Download Metabolic Pathways

Higher Biology
Unit 2
2.1 Metabolic Pathways & their
Control
Metabolism
• Metabolism is the term used to
describe all of the chemical reactions
that take place inside a living cell.
• Most of these chemical reactions form
steps in metabolic pathways
• Respiration and photosynthesis are
examples of metabolic pathways.
Metabolic Pathways
• All metabolic
pathways are
controlled by
enzymes .
• Each step in the
pathway is
controlled by a
different enzyme.
Substance
A
Enzyme 1
Substance
B
Enzyme 2
Substance
C
Metabolic Pathways
• To allow control of a
metabolic pathway,
many contain
reversible and
irreversible steps.
Intermediate 1
Intermediate 2
Intermediate 3
Intermediate 4
Metabolic Pathways
• If a step is
irreversible then
there is usually
an alternative
pathway that can
bypass it.
Metabolic Pathways
• There are two types of metabolic
pathways;
Catabolic pathways
Anabolic pathways
Catabolic Pathways
• Catabolic pathways break down complex
molecules into simpler ones.
• This results in the release of energy.
• Respiration is an example of a catabolic
pathway as glucose is broken down to
produce carbon dioxide, water and ATP.
Anabolic Pathways
• Anabolic pathways build up simple
molecules into more complex ones.
• This requires energy.
• Protein synthesis is an example of an
anabolic pathway as amino acids are
built up into proteins.
Key Points
Metabolism is the sum of all biochemical
reactions that take place in a cell.
Metabolic pathways are controlled by
different enzymes.
Metabolic pathways can have reversible
and irreversible steps and alternative
routes that can bypass steps in a
pathway.
Key Points
Anabolic pathways involve the synthesis
of molecules.
Anabolic pathways require an input of
energy.
Catabolic pathways involve the
breakdown of molecules and release
energy.
Catabolic pathways release energy.
Questions
1. Define the term “metabolism”.
2. Name both types of metabolic
pathways.
3. Describe two ways in which these
pathways differ.
4. How are the steps in metabolic
pathways controlled?