Energy transfers AQA A2 Biology PART 2 of 4 TOPICS: Aerobic and Anaerobic Respiration

Summary on all reactions that need to be known for the AQA exam includes glycolysis, link reaction, Krebs cycle and oxidative phosphorylation as well as anaerobic reaction with its similarities and differences to aerobic respiration

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TOPICS: Photosynthesis Respiration
Energy and ecosystems Nutrient cycles
Energy transfers (AQA A2 Biology) PART 2 of 4

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Aerobic Respiration: Glycolysis
Glycolysis is the first step of aerobic respiration and involves only
glucose. It takes place in the cytoplasm of cells as the cytoplasm
contains the correct enzymes for glycolysis and cannot be carried
out in the mitochondrial matrix as glucose is too big and does not
have the correct enzymes. In glycolysis glucose is phosphorylated
by Pi, a product of the hydrolysis of ATP, into glucose phosphate.
This is then phosphorylated by another Pi from hydrolysis of ATP to
make hexose bisphosphate. This is split into two to make two triose
phosphate molecules. This is then oxidised into two pyruvate
molecules as this reaction releases 2 hydrogens which are used to
reduce two NAD molecules into two NADH/Reduced NAD. The
oxidation reaction also allows four ATP molecules to be made by
condensation reactions of ADP and Pi each, a net of two ATP
molecules are made subtracting the two ATP molecules that were
hydrolysed at the start.…read more

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Aerobic Respiration: Link reaction
Pyruvate then enters the mitochondrial matrix by active
transport. The pyruvate molecule is oxidised into Acetate as
it releases a hydrogen which reduces NAD to
NADH/Reduced NAD. The oxidation reaction is also a
decarboxylation as CO2 is given off. Coenzyme A attaches to
acetate to make Acetyl Coenzyme A. NB: Each pyruvate
molecule undergoes the link reaction separately
therefore the product is doubled when talking about
both pyruvate molecules.…read more

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Aerobic Respiration: Krebs Cycle
Acetyl Coenzyme A enters the Krebs Cycle which take place in the mitochondria. It reacts
with a 4 carbon molecule (Oxaloacetate) and Coenzyme A detaches to make a 6
carbon molecule (Citrate). This is then oxidised into a 5 carbon molecule (alpha
ketoglutarate) where a hydrogen is given off to make NAD reduce to NADH/Reduced
NAD. This reaction is also a decarboxylation as CO2 is given off. The 5 carbon
molecule (alpha ketoglutarate) undergoes a series of reactions to turn back into a 4
carbon molecule (Oxaloacetate). These reactions produces 3 molecules of
NADH/Reduced NAD when NAD is reduced with three hydrogens, CO2 is given off, a
molecule of ATP is made by the condensation of ADP and Pi and FAD is reduced to
FADH/Reduced FAD by a hydrogen. NB: Each Acetyl Coenzyme A undergoes the
Krebs cycle separately so the products double when talking about both Acetyl
Coenzyme A molecules. Also the names of the molecules in brackets do not
need to be known for AQA, however it is good to know what molecules you are
talking about or if these names do come up in some circumstances. Based on
this if the names succinate and malate come up they are molecules that alpha
ketoglutarate turns into before it is oxaloacetate.…read more

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Aerobic Respiration: Oxidative
Oxidative phosphorylation takes place on the cristae of the mitochondria and
involves NADH/Reduced NAD. It attaches to the first protein and is oxidised
where it loses 2 protons (2H+) into the matrix and 2 electrons the first
protein. The electrons are passed from protein to protein in a series of redox
reactions where the electrons lose energy. This energy is used to actively
transport the protons from the matrix into the intermembrane space down its
concentration gradient. As the protons build up in the intermembrane space,
a concentration gradient is made and the protons go down their
concentration gradient back into the matrix via ATP Synthase. As they pass
through they lose energy which is used to make ATP from ADP and Pi. An
oxygen molecule attaches to the last protein with the 2 electrons and is the
final electron acceptor where it accepts both electrons. Two protons attach
to this oxygen making a molecule of water. FADH/Reduced FAD attaches to
the second protein and not the first but follows the same procedure. NB:
Each NADH/Reduced NAD goes through oxidative phosphorylation
separately.…read more

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Anaerobic Respiration
Anaerobic respiration only involves glucose and occurs in plants,
yeast, animals and bacteria. Glycolysis is the first step and is
the same as aerobic respiration. However pyruvate does not
go through the link reaction. In plants and yeast it is
converted into ethanal by a decarboxylation reaction where
CO2 is removed and then reduced into ethanol when
NADH/Reduced NAD is oxidised. Animals and bacteria
convert pyruvate into lactic acid in a reduction reaction where
NADH/Reduced NAD is oxidised.…read more


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