Enzymes for glycolysis located in the cytoplasm of the cell - not in the mitochondria
1. Two molecules of ATP phosphorylate glucose to produce hexose bisphosphate. Energy from ATP hydrolysis activates glucose, making it more reactive.
2. Hexose bisphosphate is split into two molecules of triose phosphate.
3. Each triose phosphate molecules is dehydrogenated into pyruvate, also reducing NAD. This reaction is exergonic: energy released used to synthesise 4 molecules of ATP by substrate-level phosphorylation.
OVERALL: 2xATP, 2x reduced NAD
The link reaction
Enzymes for link reaction found in the mitochondrial matrix
1. Specific pyruvate carrier proteins in the outer mitochondrial membrane transport pyruvate into the mitochondrial matrix.
2. Pyruvate is dehydrogenated and decarboxylated into acetate (2C).
3. Acetate combines with coenzyme A to form acteyl coenzyme A.
As 2 molecules of pyruvate, overall yield: 2xcarbon dioxide, 2xreduced NAD, 2xacteyl coenzyme A
Krebs cycle enzyme located in the mitochondrial matrix
1. Acetyl coenzyme A releases the 2C acetate, which combines with a 4C acid to form a 6C acid.
2. The 6C acid is dehydrogenated and decarboxylated to regenerate the 4C acid,
This, per 1 acetate fragment, produces 2xcarbon dioxide, 2xreduced NAD, 1xreduced FAD and 1 ATP by substrate level phosphorylation.
Electron transport chain
ETC chain of electron carriers located on the inner mitochondrial membrane: cristae, which have a large surface area, so more electron carriers, increasing ATP synthesis
1. Reduced coenzymes NADH2 and FADH2 act as a source of electrons and protons. FADH2 passes its protons to the second of the three proton pumps, so only 2xATP from each FADH2. NADH2 passes its protons to the first of the three proton pumps, so 3 ATPs synthesised.
2. Electron carriers are at progressively lower energy levels, so as electrons pass along the chain of carriers in a series of redox reactions, they release energy. Energy used in ATP synthesis through oxidative phosphorylation. Oxygen, the terminal electron acceptor, combines with protons and electrons to be reduced to water.
3. Energy released from electrons used to pump protons from the matrix through the inner mitochondrial membrane into the intermembrane space.
4. Protons accumulate, setting us steep electrochemical and concentration gradients. As the inner membrane is impermeable to protons, the protons have to diffuse back into the matrix via stalked particles (chemiosmotic channel protein attached to ATP synthase). Flow of protons through ATP synthases provides energy required to produce ATP from ADP and Pi.
Cyanide is a non competitive inhibitor of an enzyme associated with the final proton pump in the ETC. When cyanide attaches to the enzymes, the ETC cant funtion, so no oxidative phosphorylation.
Aerobic respiration = the complete breakdown of glucose into carbon dioxide and water.
produces 38 molecules of ATP per glucose molecule
Anaerobic respiration = incomplete breakdown of glucose into lactic acid in animals, or ethanol and carbon dioxide in plants and fungi.
produces 2 molecules of ATP per glucose
2% efficient, energy remains locked up in lactic acid/ethanol
Without oxygen, the ETC cannot occur, so reduced NAD and FAD are not oxidised back, so NAD and FAD become limiting factors... this means that no dehydrogenation in Krebs or link reaction can occur.
Only glycolysis continues: pyruvate enters a different pathway and is reduced, oxidising reduced NAD. Pyruvate converted to lactate in animals, ethanal in animals which is then reduced to ethanol, along with carbon dioxide.
The recycled NAD can then be used to oxidise triose phosphate, allowing ATP to be synthesised by substrate level phosphorylation, producing 2 molecules of ATP overall.
Alternative respiratory substrates
Glycerol converted to triose phosphate, enters glycolysis
Long chain fatty acids split into 2C fragments, enter Krebs as acteyl coenzyme A
Tissue protein hydrolysed to constiuent amino acids.
Amino acids deaminated, leaving an organic acid that can enter the Krebs cycle.