2 - ICH - Enzymes Flashcards
What are enzymes?
Biological catalysts that interact with substrate molecules to facilitate chemical reactions. Usually globular proteins.
2 main functions of enzymes?
- Biological catalysts - Speeds up a reaction in a living organisms/ cells without getting used up in the process.
- Controls reactions - The amount of enzyme available determines how quickly a reaction can proceed (as it lowers to amount of activation energy required).
Name:
- Substance that the enzyme reacts on
- New substance formed
Equation?
- Substrate
- Product
Substrate + Enzyme → Product + Enzyme
Name:
- Sum of all reactions taking place in a cell/organism
- All break down reactions
- All build up reactions
- Metabolism (metabolic reactions)
- Catabolism (catabolic reactions)
- Anabolism (anabolic reactions)
Catabolic reactions?
Reactions used to break down large molecules into smaller molecules e.g. Hydrolysis
Are exergonic = They release energy (a net loss of energy) and will form ATP.
Anabolic reactions?
Reactions used to join smaller molecules together to form larger molecules e.g. Condensation.
Anabolic reactions require energy and is usually provided by the temporary energy storage molecule called ATP.
Are endergonic = Takes in energy
What is a metabolic pathway?
What are B, C and D?
A series of connected metabolic reactions.
B,C and D are called intermediates.
Each step of the pathway is controlled by a different enzyme.
Relationship between enzymes and substrate?
Explain enzyme specificity.
They are complementary. The active site is preceisly the right shape for the substrate molecule to slot in.
Enzyme specificity = Different enzymes have different shapes of active sites so each enzyme can only bind with a particular substrate.
Collisions and the reactions? (Think collision theory)
Enzyme and substrate molecules are constantly moving as a result of their KE. They must collide with each other before they react.
Collisions are at random.
More collisions = greater rate of reaction
Define activation energy
Example of H2O2?
Activation energy = Energy required to initiate a reaction
E.G
The thermal decomposition of H2O2
Providing the activation energy for this reaction:
- Heat the H2O2
- Or can add an enzyme called catalase
State the name of the 2 hypotheses that describe how enzymes work
Lock and key hypothesis
Induced fit hypothesis
Lock and key hypothesis
What is it and how it works?
- Enzyme is a protein, tertiary structure of the protein results in the active site of the enzyme having a specific shape.
- Substrate fits the active site and an enzyme-substrate complex is formed.
- Reaction takes place and product is released.
Induced fit hypothesis
What is it and how does it work?
- Similar to lock and key hypothesis.
- Difference = The active site moulds round the substrate (like a glove on a hand)
This is a better idea of how enzymes work compared to the lock and key hypothesis.
What is the difference between intracellular and extracellular enzymes?
Intracellular enzymes = Work inside the cell
Extracellular enzymes = Are secreted and act outside the cell
Intracellular enzymes
Example?
H2O2 is a toxic product of many metabolic pathways.
Catalase is an intracellular enzyme which breaks down H2O2 to oxygen and water.
Catalase acts extremely rapidly prevently the accumulation of the H2O2 in both plants and animal tissues.
Example of extracellular enzymes?
Enzymes in the digestive system are usually extracellular.
E.G
In mammals starch is hydrolysed in a 2 step process involving 2 different enzymes (amylase then maltase).
Amylase = produced by salivary glands and pancreas.
Maltase molecules are a part of the cell surface membrane of the epithelial cells lining in the small intestine.
How are enzyme controlled reactions represented as?
Enzyme + substrate ⇔ enzyme-substrate complex ⇔ enzyme-product complex ⇔ enzyme + product
E + S ⇔ ES ⇔ EP ⇔ E + P
How does temperature affect enzyme activity?
Increasing temperature will
- Increase the KE of the reacting molecules, move faster.
- Increase chance of collision between substrate and enzyme.
- More collisions in a given time, the faster the rate of reaction.
- But above the optimum temperature the enzymes thart to denature and enzyme subsrate complexes can’t form as the active site and substrate are no longer complementary.*
Temperature coefficient (Q10)
What is it and give the equation to work it out.
Temperature coefficient (Q10) = A measure of how much the rate of a reaction increases with a 10ºC rise in temperature.
At temperatures between 0ºC and approx 40ºC most enzyme controlled reactions is 2.
For every 10ºC rise in temperature it’ll will cause the rate of an enzyme controlled reaction to double.
How does pH affect enzyme activity?
Exmaple? (2)
Has a similar effect as temperature. Outside the small range the H+ and OH<strong>-</strong> ions found in acids and bases will affect the ionic bonds. Ionic bonds help hold the tertiary structure together and if they are affected then the shape of the active site on the enzyme changes (denatured).
E.G
Amylase = optimum at pH 7
Pepsin = optimum at pH 2
How does substrate concentration affect enzyme activity?
Look at the graph. What happens between A-B and then from B-C?
When is the enzyme a limiting factor and when is the substrate concentration the limiting factor?
Graph shows:
- Enzyme conc = fixed
- Substrate conc = increasing
Between A - B:
- More substrate molecules = greater chance of collisions with enzyme molecules.
- More collisions = more enzyme-substrate complexes formed.
- Substrate conc is limiting
Between B - C:
As the substrate conc increases the rate of reaction remains constant at it’s maximum.
This is because:
- Increasing the substrate conc makes no difference to the rate of reaction as all the enzyme’s active sites are occupied.
- Enzymes are working at the maximum turnover rate.
- Enzyme conc is limiting
What are competitive inhibitors?
What do they do and their properties?
Have a similar shape to the enzyme’s usual substrate (complementary).
Can fit into active site and forms an enzyme-inhibitor complex.
Reversible competitive inhibitors = Can leave the active site after being in it.
Non-reversible competitive inhibitors = Can’t get back out of the acative site once in.
Enzyme has no effect on the competitive inhibitor molecule. As long as the competitive inhibitor remains in the active site, no other molecule can enter; while it remains it prevents access for molecules of it’s true substrate.
What are non-competitive inhibitors?
What do they do and their properties?
Has no real structural similarity to the substrate and will never fit into the active site.
It’s irreversible!
It attaches to a part of the enzyme which is not the active site. Alters the globular structure of the enzyme, shape of active site changes, active site is no longer complementary to substrate so no enzyme substrate complexes can form. Decreases the rate of reaction.
Summarise the differences between competitive and non-competitive inhibition.
1 - Shape of inhibitor compared to substrate (similar/different)
2 - Shape of active site (changed/unchanged)
3 - Substrate can still fit active site (y/n)
4 - Enzyme substrate complexes can still be formed (y/n)
5 - Rate of reaction (increase/decrease)
6 - Effect of inhibitor (reversible/irreversible)
Inhibitors and metabolic pathways?
Explain end-product inhibition
Inhibitors are very important in controlling metabolic pathways.
Metabolic pathway = Series of enzyme-controlled reactions.
Each step of the metabolic pathway is controlled by a different enzyme.
End-product inhibition:
- When enough of the end-product D is formed to meet the body’s needs, no more is formed.
- End-product D acts as a non-competitive inhibitor for enzyme E1 preventing the formation of any more B.
- No more D is produced.
