METABOLIC PATHWAYS U2 Flashcards
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
Reactions within metabolic pathways are either anabolic or catabolic.
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 an induced fit and the role of the active site on the activation energy
When a substate binds to the active site, the active site will change shape. This is to allow the active site to better fit the substrate after the substrate binds. This is known as the induced fit.
All chemical reactions require activation energy which needs to be overcome to get them started. In chemistry you can do this by heating or by adding a catalyst. Enzymes are biological catalysts.
By having the active site hold molecules in a particular orientation this allow bonds to made or broken easily. The activation energy is therefore lowered. With the addition of the enzyme, not as much energy is needed to allow the reaction to commence. (This is in addition to the enzyme speeding up a chemical reaction).
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 inhibitors
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.
