2.1.4 Enzymes Flashcards
(26 cards)
What are enzymes?
Globular proteins with complex and unique tertiary structures.
Act as biological catalysts; they increases the rate of a chemical reaction without being used up.
They allow reactions to happen at lower temperatures making biological processes more efficient.
How do enzymes speed up chemical reactions?
Lower the activation energy required for reaction to occur.
What are intracellular enzymes?
Give an example.
Intracellular enzymes act within the cell that produce them.
Example: Catalase - breakdown of hydrogen peroxide into oxygen and water.
What are extracellular enzymes?
Give examples.
Extracellular enzymes act outside the cell that produce & secrete them.
Example: Amylase - Breaks down starch into maltose
Describe the process of enzyme-catalysed reactions.
- Enzymes have unique tertiary structure which determines shape of active site, which is complementary to substrate.
- Substrate binds to active to site to form an
enzyme-substrate complex. - Temporary bonds form within active site and substrate. These bonds lower activation energy to help break down substrate into products.
- Enzyme-product complex
- Products are release from active site.
What are the two models of enzyme action?
Lock and key model
Induced fit model
Describe the lock and key model of enzyme action.
The substrate fits perfectly into the enzyme’s active site.
Describe the induced fit model of enzyme action.
Substrate does not fit perfectly into enzyme’s active site.
As substrate enters the enzyme, the active site changes shape slightly.
Creating a tighter fit and weakening the substrate’s bonds to lower activation energy.
What four factors affect enzyme activity?
(Draw graphs showing effect)
Temperature
pH
Enzyme concentration
Substrate concentration
What causes enzyme to denature?
Extreme temperature and pH levels
BHow does temperature affect enzyme activity?reak hydrogen and ionic bonds, changing the enzyme’s shape.
What is enzyme denaturation?
Denaturation is when the enzyme’s tertiary structure changes, altering the shape of the active site so the substrate no longer fits.
No enzyme-substrate complexes can form.
How does temperature affect enzyme activity?
- As temperature increases, the rate of reaction increases. The molecules have more kinetic energy, causing more collisions and enzyme-substrate complexes.
- The maximum rate is reached at the optimum temperature.Enzymes working fastest and most efficient
- As temperature increases past the optimum, the rate of reaction decreases rapidly, until it stops. Too much kinetic energy changes shape of active site, enzyme denatures.
What is the temperature coefficient (Q₁₀)?
A value that shows how much the rate of reaction changes when temperature increases by 10°C.
Q₁₀ = R2 / R1
Where R₂ = rate at higher temp, R₁ = rate at lower temp.
How does pH affect enzyme activity?
- Below the optimum pH, the rate of reaction is low or zero. In acidic conditions, H⁺ ions break ionic & H bonds and denature enzymes.
- The maximum rate of reaction is reached at optimum pH.
- Above the optimum pH, the rate of reaction is low or zero. In alkaline conditions, OH⁻ ions break ionic & H bonds and denature enzymes.
How does substrate concentration affect enzyme activity?
- As substrate concentration increases, the rate of reaction increases. There are more substrate molecules to form more enzyme-substrate complexes.
- As substrate concentration increases further, the rate of reaction plataeus. Saturation point - all active sites are occupied and enzyme concentration becomes limiting factor.
How does enzyme concentration affect enzyme activity?
- More enzymes = more active sites = faster reaction.
- Plateaus when all substrate is used – substrate concentration becomes the limiting factor.
Worked Example: If the reaction rate is 5 at 20°C and 10 at 30°C, what is Q₁₀?
2
What is an enzyme inhibitor?
Molecules that bind to enzymes to reduce their activity.
What is the difference between reversible and irreversible inhibitors?
- Reversible - Form weak bonds with the enzyme, temporary.
- Irreversible - Form strong bonds with enzyme, permanent.
What are the two main types of inhibitors?
- Competitive inhibitors - These bind to the active site, competing with the substrate
- Non-competitive inhibitors - These bind away from the active site known as the allosteric site.
How do competitive inhibitors work?
(Draw a graph)
- Have a similar shape to the substrate.
- Bind to the active site, preventing the substrate from binding.
- Decrease rate of reaction by reducing enzyme-substrate complex formation.
- Increasing substrate concentration, will reduce the effect of the competitive inhibitor.
How do non-competitive inhibitors work?
- Bind to an allosteric site.
- Cause a change in the enzyme’s tertiary structure and shape of the active site.
- Substrate can no longer bind.
- Non-competitive inhibitors do not compete with substrate for the active site, so increasing amount of substrate has no effect on the rate of reaction.
What is a cofactor?
Give an example
Non-protein substances that bind to enzymes to increase their activity.
Example: Chloride is a cofactor for the enzyme amylase.
What are two types of cofactors?
- Coenzymes - Organic cofactors
- Prosthetic groups - They are tightly bound to enzymes
