Enzymes Flashcards
major classes of enzymes
oxidoreductases
transferases
hydrolases
lyases
isomerases
ligases
oxidoreductases
catalyse redox reactions
transferases
transfer functional groups between donors and acceptors
hydrolases
catalyse hydrolysis
lyases
catalyse removal of group, not by hydrolysis or oxidation
isomerases
catalyse intermolecular rearrangement
ligases
catalyse union of 2 molecules
exergonic
products more stable than reactants
key concept of delta G
independent of path taken
free energy at equilibrium
0
no net change in concentration of reactants or products
how do enzymes work
lower activation energy of transition state by stabilising it to make its gibbs free energy lower
delta G dagger
difference in free energy between the transition state and the substrate
what type of interactions form between the enzyme and the substrate and binding energy
non covalent
releases some energy that stabilises the interaction: binding energy
in induced fit, what are the enzymes actually complementary to
the transition state
rearrangement of covalent bonds by enzymes
makes carbonyl more electrophilic so water is a strong enough nucleophile to make tetrahedral intermediate
catalytic triad
3 amino acids that interact with each other in the active site of protease to increase the nucleophilicity (ability of an atom to donate a pair of electrons to form a new covalent bond in a reaction) of the serine residue
The histidine is a base, so accepts the hydrogen, giving the oxygen a negative charge. This makes it a strong enough nucleophile to attack the carbonyl and form the tetrahedral intermediate. Electrons move back down and the double bond is reformed, which kicks out the blue section. The peptide has been cleaved but the red section is still covalently bonded to the serine residue. The serine residue has been acylated as an ester has been formed. The red section is now a better electrophile. The histidine in the catalytic triad can deprotonate a water molecule, and OH- is now a good enough nucleophile to attack the carbonyl to form another tetrahedral intermediate. The electrons move back down to reform the double bond and kicks out the serine. Product is formed and catalytic triad is reformed.
4 things enzymes do
release binding energy by forming non covalent interactions
rearrange covalent bonds
hold reactants and products close together in the necessary orientation
cause desolvation of substrate
