Enzymes and food tests (in topic 2)

Question 1

What do enzymes do?

Answer 1

Speed up chemical reactions in living things.

Question 2

What are enzymes?

Answer 2

Biological catalysts.
Proteins made up of long chains of amino acids (like all proteins).

Question 3

What is the active site?

Answer 3

Region along the membrane that has a shape that fits with specific substrate molecules.

Question 4

How does the enzyme speed up the reaction?

Answer 4

By locking onto the substrate at their active site.

Question 5

Explain the lock and key theory.

Answer 5

Was believed that the substrate fit perfectly into the active site.

Question 6

Explain the ‘induced fit’ model.

Answer 6

It was believed that substrate and active site fit perfectly but in reality, the active site changes shape a little as the substrate binds to it to get a tighter fit.

Question 7

What is optimum temperature that enzymes work best at?

Answer 7

37 degrees (body temperature)

Question 8

What happens to enzymes when it gets too hot?

Answer 8

Some of the bond holding the enzyme together break changing the shape of the active site so substrate won’t fit anymore. The enzyme is denatured.

Question 9

How does pH effect enzymes?

Answer 9

If too high or too low, interferes with the bonds holding the enzyme together. This changes the shape of active site and denatures the enzyme.

Question 10

What pH do enzymes work best at?

Answer 10

Often pH 7. Not always e.g enzymes in the stomach work best at pH 2.

Question 11

Which enzyme breaks down starch and where is it made?

Answer 11

Amylase.
-pancreas
-small intestine
-salivary gland

Question 12

Which enzyme breaks down protein and where is it made?

Answer 12

Protease.
-pancreas
-small intestine
-stomach

Question 13

Which enzyme breaks down lipids (fats)? Where is it made?

Answer 13

Lipase.
-pancreas
-small intestine

Question 14

What does starch break down into?

Answer 14

Maltose and other sugars.

Question 15

What does protein break down into?

Answer 15

Amino acids

Question 16

What do lipids break down into?

Answer 16

Glycerol and fatty acids.

Question 17

Where is bile stored and where is it released into?

Answer 17

Stored in gall bladder before it’s released to the small intestine.

Question 18

How does bile allow enzymes in small intestine to work in best conditions?

Answer 18

Hydrochloric acid in the stomach makes pH too acidic for enzymes in small intestine. Bile neutralises it and makes conditions alkaline. Enzymes in small intestine work best in these conditions.

Question 19

What does bile do to fats and why?

Answer 19

Bile emulsifies fats (breaks it into tiny droplets). This gives a bigger surface area for lipase to work on which makes digestion faster.

Question 20

How to investigate the effect of pH on enzyme activity?

Answer 20

1)Put a drop of iodine in each well of the spotting tile
2)Use a syringe to add 1 cm cubed of amylase solution of a buffer solution with pH of 5 to a boiling tube.
3) Put test tube into water bath- keep temperature constant of 75 degrees (thermometer)
4)Use a different syringe to add 5cm cubed of starch solution to the boiling tube
5)Mix contents and start stop clock
6)Use continuous sampling by dropping a pipette of sample from boiling tube every 30 seconds to a well. When iodine solution remains browny-orange starch is no longer present
7)Repeat with buffer solutions of different pH values

Question 21

Explain the method of how to test for sugars

Answer 21

1)Prepare a food sample and transfer 5 cm cubed to test tube
2)Prepare a water bath and set to 75 degrees.
3)Add some Benedict’s solution using a pipette
4)Put in water bath using a test tube holder and leave for 5 minutes.
5)If it turns from blue to yellow or brick red it has sugar.

Question 22

Explain the method of how to test for starch

Answer 22

1)Prepare food sample and transfer 5 cm cubed of sample to test tube
2) Then add some iodine solution and gently shake
3) If it turns from orange to black it contains starch

Question 23

Explain the method of how to test for proteins

Answer 23

1)Prepare food sample and transfer 2 cm cubed of sample to test tube
2)Add 2 cm cubed on biuret solution to sample and gently shake
3)Turns from blue to purple

Question 24

Explain the method of how to test for lipids

Answer 24

1)Prepare food sample (but don’t need to filter it) and add 5 cm cubed of Sudan III solution
2)Use a pipette to add 3 drops of Sudan III solution to test tube and gently shake
3)Will split in two layers, top layer is red.

Question 25

How do you prepare a food sample?

Answer 25

1)Get a piece of food and break it up using pestle and mortar
2)Transfer the ground up food to a beaker and add some distilled water
3)Give the mixture a stir with glass rod to dissolve some of food
4)Filter solution