1.4 Enzymes Flashcards
Why do enzymes only catalyse one reaction?
The active site of the enzyme has a specific shape
The substrate has a complementary shape and therefore binds into the active site
How does a competitive inhibitor work?
It has a similar shape to the substrate
It had a complementary shape to the active site
It binds to the active site
When it does bind it prevents the substrate from doing so
Fewer enzyme-substrate complexes formed
Describe and explain the effect of temperature on the rate of activity of an enzyme
- increase in rate along with increase in temperature up to optimum due to increased kinetic energy so molecules move faster and more successful collisions/ more enzyme-substrate complexes formed
- at temperatures above optimum there are increased vibrations which cause the Hydrogen bonds to break and the tertiary structure changes and a change of shape of the active site and the enzyme is DENATURED
Factors affecting enzyme activity (5)
Inhibitors Temperature pH Concentration of substrate Concentration of enzyme
Distinguish between intracellular and extracellular enzymes
Intra - work inside the cell
Extra - work outside the cell
Advantages of immobilised enzymes
- greater stability over a wider range of temperature and pH
- products are easily recovered
- products aren’t contaminated with the enzyme
- enzymes are easily added or removed
- more than 1 enzyme may be used
- enzymes can be reused
Enzymes are biological catalysts. What does this mean?
Biological - produced by cells and is a protein
Catalyst - speed up rate of reaction without being used up
What is metabolism
Series of enzyme-controlled reactions in the body
Anabolic reactions
Building up molecules
Requires ATP
Eg protein synthesis
Catabolic reaction
Breaking down molecules
Releases energy
Eg digestion of proteins
Key point about enzymes
- speed up chemical reactions
- lower the activation energy
- dont take part in the reaction
- needed in small quantities
- can be reused
- convert substrates into products
- biological catalysts
Describe the structure of enzymes
- tertiary structure that is held by Hydrogen, ionic and disulphide bonds
- creates an active site where substrate can bind
- act in aqueous environments as they’re soluble and can catalyse hydrolysis
Intracellular
Work inside the cell
Extracellular
Work outside the cell
What is an enzyme-substrate complex
Temporary complex when an enzyme binds to a substrate such that the substrates are close enough to react
What is the active site
Small region on the enzyme where the substrate binds
Lock and key model
- substrate has a complementary shape to the enzyme’s active site
- explains enzyme specificity
Induced fit theory
- suggests the active site of enzyme may not exactly correspond to the substrate
- enzyme’s shape alters slightly to accommodate substrate
- enzyme will revert back to ‘relaxed’ state after the products are formed and repelled
- suggests enzyme is flexible and not rigid
How do enzymes work
Lowering the activation energy needed to make chemical reactions to start
Factors affect the rate of enzyme action
- substrate concentration
- temperature
- pH
- enzyme concentration
- presence of inhibitors
What is inactivation
Reversible reduction of enzyme activity at low temperature as molecules have insufficient kinetic energy to from enzyme-substrate complexes
What is denatured
Permanent changes to the shape of the active site which prevents the substrate from binding
Describe the effect of substrate concentration on enzyme activity
Low concentration = low rate • limits chance of successful collisions • is a limiting factor High concentration = high rate • greater chance of successful collisions resulting in more enzyme-substrate complexes Plateau = highest rate • enzyme active sites are saturated • no longer a limiting factor
Describe effect of temperature on enzyme activity
Low temperature = low rate
• enzyme is inactivated
• insufficient kinetic energy so few successful collisions
Increase in temperature up to optimum = increase in rate
• increase in KE
•increases chance of successful collisions so more enzyme-substrate complexes
Temperature above optimum = rapid decrease
• hydrogen bonds break due to increased vibrations
• shape of active site changes and enzyme is denatured
• no successful collisions
Describe the effect of pH on enzyme activity
pH increases or decreases either side of the optimum = decreases rate
• charges on R group on AA on active site are influenced by H+ and OH-
• if too many H+ or OH- the substrate can be repelled from the active site which stops it from binding
• small changes - reversible
• excessive changes - ionic bonds break which denatures the enzyme
Look
Look
Look
What is a limiting factor
Increase in it’s value causes an increase in the rate of reaction
Describe affect of enzyme concentration on enzyme activity
- as they can be reused only a low concentration is needed to catalyse a large number of reactions
- as long as the temperature and pH are suitable and there’s an excess of substrate then the rate will be directly proportional to the enzyme concentration
Look
Reversible inhibition
Inhibitor binds temporarily
Irreversible inhibition
Inhibitor binds permanently
Describe a competitive inhibitor
- molecular shape complementary to the active site and similar to the substrate
- competes with the substrate for the active site
- when it does bind to the active site it prevents the substrate from binding which decreases the rate of reaction
- reversible
- increasing substrate concentration will decrease the effect as it is more likely that a substrate molecule will form an enzyme-substrate complex
- increasing inhibitor concentration will decrease the rate of reaction but the final mass of product ends up the same
Describe non-competitive inhibitor
- binds to the enzyme at an allosteric site and changes the shape of the enzyme
- doesn’t compete with substrate
- changes the overall shape of the enzyme which means the substrate can no longer bind and no enzyme-substrate complexes are formed
- can be reversible or irreversible
- increasing substrate concentration doesn’t reduce inhibition
- increasing inhibition concentration decreases rate of reaction and decreases final mass of product formed
What is an immobilised enzyme
Enzyme molecules bound to an inert material, over which the substrate molecules move
Name ways of immobilising enzymes
- alginate beads
* cellulose microfibrils
How can being able to control the rate of flow of the substrate over the beads be used
Slowing the flow rate will give more time for enzyme-substrate complexes to form and so yield more product
How does being in a ‘micro-environment’ affect the enzymes activity
The enzymes are less susceptible to changes in pH, temperature and the action of chemicals such as organic solvents
Advantages of immobilising enzymes
- enzymes easily recovered and reused
- product is not contaminated by the enzyme
- increased stability and function over a wider range of temperature and pH than free enzymes
- several enzymes with different temperature and pH optima can be used at the same time
- enzymes can be easily added or removed- greater control over the reaction
What is a biosensor
A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which
measures the concentration of a chemical.
What is the role of the selectively permeable membrane in a biosensor
Allows the metabolite to diffuse through to the immobilised enzyme, whilst preventing the passage of other molecules
How does a biosensor turn the metabolite into an electrical signal
- binds to the active site of enzyme and turns into product
* product combines with the transducer which turns the chemical energy into an electrical signal
