Unit 8.1
• Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
• Enzymes reduce the activation energy to speed up reactions.
• When a substrate binds to the active site on an enzyme, the active site undergoes a
conformational change.
• Due to this process, the bonds in the substrate become less stable,
lowering the overall energy level of the transition state, reducing the
activation energy.
• There are two types of inhibitors concerning enzymes:
• Competitive inhibitors fit into the active site, blocking the substrate.
They will reduce the rate of reaction, however only temporarily.
• Non-competitive inhibitors fit into the allosteric site, causing the
enzyme to undergo a conformational change. This is normally non-
reversible, resulting in permanent lower rate of reaction.
• End product inhibition is a form of negative feedback,
when the end product becomes an inhibitor.
• This stops the overproduction of products.
• Isoleucine is an amino acid which acts as an inhibitor
when too much is being produced, it binds to the
allosteric site of Threonine deaminase, until more
isoleucine is required.
Unit 8.2
• Respiration is the controlled release of energy from
organic compounds to form ATP.
• For aerobic respiration to take place, 4 processes take
place, all of which involve the reduction of electron
carriers NAD+ and FAD:
• Glycolysis:
• Occurs in the cytoplasm and does not require
oxygen.
• Glucose is phosphorylated using phosphate from
two ATP molecules, forming hexose diphosphate
which is less stable.
• The molecule then undergoes lysis (splitting) and
becomes triose phosphate.
• Finally, the molecules are oxidised to form
pyruvate. The electron carried NAD+ is reduced
into NADH+.
• This produces 4ATP, giving a net yield of 2ATP.
• In animals, if no oxygen is present then pyruvate
will be converted into lactic acid.
• Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
• Enzymes reduce the activation energy to speed up reactions.
• When a substrate binds to the active site on an enzyme, the active site undergoes a
conformational change.
• Due to this process, the bonds in the substrate become less stable,
lowering the overall energy level of the transition state, reducing the
activation energy.
• There are two types of inhibitors concerning enzymes:
• Competitive inhibitors fit into the active site, blocking the substrate.
They will reduce the rate of reaction, however only temporarily.
• Non-competitive inhibitors fit into the allosteric site, causing the
enzyme to undergo a conformational change. This is normally non-
reversible, resulting in permanent lower rate of reaction.
• End product inhibition is a form of negative feedback,
when the end product becomes an inhibitor.
• This stops the overproduction of products.
• Isoleucine is an amino acid which acts as an inhibitor
when too much is being produced, it binds to the
allosteric site of Threonine deaminase, until more
isoleucine is required.
Unit 8.2
• Respiration is the controlled release of energy from
organic compounds to form ATP.
• For aerobic respiration to take place, 4 processes take
place, all of which involve the reduction of electron
carriers NAD+ and FAD:
• Glycolysis:
• Occurs in the cytoplasm and does not require
oxygen.
• Glucose is phosphorylated using phosphate from
two ATP molecules, forming hexose diphosphate
which is less stable.
• The molecule then undergoes lysis (splitting) and
becomes triose phosphate.
• Finally, the molecules are oxidised to form
pyruvate. The electron carried NAD+ is reduced
into NADH+.
• This produces 4ATP, giving a net yield of 2ATP.
• In animals, if no oxygen is present then pyruvate
will be converted into lactic acid.
