Enzymes Flashcards
Enzymes role
Increase rate of chemical reactions
Doesn’t change free energy of products or reactants
Decrease activation energy
Basis of catalysis
Reactions through high-energy transition states
Oxidoreductases
Redox
Transferases
Transfer of functional groups
Hydrolases
Hydrolysis reactions
Lyases
Non-hydrolytic breaking/making bonds
Isomerases
Transfer within molecule yield isomeric form
Ligases
Join 2 molecules
Active site
Bind substrate via a.a side chains via weak interactions
Determines specificity of reaction
Types of bonds
Ionic
Hydrogen
Van der Waals interactions
Covalent
Models for enzyme fits
Lock and key
Induced fit
Complementary to substrate
Enzymes fit bonds
Many weak interactions
Specificity and reversibility
Types of catalysis
Acid-base Covalent Redox & radical Geometric effects Stabilisation through transition state Co factors
Types of co-factors
Metal ions - orientates substrates Co enzymes (from vitamins)
Evolutionary history
Same structure, unique specificties
Convergent evolution
Same catalytic triad - different order & structure
Chymotrypsin
Acid - base and covalent cataysis
Cleaves protein at hydrophobic residue = easy to be absorbed in digestion
Oxyanion hole lowers..
activation energy
Model for Michaelis-Menten equation
E+S <=> ES -> E+P
K1 & K-1 =
How tightly substrate binds
K2 =
Rate of cataylsis, energy of activation
[ES] =
Controls rate
Progress curve
Appearance of products over time
Vo
Tangant to beginning of reaction
Vo proportional [E] when
substrate excess
Vmax =
max velocity when [S] infinite
Km =
Vmax/2
Michaelis-Menten equation
Vobs = Vmax[S]/
Km + [S]
Michaelis-Menten assumptions
Product not convented to substrate
Rate of [ES] formation and breakdown equal
Inital rate = [S] doesn’t change significantly
First order kinetics
ES -> E + P
Lineweaver-Burk Plot x and y axis
x = 1/[S] y = 1/Vo
Lineweaver-Burk Plot x and y intercept
x = -1/Km y = 1/Vmax
Km high/low =
low/high affinity (opposite)
Kcat
No of substrate converted to product, per enzyme, per unit of time
Catalytic activity
Catalytic efficiency
kcat/km = higher the better
Limit - diffusion controlled rate (10^8s-1m-1)
Inhibitors function
bind to enzyme and reduce activity
Irreversible inhibitor
Binds covalently
Permantly inactivates
Reversible inhibitor
Bind noncovantly
Can be released
Competitive and noncompetitive
Competitive reversible inhibitor
Compete with substrate in active site Vmax same Km increase [S] increase = outcompete inhibitor Slower rate
Noncompetitive reversible inhibitor
Binds to different site to active site
Pure
Mixed
Pure noncompetitive reversible inhibitor
Vmax decrease
Km same
Mixed noncompetitive reversible inhibitor
Vmax decrease
Km increase
Enzymes and treatment eg 2 types of alcohol
Toxins produced during metabolism of some alcohols
Alcohol with lower km = likely to be metabolised e ethanol
Receptors types
Across membrane
Transmit signal across membrane
Membrance bound enzymes
Intracellular
Enzyme features
1 active site
BInds and changes substrates into products
Membrane bound/free in cytosol
Receptor features
Several binding site
Bind and release ligans unchanges
Membrane bound/free in cytosol
Receptor definition
Protein molecules that receives chemical signals outside cells
Ligand definition
Molecule/drug that binds to receptor
Agonist
Chemical capable of activating receptor to indue response
Antagonist
Blocks receptor and stops effects
Alcohol _____ at _____ receptor
agonist at GABAa
GABAa receptor
Membrane bound ligand gated Cl- channel
Iinhibitory
GABAa receptor + alcohol
Open channel, allows Cl- into cell
Decrease activity in nervous system
Consequences of alcohol
Varies on dose and person
Person = different expression of receptor = different response
Useful features to build drug
Catalyse reactions
Active site
Preferred substrates
Can be inhibited (competitive)
Design inhibitor
Know active site and substrate
HIV Protease inhibitor active site
Cleaves a.a. with common structure with hydrophobic rings (bulky)
+ Asp residues = position substrate
HIV Protease inhibitor substrate
Cleave peptide bond from long a.a chain
Making drug
1) build peptide-like backbone
2) add bulky side groups to fit active site
3) rest of drug = soluble
Testing
Competitive = Vmax same, Km increase
