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Chapter 4 – Respiration
Where does glycolysis fit into the overall process of respiration?

Cellular respiration is the conversion of glucose into ATP, a manageable store of energy
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It occurs at the beginning of both aerobic and anaerobic respiration
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Glucose is activated with the addition of 2 x Pi molecules from
the conversion of 2 molecules of ATP to ADP + Pi
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The
product is phosphorylated glucose
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Phosphorylated glucose is split into 2 x 3C molecules known as
triose phosphate
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A hydrogen atom is removed from each triose phosphate
molecule (oxidation) and are donated to 2 x NAD molecules to
produce 2 x molecules of reduced NAD
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The 2 x molecules of oxidised triose phosphate are converted
into 2 x molecules of pyruvate, an acid
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The products of glycolysis are therefore, 2 molecules of pyruvate, 2 molecules of ATP (4
were produced overall, but 2 were used in the activation of glucose) and 2 molecules of
reduced NAD
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The pyruvate can then be converted into lactic acid/ethanol and CO2 in anaerobic
respiration or used in the Krebs cycle in aerobic respiration
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What is the link reaction?

Pyruvate produced by glycolysis in the cytoplasm needs to be oxidised to take part in the
Krebs cycle, so it is actively transported into the mitochondria
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1
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2
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The remaining 4C oxaloacetate is then recycled to react with
another molecule of acetyl CoA
The Krebs cycle is significant for several reasons:
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It produces reduced NAD/FAD which are required for the electron transport train is
oxidative phosphorylation of chemiosmosis
Regenerates oxaloacetate to combine with acetyl CoA, which would otherwise
accumulate
A useful source of intermediate compounds used in cells e
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to form amino
acids/chlorophyll
What are hydrogen carrier molecules and what is their role in the Krebs cycle?

Hydrogen carrier molecules include FAD, NAD (respiration) and NADP (photosynthesis)
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Where does the electron transport chain take place?

The electron transport chain is found on the inner membrane of the mitochondria (the
cristae)
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How is ATP synthesised in the electron transport chain?



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Reduced NAD and FAD from the Kreb’s cycle release the electrons from the
hydrogen atoms they hold, these electrons are picked up by an electron transport
chain
Losing their electrons causes the protons to be released from the coenzymes; these
protons are then actively transported into the inter-membrane space
Mean whilst the electrons move down energy levels along the ETC in a series of
reduction/oxidation reactions, giving out energy used to form ATP (any remaining
energy is released as heat)
Protons move down their concentration gradient back into the matrix through
stalked particles – at the end of which is ATPsynthase – which forms ATP from ADP
and Pi
The electrons at the end of the ETC combine with the protons and oxygen to form
water, therefore oxygen is the final electron acceptor

What is the role of oxygen in aerobic respiration?

Oxygen acts as the final acceptor of hydrogen
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How is energy released by respiration in the absence of oxygen?

The absence of oxygen means the pyruvate produced at the end of glycolysis cannot join the
Krebs cycle or ETC
...

This done where the pyruvate molecules accept hydrogen from the reduced NAD, in plants
and animals this forms different products
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How is lactate produced by anaerobic respiration?

In organisms, the ability to overcome the oxygen shortage by producing lactate is adaptive,
and often occurs in the muscles with strenuous exercise - as the oxygen demand outweighs
supply (an oxygen debt)
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Lactate causes cramps and muscle soreness,
so is carried away from the muscles in the blood stream to the liver to be converted to
glycogen
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Anaerobic respiration produces much less ATP than aerobic respiration because oxygen is
not present for the Kreb’s cycle/ETC
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