Enzymes Flashcards
Define “enzyme”
Biological catalysts that increase the rate of reaction by lowering activation enthalpy
Define “activation enthalpy”
Amount of energy needed for a reaction to occur
What is activation enthalpy for? 2
- To make substrates into products, energy is needed to break the chemical bonds between substrates and start reaction
- Heat energy agitates atoms within molecules, they become unstable, reaction starts
Why is it that enzymes reducing activation enthalpy is useful in body cells? 2
- More collisions of substrate particles have sufficient energy for a successful reaction
- Allows reactions to occur at cellular temperature much faster
How do enzymes interact with substrates? 2
- Substrate fits into enzyme active site
- Forms enzyme-substrate complex
What 2 types of reaction do enzymes catalyse?
- Breakdown of molecules
- Joining together of molecules
How do enzymes catalyse the breakdown of molecules? 2
- Fitting into the active site puts strain on substrate bonds
- Substrate molecule breaks up more easily
How do enzymes catalyse the joining together of molecules? 4
- 2 substrate molecules attached to the enzyme
- Holds them closer together
- Minimises repulsion between molecules
- Bonds form more easily
Define “active site”
The part of the enzyme that binds to the substrate to form an enzyme-substrate complex
Where levels do enzymes catalyse a reaction at?
- Cellular level e.g respiration
- Organism as a whole e.g digestion
What 2 things do enzymes affect?
- Structures
- Functions
What are the 2 models of enzyme theory?
- Lock and Key
- Induced Fit
Explain the lock and key model 4
- Substrate has complementary shape and charge to active site
- Substrate binds to active site and forms an
enzyme-substrate complex - Substrate converted to product
- Product no longer complementary in shape and charge and so is released
Explain the induced fit model 4
- Substrate binds to active site
- Active site shape changes - closer fit between
active site and substrate - More bonds form between substrate and
active site - Forms enzyme-substrate complex
Why is each enzyme specific to its function? 3
- Tertiary structure of the active site
- Complimentary to the shape of the substrate
- Forms specific enzyme-substrate complex
How does a mutation make an enzyme not functional? 5
- Changes primary structure
- Changes tertiary structure
- Changes shape of active site
- Substrate no longer complimentary
- No enzyme - substrate complex can be formed
How does the enzyme denaturing make it not functional? 5
- Changes ionic bonds
- Changes tertiary structure
- Changes shape of active site
- Substrate no longer complimentary
- No enzyme-substrate complex formed
What 4 things affect the rate of reaction for enzyme controlled reactions?
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
Define “denatured”
Permanent change to the active site so no more E-S complexes are formed
Explain how increasing temperature up to optimum increases enzyme rate of reaction - 4
- Increase in temperature: increase in molecules vibrating
- More collisions
- Higher number of collisions with activation energy
- More E-S complexes are formed
Explain how increasing temperature past optimum decreases rate of reaction - 4
- Molecules vibrate and break internal bonds e.g ionic and disulphide bridges
- Changes shape of active site
- No E-S complexes can be formed
- Enzyme is denatured
Explain how changes in pH affects rate of enzyme reaction 7
- Enzymes have an optimum pH
- If pH is increased/decreased away from optimum enzyme activity decreases
- The OH- group of alkali or H+ of an acid will interact with hydrogen/ionic bonds
- Changes shape of tertiary structure
- Changes shape of active site
- Fewer/no E-S complexes formed
- Enzyme is denatured
How does increase in enzyme concentration affect rate of reaction? 8
- At first, increase in enzyme concentration : increase in rate of reaction: positive correlation
- More enzyme molecules : more active sites
- More likely for substrate molecules to collide with an active site to form enzyme-substrate complex
- But after optimum increase in enzyme concentration has no effect on rate of reaction
- Amount of substrate is limited so there are more than enough enzyme molecules
- Adding more enzyme molecules has no effect and no more enzyme-substrate complexes formed
- As substrate molecules go down, products go up
- Products formed hit the enzymes and stop substrate reacting with them
How does increase in substrate concentration affect rate of reaction?
- At first: higher substrate concentration: increased rate of reaction: positive correlation
- More substrate molecules: more collisions between substrate and enzyme
- More active sites used: more enzyme-substrate complexes are formed
- After the optimum the rate of reaction decreases
- All active sites are occupied
- No E-S complexes can be formed
Adding more substrate will make no difference as enzyme concentration is the limiting factor
