Biological Molecules

Question 1

What are carbohydrates?

Answer 1

Contain carbon, hydrogen and oxygen
Starch and glycogen are large, complex carbohydrates made up of many smaller units (simple sugars), e.g. glucose and maltose, joined together in a chain

Question 2

What are proteins?

Answer 2

Contain carbon, nitrogen, oxygen and hydrogen atoms
Made up of long chains of animo acids

Question 3

What are lipids?

Answer 3

Contain carbon, hydrogen and oxygen molecules
Made of fatty acids and glycerol

Question 4

What is the test for glucose?

Answer 4

1. Prepare food sample and put in test tube
2. Set a water bath to 75°C
3. Add excess of Benedict’s solution to the test tube with a pipettes
4. Place test tube in water bath for 5 minutes
5. If glucose is present, then the solution will change from blue to brick-red (or green/yellow)

Question 5

What is the test for starch?

Answer 5

1. Place food in well on spotting tile
2. Using a pipette drop iodine onto the food
3. If starch is present, it will change from brown-orange to black or blue-black

Question 6

What is the test for proteins?

Answer 6

1. Place food in test tube
2. Add biuret solution and shake the test tube
3. If protein is present, then the solution will change from blue to purple, if not then the solution will remain blue

Question 7

What is the test for lipids?

Answer 7

1. Place food in a test tube
2. Add equal volumes of ethanol
3. Shake vigorously and leave of one minute
4. Pour the solution into a test tube of water
5. If a milky-white emulsion forms, then the substance contains lipids. This is because lipids will dissolve in ethanol, but not water so form an emulsion

Question 8

What do enzymes do in metabolic reactions?

Answer 8

Catalysts that control metabolic reactions are called enzymes, and because they work in living cells they are know as biological catalysts. They help to carry out life processes quickly, without them these reactions would happen too slowly to sustain life.

Question 9

How do temperature changes affect enzyme function?

Answer 9

If the temperature changes, some of the bonds holding the enzymes together will break, which changes the shape of the enzyme’s active site. So, the substrate won’t fit anymore and the enzyme is denatured

Question 10

How do pH changes affect enzyme function?

Answer 10

If the pH is too high or low, then it interferes with the bonds holding the enzyme together and causes change in the active site. This is denaturing.

Question 11

Investigate how enzyme activity can be affected by changes in temperature

Answer 11

1. Set up 5 water baths at room temp 30, 40, 50 and 60°C
2. Get 2 spotting tiles and put iodine in each one
3. Add 6cm3 of starch solution to a test tube
4. Then add 2cm3 of amylase solution to test tube, mix and put in water bath
5. Use a glass rod, dip into the solution and then drop into iodine in spotting tile
6. Every 30 secs, add another drop to another well on the spotting tile
7. Record time taken for starch solution to stop turning iodine black (all digested)
8. Repeat for all temperatures 3 times and average results

Question 12

Investigate how enzyme activity is affected by changes in pH

Answer 12

1. Add 5cm3 of egg white to 4test tubes
2. Test tube 1 (control) : egg white + HCl
3. Test tube 2: egg white+ pepsin+distilled water
4. Test tube 3: egg white + pepsin +HCl
5. Test tube 4: egg white + pepsin + sodium hydrogen carbonate
6. Use universal indicator to measure the pH of each test tube and record
7. Add to a water bath at 37°C
8. After 10 mins, remove test tube and see if contents are cloudy or colourless (if clear, then egg white broken down)