Enzymes Flashcards
What are enzymes
Biological catalysts (not consumed/changed), globular proteins (1,2,3 sometimes 4 structure).
Apoenzyme vs Holoenzyme
Apoenzymes have no prosthetic groups
How do you increase speed of chemical reactions
Heat or a catalyst
Which non-covalent interactions stabilize enzymes
Hydrophobic interactions, H-bonds, ion pairs, VDW, disulphide bridges
Differences between enzymes and non-biological catalysts
Higher rxn rates, milder rxn conditions, greater rxn specificity, capacity for REGULATION
Why can enzymes regulate
Conformational change in protein structure is possible
Why is ATP a high energy molecule
Decreased electrostatic repulsion, resonance stabilization
When is a reaction “thermodynamically favourable” (rxn proceeds)
At negative delta G = spontaneous =free E released
What determines the speed of a reaction
Size of the activation energy barrier
What do enzymes affect
Activation energy/reaction rates = speed up reactions
What don’t enzymes affect
Free energy change (deltaGrxn)
What does the design of the active site contribute to
Affinity, specificity
What is the correct substrate binding model
Induced fit, binding changes shape of active site
What is desolvation / why is it advantageous
Removing substrates from aqueous solutions. Prevents interference by water, formation of H-bonds more effective, eliminates energy barrier imposed by ordered solvent molecules (water)
What is the proximity and orientation effect
orientation and movement of the substrate molecules when binding to enzyme active sites. Thousand-fold increase in rxn rates
How do catalysts lower the activation energy barrier
- Desolvation
- Proximity and orientation effect
- Taking part in the reaction mechanism
- Stabilizing the TS
How do enzymes take part in reaction mechanisms
positioning aa side chains in the active site so they can react with substrates (acid-base catalysis), provide other chemical substances at the active site (cofactors)
How do enzymes stabilize the transition state
Active site binds TS better than it binds the substrate. Free E of TS lowered
What are the mechanisms for the regulation of enzyme activity
Competitive inhibition, allostery, reversible covalent modification, regulation of gene expression
What is competitive inhibition
The inhibitor is similar to the substrate in shape/size but differs chemically and cannot react, binds to site before substrate
What do competitive inhibitors do to the enzyme/substrate Km?
Increase it (decrease affinity)
Describe allosteric enzymes
Sigmoidal curve, conformational change in response to effector, quaternary structure. Molecule binds at site other than active site and either improve binding (+ive cooperation/homoallostery) or decrease binding (negative effector). They have a T and R (relaxed, high activity) state
What is the role of kinases
Transfer phosphate from one group to another
Addition of phosphate group results in…
Increase in size, polarity, hydrophilicity. Addition of two negative charges, capability of making new H bonds
