AQA A2 Biology Unit 4 3.4.4 Respiration

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Preview of AQA A2 Biology Unit 4 3.4.4 Respiration

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3.4.4 Respiration
Aerobic Respiration
Takes place in the cytoplasm of the cell.
Glucose is first phosphorylated by 2 phosphate groups from 2 molecules of ATP to produce 2
molecules of glyceraldehyde-3-phosphate (GALP).
GALP is then oxidised and dephosphorylated into pyruvate.
In this process, the phosphate groups are transferred to ADP producing 2 molecules of ATP.
A hydrogen ion is transferred to a molecule of NAD producing NADH.
The net yield of glycolysis per glucose is;
2 pyruvate
The pyruvate produced then diffuses into the mitochondria.
The Link Reaction
Takes place in the matrix.
Pyruvate undergoes oxidative decarboxylation.
Electrons and hydrogen from the pyruvate are transferred to NAD producing NADH.
Carbon dioxide is removed which converts the pyruvate into acetate.
The acetate then combines with CoenzymeA to produce Acetyl CoenzymeA.
Since 2 molecules of pyruvate were produced in glycolysis, the net yield of the link reaction
per glucose is
2 Acetyl CoenzymeA
2 Carbon dioxide
The Krebs Cycle
Takes place in the matrix.
Closed cycle of enzyme controlled reactions.
It provides a continuous supply of reduced electron carriers for the
electron transport chain.
AcetylCoA combines with a 4-C compound to produce citric acid, a
6-C compound.
The citric acid then undergoes;
A decarboxylation reaction which removes carbon dioxide.
A series of oxidation reactions which remove hydrogen ions and
H + ions and e ­ are picked up by NAD and FAD and they
become NADH and FADH.
At the end of the cycle the 4-C compound is recycled so the cycle
can continue.
Since each glucose molecule produced 2 molecules of pyruvate and
so 2 molecules of AcetylCoA, the yield per glucose for the Krebs
cycle is;
4 carbon dioxide

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Electron Transport Chain
Found on the cristae of the mitochondria which provide a large surface
area for this to take place.
The electron carriers are arranged in descending energy levels.
When electrons pass through the carriers, the energy released is used
to move hydrogen ions from the matrix into the intermembrane space.
This creates a large concentration gradient of H+ ions and so they
diffuse back into the mitochondrial membrane by diffusion via ATP
synthase.…read more


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