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Cell Metabolism
Higher Human Biology
Unit 1 – Section 6
Metabolic Pathways
Learning Intentions
By the end of this section you should be able to:
• State what is meant by cell metabolism
• State that metabolic pathways are controlled at each step
by enzymes and can also be controlled by intracellular and
extracellular signalling molecules.
• Describe the difference between anabolic and catabolic
processes, and explain how metabolic pathways can be
reversible and irreversible steps as well as alternative
processes.
• The key role played by specific enzymes in regulating rates
of reactions.
What is Cell Metabolism?
• This is the collective term for all
chemical reactions that take place
cell. These are usually connected
integrated into pathways that
catalysed by enzymes.
the
in a
and
are
Metabolic Pathways
• There are two types of metabolic pathways:
• Catabolic – these bring about the breakdown of complex
molecules to simpler ones, usually releasing energy and
often producing building block molecules
• E.g. aerobic respiration.
• Anabolic – these bring about the synthesis of complex
molecules from simpler building block molecules and as
such require energy. E.g. protein synthesis
• E.g. protein synthesis
• http://www.youtube.com/watch?v=iIW5SPY-vwI
The two types of metabolic pathway
Carbon
Dioxide
e.g. Amino
Acids
ATP
Energy
+
Energy
Water
Catabolic – Aerobic
Respiration
Glucose
+
Oxygen
Respiration
Catabolic
Energy
ENERGY TRANSFER
ADP
+
Anabolic –
e.g. Protein
synthesis
Energy
Protein
molecule
Pi
Protein Synthesis
Anabolic
Synthetic (anabolic) reactions
Another example:
glucose-1-phosphate
phosphorylase
starch
This reaction requires the input of energy to
proceed (anabolic reaction).
Breakdown (catabolic) reactions
Another example:
starch
amylase
maltose
This reaction releases energy (catabolic
reaction).
What else do you need to
know?
• Metabolic pathways can have reversible and
irreversible steps.
AND
• Alternative pathways may exist that can
bypass steps in a pathway.
• Example of
reversible/
irreversible
pathways
Irreversible
to maintain
a low
glucose conc
Reversible
for storage
Irreversible
regulatory
point
• Example of
alternative
routes in
metabolism