GLYCOLYSIS
Grade 11Term 2
Objectives
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I can describe the energy-investment stage of glycolysis.
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I can describe the energy-harvesting stage of glycolysis.
Glycolysis
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Takes place in the cytoplasm –
outside the mitochondria.
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C6 is broken down to C3 pyruvate
molecules.
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Glycolysis occurs in all organisms,
so we think this evolved before
mitochondria.
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This is why it happens in the
cytoplasm without oxygen.
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Glycolysis is a metabolic pathway
with 10 reactions.
Glycolysis
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10 steps
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2 stages: energy investment,
energy harvesting
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Energy investment stage –
uses ATP to jump-start
glycolysis
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Energy harvesting stage –
produces ATP
Energy-Investment Step
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2 ATP activate glucose by adding
phosphate.
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ATP releases energy and P when it changes
back to ADP.
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This energy makes the glucose split into 2 x
C3 molecules.
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Each of these pyruvate molecules contains P
released by ATP changing to ADP.
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These are G3P – glyceraldehyde-3phosphate.
Energy-Harvesting Step
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G3P is oxidized to remove electrons and H+.
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These electrons and H+ are used to change 2 NAD+ to NADH.
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When O2 becomes available, each NADH carries a high energy electron to
the electron transfer chain and becomes NAD+ again – it is recycled.
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2 NAD+ +
4 e- + 2H+
2NADH
Energy-Harvesting Step
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Inorganic phosphate is added creating a
high energy phosphate group on each C3
molecule.
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These phosphate groups are later used to
form 2 ATP molecules in the substrate-level
ATP synthesis or substrate-level
phosphorylation.
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Phosphorylation = an enzyme passes the
high energy phosphate to ADP to form ATP.
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This is a coupled reaction.
Energy-Harvesting Step
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Oxidation occurs again removing H2O.
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Substrate level ATP synthesis occurs again.
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This results in pyruvate.
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2 ATP are used to start with. 4 are produced during glycolysis.
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4 – 2 = 2 ATP This is the net ATP gain during glycolysis.
Inputs and Outputs of Glycolysis
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Inputs
Outputs
C6glucose
2 x C3 pyruvate
2 NAD+
2 NADH
4 ADP + 4 P
2 ADP
2 ATP
4 ATP
NET GAIN = 2 ATP
The pyruvate now enters the mitochondria.
SEE page 116 Figure 3.4