1. Higher Human Biology Unit 1 – Section 6 Metabolic Pathways
Cell Metabolism
Higher Human Biology
Unit 1 – Section 6
Metabolic Pathways

2. 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.

3. What is Cell Metabolism?
This is the collective term for all the chemical reactions that take place in a cell. These are usually connected and integrated into pathways that are catalysed by enzymes.

4. 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

5. The two types of metabolic pathway
Glucose +
Oxygen
Carbon Dioxide
Water
Energy
ATP
ADP Pi
e.g. Amino Acids
Protein molecule
Catabolic – Aerobic Respiration
ENERGY TRANSFER
Anabolic – e.g. Protein synthesis
Respiration Protein Synthesis
Catabolic Anabolic

6. Synthetic (anabolic) reactions
Another example: glucose-1-phosphate phosphorylase starch This reaction requires the input of energy to proceed (anabolic reaction).

7. Breakdown (catabolic) reactions
Another example: starch amylase maltose This reaction releases energy (catabolic reaction).

8. 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.

9. Irreversible regulatory point
Example of reversible/ irreversible pathways
Irreversible to maintain a low glucose conc
Reversible for storage
Irreversible regulatory point

10. Example of alternative routes in metabolism