Module 2.4 - Enzymes Flashcards
(MA) General points about enzymes.
- enzymes are globular proteins
- enzymes are specific
- refer to active site if talking about how enzymes work/denature/anything binding to them/function
- substrates are complementary in shape to the ACTIVE SITE of the enzyme
- talking about the enzyme substrate complexes (ESCs) forming/not forming
- lock + key hypothesis/induced fit hypothesis when talking about enzyme action
(MA) Why are enzymes knew as specific?
- shape of active site
- complementary
- to correct substrate
- forms ESCs
- any other substrate will not
(MA) Describe enzyme action using the induced fit hypothesis as an example.
- as the substrate binds to the active site, the enzyme changes shape slightly
- active site is tighter around substrate molecules
- oppositely charged groups on the substrate + active site interact + hold the substrate molecule in place. This is the enzyme substrate complex (ESC)
- enzyme’s shape change puts strain on the bonds in the substrate which destabilises it, causing the reaction to occur more easily
- the product(s) is formed (enzyme product complex) + because it’s a different shape to the reactant it’s released from the active site
(MA) Explain the effect of temperature on enzyme activity.
Up to optimum:
-as molecules are heated they gain KE + move faster resulting in more frequent collisions
-this results in more ESCs + therefore a higher (max) rate of reaction + more product formed
Above optimum:
-molecules have more KE
-enzymes vibrate too much + weaker bonds are broken (ionic + H)
-tertiary structure of the enzymes are changed
-meaning active site loses its complementary shape
-no ESCs can form as substrate doesn’t fit into active site
-enzymes have denatures
-this is irreversible so reaction stops
(MA) Explain the effect of pH on enzyme activity.
Not at optimum:
-change in pH or H+ ions alters distribution of charge on enzyme molecule
-causes H bonds + ionic bonds to break
-means the enzyme loses its tertiary structure
-changes the shape of the active site of the enzyme
-substrates are no longer attracted to the active site because H+ ions have altered its charge
-substrates cant bind to active site as its no longer complementary
-no ESCs can form = no product = no reaction
-enzymes are denatured at extremes of pH (for that enzyme)
At optimum:
-at optimum, the conc of H+ ions gives the tertiary structure the best shape = most complementary active site
(MA) Explain the effect of increasing enzyme concentration on enzyme activity when there is a fixed concentration of substrate.
-no enzyme = no ESCs = no reaction
As long as the substrate is in excess:
-as enzyme conc increases, the rate of reaction increases
-more enzymes = more active sites = more ESCs form so more product = higher rate of reaction
-as long as substrate in excess the rate will continue to rise w an increase in enzyme conc
As substrate is used up (not in excess):
-all substrate molecules are occupying active sites; max rate of reaction
-increasing enzyme conc further will have no effect on rate
-when substrate is used up the rate will decrease as less product is formed
-substrate is limiting
(MA) Explain the effect of substrate concentration on enzyme activity when there’s a fixed concentration of enzyme.
-no substrate = no ESCs = no reaction
As long as enzyme is in excess:
-as substrate conc increases, rate of reaction increases
-more substrate = more frequent collisions between active sites + substrate = more ESCs = more product = higher rate
When all active sites occupied:
-it’s not possible for more ESCs to form at any one time = increasing the substrate conc further has no effect of rate, rate plateaus
-enzyme conc is a limiting factor
(MA) How do competitive inhibitors work?
- competitive inhibitors have a similar shape to an enzymes’ substrate
- their shape is complementary to the active site so they can bind with it + block it, forming an EIC
- prevents ESCs from forming + slows rate of reaction so no products can be formed
- don’t bind permanently to active site; is reversible
(MA) How do non-competitive inhibitors work?
- fit into the allosteric site on an enzyme
- alters the tertiary structure of the enzyme + changes the shape of the active site
- meaning the substrate can no longer fit into the active site, so no ESCs can form; rate of reaction decreases
- bind permanently to the enzymes; their effect is reversible; the enzymes become useless
(MA) Explain the effect of competitive inhibitor/substrate concentration on enzyme activity.
- rate determined by relative concentrations of substrate/inhibitor
- more inhibition if substrate conc is lower than inhibitor conc
- there’s a higher chance of inhibitor entering active site than substrate = less ESCs = less product
- more substrate = less inhibition = higher rate of reaction as more likely to collide w active site than an inhibitor
- effects can be reversed by increasing substrate conc
(MA) Explain the effect of non-competitive inhibitors on enzyme activity.
- increasing substrate conc has no effect on the rate because they bind irreversibly, if all enzymes have a non competitive inhibitor bound, the reaction will stop
- changing the conc of inhibitors will reduce the rate further = fewer ESCs = less product
Why is the tertiary structure of enzymes important?
Gives the specific shape of the active site so that it is complementary to the substrate
Give examples of what enzymes might be used for.
- control metabolic reactions
- control DNA replication
- protein synthesis
- formation/breakage of bonds
Which enzyme breaks down lactose?
Lactase
Which enzyme breaks down ATP?
ATPase
Why do the enzymes in endotherms usually not need to be adapted for extremes?
- maintain internal body temp
- maintain optimum temps for thermoregulation
How do heterotrophic feeders use enzymes in digestion?
- consume other organisms + digest them in the body w the aid of enzymes
- e.g. animals
How do saprophytic feeders use enzymes in digestion?
- release enzymes onto their food
- digests the food outside of the body
- absorb the monomers
- e.g. fungi
How can enzymes be used as a defence again disease?
Digest or help digest pathogens
What kind of enzymes are extracellular enzymes?
Most digestive enzymes
Where are intracellular enzymes found?
Catalyse within cytoplasm/on the membrane
What do you call a cofactors permanently bound to an enzyme and through what type of bond does this occur?
- prosthetic group
- covalent bond
Give an example of a prosthetic group.
The carbonic anhydrase enzyme contains a zinc ion permanently bound as the prosthetic group
How can cofactors act as co-substrates?
They + the substrate together form the correct shape to bind to the active site of the enzyme