Enzymes + food tests 1.7 - 1.14B

How do enzymes work?

- they have an aztive site complementary to the substrate

- for the enzyme to work the substrate has to fit into the active site

- if the substrate's shape doesn't match, then the reaction won't be catalysed

What's the enzyme mechanism called?

The lock and key mechanisms s the substrate fits into the enzyme like a key fits into a lock

How an increase in temperature affects rate of reaction

- as temp increased rate of an enzyme-catalysed reaction increases at first

- when too hot some bonds holding the enzyme together break

- this changes the shape of the active site and causes it to denature

- this means the substrate no longer fits

- enzymes have an optimum temperature that they work best at

How pH affects enzyme activity

- PH to high or too low interferes with the bonds holding the enzyme together

- this changes the shape of the active site and denatures the enzyme

- all enzymes have an optimum pH - usually 7. Changes depending on the enzyme

How substrate concentration affects enzyme activity

- the higher the substrate concentration the faster the reaction, due to it being more likely that the enzyme will meet up and react with a substrate molecule

- this is only up to a certain point, all the actives sites are full so no more substrates can fit, so adding more makes no difference

CORE PRACTICAL - effect of pH on enzyme activity

- place a drop of iodine solution into every well of a spotting tile

- place a Bunsen burner on a heat-proof mat, and a tripod and gauze over the Bunsen burner. Put a beaker of water on the tripod and heat the water until 35C, use a thermometer to measure and keep constant

- use a syringe to add 3cm^3 of amylase solution and 1cm^3 of buffer solution with pH 5 to a boiling tube. Using test tube holders put the boiling tube into the beaker of water and wait for 5 minutes

- use a different syringe to add 3cm^3 of starch solution to the boiling tube

- immediately mix the contents of the boiling tube and start a stop clock

- use continuous sampling to record how long it takes for the amylase to break down all of the starch

- use a dropping pipette to take a fresh sample from the boiling tube every 10 seconds and put a drop into the well

- when iodine remains browny-orange starch is no longer present

- repeat experiment with different pH of buffer solution to see how pH affects the time

Core practical rate of reaction calculation

Rate = 1000/time

Rate of reaction equation

Amount it has changed by/time taken

Why must big molecules be broken down

They are broken down into smaller components so they can be used for growth and other life processes

Breakdown of carbohydrates

Carbohydrases such as amylase convert carbohydrates into simple sugars

breakdown of proteins

Proteases (protease) convert proteins into amino acids

Breakdown of lipids

Lipases (lipase) convert lipids into glycerol and fatty acids

Test for sugar

Benedict's solution

- add Benedict's reagent to a sample and heat in a water bath that's set to 75 degrees

- if the test is positive it will form a coloured precipitate

- the higher the concentration of reducing sugar the further the colour change

Benedict's colour change (low and high concentration)

Low from blue to green/yellow

High from blue to brick red

Test for starch

Add iodine

Colour change for starch

browny-orange --> black/blue

Test for lipids

Emulsion test

- shake the test substance with ethanol until it dissolves, then pour solution into water

- if there are lipids present, they will precipitate and show up as a milky emulsion

Change in solution for lipids

Colourless to milky white

Test for protein

Biuret test

- add a few drops of potassium hydroxide solution to make the solution alkaline

- then add copper (II) sulfate solution

Colour change for protein

No protein - stay blue

Protein - purple

How to measure the energy contained in food

Calorimetry

How to calculate the amount of energy in food

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

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