enzymes Flashcards
enzymes
globular proteins acting as biological catalysts so that reactions in metabolising organisms may work at a suitable pace.
active site
where the specific substrate binds, created by the precise folding of the enzyme’s amino acid chain.
properties of catalysts
high molecular weight
temp sensitive
pH sensitive
specific
lock and key process
- enzyme binds to substrate, forming enzyme-substrate complex > active site doesn’t change shape
- reaction occurs, forming an enzyme-product complex
- products diffuse away from active site
induced fit model
substrate binds to the enzyme at the active site, inducing the enzyme to change shape to fit exactly.
proteins have a 3 dimensional flexibility. weak chemical bonds form which strain bonds in the substrate to lower the energy required to reach transition state, leading to an intermediate ES complex. reactions happen after substrate fit has occurred.
activation energy
amount of energy given to a reaction in order for it to proceed.
methods enzymes use to lower the AE
hold substrates at correct angle for collision
donation/acceptance of protons
allowing initial breaking of bonds within the substrate to happen more easily by destabilising bonds within the substrate
factors affecting rate of enzyme-catalysed reactions
pH
substrate/enzyme concentration
inhibitors
activators
temp effect on enzyme catalysed reactions
increases speed of motion and therefore no. of collisions
at higher temps, more enzyme-substrate complexes are formed and more product molecules are found at higher temps as molecular motion and collisions increase
past optimum temp, bonds stabilising the enzyme’s tertiary structure are broken and the enzyme changes shape so can’t bind to substrate (denatured)
rate of increase in RoR for temp
between 4 and 40 degrees RoR doubles for every 10 degree rise in temp until an optimum temp is reached
Q10=2
pH effect on enzyme controlled RoR
changes ionic and hydrogen bonding, holding the tertiary shape of enzymes , extremes of pH can then break these bonds and denature the enzyme
substrate conc effect on RoR
increases as substrate concentration increases and reaches a maximum, past which has no effect on RoR as all active sites are full, therefore enzyme conc is the limiting factor.
enzyme conc effect on RoR
RoR is proportional to enzyme concentration (usually lower than substrate conc which is rarely a limiting factor.
how is RoR measured?
disappearance of a substrate
appearance of a product
what will occur as the reaction proceeds
fewer collisions, fewer enzyme complexes formed, less product formation, RoR slows and eventually stops when all the substrate has converted into product
enzyme inhuibitors
reduce rate of enzyme-catalysed reaction
types of enzyme inhibitors
non-reversible
reversible
competitive
non-competitive
competitive reversible inhibitors
decrease RoR via reversible combination with enzyme
similar shape to normal substrate, competing for active site, forming enzyme-inhibitor complex, preventing ES complex forming
more inhibitor present in relation to substrate, greater degree of inhibition
example of competitive reversible inhibitor
ethanol
slows oxalic acid production from ethylene glycol in body so kidney is damaged
non-competitive reversible inhibitor
binds to enzyme at allosteric site, disrupting hydrogen bonds and hydrophobic interactions in the tertiary structure of the enzyme, causing the enzyme to change shape, including active site so that no ES complex can be formed.
substrate conc effect on degree of inhibition w non-competitive reversible inhibitors
no effect
effect on inhibitors when substrate conc is decreased
competitive inhibitors compete for active site and fewer substrate molecules are converted into product, decreasing RoR
non-competitive reduce RoR
effect on inhibitors when substrate concentration is increased
effect of competitive inhibitor is overcome and max RoR is reached
non-competitive effect isn’t overcome as all bound enzymes don’t convert into products
metabolic pathways
series of chemical reactions, each catalysed by a different enzyme
end product inhibition
a system used to control metabolic pathways
end product acts as non-competitive reversible inhibitor to the first enzyme, preventing further produvt from being formed until product is used up
why is end-product inhibition useful?
would be wasteful to produce a product in excess
Michaeles-Menten constant
measure of the affinity of an enzyme for its substrate
higher affinity» lower Km and faster RoR
Vmax
max rate of reaction possible for a particular enzyme, assuming unlimited substrate
formula for Km
Vmax/2 = substrate concentration
immobilisation of enzymes
converting enzymes into their insoluble form via binding with an insoluble polymer
purpose of enzyme immobilisation
enables reuse of enzymes and prevents contamination rather than difficulty in extraction of enzyme once placed in solution
process of enzyme immobilisation
mixture w an inert gel (eg. alginate) and addition of calcium chloride forms small beads containing the enzyme.
substrate can then diffuse into the bead, forming an ES complex and then product.
example of enzyme immobilisation
immobilised lactase in order to convert lactose in milk into galactose and glucose
positives of immobilisation
thermostable and pH stable can be removed at a set time reusable don't contaminate substrate can continuously be added into reaction
negatives of immobilisation
less active
enzyme alteration can affect specificity
more expensive
methods of immobilisation
adsorption
membrane separation
covalent bonding
adsorption
enzyme is physically attached to a support via weak binding forces
covalent bonding immobilisation
enzyme bound to an inert substance via covalent bonds and enzymes may also be bound by cross-linking agents
membrane separation
enzyme is separated from a substrate via a partially permeable membrane
hydrolases
enzymes catalysing hydrolysis reactions
maltose
disaccharide consisting of 2 alpha glucose molecules joined by glycosidic bond
maltase
a hydrolase enzyme that catalyses hydrolysis of maltose into 2 glucose molecules
transferases
enzymes that catalyse reactions involving the transfer of atoms or groups of atoms from one molecule to the other
example of transferase
during respiration, a phosphate group is transferred from ATP to a glucose molecule, activating the glucose
oxireductase
enzymes that catalyse reactions involving oxidation and reduction
have a role in the biochemistry of respiration
krebbs cycle
the stepwise oxidation of a 6 carbon acid into a 4 carbon acid in which hydrogen atoms are removed in pairs
dehydrogenase is a type of oxireductase speeding up this reaction
active site
where specific substrates bind, shape and chemistry is specific and a function of the polypeptide, complex tertiary structure
what must happen for a reaction to occur
reactants must collide with sufficient speed at the correct orientation
intracellular enzyme
enzyme performing function within the cell that produces it
extracellular enzyme
an enzyme that functions outside the cell from which it originates
why are digestion enzymes mostly extracellular?
must be broken down outside before they can enter cells directly as are too big.
why would an extracellular enzyme be produced in an inactive form?
so that it doesn’t damage other proteins while in its active form
catabolic reactions
chemical bonds broken within a substrate molecule, causing it to break apart to become two separate molecules
exergonic
examples of catabolic reactions
hydrolysis/cellular respiration
exergonic
net release of energy
anabolic reactions
chemical bond formation, causing two substrate molecules to form a single molecule
endergonic
examples of anabolic reactions
protein synthesis and photosynthesis
endergonic
involving a net use of energy
how do enzymes lower the Ea of a reaction
influence bond stability in reactants, creating an unstable transition state in the substrate so is more reactive.
basis of lock and key model
enzymes are rigid structures and the active site was perfectly matching to the substrate or the reaction wouldn’t proceed.
supported by early x ray crystallography studies, since modified to recognise the flexibility of enzymes.
immobilised enzyme
an enzyme bound to a stationary support
