NAD

1. The Cytochrome system O2 a NAD H2 c d H2 b H2 Cytochrome Oxidase b d O NAD c a H2 H2 ADP + Pi ATP ADP + Pi ATP ADP + Pi ATP

2. The Cytochrome system • The total gains from a single molecule of glucose so far are • a) 2 ATP from glycolysis • b) 12 NADH. 2 from glycolysis and 10 from the kreb’s cycle. • The final stage of respiration is known as the cytochrome system.– see handout • This system of hydrogen carriers is the most important means of releasing energy in respiration. • This is a system of carrier molecules is found on the cristae of the mitochondria. • Hydrogen bound to the carrier molecule NAD is passed down a series of molecules successively reducing (gain)and oxidising (loss) each carrier in turn • Hydrogen is finally received by oxygen to form water. • If oxygen is not present to act as the final accceptor, the hydrogen cannot pass through the system and complete oxidation cannot take place.

3. Each molecule of NADH which passes its hydrogen into the cytochrome system gives releases enough energy to synthesise 3 A.T.P molecules • The process of respiration has released 12 NADH which after passing the hydrogen into the cytochrome system results in 36 ATP • Glycolysis released a further net gain of 2ATP • 1 molecule of glucose therefore gives rise to 38 ATP • During respiration energy may be released from a few individual steps in the overall process, but that most of the energy is made available by the cytochrome system. • Carbohydrates such as glucose are the main respiratory substrate but if they are not available fats and proteins may be used as an alternative. • The Fatty acids from fats are converted to Acetyl Co-A and enter the Krebs cycle. Fats release twice the energy/gram compared to carbohydrates but the energy is released much more slowly. • The amino acids from proteins may also be used but only during periods of starvation