1 Biological molecules

Question 1

What is the difference between alpha glucose and beta glucose?

Answer 1

Alpha glucose- both Hs up
Beta glucose- one H, one OH up

Question 2

Describe the reducing sugars test

Answer 2

1. Grind up the food sample in water.
2. Add an equal volume of Benedict’s reagent
3. heat mixture gently in boiling water for 5 minutes.
4. observe the colour change from blue to orange-brown (brick red)

Question 3

Describe the non-reducing sugars test

Answer 3

1. First carry out the reducing sugars test, do the if it is negative.
2. grind up sample in water, add equal amounts of hydrochloric acid (this hydrolyses the disaccharides). Place in water bath for 5 mins.
3. Add an alkali solution to neutralise it. Test with PH paper.
4. Re-test- add benedicts solution and heat. observe colour change.
   colour change- blue to orange-brown.

Question 4

Describe the test for starch

Answer 4

1. Add some drops of iodine to a food sample.
2. Observe colour change from orange to blue-black.

Question 5

Describe the properties of triglycerides related to their function.

Answer 5

• High ratio of energy storing carbon-hydrogen bonds to carbon atoms (excellent source of energy)
• Low mass to energy ratio- Good storage molecules as energy can be stored at a small volume.
  -Large and non-polar- they are insoluble in water so do not change water potential.

Question 6

Describe the properties of phospholipids related to their function.

Answer 6

Polar- hydrophilic head and hydrophobic tails mean that they form a bilayer in water
Hydrophilic heads- hold together the surface of the cell membrane.
Structure allows them to form glycolipids on the surface of the membrane (recognition sites)

Question 7

Draw an amino acid- what are its components.

Answer 7

amino group (NH2), carboxyl group (COOH), hydrogen atom (H), R group (variant of any of 20 amino acids)

Question 8

What bonds help to form the different structures of proteins?

Answer 8

Primary- just the sequence of amino acids
Secondary- hydrogen bonds
Tertiary- disulphide, ionic and hydrogen
Quaternary- same as tertiary.

Question 9

Describe the test for proteins

Answer 9

1. Grind up food sample in water and add biurets reagent.
2. Observe colour change from blue-lilac

Question 10

Factors affecting enzyme action:enzyme concentration

Answer 10

increases rate of reaction as it increases because the substrates are being broken down quicker and more effectively.

Question 11

Factors affecting enzyme action: substrate concentration

Answer 11

Increases rate of reaction originally, until all enzymes active sites are occupied and there are substrates that are not actively being broken-down, causing the rate of reaction to slow.

Question 12

Factors affecting enzyme action: competitive/non-competitive inhibitors

Answer 12

if the concentration increases, then rate of reaction will slow due to active sites being occupied/active sites being changed shape so they no longer fit their substrate.

Question 13

Factors affecting enzyme action: PH and temperature

Answer 13

Temperature-increases rate of reaction due to more kinetic energy and collision theory until it exceeds the optimum and enzymes denature.
PH: Alters the tertiary structure of the enzyme causing it to denature and no longer fit the substrate.