AQA Unit 4 Respiration

Glycolysis

Occurs in the cytoplasm
Glucose is activated by the addition of phosphate (from the hydrolysis of ATP to ADP)
Phosphorylated glucose is split into two molecules of 3-carbon TP (triose phosphate)
Hydrogen is removed from each TP and transferred to NAD
NAD is reduced by the addition of hydrogen
Enzyme controlled reactions convert each TP to pyruvate
Two molecules of TP are regenerated from ADP

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The pyruvate molecules in the cytoplasm are actively transported into the mitochondrial matrix
Here, pyruvate is oxidised by removing hydrogen
This hydrogen is accepted by and reduces NAD
The 2-carbon molecule that is produced, acetyl group, combines with coenzyme A
AcetylcoenzymeA is formed
A molecule of CO2 is formed

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The 2-carbon molecule acetylcoenzyme A from the link reaction combines with a 4-carbon molecule
A 6-carbon molecule is produced
6-carbon molecule is oxidised by the loss of hydrogen and a molecule of carbon dioxide
A 4-carbon molecule and a single molecule of ATP is formed in substrate-level phosphorylation
The 4-carbon molecule that is formed can recombine with another molecule of acetylcoenzyme A

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The hydrogen atoms produced in glycolysis and the Kreb's Cycle combine with NAD and FAD
The reduced NAD and FAD donate electrons to the first molecule in the electron transport chain
This releases protons from the hydrogen atoms, the protons are then actively transported across the inner mitochondrial membrane
The electrons pass down the electron transport chain in a series of redox reactions
The electrons lose energy as they pass down the chain
Some of this energy is used to combine ADP and Pi to form ATP, and the remaining energy is used as heat
The protons accumulate in the space between the two mitochondrial membranes before they diffuse back into the mitochondrial matrix through protein channels
The electrons combine with protons and oxygen to form water

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