Enzymes Flashcards
what are enzymes?
- biological catalysts with specific tertiary structures, allowing their active site to bind to specific substrates
- not used up and lower activation energy of reactions
what does the lock and key model describe
describes the substrate being perfectly complementary to the active site.
what does the lock and key model not explain
how the ES complex is stabilised
what does the induced fit model describe
it describes how the active site changes shape to add a strain to the substrate, reducing the activation energy of the reaction
what are extracellular enzymes
enzymes produced inside cells but secreted out of cell and act outside of cell
examples of extracellular enzymes
trypsin and amylase
what are intracellular enzymes
enzymes produced in cells that act in cells
what are catabolic reactions
large molecules broken down into smaller ones releasing energy
what are anabolic reactions
large molecules made from smaller ones using energy
what’s hydrogen peroxide
- harmful by-product of many metabolic processes
- rapidly broken down to oxygen and water by intracellular enzyme catalase
action of amylase
- catalyses hydrolysis of starch into maltose
action of trypsin
- catalyses the breakdown of peptide bonds, breaking down polypeptides into smaller ones
where is trypsin made and where does it act
- produced in pancreas
- acts in small intestine
where is amylase made and where does it act
- made in the salivary glands
- acts in the mouth
what’s enzyme activity limited by
rate of successful collisions with substrates and by shape of active site
what effect does increasing temp have on enzyme activity
- kinetic energy of the molecules increases, increasing successful collisions
- above the optimum temperature, bonds break and tertiary structure is denatured
- shape of active site changes so substrate no longer fits
what effects does change in pH away from optimum have on enzyme activity
- alters the charges of amino acids as well as the ionic and hydrogen bonds, altering the tertiary structure and denaturing the enzyme
- shape of active site changes so substrate no longer fits
what does the temp coefficient show
the increase in ror when temp increases by 10C
equation for temp coefficient
Q10 = ror at (T+10C) / ror at TC
effect of enzyme concentration of enzyme activity
- as conc of enzyme increases so does the rate as its more likely that a substrate molecule collides successfully with with active site and form ESC
- ror increases until substrate conc becomes the limiting factor so adding more enzyme has no effect
effect of substrate concentration of enzyme activity
- as substrate conc rises form 0, ESC form faster and rate increases as more substrate means that successful collision between enzyme and substrate is more likely
- eventually, all active sites will be saturated and rate plateaus as all active sites are are full
- rate will decrease over time if no more substrate is added
what are enzyme inhibitors
molecules that affect the way substrate and enzymes interact and affect product turnover
what are competitive inhibitors
- have similar shape to substrate and compete with it for the active site. Higher substrate conc will overcome this
what are non-competitive inhibitors
- bind to the allosteric site on enzymes and alter the shape of the active site, reducing maximum ror
what bonds do reversible inhibitors form with enzyme
- weak ionic or H bonds
what bonds so irreversible inhibitors form with enzyme
- strong covalent bonds
what are cofactors
- non-protein substance that binds to enzyme that allows it to function
- aren’t used up in reactions and don’t change
what are coenzymes
organic cofactors
what’s a prosthetic group
cofactor that is tightly and permanently bound to enzyme
cofactor for amylase
Cl-
what are sources of coenzymes
vitamins
cofactor/prosthetic group for carbonic anhydrase
Zn2+
role of carbonic anhydrase
catalyses the production of carbonic acid from H2O and CO2 in RBCs
medicinal drugs that act as enzyme inhibitors
- antiviral drugs - reverse transcriptase inhibitors
- antibiotics - penicllin
how do antiviral drugs (reverse transcriptase inhibitors) act as enzyme inhibitors
- reverse transcriptase inhibitors inhibit the enzyme reverse transcriptase, which catalyses the replication of viral DNA. This prevents the virus from replicating
how do antibiotics act as enzyme inhibitors
- penicillin inhibits the enzyme transpeptidase, which catalyses the the formation of proteins in bacterial cell walls. This weakens it a prevents regulation of osmotic pressure so cell bursts and dies
metabolic poisons that act as enzyme inhibitors
- cyanide
- malonate
- arsenic
- snake venom
how does arsenic act as an enzyme inhibitor
inhibits pyruvate dehydrogenase, another enzyme that catalyses respiration reactions
how does malonate act as an enzyme inhibitor
inhibits succinate dehydrogenase which catalyses respiration reactions
how does cyanide act as an enzyme inhibitor
irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiration reactions. cells that can’t respire die.
how does snake venom act as an inhibitor
- contains chemical that inhibits acetylcholinesterase which leads to paralysis as ACh not broken down and stays attached to receptors on muscle membrane, keeps it contracted
what’s a metabolic pathway
- Series of connected metabolic reactions.
- Product of first reaction takes part in second reaction and so on.
- Each reaction is catalysed by a different enzyme
what’s end-product inhibition
- where final product can provide negative feedback on the reactions that form them by inhibiting enzymes earlier on in the metabolic pathway
- when level of product starts to drop, there will be less inhibition so more product is formed and vice versa
why are some enzymes produced as inactive precursor molecules in metabolic pathways
- to prevent damage being caused to cell (like protease that may break down proteins in the cell)
- once part of precursor molecule that inhibits enzyme is removed, enzyme becomes active
what does enzyme availability depend on
balance of synthesis and degredation
