What 2 ways can rxns be accelerated?
- Adding heat: increase # of reactants w/ energy to overcome activation energy barrier
- Adding catalyst: decrease activation energy barrier but doesnt react
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| Term | Definition |
|---|---|
What 2 ways can rxns be accelerated? | - Adding heat: increase # of reactants w/ energy to overcome activation energy barrier
- Adding catalyst: decrease activation energy barrier but doesnt react |
What is the key for enzyme nomenclature? | (Process name) - ase |
T/F: enzymes are unregulated | False |
T/F: A rxn will proceed ONLY if free energy of products is LESS THAN free energy of reactants | True |
What is the ΔG rxn equation? | ΔG = G(products) - G(reactants) |
What does is mean when ΔG is negative? | Rxn is exergonic
- Thermodynamically favourable
- Spontaneous |
Where in the rxn is free energy the highest? | Transition state |
What is the equation for the ΔG of the activation energy? | ΔG = G (TS) - G (Reactants) |
T/F: enzymes change the free-energy change of the rxn | False
- Only reduce the free energy of the TS |
What are the 4 ways enzymes can reduce the free energy of the TS? | - Remove substrates from aq soln (desolvation)
- Proximity/orienation
- Taking part in rxn mechanism
- Stabilize TS |
Where does catalysis occur on an enzyme? | Active site |
What 3 things do active sites determine? | - Affinity
- Specificity
- Rate |
What creates an active site? | Clustering |
What does complementarity mean for substrate binding? | Increase favourable interactions = increased affinity |
What is desolvation? What are the 3 advantages? | Exclusion of water
- Removing water shell accelerates rxns
- Enhances polar interactions
- Prevents side rxns (water is rlly reactive) |
What is induced fit? | - Enzymes change chape when substrate binds
- Closes off active site
- Brings catalytic/reactive groups together
- Open vs Closed states |
What 3 types of catalysis can enzymes participate in? | - Acid base: p+ transfer
- Covalent: Transient
- Metal ion: oxidation/reduction |
How can enzymes participate in rxns by positioning their functional groups near substrates in the active site? | - AA's
- Cofactors |
Which AA's are less likely for acid base rxns? | Cys
Tyr |
Which AA's are common at power pH's? | Asp
Glu |
What process enhances an AA as a nucleophile? | Deprotonation |
What is a holoenzyme? | Polypeptide combined w/ prosthetic group tto form functional tertiary structure |
What is an apoenzyme? | Without prosthetic group, polypeptide forms tertiary structure |
The more ____ an enzyme binds to TS relative to substrate, the _____ the catalytic activity of enzyme | - Tightly
- Greater |
TS analogs are strong ______ of enzymes | Inhibitors |
Do TS analogs bind to enzyme w/ higher or lower affinity than substrate | Higher |
What do Vo and Vmax mean in enzyme kinetics? | Vo: Initial velocity (rate of product formation)
Vmax: Max rate of product formation |
What does Km mean? | Michaelis constant
- similar to Kd (ligand binding) |
When does Vo = 50% of Vmax | When concentration of substrate is equal to Km |
Does Km get smaller or larger when affinity increases? | Smaller |
What mechanisms for enzyme regulation affect the intrinsic activity of an enzyme?
4 | - Competitive inhibition
- Allostery
- Reversible covalent modification
- Ionic signals |
What mechanisms for enzyme regulation DO NOT affect the intrinsic activity of an enzyme?
2 | - Regulation of gene expression
- Changes in subcellular localization |
What are competitive inhibitors?
3 | - Bind reversibly in active site
- Resemble substrate or TS
- Physically block active site (prevent binding) |
Do competitive inhibitors increase or decrease Km? Why | - Increase
- Fewer active sites available = lower rxn rates = curve shifts right |
T/F: Increasing substrate concentration will NOT overcome inhibiton | False, IT WILL |
Does increasing substrate conc change Vmax? | No |
T/F: Substrate analogs make better competitive inhibitors than TS analogs | False, TS are better |
What type of relationship do allosteric enzymes have between substrate and rxn velocity? | Sigmoidal |
How is an allosteric enzyme's catalytic activity regulated? | By noncovalent binding of specific molecules at site other than active site
- Heteroallostery |
What is the most common type of reversible covalent mod? | Phosphorylation |
Does covalent mod change primary, secondary, or tertiary structure of a polypeptide? | Tertiary |
What catalyzes phosphorylation of proteins? | Protein kinases |
What catalyzes the dephosphorylation of proteins | Protein phosphatases |
T/F: Protein kinases/phosphotases are regulated | True |