answer: C: Tyrosine 
Explanation: Glycogenin protein primer for glycogen synthesis. has self-glucosylation capacity. Glucose residues are added to the OH group of tyrosine residues of glycogenin through O-glycosidic bond. catalyse the addition of up to 8 glucose residues aalpha (1-4) glucosidic bond.