Section 1 - Key concepts - Enzymes, breakdown and synthesis, testing for biological molecules and energy in food

Question 1

What are enzymes?

Answer 1

Biological catalysts produced by living things

Question 2

What is the ‘lock and key’ mechanism?

Answer 2

When the substrate fits into the specifically shaped active site of an enzyme

Question 3

What 3 things affect rate of enzyme-catalysed reaction?

Answer 3

Temperature, pH and substrate concentration

Question 4

What happens to enzyme when temperature or pH is too high?

Answer 4

Active site of enzyme changes shape and becomes denatured so substrate can’t fit anymore.

Question 5

What is the optimum temperature or pH?

Answer 5

The point where enzyme works best at

Question 6

Formula to calculate rate of reaction?

Answer 6

Rate = 1000 ÷ time

Question 7

What enzyme breaks down carbohydrates into what? What does amylase do?

Answer 7

Carbohydrases break down carbohydrates into simple sugars.

Amylase breaks down starch into maltose and other simple sugars

Question 8

What enzyme breaks down proteins into what?

Answer 8

Proteases break down proteins into amino acids

Question 9

What enzyme breaks down lipids into what?

Answer 9

Lipases break down lipids into glycerol and fatty acids.

Question 10

Which one out of temperature, substrate concentration and pH doesn’t denature the enzyme if it’s too high?

Answer 10

Substrate concentration

Question 11

What happens to an enzyme after a reaction?

Answer 11

Remains unchanged

Question 12

What does the enzyme glycogen synthase do?

Answer 12

Synthesis glycogen by joining together lots of chains of glucose molecules

Question 13

How can you test for reducing sugars using Benedict’s Reagent?

Answer 13

Add Benedict’s reagent (which is blue) to a sample and heat in water bath set to 75˚C. If test is positive, it will form a coloured precipitate.

Question 14

What does a further colour change mean when testing for reducing sugars using Benedict’s reagent and what is the colour change from and to?

Answer 14

The higher the concentration of reducing sugar, the further the colour change goes
From blue to brick red (reverse rainbow) with red having highest concentration

Question 15

What do you use to test for starch and what colour does sample change to when this solution is added if starch is present?

Answer 15

Iodine solution used

From browny-orange to blue-black

Question 16

How do you test for lipids using emulsion test?

Answer 16

Shake test substance with ethanol until it dissolves then put solution into water. If any lipids present, they will precipitate out of liquid, show up as a milky emulsion. More lipid there is, more noticeable milky colour is

Question 17

How do you test for proteins using biuret test?

Answer 17

Add few drops of potassium hydroxide solution to make solution alkaline then add some copper (II) sulfate solution (bright blue colour). If protein present, solution turn to purple but stays blue if not present

Question 18

What is calorimetry?

Answer 18

Burning food to see how much energy it contains

Question 19

Formula for energy in food?

Answer 19

Energy in food (J) = mass of water (g) x temperature change of water (˚C) x 4.2

Question 20

Formula for energy per gram of food?

Answer 20

Energy per gram of food (J/kg) = energy in food (J) ÷ mass of food (g)