Topic 3-L3 - Enzymes Flashcards
(generally) Proteins made by cells that act as
catalysts
There are RNA enzymes as well, called
ribozymes
Vast majority of enzymes are
proteins – metabolism mediated by
protein enzymes
Are catalysts specific to specific rxns?
Yes
Enzyme names generally end with the “___” suffix.
ase
Formation of H2O is exergonic and energetic s are favourable, but won’t occur without catalyst why?
Activation energy way to high and needs to be lowered
Enzymes work by lowering the
activation energy of a reaction, therefore increasing the rate for rxn
Do catalysts change energetics of ΔG or equilibrium of rxn
They do NOT change the energetics (ΔG) or the equilibrium of the reaction
How do enzymes lower the activation energy of a reaction??
- Local concentrations of substrates are increased at the active site of the enzyme
- enzymes alter the electronic distribution and
conformational structure of the substrate(s), which enhances reactivity. - stabilization of transition metals
Catalysts stabilizing transition metals involve
the use of coenzymes or prosthetic
groups – some use metallic elements (E.g. - Fe, Mg, Zn, Co…)
Steps for a enzyme-catalyze rxn
1) substrate bound to enzyme active site
2) enzyme substrate complex forms
3) strain is placed on bond
4) produces are released
5) enzyme is ready to begin new catalytic cycle
How do enzymes influence cell metabolism?
Enzymes catalyze specific reactions, allowing the for accumulation of those specific products
- In metabolic pathways, products from one reaction are the reactants in the next – prevents accumulation of products of the individual reactions (accumulation of products promotes the reverse reaction)
Most biological reactions will not occur at a significant rate in the absence of an enzyme ?
Yes
Enzyme activities can be controlled by regulating the amounts of the
enzymes or by controlling their activity (via competetive inhibitors)
Competitive inhibitors of an
enzyme “fit” in the same active sit as
the substrates – inhibit substrate binding (and thus the reaction)
Competetive inhibitors is the way many drugs work (example below is from
sulfa drugs – antibiotics that inhibit folate biosynthesis)
Positive effector (“allosteric activator”):
Promotes binding of substrate and catalysis
Negative effector (“allosteric inhibitor”):
Prevents substrate from binding
Types of effectors
postive (allosteric activator) and negative (allosteric inhibitor)
Allosteric activators steps for action
- Effector binds to allosteric site
- Causes conformational change in active site
- Substrate fits into active site
- Substrate will be converted to product
Allosteric inhibitors steps for action
1) Effector binds at regulatory site
2) Causes conformational change in active site
3) Substrate can not bind (no “fit” in active site)
4) Reaction inhibited
Absences of effector causes
- Substrate binds to active site
- Catalysis proceeds
Feedback inhibition is A common strategy used to
control metabolic pathways
Feedback inhibition:
- End product is negative modulator:
- Binds to first enzyme in pathway & inhibits its activity.
- End product shuts down its own production when it’s in excess
- Once end product used up, pathway resumes
