Enzymes Flashcards
1
Q
Enzymes
A
Globular proteins with a specific tertiary structure which catalyse metabolic reactions in living organisms. Enzyme actions can be intra or extracellular
2
Q
Enzymes at work - lock and key hypothesis
A
- specific shape of the active site, complementary to the substrate molecule
- the substrate (the key) fits into the enzyme (the lock) and is held in one place while the reaction occurs.
3
Q
Enzymes at work - induced fit hypothesis
A
- enzymes reduce the activation energy required for a reaction to take place
- enzyme’s active site changes shape slightly when the substrate collides with it
- the active site fits more closely, holding the substrate in place. Also held due to oppositely charged groups on the substrate and the active site are found near each other
- this is an enzyme-substrate complex
- change in shape of the active site puts strain on the substrate, destabilising it so the reaction occurs more readily
- the product is an enzyme-product complex
- product(s) don’t fit the active site, so they move away
- enzyme can go on to catalyse more reactions
4
Q
Effect of pH on enzyme activity
A
- pH is a measure of H+ ions in a solution
- if there is a change in H+ ions, this can interfere with an enzyme’s shape, as it is held together by many ionic and hydrogen bonds
- charges around/on the active site will also be affected
- enzymes tend to work at a relatively narrow pH range, centred around the optimum pH
- small changes in pH will effect the enzyme’s activity, but not necessarily its shape - it could function again if the pH was returned. Large changes in pH will denature the enzyme
- rate of reaction against pH graphs shows a sharp peak (0 the rest of the time)
5
Q
Effect of temperature on enzyme activity
A
- rate of reaction increases from 0 as temperature increases as molecules gain kinetic energy as more collisions occur
- as heat increases, molecules vibrate more, putting strain on bonds
- as enzymes are held together by some weaker bonds, e.g. hydrogen and ionic, these can break
- the tertiary structure of the enzyme unravels, and the shape of the active site is deformed
- the enzyme has become denatured irreversibly
- graph of rate of reaction against temperature will gradually increase from 0, peak at the optimum temperature then fall quicker than it rose
6
Q
Effect of substrate concentration on enzyme activity
A
- initially, as substrate concentration increases, so does the rate of reaction, as more enzyme-substrate complexes are made
- at a point, all the enzyme molecules will be forming enzyme-substrate complexes as fast as possible
- the reaction rate will level off, as, in effect, all the active sites will be occupied at all times, so increasing the concentration of the substrate will have no further effect on the rate of reaction
- enzyme concentration is the limiting factor
- graph starts from 0, goes up linearly, then curves off at a certain point to be flat
7
Q
Effect of enzyme concentration on enzyme activity
A
- as enzyme concentration increases, more active sites become available
- more enzyme substrate complexes form, so reaction rate increases
- reaction rate reaches a maximum for the fixed substrate concentration
- more enzymes won’t give a higher rate past this point
- substrate concentration is the limiting factor
- graph starts from 0, goes up linearly, then curves off at a certain point to be flat
8
Q
Testing for effect of pH on enzyme activity
A
- carry out enzyme controlled reactions at different pH values using buffer solutions
- production of product/disappearance of substrate can be measured to find rate
9
Q
Testing for effect of temperature on enzyme activity
A
- carrying out enzyme controlled reactions at different temperatures, using water baths controlled by a thermostat
- production of product/disappearance of substrate can be measured to find rate
10
Q
Testing for effect of substrate concentration on enzyme activity
A
- carry out enzyme controlled reactions at different substrate concentrations
- production of product/disappearance of substrate can be measured to find rate
11
Q
Testing for effect of enzyme concentration on enzyme activity
A
- carry out enzyme controlled reactions at different enzyme concentrations
- production of product/disappearance of substrate can be measured to find rate
12
Q
Enzyme inhibitors
A
Reduce the rate of enzyme controlled reactions by effecting the enzyme molecule
13
Q
Competitive inhibitors
A
- have a similar shape to that of the substrate molecule: complementary to the active site of the enzyme
- competes with the substrate for a position on the active site
- forms enzyme-inhibitor complexes
- substrate can’t enter to form enzyme-substrate complexes and react, slowing down the reaction rate
- as concentration of the substrate increases, rate of reaction increases to the same level it would be at, even if there were no inhibitors, as the chance an inhibitor will collide with an enzyme decreases
- graph looks like a linear line of a lower gradient to the line with no inhibitor, but reaches same peak and flattens out
14
Q
Non-competitive inhibitors
A
- attach to a region of the enzyme away from the active site
- when they attach, the shape of the active site changes (tertiary structure), so a substrate can’t bind there and no enzyme-substrate complexes can form
- level of inhibition doesn’t depend on substrate concentration, but on inhibitor concentration, as the inhibitor isn’t competing for the active site
- if there are enough inhibitor molecules to bind with all the enzymes, the rate of reaction will stop
- graph begins linearly at a shallower gradient, then levels off before it reaches height of graph without inhibitor
15
Q
Reversible/irreversible inhibitors
A
- most competitive inhibitors are reversible - they bind to the active site for a bit, then leave
- most non-competitive inhibitors are irreversible - the bind to the enzyme permanently, denaturing the enzyme
- don’t assume though!!
