enzymes Flashcards
Enzymes:
protein that acts as catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction
enzymes are
Are biological catalysts
why enzymes are biological catalysts
biological because they are made in living cells, catalysts because they speed up the rate of chemical reactions without being changed
Enzymes are necessary to
all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life For example, if we did not produce digestive enzymes, it would take around 2 – 3 weeks to digest one meal; with enzymes, it takes around 4 hours
How do Enzymes Work?
Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate This is because the enzyme is a protein and has a specific 3-D shape This is known as the lock and key hypothesis When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate
Effect of Temperature on Enzyme Function
Enzymes are proteins and have a specific shape, held in place by bonds
This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed
Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C
Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation
Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
Denaturation is irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop
Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
This means that low temperatures do not denature enzymes, they just make them work more slowly
Effect of pH on Enzyme Activity
The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed
This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop
Effect of Temperature on the Enzyme Amylase
Amylase digests starch into maltose
Starch can be tested for easily using iodine solution
Starch solution is heated to a set temperature
Iodine is added to wells of a spotting tile
Amylase is added to the starch solution and mixed well
Every minute, droplets of solution are added to a new well of iodine solution
This is continued until the iodine stops turning blue black (this means there is no more starch left in the solution as the amylase has broken it all down)
Time taken for the reaction to be completed is recorded
Experiment is repeated at different temperatures
The quicker the reaction is completed, the faster the enzyme is working
Testing the effect of changing temperature on the rate of enzyme activity
Effect of pH on the Enzyme Amylase
Place single drops of iodine solution in rows on the tile
Label a test tube with the pH to be tested
Use the syringe to place 2cm3 of amylase in the test tube
Add 1cm3 of buffer solution to the test tube using a syringe
Use another test tube to add 2cm3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette
After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue black
Wait another 10 seconds and place another drop of mixture on the second drop of iodine
Repeat every 10 seconds until iodine solution remains orange brown
Repeat experiment at different pH values – the less time the iodine solution takes to remain orange brown, the quicker all the starch has been digested and so the better the enzyme works at that pH
Describing and explaining experimental results for enzyme experiments is a common type of exam question
So understand what is happening and, for a 7, 8 or 9, be able to:
relate this to changes in the active site of the enzyme when it has denatured
or, if it is a low temperature, relate it to the amount of kinetic energy the molecules have.
