Enzymes

biological catalysts, speed up rate of reaction without being used up in the process highly specific

based on primary, secondary and tertiary structure globular protein amino acid sequences specifies 3d conformation active site made up of binding site (bind and orient substances) and catalytic site (reduce activation energy)

metabolism, movement, digestion, coupling unfavourable reactions, cell signalling, gene expression

malfunction in enzyme activity can disrupt homeostasis dna mutations single amino acid sub could destabilise protein stucture

genetic disorder- mutation in phenylalanine hydroxylase reduced metabolism of phenylalanine build up in blood/ brain is toxic

active site is highly specific forms a crevice on surface of enzyme substrate enters active site bound by weak forces incl hydrogen bonding, electrostatic forces

lock and key- considers it is rigid and fixed induced fit- conformational change when binding

amino acids residues determine substrate specificity complementary shape, charge and hydrophobic/phillic interactions highly selective for substrate

away from active site binding to allosteric site can induce conformational change (change in ror) mechanism of regulation activate or inhibit reactions acts as feedback mechanism

some enzymes require co factors for optimal activity; in order to catalyse reaction inorganic molecules/ organic compounds coenzyme- transiently bound, may be altered during reaction, often vitamin precursors (deficient diseases if inadequate) prosthetic groups- metal/ coenzyme covalently bonded (not altered during reaction)

transfer of oxygen or hydrogen atoms or electrons from one substrate to another

abundant in secretions, anti bacterial defence cleaves glycosidic bonds of peptidoglycan

E+S- binding = ES complex- catalysis = E+P enzymes only alter the rate of reaction, not amount of product formed product formation levels off= equilibrium

spontaneous reactions can only occur if free energy of a system is negative (exergonic) input of energy is required if ΔG is positive (endergonic)

all reactions need to overcome the energy barrier (activation energy) enzymes reduce activation energy required for the reaction to proceed transition state- transient molecule state that is no longer substrate but not yet product types; exergonic= spontaneous endergonic= unfavourable

exergonic= spontaneous endergonic= unfavourable ( need a reaction coupled)

influences microenvironment eg pH orientation hydrophobic interactions ionic/hydrogen/ covalent bonds

catalysis by approximation- bringing the reactants closer covalent catalysts- chymotripsin (formation of covalent bond- share an electron- between enzyme and substrate) acid base catalysis- H+, -OH- adding acid/base helps to catalyse reaction metal ion catalysis- zinc, ion- enzyme requires cofactor for reaction to proceed

rate of reaction= V0- at time zero/first 10% of substrate (umol/min) =amount of substrate converted to product per unit of time reported as values at time zero (or before 10% of S is converted) to ensure reaction is at fastest rate, least amount of P, highest S concentration substrate conc affects initial velocity, doubling S will double V0- if enzymes are saturated there will be no increase in V0 reaction rate dependent on P dissociation from enzyme- double E will double V0

on conc against ror graph Vmax- maximum RoR half Vmax extrapolate down to subsrate conc= Km Km= measure of enzyme affinity for substrate (michealis constant) measured in units of conc- molar (M) determined experimentally- conc of S is where velocity = half of Vmax high Km- weak binding (low enzyme affinity) low Km- strong binding (high enzyme affinity)= greater V0= faster RoR

rise in temp; - increases thermal energy to overcome activation energy - beyond optimal will have rapid decrease in reaction rate, breaking weak bonds, altering active site and denaturing protien structure

diversity of optimal pH conditions around the body small deviations will result in reduction in activity -ionisation of groups in active site large deviations lead to denaturation

monitiors the dissapearance of substrate or appearance of product can be measured change in colour/ absorbance, chromotography, radiography etc can be used to measure enzyme kinetics using initial rate (V0) and time course (Vmax and Km)

chemical compounds similar in structure to substrate + bind to active site eg poison, drug, antibiotic etc in vivo- involved in regulation as inhibitors of enzymes many drugs that treat disease act via enzyme inhibition