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
What is an intracellular enzyme?
Enzyme catalysing reactions within the cell
What is an extracellular enzyme? 3
- Enzymes all made within cells in transcription and translation
- Exported by exocytosis
- To catalyse reactions outside the cells
