4 - Enzymes Flashcards
Define co-enzyme
A cofactor that is an organic molecule
Define catabolic
Reactions that break down large molecules into small ones
What 4 factors affect the rate of enzyme-controlled reactions?
- temperature
- pH
- enzyme conc
- substrate conc
Explain how denaturing leads to a loss of enzyme function
- bonds holding the secondary and tertiary structure together are broken
- changes the precise shape of the enzyme and active site
- substrate no longer complimentary
Describe how the induced fit model works
- substrate not initially complimentary to active site
- active site is flexible
- molds itself around substrate
- returns to original shape after
What is an enzyme’s temperature coefficient?
Q10
How much the rate of reaction increases for a 10-degree rise in temperature
Usually around 2
Define anabolic
Reactions that build large molecules from small monomers
How are prosthetic groups a part of enzymes? Give an example
Bound permanently and are part of its structure
eg. Zn2+ part of carbonic anhydrase in RBCs
How do coenzymes work? Give an example.
Bind temporarily to enzyme, transfer chemical groups in substrate
eg. vitamins
How do ions act as cofactors for enzymes?Give an example.
Bind to allosteric site and ensure active site is the right shape
Cl- ions for amylase
Explain how pH can affect the 3d structure of an enzyme
high conc of H+ ions interact with the charged/polar R groups and distorts the 3d shape
Define cofactor
A non-protein molecule that is required for a molecule to function (by binding to allosteric site)
Name an intracellular enzyme and its function
catalase
breaks down hydrogen peroxide into water and oxygen
Give an example of an extracellular enzyme
Any digestive enzyme eg. salivary amylase, pepsin, maltase…
Define intracellular with regards to enzymes
An enzyme that catalyses a reaction within the cell it is produced in
Define extracellular with regards to enzymes
An enzyme that catalyses a reaction outside of the cell it is produced in
Define substrate
A specific molecule which interacts with an enzyme, fits into the active site
Define activation energy
The energy that needs to be supplied for a chemical reaction to start
Define active site
A specific region of an enzyme that is complementary to the substrate molecule
How do enzymes affect a reaction in terms of energy
They lower the activation energy therefore less energy has to be supplied to start the reaction
What is Vmax
The maximum rate at which the enzyme catalyses a reaction
Explain how increasing the temperature increase the rate of an enzyme controlled reaction?
As temp increases KE of enzyme and substrate increases
collide more frequently
more frequent successful collisions
more E-S complexes formed
Explain how low temperatures affect the rate of an enzyme controlled reaction?
As temp decreases KE of enzyme and substrate decreases
collide less frequently
less frequent successful collisions
fewer E-S complexes formed
Explain how very high temperatures affect the rate of an enzyme controlled reaction?
- High temperatures can put strain on the bonds holding the enzyme together as there is more kinetic energy moving them around etc.
- Bonds can distort and break
- substrate no longer complementary to active site
- enzyme not functional
How do extreme pHs affect the rate of an enzyme controlled reaction?
At extreme pHs, high conc. of H+ and OH- ions disrupt and break bonds between amino acids
Substrate no longer complementary to active site
-enzyme not functional
Describe the lock and key model
Enzyme complementary to active site of enzyme
fit together and temporary bonds form, forming an E-S complex
State any assumptions the lock and key model makes
- enzyme is rigid and doesn’t change at all
- substrate is perfectly complementary to shape of active site
Describe how the induced fit model is different from the lock and key model
Substrate not initially complementary to the active site
Active site flexible
Moulds itself to the substrate
Distorts the bonds in the substrate, lowering activation energy
Returns to original shape after
What would this graph look like:
rate of reaction as substrate conc. changes?
Rate of reaction increases as substrate conc. increases and then plateaus as all active sites are saturated
What would this graph look like:
rate of reaction as enzyme conc. changes?
Rate of reaction increases as enzyme conc. increases and then plateaus as other limiting factors eg. substrate conc.
What could your dependent variables be in an experiment to measure the rate of a reaction?
How quickly substrate used up
How quickly product formed
How do competitive inhibitors work?
Similar shape to substrate
binds to active site so substrate can’t
How do competitive inhibitors affect the rate of reaction and why does this happen?
Rate of reaction for given substrate conc. decreases however the Vmax is still reached because there will eventually be considerably more substrate than inhibitor so it will not effect it
Name 2 examples of competitive inhibitors and their roles
Statins- inhibit cholesterol production
Asprin - inhibit chemicals responsible for pains and fevers
How do non-competitive inhibitors work?
Complimentary to allosteric site, creates a conformational change to the shape o the active site
Substrate can’t bind
How do non-competitive inhibitors affect the rate of reaction and why does this happen?
Increasing substrate conc. will not overcome the inhibition, the graph would be lower (ROR slower) and plateaus beneath normal graph
How do end product inhibitors work?
-end product acts as a negative feedback by inhibiting a previous step in its production, this prevents an accumulation of certain substances
Enzymes that are not yet active are called
Apoenzymes
Define apoenzyme
An enzyme that is not yet active
Enzymes that have been activiated with the addition of a cofactor are called
Holoenzymes
Define holoenzymes
Enzymes that have been activiated with the addition of a cofactor
Why could precursor activation be necessary for enzymes?
The active enzyme could cause damage in one area so is only activated when it gets to its site
Give an example of a precursor enzyme and why it is necessary for it to be activated somewhere else
Pepsin (hydrolyses proteins into amino acids)
could be dangerous in cells so it in secreted inactively
Describe 2 ways cofactors are necessary for enzymes function
cofactors transfer groups between reactants
form part of the active site
