Section 1 - Key concepts - Enzymes, breakdown and synthesis, testing for biological molecules and energy in food Flashcards
What are enzymes?
Biological catalysts produced by living things
What is the ‘lock and key’ mechanism?
When the substrate fits into the specifically shaped active site of an enzyme
What 3 things affect rate of enzyme-catalysed reaction?
Temperature, pH and substrate concentration
What happens to enzyme when temperature or pH is too high?
Active site of enzyme changes shape and becomes denatured so substrate can’t fit anymore.
What is the optimum temperature or pH?
The point where enzyme works best at
Formula to calculate rate of reaction?
Rate = 1000 ÷ time
What enzyme breaks down carbohydrates into what? What does amylase do?
Carbohydrases break down carbohydrates into simple sugars.
Amylase breaks down starch into maltose and other simple sugars
What enzyme breaks down proteins into what?
Proteases break down proteins into amino acids
What enzyme breaks down lipids into what?
Lipases break down lipids into glycerol and fatty acids.
Which one out of temperature, substrate concentration and pH doesn’t denature the enzyme if it’s too high?
Substrate concentration
What happens to an enzyme after a reaction?
Remains unchanged
What does the enzyme glycogen synthase do?
Synthesis glycogen by joining together lots of chains of glucose molecules
How can you test for reducing sugars using Benedict’s Reagent?
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.
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?
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
What do you use to test for starch and what colour does sample change to when this solution is added if starch is present?
Iodine solution used
From browny-orange to blue-black
How do you test for lipids using emulsion test?
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
How do you test for proteins using biuret test?
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
What is calorimetry?
Burning food to see how much energy it contains
Formula for energy in food?
Energy in food (J) = mass of water (g) x temperature change of water (˚C) x 4.2
Formula for energy per gram of food?
Energy per gram of food (J/kg) = energy in food (J) ÷ mass of food (g)
