Metabolic pathways

State the meaning of a metabolic pathway

Metabolic pathways are integrated and controlled pathways of enzyme- catalysed reactions within a cell.
Metabolic pathways can have reversible, irreversible and alternative routes

Describe anabolic and catabolic reactions

Anabolic reactions involve the building up of large molecules from small molecules and require energy.

Catabolic reactions breakdown large molecules into smaller molecules and release energy.

Describe the functions of proteins embedded within membranes

Proteins in the membrane act as:

• Pores (allowing molecules to pass through)

• Pumps (allowing molecules to pass through the membrane, however this requires energy – so the molecule is actively pumped inside or outside of the cell.)

• Enzymes (catalysing chemical reactions)

State what controls metabolic pathways and how this is regulated

Metabolic pathways are controlled by the presence or absence of key enzymes.

Factors that control the rate of enzyme activity such as temperature and pH, will also regulate the rate of a metabolic pathway.

Describe affinity in terms of the substrate and product and state how the presence or absence of these molecules controls metabolic pathways

Substrate molecules have high affinity for the active site which allows the substrate to bind easily.

The product molecules have a low affinity for the active site and this allows the product(s) to leave the active site and allows the active site to bind again with another substrate molecule.

Some metabolic pathways are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.

Describe competitive inhibition

Competitive inhibitors bind at the active site preventing the substrate from binding. Competitive inhibition can be reversed by increasing the substrate concentration

Describe non-competitive inhibitors

Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding. This type of inhibition cannot be reversed by increasing the substrate concentration.

Describe feedback inhibition

Feedback inhibition occurs when the end-product in the metabolic pathway reaches critical concentration. The end-product inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end product.