5. Enzymes

Question 1

Enzyme definitions

Answer 1

Are biological catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction. Are also proteins

Question 2

What is a biological catalyst?

Answer 2

• BIOLOGICAL because they are made in living cells

- CATALYSTS because they speed up the rate of chemical reactions without being changed

Question 3

Why are enzymes necessary?

Answer 3

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

Question 4

What is special about enzymes?

Answer 4

Enzymes are specific to one particular substrate, as the enzyme is a complementary shape to the substrate

Question 5

What is a substrate?

Answer 5

molecule/s that get broken down or joined together in the reaction

Question 6

What causes an enzyme to become specific?

Answer 6

• 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

Question 7

What is enzyme specificity known as?

Answer 7

lock and key hypothesis

Question 8

What is it called when the substrate moves into the enzyme’s active site?

Answer 8

they become known as the enzyme-substrate complex

Question 9

What happens after the reaction has occurred?

Answer 9

the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate

Question 10

Describe process of how enzymes work

Answer 10

1. Enzymes and substates randomly move about in solution
2. When an enzyme and its complementary substrate randomly collide – with the substrate fitting into the active site of the enzyme – an enzyme-substrate complex forms, and the reaction occurs.
3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions.

Question 11

What is the enzymes specific shape held in place by?

Answer 11

Enzymes are proteins and have a specific shape, held in place by BONDS

Question 12

Why is the specific shape important?

Answer 12

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

Question 13

When do enzymes work fastest?

Answer 13

Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C

Question 14

What happens to enzymes when they’re heated to high temperatures?

Answer 14

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

Question 15

Why is denaturation such a problem?

Answer 15

Substrates cannot fit into denatured enzymes as the shape of their active site has been lost

Question 16

Is denaturation reversible?

Answer 16

NO

- Denaturation is irreversible – once enzymes are denatured they cannot regain their proper shape and activity will stop

Question 17

What happens to enzymes when you increase the temperature from 0 degrees to the optimum?

Answer 17

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

Question 18

What do low temperatures do to enzymes?

Answer 18

This means that low temperatures do not denature enzymes, they just make them work more slowly

Question 19

What is the general optimum PH for enzymes? What are some exceptions?

Answer 19

The optimum pH for most enzymes is 7

• some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2)
• some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)

Question 20

What can happen to enzymes if the pH is too high or too low?

Answer 20

• 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

Question 21

What happens when the conditions move too far away from the optimum pH of the enzyme?

Answer 21

Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop

Question 22

What happens to enzyme activity when the conditions move too far away from the optimum pH of the enzyme?

Answer 22

This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity

Question 23

What is an enzymes that digests starch and what is it turned into?

Answer 23

Amylase is an enzyme that digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose).

Question 24

Describe procedure for Investigating the Effect of Temperature on Amylase

Answer 24

• 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

Question 25

Describe procedure for Investigating the Effect of pH on Amylase

Answer 25

• 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