Module 2 - Enzymes Flashcards
how can the rate of metabolic activity be controlled?
different steps of a reaction are controlled by different enzymes regulating the rate and yield of product formation
how can enzymes be activated?
with a cofactor
how can enzymes be inactivated?
with an inhibitor
what is competitive inhibition?
a molecule of similar shape will bind to enzyme preventing the complimentary substrate from binding and therefore preventing the reaction
the substrate and non-substrate will complete with each other to bind to the active site reducing the number of enzyme-substrate complexes from forming slowing the rate
what does the degree of inhibition depend on?
relative concentration of substrate, inhibitor, and enzyme
how doe competitive inhibitors work?
1- molecule of similar shape will bind to the enzyme preventing the complimentary substrate from binding
2- the prevents the enzyme catalysing the reaction
3- the enzyme cannot carry out its function and is said to be inhibited
how do competitive inhibitors impact the Vmax?
they reduce the rate of reaction for a given conc. of substrate HOWEVER they do not change the Vmax of the enzyme it inhibits
= if substrate conc. is increased enough then there will be more substrate then inhibitor and so the Vmax can still be reached
what are examples of competitive inhibitors?
> statins are CIs used in the synthesis of cholesterol - they’re regularly prescribed to help reduce blood cholesterol conc. as high levels can result in heart disease
aspirin irreversibly inhibits the active site of COX enzymes preventing the synthesis of the protein responsible for producing pain and fever
what is a non-competitive inhibitor?
does not compete with the substrate for the active site as it binds elsewhere at the allosteric site
how does non-competitive inhibition work?
1- inhibitor binds to enzyme at any location other then the active site = called the allosteric site
2- this inhibition caused the tertiary structure of the enzyme shape = active site changes shape
3- results in active site no longer having a complimentary substate = enzyme-substrate complex not able to form
4- enzyme cannot carry out its function and is inhibited
what effect do non-competitive inhibitors have on rate of reaction?
increasing conc. of enzyme or substrate will not overcome the effects of inhibition
increasing conc. of inhibitor will decrease the rate of reaction further as more active sites become unavailable
example of an irreversible non-competitive inhibitor?
irreversible inhibition cannot be removed from the area of enzyme they’re attached to
they’re often very toxic (not always)
Proton Pump inhibitors (PPI) are used to treat long term indigestion as they irreversibly block the enzyme system responsible for secreting H into the stomach reducing the production of excess acid - if left untreated leads to formation of stomach ulcers
what is end-prouduct inhibition?
term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to they enzyme that produces it
how does end product inhibition act as a control mechanism?
it is an example of negative feedback
excess products are not made and resources are not wasted
what type of inhibition is end product inhibition?
non-competitive reversible inhibition
what is a cofactor + coenzyme?
they are non-protein ‘helper’ components that are required by some enzymes to help carry out their function
(if the cofactor is an organic molecule its called a coenzyme)
how are inorganic cofactors obtained?
via the diet as minerals e.g iron, calcium, chloride
what is end product inhibition?
term used for the enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
they’re en example of negative feedback
how do end product inhibitors act as control mechanisms?
excess products are not made and resources are not wasted
what are end product inhibitors an example of?
non-competitive reversible inhibitors
what are cofactors and coenzymes?
non-protein ‘helper’ component that are required by some enzymes to help them cary out their function
if the cofactor is an organic molecule then its a coenzyme
why is the function of coproduction/coenzymes?
they may transfer atoms/groups from one reaction to another in a multi-step pathway
they may form part of the enzymes active site
how are inorganic cofactors obtained?
via the diet as minerals
e.g iron, calcium, chloride, zinc ions
inorganic cofactor example:
enzymes amylase (catalyses the breakdown of starch) contains Cl- ions necessary for the formation of a correctly shaped active site
how are organic coenzymes derived?
via vitamins found in the diet
examples of a coenzyme:
vitamin B3 used to synthesise NAD = coenzymes responsible for the transfer of H between molecules in respiration
also used to synthesise NADP which plays a similar role in photosynthesis
vitamin B5 is used to make coenzyme A which is essential for the breakdown of fatty acids and carbohydrates in respiration
how are prosthetic groups cofactors?
they’re required by certain enzymes to carry out their catalytic function
what’s the difference between prothetic groups and normal cofactors?
prosthetic groups are tightly bound and form a permanent feature on the enzyme/protein
normal coenzymes are temporarily bound in order to activate them
what is precursor activation?
enzymes are produced in an inactive form = precursor enzymes
to activate them they often need to undergo change to their 3* shape - particuarlly at the active site - to be activated
how is activation of a precursor enzyme achieved?
by the addition of a cofactor
what is the protein called before activation?
apoenzyme
what is the protein called after activation?
once cofactor is added and the enzyme is activated it is called a holoenzyme
