enzymes Flashcards
(25 cards)
give an example of an enzyme that catalyses intracellular reactions
catalase: catalyses the decomposition of hydrogen peroxide into water and oxygen
what are enzymes
biological catalysts
give two examples of enzymes that catalyse extracellular reactions
amylase: carbohydrase catalyses digestion of starch to maltose in saliva
trypsin: pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine lumen
explain the induced fit model
a substrate binds to an active site and both change shape slightly, creating an ideal fit
explain the lock and key theory
enzymes have a specific active site shape that directly corelates to the shape of the substrate
name 5 factors that affect the rate of enzyme controlled reactions
~enzyme concentration
~substrate concentration
~concentration of inhibitors
~ph
~temperature
how does substrate conc affect the rate of reaction
~given that enzyme concentration is fixed, rate increases proportionally to substrate concentration
~the rate levels off when maximum number of enzyme-substrate complexes form at any given time - vMAX is reached
how does enzyme conc affect rate of reaction
given substrate in excess, rate increases proportionally to enzyme conc
~rate levels of when max collisions is occurring
how does temp affect rate of reaction
~rate increases as kinetic energy increases + peaks at optimum temp
~above optimum - denaturation - ionic and H-bonds in 3d structure break and active site no longer complementary to substrate
what is the temperature coefficient
Q10 measures the changes in the rate of reaction per 10 degree temp increase
how does PH affect rate of reaction
low ph- high conc H+
high pH- low conc H+
~diff enzymes have diff optimums
~change of ph can break H+ bonds and change active site
how do competitive inhibitors work
bind to active site as they have similar shape to substrate
~temporarily prevents ES complexes from forming until releases
~increasing substrate conc reduces effect
how do non-competitive inhibitors work
~bind to allosteric site
~trigger conformational change of active site
~increasing substrate conc has no impact on there effect
what is end-product inhibition
~final product of the pathway inhibits an early-stage enzyme
~effect of this is to reduce the rate of the metabolic pathway
~example of negative feedback
~prevents further formation of products
what are irreversible inhibitors
~permanently prevent formation of ES complexes
~bind to enzymes by strong covalent bonds
what are reversible inhibitors
bind to enzymes temporarily - by h-bonds or few ionic bonds
~ES complexes can form after the inhibitor is released
define metabolic poison
substance that damages cells by interfering with metabolic reactions - usually an inhibitor
give some examples of metabolic poisons
cyanide: non-competitive, irreversible, inhibits cytochrome c oxidase
arsenic: competitive, inhibits pyruvate dehydrogenase
how do some medicinal drugs act as inhibitors
penicillin: non-competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross-links in bacterial cell wall
what are inactive precursors in metabolic pathways
to prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors
~one part of the precursor acts an inhibitor ES complexes form when it is removed
what are cofactors
non-protein compounds required for enzyme activity
~coenzymes
~inorganic cofactors
~prosthetic groups
what are coenzymes
~organic cofactors
~do not bind permanently
~often transport molecules or electrons between enzymes
~frequently derived from water-soluble vitamins
what are inorganic cofactors - give an example
~facilitate temporary binding between substrate and enzyme
~CL- is the cofactor for amylase
what are prosthetic groups - give an example
tightly-bound cofactors act as a permanent part of enzymes binding site
~Zn2+ for carbonic anhydrase
