2.4 enzymes Flashcards
enzyme type of protein
globular
intracellular enzyme example
catalase
hydrogen peroxide -> hydrogen + water
extracellular enzyme example
amylase (starch-> maltose)
trypsin (protein -> amino acids)
active site
- part of enzyme that the substrate binds to
- COMPLEMENTARY and SPECIFIC shape
lock and key model
- enzyme = lock, substrate -= key
- specific shape (enzyme only catalyses ONE type of reaction)
how do enzymes catalyse reaction
alternative pathway with a lower activation energy
induced fit hyporthesis
- AS of enzyme not perfectly completmentary
- substrate moves into active site, interacts with active site, interferes with bonds and changes the shape of active site so its a perfect fit
- affects bonds in substrate (easier to make or break)
4 steps of enzyme reaction
- enzyme and substrate (separate)
- enzyme substrate complex
- enzyme product complex
- enzyme and product (separate)
pH on enzyme
- denatures at extremes
- optimum differs for every enzyme
- high conc of H+ ions
- disrupt interactions between r groups (ionic bonds/H bonds)
- change tertiary structure
- substrate no longer can bind to active site
- enzymedenatured
denaturing
- tetriary structure altered
- shape of active site changed
- AS no longer complementary to subtrate
- S cannot bind to form ESC
- rate slows
typical optimum temperature in animals
37 degrees
effect of temp on enzymes
- low temp enzymes are inactive, KE too low, infrequent collisions so few ESC formed
- as temp increases, KE increases, move more quickly, more ES collisions so more ESC formed
- temp too high, R group interactions in tertiary structure broken, shape changes, denatured
enzyme and substrate conc
- as conc increases, rate increases up until v max
- more frequent successful collisions between ACTIVE SITE and substrate
- more ESC’s formed
- plateau at v max (max rate)
- active site saturation
- substrate conc no longer limiting reagent- enzyme concentration is limiting
PRACTICAL CONSIDERATIONS (6)
- vol and conc of enzyme
- vol and conc of substrate
- temperature control (thermostatic water bath)
- pH control (buffer solution)
- repeat and mean (reliability)
- range bars
coenzymes
- organic
- take part in reaction and are changed
- then recycled for other reactions- carry chemicals between enzymes
cofactors
non protein substance required by an enzyme in order to function
prosthetic group
- PERMANENT cofactor
- contributes to final 3d shape
eg Zn2+ in carbonic anhydrase
coenzyme example
derived from vitamins
prosthetic group example
zinc in carbonic anhydrase
inroganic ion cofactor + example
- combine w enzyme or sustrate to allow ESC to form more easily
- amylase and cl- ions
competitive inhibitors explain
- shape similar to substrate, complementary to active site
- bind to active site, TEMPORARILY preventing substrate from entering
- fewer active sites available for substrate
- eventaully, substrate out competes inhibitor so rate reaches normal as more ESC formed
non-competitivie inhibitors
- fit into allosteric site
- cause a confrimational change in the shape of the enzyme
- affects active site, no longer complementary so substrate cant bind
non-reversible inhibitors
bind permanently to enzyme
product inhibition
- product inhibits the enzyme
- prevents too much product from being made: negative feedback???
reversible inhibitors
occupy ennzyme briefly
Q10
- for every 10 degree increase, how much rate is affected
- CALCULATE: rate at t+10/rate at t
effects of altering low temp vs high temp
low = REVERSIBLE
high = IRREVERSIBLE
experiment for cofactor action
- reaction without cofactor
- with 3 diff concs of cofactor
- control [enzyme], [substrate], optimum temp and pH
- repeat and mean
why do scientist accept induced fit over lock and key
more evidence to support
evidence from graph of competitive
- at high substrate conc
- rate approaches rate WITHOUT inhibitor, as increased substrate conc overcomes inhibition
how can you tell its a competitive inhibitor(visually)
- substrate and inhibitor similar shape
- specific shape complementary to active site, able to bind
- reference the same bond if shown
