Question

Why does ATP yield vary in cellular respiration (think about how NADH from glycolysis enters mitochondira)?

Answer 1

2 ATP molecules are produced from glycolysis, 2 ATP molecules are produced from Kreb's cycle and 34 ATP molecules are produced from oxidative phosphorylation (by electron transport system). Hence in total 38 (2+2+34= 38) ATP molecules are produced during cellular respiration. But this rarely happens because some ATPs are lost in moving pyruvate and ADP in matrix of mitochondria and some are lost due to leakage through membranes. Hence the actual yield of ATP in cellular respiration ranges around 30.

In Oxidative phosphorylation firstly oxidation of NADH and FADH2 happens and then secondly phosphorylation happens. NADH transfers its energy molecules to protein complex 1 and FADH2 transfers its energy molecules to protein complex 2 which leads to their oxidation. Process of NADH oxidation causes pumping of protons via protein complex 1 from the matrix to the intermembrane space which causes ADP to bind with inorganic phosphate (Pi) which produces ATP.