Enzymes

Define Enzyme

• biological catalysts made from proteins or RNA

define catalyst

• speeds up a chemical reaction without being used up

catabolic

• breaks down a substance

anabolic

• builds a substance

Characteristics of enzymes

• can be reused

• unchanged after a reaction

• lowers activation energy

• required for all metabolic reactions

• only needed in small amounts

• substrate specific

• saturated by high sub concentration

• affected by temp, ph, inhibitors etc.

Exergonic vs Endergonic

(Include in each case whether products or reactions have more energy etc etc)

Exergonic	Endergonic
means that the reactants have more energy that the products, so they released energy	means that the products have more energy than the reactants so energy is absorbed
ENERGY RELEASED	ENERGY REQUIRED

Gibbs Free Energy

delta G

energy available to do work within a cell

DOES NOT CHANGE WITH A CATALYST!!!

Negative Gibbs Free Energy

• exergonic (reaction releases energy)

Positive Gibbs Free Energy

• endergonic reaction (requires energy)

Activation energy

• energy required for chemical reaction to get started

activation and rate of reactions, how do enzymes affect this

• High E_A means a slow rate of reaction

• enzymes lower E_A to speed up the rate of reaction

3 main areas where enzymes are found

• suspended in solution - glyolysis of respiration

• in cell membranes - enzymes used to transport amino acids and sugars

• part of an organelle membrane - enzymes found on thylakoid membrane of chloroplasts, or etc of respiration in mitochondria

function of an enzyme is related to

tertiary and quaternary structure

by which bonds does an enzyme-substrate complex form

• hydrogen bonds

• ionic bonds

• hydrophobic/hydrophilic interactions

2 main theoretical models concerning enzyme-substrate complex

• Lock and Key Hypothesis

• Induced Fit Hypothesis

Lock and Key Hypothesis

• enzyme is rigid and specific to enzyme due to shape, size and charge of active site

  • complementary binding

Induced Fit Hypothesis

• enzyme is flexible and can change its conformation to fit around the substrate

  • increases bond strain and facilitates reaction to take place

Effect of Temperature on Enzymes

• optimum temperature - when an enzyme is functioning most efficiently

• low temperatures - enzyme is inactive due to low kinetic energy, decreases chances of enzyme substrate collision happening

• high temperatures enzyme is denatured as heat causes molecule to twist so rapidly that hydrogen and ionic bonds break destroying tertiary structure

  • Q10 - temperature coefficient

Q10

• temperature coefficient

• effect of temperature on the rate of reaction w

what can be said about the rate of an enzyme controlled reaction with an increase of 10c

with every rise in 10c the rate of reaction double

GRAPH FOR ENZYME CONTROLLED REACTION

Effect of pH on Enzymes

• narrow range

• low/high pH enzymes become denatured this is because the charges on the -COOH and -NH2 - tertiary structures change

• More acidic = more h+ so disruption of ionic bonding

  • most cases is reversible but some cases it is permanent

Effect of Enzyme concentration on Enzymes

• if substrate conc, ph and temp are kept constant with increasing enzyme conc comes an increase in rate of reaction

• more active sites are open

• even at low conc - ror is still high as they process and release products quickly

• rate at which an enzyme uses a substrate is turnover number

graph for enzyme conc

Substrate conc and its effect on enzymes

• with increasing substrate concentration comes an increase in ror, then a plateu is reached

• this is saturation when all active sites are full

• Vmax theoretical value which all enzymes are forming an ES complex is never actually reached

graph for substrate conc

Non - Protein Parts

• needed for proper enzyme function

• changes to fulfil shape of active site

  • Inorganic Ions as Cofactors

  • Prosthetic Groups

  • Coenzyme

Inorganic Ions as Co-Factors

• mould enzyme into a specific shape allowing ES to form

  • Cl- increases activity of salivary amylase

Prosthetic group

• organic compounds bound tightly to enzyme’s active site

• carrier of electrons - needed in metabolic pathways

  • Haem

Coenzyme

• organic compounds, loosely associated with an enzyme

• derived from vitamins - NAD+ ATP

Inhibitor

• small molecules which decrease the rate of reaction of enzymes

  • found naturally in cells or in drugs or poision

Irreversible inhibitor

• permanently binds to side chain of active site

• destroys catalytic properties

• heavy metals and insecticides

Reversible Inhibitor

• temporarily bind to enzyme

• resume catalytic properties once removed

  • Competitive and Non competitive

Competitive Inhibitors

• structurally similar to substrate and bind to enzyme instead of it

• no reaction occurs

  • removed by increasing substrate concentration as this raises the chances that a collision between substrate

Non Competitive Inhibitors

• binds to allosteric site on enzyme

• changes the conformation of the enzyme,(triggers certain bonds to break temporarily) substrate can still bind but NO CATALYSIS OCCURS

• enzyme inhibitor complex is formed instead

• cannot be removed with increasing substrate concentration

graph of inhibitors

what is an allosteric enzyme

• large quaternary structures

• can be regulated by an effector binding to their allosteric site → undergo a conformational change

two types of effectors

• allosteric activators

• allosteric inhibitors

allosteric inhibitors

• bind to allosteric site

• cause a conformational change → change in affinity

  • decreased ror

Allosteric activators

• bind to enzymes allosteric site, allowing for shape to be restored

• allow es to form

• Increase R.O.R

negative feedback

change in a system triggers a response to counteract that change to maintain a stable environment

negative feedback and allosteric regulation

• form of negative feedback

• prevents excess product formation as this can reduce catalysis of previous enzymes

• allosteric inhibition → end product acts as allosteric inhibitor

  • prevents build up of product and makes sure reactants are used efficiently

PFK

phosphofructokinase - enzyme in respiration

inhibition of PFK

• ATP (end product) inhibits phosphofructokinase

• stops conversion between fructose 6 phosphate, to fructose 1-6 biphosphate

• ADP and AMP activate it

  • they activate it as, when atp gets low all youll have is ADP and AMP this will make production of AMP start again

oxidoreductases

• remove or add electrons O or H

transferases

• transfer chemical groups between molecules

hydrolases

• adding water to break chemical bonds

proteases

• hydrolysis of proteins

ligases

• formation of bonds using ATP