Enzymes. Flashcards
Lock and key model
Substrate has a complimentary shape to the enzymes active site.
Substrate fits into the active site, exactly forming an enzyme-substrate complex.
Induced fit model
Substrate is similar in shape to the active site.
Substrate fits into the active site.
The active site changes shape, bonding with the substrate forming an enzyme substrate complex.
Substrate bonds are put under strain, lowering the activation energy.
Explain how enzymes act as a biological catalyst, speeding up biochemical reactions.
Substrate is similar in shape to the active site.
The substrate fits into the active site.
Active site changes shape, bonding with the substrate forming an enzyme substrate complex/ induced fit model.
Activation energy for the reaction is lowered.
Substrate bonds are put under strain/ stress.
Substrate changes into product.
Product released from the active site and the enzyme returns to its original shape.
Enzyme is unused in the reaction.
Explain a typical product-time graph
Reaction is fastest at the start as there is more substrate and a higher frequency/ more enzyme substrate complexes can form.
The reaction slows as substrate is being converted to product, so enzyme substrate complexes are forming less often.
Eventually all the substrate has been converted to product (reaction has stopped/ plateau).
How does substrate concentration affect the rate of an enzyme catalysed reaction?
- At lower concentrations not all the enzymes active sites are occupied.
- Increasing substrate concentration increases the frequency of successful collisions/ enzyme substrate complexes are formed more rapidly, producing products faster.
- At high substrate concentration all the active sites are fully occupied so the rate is at its maximum.
How does enzyme concentration affect the rate of an enzyme catalyses reaction?
Increasing the concentration of enzyme increases the rate of reaction.
More active sites become available so more enzyme substrate complexes can form at any point, forming products faster.
How does temperature affect the rate of an enzyme catalysed reaction?
Increasing the temperature from low up to the optimum increases the kinetic energy of the substrates/ enzyme molecules.
More/ higher frequency if successful collisions/ enzyme substrate complexes form more rapidly.
Product is produced faster.
Increasing temperate above the optimum rapidly decreases the rate.
The heat denatures the enzyme.
The bonds in the tertiary structure break so the active site is destroyed and cannot bind to substrate.
How does PH affect the rate of an enzyme catalysed reaction?
Changing the PH from the optimum causes disruption of the tertiary structure of the enzyme.
Tertiary bonds are distorted so is the shape of the active site.
Fewer enzyme substrate complexes can form because the substrate is no longer complimentary to the enzyme.
Extreme PH’s will denature the enzyme completely.
What is protein denaturation?
Heat/ changes in PH can break the R group interactions within the enzymes.
The tertiary structure of the polypeptide is disrupted.
Hydrogen bonding, hydrophobic/ ionic interactions, disulphide bonds are broken.
Polypeptide structure unfolds.
The active site is destroyed.
Substrate molecules can no longer bind/ cannot form enzyme- substrate complexes.
Irreversible/ permanent.
What does controlling key variables mean when conducting enzyme experiments? And what’s a control?
Controlling key variables- if you’re changing a factor (IV) then all other factors that can affect enzyme rate must be kept the same e.g. temp, enzyme conc, PH.
Control- removing what’s responsible for the changes you observe.
Can be used as a comparison.
Competitive inhibitors
How to continue reaction?
Similar in shape to the substrate.
They fit into the enzyme’s active site.
They block the active site and prevent the substrate binding/ prevent enzyme substrate complexes being formed.
Increasing substrate concentration can dilute a competitive inhibitor effect.
Non- competitive inhibitors
Bind to the enzyme’s allosteric site.
Enzymes active site changes shape (tertiary structure).
Prevents substrate binding/ enzyme substrate complexes being formed because the substrate is no longer complimentary to the enzymes active site.
Increasing substrate concentration cannot dilute a competitive inhibitor effect.
Explain enzyme feedback inhibition with biochemical pathways.
If a lot of product is produced at the end of an enzyme pathway it acts as a non-competitive inhibitor on the first enzyme, turning off its own production.
If the product is being used up elsewhere then there is less feedback inhibition so more product is made.
Self-regulates.
