higher biology - unit 2.1: metabolic pathways and their control

cell metabolism

all the biochemical reactions that occur within a living cell

metabolic pathways

integrated and controlled pathways of enzyme-catalysed reactions, series of chemical reactions

steps in a metabolic pathway can be...

reversible and irreversible.

alternative pathways

are pathways that exist through substances that allow certain stages controlled by enzymes to be bypassed

two categories of metabolic pathway?

anabolic + catabolic

anabolic

build up of larger molecules from smaller molecules and requires energy

catabolic

break down of larger molecules into smaller molecules and releases energy

membrane proteins

protein pores, protein pumps and enzymes are embedded in membranes

protein pores

channel proteins which span the membrane, allow specific larger molecules to pass through the membrane by diffusion

protein pump

carrier proteins which bind to specific molecules or ions temporarily, enabling them to cross the membrane by active transport

enzymes

catalyse for a specific reaction

how do enzymes control metabolic pathways?

their presence or absence / the regulation of the rate of reaction of key enzymes

activation energy

energy needed to get a reaction started

what do enzymes do to activation energy?

lower it, meaning a quicker reaction

induced fit

the change in shape of the active site of an enzyme so that it binds more snugly to the substrate, induced by entry of the substrate

high affinity

the substate molecules have this for the active site

low affinity

once a reaction is complete, the products have this for the active site

concentration of substrate and product

direction of enzyme action

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

how can metabolic pathways be controlled?

regulating enzyme activity through inhibitors

competitive inhibition

inhibitors bind at the active site and prevent substrates from binding, can be reversed by increasing substate concentration

non-competitive inhibition

inhibitors bind away from the active site, but change the shape of the active site. Cannot be reversed by increasing substrate concentration

feedback inhibition

inhibition occurs when end product reaches a critical concentration. The end product then inhibits an earlier enzyme blocking the pathway and prevents further synthesis of end product