2.5 identify the chemical elements present in carbohydrates, proteins and lipids
(fats and oils)
Carbohydrates and lipids (fats and oils) are both made up of the following elements;
- Carbon
- Hydrogen
- Oxygen
Proteins are made up of the following elements;
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
- Sulphur
- Phosphorous
2.6 describe the structure of carbohydrates, proteins and lipids as large
molecules made up from smaller basic units: starch and glycogen from
simple sugar; protein from amino acids; lipid from fatty acids and glycerol
Starch and glycogen are large, complex carbohydrates that are made up of many smaller units held together in a long chain. These smaller units are 'simple sugars' and examples include; glucose and maltose molecules.
Proteins are made up of long chains of amino acids.
Fats and oils (lipids) are composed of fatty acids and glycerol. (Glycerol + 3 fatty acids)
2.7 describe the tests for glucose and starch
Glucose
- . Add a few drops of Benedict's reagent to the solution. (Benedict’s reagent is blue and will turn the sample blue.)
- Place the test tube in a water bath at around 60/70 degrees celcius from 2-3 minutes. (Make sure the solution doesn’t boil.)
- If the test is positive (and glucose is present) then a coloured precipitate will form. (Orange/red for strong solutions of glucose, green for weak solutions of glucose.
Starch
1)
Add a few drops of iodine solution to the test
sample of starch you have.
2)
If the sample changes from browny-orange to a
dark, blue-black colour, then starch is present.
3)
If the sample remains the same browny-orange
colour, then there is no starch present.
2.8 understand the role of enzymes as biological catalysts in metabolic reactions
Enzymes speed up chemical reactions without being used up in them. They are therefore catalysts (biological catalysts). The reactions that enzymes speed up are very important metabolic reactions, which are defined as: chemical processes that occur in living organisms in order to maintain life.
2.9 understand how the functioning of enzymes can be affected by changes in
temperature, including changes due to change in active site
All enzymes have an optimum temperature, the temperature at which they function best and their activity is greatest. When this temperature is raised too high, some of the bonds holding the enzyme together will break. This means that the enzyme will lose its shape, and therefore its active site will no longer fit the substrate, so the reaction will stop as the enzyme has been denatured.
2.10 understand how the functioning of enzymes can be affected by
changes in active site caused by changes in pH
The functioning of enzymes can also be affected by changes in pH. Again, enzymes have an optimum pH at which they work best. If the pH becomes too high or too low for the enzyme, its bonds will break and the active site will change shape. This means that the reaction will stop as the size of the active site has changed, and the enzyme has been denatured.
2.11 describe experiments to investigate how enzyme activity can be affected by
changes in temperature.
- Amylase is an enzyme that catalyses the breakdown of starch to maltose.
- In this experiment, the starch solution and amylase enzyme should be kept in a test tube in a water bath which remains at a constant temperature.
- Starch is the substrate in this experiment, and it is easy to detect. Pour a few drops of iodine solution into the amylase solution. If starch is present, the iodine solution will change from an orange/brown colour to a blue-black colour.
- You can then time how long it takes for the starch to disappear by regularly sampling the solution (say every minute or so). Then use the times and the amount of starch present to compare rates between different tests.
- By adjusting the temperature of the water bath, it will become clear how the temperature affects the activity of amylase when continuing to compare these sampling results with the past results.
