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When answering questions on concentration of substrate or enzyme, what should you link it to?
More concentration leads to more enzyme-substrate complex being formed. So more product formed.
Why is the highest reaction rate known as the initial reaction rate?
- Because it is when enzyme and substrate are mixed for first time is the point where rate is greatest.
- This is because the concentration of reactants (substrates) are highest and concentration of products lowest, so increase collision rate, and more enzyme-substrate complex formed.
What is a limiting factor?
A factor in a situation where, if all other conditions are kept constant, increasing the conc of that factor alone will increase reaction rate.
Why are enzyme concentrations in cells quite low?
- Becuase they can be reused.
- Also means enzyme activity can be more easily controlled (by changing conc of enzyme or substrate or changing conditions)
What is an enzyme inhibitor?
Any substance or molecule that slows down rate of an enzyme-controlled reaction by affecting the enzyme molecule in some way.
How does a competitive enzyme inhibitor work?
- Inhibitor molecules have similar shape to that of the substrate molecules.
- Competes for the active site and occupies it, forming enzyme-inhibitor complexes. (products not formed because inhibitor is not the same as the substrate).
- It reduces rate of reaction because it reduces the number of substrates which can enter the active site and hence produce enzyme-substrate complexes.
How does the conc of substrate affect the level of inhibition?
- Level of inhibition depends on conc of inhibitor and substrate.
- Where conc of substrate molecules increased, level of inhibition decreases.
How does a non-competitive inhibitor work?
- Attach to enzyme in a region away from active site
- Distorts the tertiary structure - leads to change in shape of active site
- So enzyme-substrate complexes cannot form.
- Many (not all) permanently bind to the enzyme - therefore it is irreversible, enzyme effectively denatured.
Level of inhibition in a non-competitive inhibitor depends on what?
- The number of inhibitor molecules present.
- Changing the substrate concentration will have no effect on this form of inhibition.
Suggest a method of determining whether inhibition of an enzyme-controlled reaction is competitive or non-competitive.
- Test with various substrate concentrations.
- If the rate of reaction increases to the point where it is the same as a reaction with no inhibitor, then it is a competitive inhibitor.
Why is inhibition of enzyme activity important in controlling metabolic processes?
- Cells must be able to control the concentration of various molecules in the cell.
- If they are products of enzyme-controlled reactions, it is important to regulate enzyme activity in order to achieve and maintain optimum level of the product.
What is a cofactor?
- Any substance that must be present to ensure enzyme-controlled reactions take place at an appropriate rate.
- Some are part of the enzyme (prosthetic groups), others affect enzyme on temporary basis (coenzymes and inorganic ion cofactors)
What are coenzymes and what are their roles usually?
- Small, organic, non-protein molecules that bind for a short period to the active site.
- In many reactions, they take part in reaction and change in some way. (But unlike substrates, they are recycled back to be used again).
- Role is often to carry chemical groups between enzymes so to link together enzyme-controlled reactions that need to take place in sequence.
What is a prosthetic group?
- A coenzyme that is a permanent part of an enzyme molecule.
- Vital to function of enzyme and other molecule (eg. haem group in haemoglobin). They contribute to shape and other properties like charges.
What are the roles of inorganic ion cofactors?
- Presence of certain ions increase reaction rate
- Affects the charge distribution and sometimes the shape of enzyme-substrate complex.
- Thus the enzyme-substrate complex forms more easily.
- (eg. amylase catalyse breakdown of starch to maltose only if chloride ions are present)
Prosthetic groups are bound to enzymes as it is being made. Suggest where in the cell this processing takes place.
The Golgi apparatus
Give an example of a poison and how it affects the body.
- Potassium cyanide
- Non-competitive inhibitor for a vital respiratory enzyme called cytochrome, found in mitochondria.
- Inhibition of this enzyme decreases use of oxygen, so ATP cannot be made, & more lactic acid builds up in the blood because organism respires anaerobically.
- Metabolic poisons can often be enzyme inhibitors
Why is alcohol a treatment for thylene glycol poisoning?
Because it acts as a competitive inhibitor on the enzyme Alcohol dehydrogenase.
How does penicillin work to inhibit growth of microorganisms?
- It inhibits the enzymes responsible for building the cell wall. Because penicillin is similar in shape to one of the substrates used in wall building.
- But penicillin is different from the substrate, therefore makes the wall weak and fall apart.
How do you work out the initial reaction rate from a graph?
- Take a tangent to the steepest portion of graph and measure the gradient of the tangent, and this will be your intial rate of reaction.
- eg. x-axis - time(s); y-axis - volume of O2
- then take steepest tangent and do
Exam questions often give experimental procedures and ask for comments on how they might be improved. Read information about how variables were controlled, whether repeat readings were taken, and whether a control was used.
Metabolic processes where products of one enzyme-controlled reaction is the substrate of another, and so on in a chain of enzyme reactions is called what?
A metabolic pathway.
Many diseases are caused by the lack of a functioning specific enzyme in a metabolic sequence because of a faulty gene for example. These are called?
Inborn errors of metabolism.
What is end-product inhibition?
- Where end product can attach to one of the enzymes early in the sequence and act as a non-competitive inhibitor.
- This controls the amount of end-product produced, and ensures it doesn't build up.
- eg. ATP is end-product inhibitor of one enzyme that catalyses an early reaction in sequence of respiration.