Enzymes

Question 1

enzymes

Answer 1

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

Question 2

enzyme structure

Answer 2

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)

Question 3

enzyme functions

Answer 3

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

Question 4

enzymes in disease

Answer 4

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

Question 5

PKU- disease example

Answer 5

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

Question 6

active site

Answer 6

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

Question 7

enzyme binding

Answer 7

lock and key- considers it is rigid and fixed

induced fit- conformational change when binding

Question 8

substrate specificity

Answer 8

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

Question 9

allosteric site

Answer 9

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

Question 10

enzyme co factors

Answer 10

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)

Question 11

oxidoreductases

Answer 11

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

Question 12

lysozyme

Answer 12

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

Question 13

when increasing RoR

Answer 13

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

Question 14

biological reactions

Answer 14

spontaneous reactions can only occur if free energy of a system is negative (exergonic)

input of energy is required if ΔG is positive (endergonic)

Question 15

enzyme reactions

Answer 15

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

Question 16

coupled reactions

Answer 16

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

Question 17

reducing activation energy

Answer 17

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

Question 18

catalytic mechanisms

Answer 18

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

Question 19

enzyme velocity (V0)

Answer 19

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

Question 20

michealis-mentin kinetics

Answer 20

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

Question 21

temperature

Answer 21

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

Question 22

pH

Answer 22

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

Question 23

enzyme assays

Answer 23

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)

Question 24

substrate analogues

Answer 24

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

Question 25

feedback regulation

Answer 25

many biological processes are regulated and respond to feedback mechanisms
eg homeostasis- blood glucose, body temp etc
mediated by effector molecules- activators and inhibitors
inhibition- end products inhibit earlier pathway steps- prevents build up of unnecessary metabolites and energy use

Question 26

enzyme inhibition

Answer 26

inhibiting product often binds to allosteric site
inhibition- end products inhibit earlier pathway steps

reversible- bind to enzyme by weak non covalent interactions eg hydrogen bonds, ionic bonds- dont change enzyme chemically
non specific- denaturing enzymes eg by altering pH, increasing temp (irreversable)
specific- reversible- competitive, non competitive, uncompetitive

Question 27

competitive

Answer 27

have some affinity for active site
similar shape/ binding properties as substrate
substrate is competing
can be overcome by increasing S

Vmax is not changed (half Vmax also same)
Km increases as reaction occurs slower
needing to add more substrate for reaction to occur

Question 28

non competitive

Answer 28

inhibitor binds to allosteric site
conformation of active site changes
substrate can no longer bind
depends on conc of inhibitor

Vmax is reduced (half Vmax reduced)
Km doesn’t change

Question 29

uncompetitive

Answer 29

inhibitor only binds when enzyme substrate complex has formed
inhibits catalysis

Vmax greatly reduced (half Vmax also reduced)
Km also reduced

Question 30

allosteric enzymes

Answer 30

eg Hb
usually multi subunit enzymes- active site on each subunit
cooperatvity- binding substrate to one active site causes conformational change and increases affinity of other active sites for substrate

Question 31

transferases

Answer 31

transfer functional groups eg phosphates from one substrate to another
eg hexokinase

Question 32

hydrolases

Answer 32

hydrolysis of a substrate
eg digestive enzymes

Question 33

lysases

Answer 33

addition or removal of a group to form a double bond
eg pyruvate decarboxylase

Question 34

isomerases

Answer 34

transfer groups within a molecule
maleate isomerase

Question 35

ligases

Answer 35

bond formation coupled with atp hydrolysis
pyruvate carboxylase

Question 36

allosteric enzyme kinetics

Answer 36

sigmoidal curve- show rapid increase in enzyme velocity over a narrower range of substrate conc
allows AE to be sensitive to small changes in substrate conc

Question 37

regulation- reversible covalent modification

Answer 37

protein kinases- phosphorylate
protein phosphatases- dephosphorylate
rapid and reversible metabolic switch

Question 38

regulation- proteolytic activation

Answer 38

zymogen/ proenzyme- inactivated form of enzyme at start of reaction eg digestive enzymes

produced in pancreas
once hydrolysed they are active (irreversable)

apoptosis- programmed cell death

series of caspases (cascade event) to form an active version of the molecule

Question 39

regulation- enzyme synthesis/ breakdown

Answer 39

synthesis- gene expression regulates enzyme synthesis, regulation at transcription and translation
enzymes have short lived mRNA to control rate of protein expression

breakdown- enzymes have short half life (most enzymes involved with metabolic activities)- labile enzymes
broken down by proteolytic degradation