Enzymes Flashcards
What are enzymes?
Biological catalysts that speed up the reaction but arent used up in the reaction itself
What do enzymes do in a reaction?
They lower the activation energy of a reaction. This speeds up the rate of reaction.
Why do enzyme substrate complexes lower the activation energy of a reaction?
- if two substrate molecules need to be joined, being attached to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily.
- If the enzyme is catalysing a breakdown reaction, fitting in to the active site puts a strain on bonds in the substrate, so it breaks down more easily.
Describe and explain the induced fit model.
The model helps explain why enzymes are so specific and only bond to one particular substrate.
To work, the substrate has to be the right shape to fit the active site, and has to make the active site change shape in the right way as well.
How do enzyme properties relate to their tertiary structure?
- enzymes are very specific and usually only catalyse one reaction
- the active sites shape is determined by the enzymes tertiary structure
- each diff enzyme has a diff tertiary structure, and so a diff shaped active site
- if the tertiary structure of an enzyme is altered in any way, the shape of the active site will change and he enzyme will lose its function
- the primary structure of a protein is determined by a gene
What factors affect enzyme activity?
Temperature, pH, Enzyme concentration, substrate concentration, Inhibitors
How does temperature affect enzyme activity?
- the rise in temp makes the enzymes molecules vibrate more and work faster
- if temp goes above certain level the vibration breaks some of the bonds that hold the enzyme in shape
- active site changes shape and the enzyme is denatured.
How does pH affect enzyme activity?
Above and below the optimum pH (7), the H+ and OH- ions found in acids and alkalis mess up the ionic and hydrogen bonds that hold the enzymes tertiary structure in place, denaturing enzyme
How does enzyme/substrate concentration affect rate of reaction?
The more enzymes/substrates there are in a solution, the more likely it becomes that successful collisions will happen and create enzyme substrate complexes.
- This only works up to a point as if all the substrates/enzymes have been used up then the other party becomes the limiting factor as all the other enzyme/substrate have been used up.
How does competitive inhibition work?
- Competitive inhibitor molecules have a similar shape to substrate.
- They compete with substrate to bind to active site, but no reaction takes place
- Instead they block the active site, so no substrate molecule can fit in.
- If theres a high conc of inhibitor, itll take up nearly all active sites and will stop reaction happening quickly
- So, increasing substrate conc will increase rate of reaction.
How does non competitive inhibition work?
- Non comp inhibitor molecules bind to enzyme away from its active site.
- This causes active site to change shape so substrate can no longer bind to it.
They dont ‘compete’ with substrates bc they are a diff shape. - Increasing conc of substrate wont make any difference to reaction rateb, enzyme activity will still be inhibited.
Name two ways to measure the rate of an enzyme-controlled reaction
- measuring how fast the product of the reaction is made
- measuring how fast the substrate is broken down
How do you calculate the initial rate of reaction?
Drawing a tangent (on a graph) to the curve using a ruler so its an equal distance from the curve at both sides.
Then calculate gradient of tangent. gradient= change in y axis/change in x axis
