Energy in food

Carbohydrates (17 kJ g^-1), Proteins (17 kJ g^-1), Lipids (34 kJ g^-1). These are sources of reduced carbon which can supply

Energy transformations

A stepwise energy release is needed

Complete oxidation of glucose:

Complete oxidation of a fat (lipid):

• This is too much to handle all at once.
• Therefore energy is released step by step and the energy released is coupled to ATP synthesis.
• The energy in 1 molecule of glucose is used to synthesise 36 molecules of ATP (37.5 % efficient). This is a very efficient energy conversion (most machines can only manage 20% efficiency).
• This is because the release of the energy from the food molecules is done stepwise.

Reaction pathways:

GLYCOLYSIS in the cytoplasm

KREB'S CYCLE in mitochondria of eukaryotes (in the cytoplasm of prokaryotes)