SET 2 biology chapter 3 enzymes

enzymes def.

proteins that act as biological catalysts to speed up biological reactions by lowering activation energy required to initiate a given reaction

enzyme features

• reusable

• have an active site specific to substrate

• speed up not create

• are proteins (most??)

• all enzymes are catalysts but not all catalysts are enzymes

• can influence entire biochemical pathways

• often end in ‘ase’

• above the arrow in a reaction (not a reactant or product)

the enzyme active site and substrate are…

complementary in shape

how an enzyme works

substrate bind to specific complementary enzyme active site → together they form enzyme-substrate complex → active site conformationally changes to accomodate substrate → substrate small change → reaction occurs → products leave enzyme active site → enzyme can be reused

activation energy

minimum energy amount required to energise atoms to state where they can undergo chem. transformation

anabolic vs catabolic

anabolic = smaller molecs. combine, form bigger molecule (think assemble)

catabolic = large molecule breaks down, form smaller molecs.

factors on enzyme activity — TEMPERATURE

• too cold: less kinetic energy → less enzyme active site and substrate collision → lowered enzyme activity

  BUT can regain functionality by heating

• too hot: causes enzyme denaturation → active site conformationally change → substrate cannot fit, reduced enzyme activity

  this is irreversible

factors on enzyme activity — TEMPERATURE graph

factors on enzyme activity — pH

optimal level varies between dif. enzymes based on their location

• too acidic or too basic → enzyme denaturation → active site conformationally change → substrate cannot fit, reduced enzyme activity

factors on enzyme activity — pH graph

optimal def. and tolerance range def.

• optimal level = point for a given condition where max. function of enzyme occurs

• tolerance range = wider range of given condition that an enzyme can function under

factors on enzyme activity - CONCENTRATION

• substrate conc. = enzyme conc. constant while substrate conc. increases → increase in enzyme activity until saturation point → here all enzyme active sites occupied hence plateau

• enzyme conc. = substrate conc. constant while enzyme conc. increases → more active sites hence increase in activity until saturation point → here all substrates used up hence plateau

factors on enzyme activity - CONCENTRATION graphs (substrate and enzyme concentration)

saturation point def.

point where substance cannot receive more of another substance → plateau of graph here

limiting factor def.

factor that prevents rate of reaction from increasing

inhibitors def.

molecs. bind to enzyme and prevent its functioning

competitive and non-competitive inhibition

• competitive inhibition = inhibitor bind to enzyme active site → blocks substrate from binding → inhibitor shape is complementary to active site enzyme hence inhibitor shape similar to substrate shape (as they both complement to same active site)

  influenced by substrate conc.

• non-competitive inhibition = inhibitor binds to site on enzyme other than active site (allosteric site) → causes conformational change to active site → substrate cannot bind to it

  not influenced by substrate conc.

reversible and irreversible inhibition

• reversible inhibition = bonds formed between inhibitor and enzyme are weak → can be broken → slows rate of reaction not stops

  can be competitive and non-competitive

• irreversible inhibition = bonds formed between inhibitor and enzyme strong → can‘t be broken easily → reaction never occurs with enzyme

  generally competitive

biochemical pathway inhibition

when end product (of pathway) inhibits enzymes in the pathway → halts pathway → so production is regulated

coenzyme def.

organic non-protein that assists enzyme function (releases energy, recyclable)

e.g. ATP

cofactor def.

organic or inorganic molecule that assists enzyme function

coenzymes are a subset of cofactors