Enzymes Flashcards
How many types of substrates does one enzyme bind?
very few - they are highly specific
What part of an enzyme does a substrate bind to?
it binds to the active site
What is the energy of activation?
- all chemical rxns must cross an energy barrier between substrates and products -
free energy of activation is the difference in energy between the starting substrate and the transition state
If this energy is ‘high’ then the reaction is less likely to occcur
What effect do enzymes have on the energy of activation?
enzymes lower the free energy of activation
How do enzymes lower the free energy of activation? What are the two mechanisms ?
They provide alternative reaction pathways with lower free energy of activation using their active site
1) geometric complimentarity - transition state stabilization
2) electronic complimentarity - AA side chains can donate/accept protons and stabilise the enzyme/substrate complex
What do oxidoreductases do?
these enzmes oxidize or reduce reactions
What do transferase enzymes do?
Transfer functional groups
What do hydrolases enzymes do?
cleave bonds by the addition of water
What do lyase enzymes do?
They cleave CC, CS and CN bonds
What do isomerase enzymes do?
they interconvert isomers
What do ligase enzymes do?
they catalyze bond formation
What is the difference between cofactors and coenzymes?
cofactor = metal ions like Mg, Zn, or Fe
coenzyme = organic molecules like vitamins
What is an apoenzyme?
enzyme without a cofactor (inactive)
What is a haloenzyme?
Enzyme with a cofactor (active)
Where do coenzymes come from?
They are synthesized in the body or they come from the diet
What factors effect reaction rate?
temp
pH
Substrate conc.
What is the michealis constant?
The michealis constant (Km) is the substrate concentration necessary to reach half of the maximum reaction velocity
What does the Km represent?
the binding affinity of the enzyme for the substrate
What is the x axis and the y axis representative of in a lineweaver burk plot?
x axis = 1/[s]
y axis = 1/[Vo]
What does Hexokinase do?
it phosphorylates hexose sugars
What makes an inhibitor reversible vs. irreversible?
reversible inhibitors bind to enzymes with non-covalent bonds - so they can be dissociated
irreversible inhibitors form covalent bonds with the enzyme therefore they cannot regain their activity - aspirin does this
What is competitive inhibition
the inhibitor binds to the same site as the substrate
What is non-competitive inhibition?
inhibitor and substrate bind to different sites
What is the effect of competitive inhibition on the michaelis menton plot?
Vmax: stays the same
Km: increases the Km
*competitive inhibitors compete for the same substrate, the Vmax is still the same because there is no change in the enzymes inate ability to form the enzyme/substrate complex, BUT you do require more substrate to outcompete the inhibitor - therefore the Km increases*
What is the effect of the non-compettive inhibitor on the machaelis menton graph?
Vmax: decreases
Km: remains constant
*a non-competitive inhibitor binds to a different active site than the substrate therefore it does effect the inherent velocity of substrate/enzyme complex. However, you cannot ‘outcompete’ the inhibitor by adding more substrate- so the Km remains the same
Does phosphorylation activate or deactivate an enzyme?
dependent on the enzyme the phosphorylated form may be more or less active
*more often, however, it increases the activity of the enxyme
What is allosteric regulation?
regulation of an enzyme activity by binding small molecules to sites on the subunit other than the catalytic site -
these can be positive or negative effectors
What is a homotropic effector?
it is an allosteric regulator that acts as the substrate itself
the presence of substrate at one site enhances the catalytic properties of other substrate binding sites
What is a heterotrophic effector?
It is an allosteric regulator that is different to the primary substrate = overall this produces a negaitive effect on the enzyme/substrate activity
