This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory chain, Subject name: Biochemistry
MELAS is an inherited condition which occurs due to deficiency of 
Select and explain. 
A. Complex I, B. Complex II, C. Complex III, D. All the above
A: Complex I
Answer: A: Complex I 
Explanation: MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke) is an inherited condition due to NADH-Q oxidoreductase (Complex I) or cytochrome oxidase (Complex IV) deficiency. It is caused by a mutation in mitochondrial DNA and may be involved in Alzheimer disease and diabetes mellitus. Reference: Harper; 30th edition; Page no: 135