4 - ENZYMES Flashcards
What are enzymes?
They are globular proteins which act as biological catalysts becauses they speed up metabollic reactions in living organisms without running out by lowering the activation energy
What are catabolic enzymes?
Enzymes which break down substances
What are anabolic enzymes?
Enzymes which synthesise large molecules
What are intracellular enzymes?
Enzymes which act within the cells which they are made in
What are extracellular enzymes?
Enzymes which leave the cells they are made in by exocytosis and act outside on other target cells
Describe the lock and key model.
The active site of an enzyme is specific to substrates with a complementary shapes and when they collide they form temporary bonds in an enzyme-substrate complex (ESC)
Describe the induced fit theory.
Although the shape of the active site is complementary to that of a substrate, subtle changes occur in the shape of the side chains or R groups of amino acids which give them a more precise conformation in the active site
What is a co-factor?
A substance that aids the function of an enzyme, either in the form of a co-enzyme (temporarily bonded) or a prosthetic group (permanently, covalently bonded)
What is the role of a co-factor?
- eases the formation of ESCs
- acts as co-substrate by combining with the substrate to make it fit perfectly in the enzyme’s active site
- changes the charge distribution on the surface of the enzyme or the substrate to make the temporary bonds between them easier to form
What happens once an ESC forms?
The enzyme acts anabollically or catabollically, forming an enzyme-product complex (EPC) before release the products
What factors affect the rate of enzyme-controlled reactions?
Temperature, pH, enzyme concentration, substrate concentration, cofactors and inhibitors
What is Vmax?
The maximum rate of reaction/activity of an enzyme
What is the effect of temperauture on enzyme activity?
- increases kinetic energy of the enzyme and the substrate so they collide together more, forming more ESCs
- at the enzyme’s optimal temp, Vmax is achieved
- further increases to the temp cause H bonds to breqk but there is chance of their reformation
- once temp is increased even further, the enzyme denatures
What is the affect of pH on enzyme activity?
- different enzymes have different optimum pH levels at which they work most efficiently and achieve Vmax
- further changes to pH cause H bonds to break but there is chance of their reformation
- once pH changes even further, the enzyme denatures
How does an enzyme become denatured?
- hydrogen bonds and ionic bonds in its tertiary structure break
- the shape of the active site changes permanently
- the enzyme can no longer carry out its function
What is the effect of enzyme/ substrate concentration on enzyme activity?
- as concentration (of one) increases, rate of reaction increases
- concentration becomes limiting factor of the reaction, since the rate begins to slow
- once the concentration increases further, Vmax is achieved
- further increases in concentration have no effect on the rate
- the concentration of the other now becomes the limiting factor
What are competitive inhibtors?
Inhibitors which:
- can fit into active site of an enzyme without reacting
- compete with subtrate molecules for access to the active site
- affects activity depending on concetration
- can be minimised by raising the concentration of substrate
- have reversible effects on the enzyme as they detach themselves after a while
What are non-competitive inhibitors?
Inhibitors which:
- binds to allosteric site (the place on an enzyme where a molecule that is not a substrate may bind)
- change the shape of the molecule, preventing it from working
- effect is independent of substrate concentration and irreversible
What are metabollic inhibitors?
Poisons and medicines which inhibit the metabollic reactions of cells for an adverse or beneficial effect
