Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts

Question 2

What is a catalyst?

Answer 2

A substance that increases the rate of reaction without being changed or used up in the reaction

Question 3

What are enzymes made from?

Answer 3

Large proteins - formed from amino acids

Question 4

How are enzymes specific?

Answer 4

Folded into a specific shape - active site is specific - can only catalyse a specific reaction

Question 5

Describe the induced fit model of enzyme action

Answer 5

When the substrate is close to the active site, the active site changes shape to bind to the substrate

Question 6

Describe how the rate of enzyme catalysed reactions can be changed

Answer 6

By changing the temperature and pH
As temperature increases there are more frequent collisions as particles have more energy so rate of reaction increases up until a point where the temperature becomes so high the enzyme denatures and rate of reaction decreases as the enzyme can no longer catalsye the reaction.
The pH interferes with the bonds in the protein in the active site changes the shape of the active site and denaturing the enzyme.

Question 7

At what pH does pepsin work best at?

Answer 7

2

Found in acidic conditions in the stomach

Question 8

At what pH do most enzymes work best at?

Answer 8

7 - neutral

Question 9

How can you investigate the effect of pH on enzyme activity?

Answer 9

Practical with amylase catalysing the breakdown of starch to maltose using iodine solution

Question 10

How is the rate of reaction calculated?

Answer 10

Amount something has changed / time taken

Question 11

Describe the digestion of starch

Answer 11

Starch is digested into maltose and other sugars e.g dextrins by carbohydrase enzyme amylase

Question 12

Where is amylase made?

Answer 12

Salivary glands
Pancreas
Small intestine

Question 13

Describe the digestion of proteins

Answer 13

Proteins are digested by proteases into amino acids

Question 14

Where are proteases made?

Answer 14

Stomach (pepsin)
Pancreas
Small intestine

Question 15

Describe the digestion of fats/lipids

Answer 15

Lipids are digested by lipases into fatty acids and glycerol

Question 16

Where are lipases made?

Answer 16

Pancreas

Small intestine

Question 17

Where are the products of digestion used?

Answer 17

To make new proteins and carbohydrates

Glucose used in respiration

Question 18

Why is digestion necessary?

Answer 18

Large molecules like proteins and fats cant diffuse into the blood and can not be absorbed so must be broken down into smaller molecules

Question 19

Where is bile produced, stored and release?

Answer 19

Produced by liver and stored in the gallbladder before it is released into the small intestine

Question 20

What is the purpose of bile?

Answer 20

Neutralises the hydrochloric acid from the stomach and provides an optimum pH for enzymes to work in the small intestine
Emulsifies fats- breaks the fats into smaller droplets increasing the surface area for which lipases can work

Question 21

Describe the function of the salivary glands in digestion

Answer 21

Produce amylase in the saliva

Question 22

Describe the function of the oesophagus in digestion

Answer 22

Passage of food from mouth to the stomach

Question 23

Describe the function of the stomach in digestion

Answer 23

Pummels food with its muscular walls
Produces protease enzyme pepsin
Produces hydrochloric acid which kills bacteria and gives the right pH for the protease enzyme to work (pH 2)

Question 24

Describe the function of the pancreas in digestion

Answer 24

Produces protease, amylase and lipase enzymes

Releases these into the small intestine

Question 25

Describe the function of the small intestine in digestion

Answer 25

Produces protease, amylase and lipase enzymes to complete digestion
This is where all the food is absorbed out of the digestive system into the blood

Question 26

Describe the function of the liver in digestion

Answer 26

Produces bile which neutralises stomach acid and emulsifies fats

Question 27

Describe the function of the gallbladder in digestion

Answer 27

Stores bile and releases it into the small intestine

Question 28

Describe the function of the large intestine in digestion

Answer 28

Where excess water is absorbed from the food

Question 29

Describe the function of the rectum

Answer 29

Where the faeces are stored before they leave the anus

Question 30

How do you prepare a food sample for a food test?

Answer 30

Break up food using pestle and mortar
Transfer food to beaker and add distilled water
Stir mixture with glass rod to dissolve the food
Filter solution using funnel lined with filter paper to get rid of solid bits of food

Question 31

Describe the benedicts test

Answer 31

Used to test for reducing sugars
Prepare food sample and transfer 5cm3 into a test tube

Prepare water bath so it is set to 75degreesC

Add benedicts solution to test tube using a pipette (10drops)

Place test tube in a water bath and leave it there for 5 mins

If the food sample contains a reducing sugar the solution will change colour from normal blue colour to green, yellow or brick red - depending on how much reducing sugar is present

Question 32

Describe the iodine test

Answer 32

Used to test for the presence of starch
Make food sample and transfer 5cm3 into test tube
Add few drops of iodine solution and gently shake to mix contents
If solution contains starch the colour of the solution will change from browny-orange to black or blue-black

Question 33

Describe the biuret test

Answer 33

Used to test for protein
Prepare sample of food and transfer 2cm3 into a test tube
Add 2cm3 of biurets solution and mix by shaking gently
If protein is present the sample will turn from blue to pink or purple. It will stay blue if no protein is present

Question 34

Describe the sudan III test

Answer 34

Test for lipids
Prepare sample of food and transfer 5cm3 to test tube
Use pipette to add 3 drops of sudan III stain solution to test tube and gently shake
Sudan III stain solution stains lipids, if the mixture contains lipids the mixture will separate out into two layers the top layer will be bright red. If no lipid is present no separate red layer will form at the top of the liquid