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UNIT 4 - RESPIRATION
FOUR STAGES IN AEROBIC RESPIRATION
1. Glycolysis making pyruvate from glucose
2. Link reaction - converting pyruvate to acetyl coenzyme A
3. Krebs cycle producing reduced coenzymes and ATP
4. Oxidative phosphorylation producing a large amount of ATP
o Splitting one glucose (6C) 2 pyruvates (3C)
o Doesn't need oxygen to take place is anaerobic.
o In cytoplasm of cells.
o Stage 1 Phosphorylation: Glucose phosphorylated 2 phosphates added from
2ATP. This creates 2 molecules of triose phosphate and 2ADP
o Stage 2 Oxidation: Triose phosphate oxidised loses hydrogen, forming 2
molecules of pyruvate. NAD collects H ions, forming 2reducedNAD. 4ATP
produced, but 2 used in phosphorylation, so net gain of 2ATP.
o The two molecules of reduced NAD go to oxidative phosphorylation.
o The 2 pyruvate molecules go into the matrix of the mitochondria for link
o Decarboxylases (removeCO2) pyruvate.
o Reduces NAD collects hydrogen from pyruvate, changing pyruvate to
o Combines acetate with coenzyme A to form acetyl coenzyme A.
o No ATP produced
o In mitochondria
o Occurs twice for every glucose molecule -2 pyruvate made for every
glucose that enters glycolysis. Means link r.&Krebs cycle happen 2x for every
o For each glucose: 1)Two molecules of acetyl coenzyme A go into Krebs cycle.
2)Two CO2 released 3)Two reduced NAD are formed and go to oxididative
o Series of oxidation-reduction reactions
o In the matrix of the mitochondria
o Happens once for every pyruvate molecule(2x for every glucose)
1. Acetyl CoA from link reaction combines with oxaloacetate to form
citrate. Coenzyme A goes back to link reaction to be used again.
2. 6C citrate molecule is converted to 5C molecule. When this happens
decarboxylation and dehydrogenation occur. The hydrogen is used
to produce reduced NAD from NAD.
3. 5C molecule is then converted into a 4C molecule. Decarboxylation
and dehydrogenation occur between intermediate compounds,
producing one reduced FAD and two reduced NAD.
ATP is produced by the direct transfer of a phosphate group
from an intermediate compound to ADP (substrate-level
phosphorylation). Citrate has now been converted to
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UNIT 4 - RESPIRATION
From Krebs Cycle: 1CoA reused in link reaction,
oxaloacetate regenerated for use in Krebs Cycle,
2CO2 released as waste product,
1ATP used for energy,
3reducedNAD and 1reduced FAD used in oxidative
o Where energy carried by electrons from reduced coenzymes (reduced NAD & reduced FAD)
is used to make ATP.
o Involves two processes the electron transport chain and chemiosmosis.…read more