T1 - Enzymes (UNFINISHED)

Enzymes

Enzymes

• biological catalysts produced by living things

• reduce the need for high temperatures, so we use them to speed up useful chemical reactions in the body

Catalyst

Substance that increases the speed of reaction, without being changed or used up in the reaction

Substrate

molecule changed in the reaction

Active site

the part where the enzyme joins onto its substrate to catalyse the reaction

Why do Enzymes only work with one substrate?

• they have high specificity for their substrate

• for the enzyme to work, the substrate has to fit into the active site

• if the substrate’s shape doesn’t match the active site’s shape, the reaction won’t be catalysed

How does the ‘lock and key mechanism’ work?

the substrate fits into the enzyme like a key fits into a lock

Why does an Enzyme need the right temperature?

• changing the temperature changes the rate of an enzyme-catalysed reaction

• a higher reaction increases the rate at first

• if it gets too hot, the bond holding the enzyme together break

• this changes the shape of the enzyme’s active site, so the substrate won’t fit anymore (enzyme is denatured)

• all enzymes have an optimum temperature they work best at

Why does an Enzyme need the right pH?

• if the pH is too high or too low, it interferes with the bonds holding the enzyme together

• this changes the shape of the active site and denatures the enzyme

• all enzymes have an optimum pH, which is often pH 7 but not always.

Why does an Enzyme need the right Substrate Concentration?

• the higher the substrate concentration, the faster the reaction, because it’s more likely that the enzyme will meet up and react with a substrate molecule

• however if all active sites are full, adding more substrates make no difference to the rate of reaction

How to investigate the effect of pH on Enzyme Activity? (enzyme being amylase)

1. put a drop of iodine solution into every dimple of a dimple tile

2. place a bunsen burner on a heatproof mat, and a tripod and gauze over the bunsen burner. Put a beaker of water on top of the tripod and heat the water until it is 35 degrees celsius using a thermometer

3. use a syringe to add 3cm cubed of amylase solution and 1cm cubed of a buffer solution with a pH of 5 to a boiling tube. using test tube holders, put the tube into the beaker of water and wait for 5 minutes

4. next, use a different syringe to add 3cm cubed of a starch solution to the boiling tube

5. immediately mix the contents of the boiling tube and start a stop clock

6. use continuous sampling to record how long it takes for the amylase to break down all of the starch. to do this, use a dropping pipette to take a fresh sample from the boiling tube every ten seconds and put a drop into a dimple.

7. repeat the whole experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down

8. remember to control any variables each time (e.g. concentration and volume of amylase solution) to make it a fair test.