enzyme's catalytic power

what are the four different stages that happen when substrate is turned into product by an enzyme?

E+S ⇌ ES ⇌ EP ⇌ E+P

how do enzymes increase rate of reaction?

enzymes accelerate rate of reaction by lowering activation energy of the reaction (stabilise the transition state)

enzymes never change the ΔG of a reaction, they can only alter kinectics

what are reaction intermediates?

temporary chemical species formed during a multi-step reaction that are produced in an early step and consumed in a later step

e.g. ES and EP are reaction intermediates

reaction coordinate diagram of reaction with and without enzyme?

what is rate enhancement?

factor by which enzymes accelerate reactions compared to uncatalysed ones

rate of catalysed reactions typically 10⁶ - 10¹⁴ times greater

equation for rate enhancement

R = gas constant

ΔΔG is the difference in free energy (ΔG_cat - ΔG_uncat)

why are enymes designed to bind the transition state more tightly than substrate

• tighter binding leads to release of more energy, lowering E_A

• entropy is reduced: enzyme holds substrate/TS in place

• desolvation: water is removed from substrate, exposing reactive groups

• proper alignment: substrate is positioned in correct orientation for reaction to occur

what are the three main models for substrate binding?

• lock and key

• induced fit

• conformational selection

what is the lock and key model?

• enzyme and substrate are rigid structures

• binding interface matches perfectly

• only correctly sized enzyme and substrate can bind

what is the induced fit model?

• assumes that enzyme and substrate have some flexibility in structure

  • minor conformational changes can be made to bind to each other

what is the conformational selection model?

• an enzyme naturally shifts between different shapes on its own

• substrate binds to enzyme shape that already fits it best (bind selectively)

what are the three main catalytic mechanisms?

• acid catalysis

• base catalysis

• covalent catalysis

what is acid catalysis?

partial proton transfer from donor to acceptor

what is base catalysis?

partial proton abstraction by acceptor

what is covalent catalysis

interactions between substrate and enzyme’s functional group

what example enzyme displays all these modes of catalysis?

lysosyme

• Asp52 covalent catalyst (displaces monosaccharide unit E)

• Glu35 acid catalyst (protonates unit E to facilitate departure)

• Glu35 base catalyst (abstracts proton from water to form OH^-)

what factors affect enzyme activity?

• temperature

• pH

• enzyme concentration

• substrate concentration

• inhibitor

• activator

what factors affect enzyme activity?

• temperature

• pH

• increasing enzyme activity

• increasing substrate concentration

• inhibitors

• activators

regulation of enzymes?

look at o