Learning outcomes:
2.5
identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)
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
2.7
describe the tests for glucose and starch
2.8
understand the role of enzymes as biological catalysts in metabolic reactions - and another
2.9
understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site
2.10
understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH
2.11
describe experiments to investigate how enzyme activity can be affected by changes in temperature.

Food Tests:


Lipids are tested for using the Emulsion test - add ethanol --->cloudy white precipitate = positive

Proteins are tested for using the Biuret test - add Biuret solution ---> blue to purple = positive

Starch is tested for using Iodine solution - add iodine ---> orange to blue/black = positive

Glucose is tested for using Benedict’s test - add Benedict's solution, heat up in test tube ---> blue to brick red/orange = positive

Components of the main Food Groups:


The main food groups are carbohydrates, lipids and proteins. All three groups are made from smaller molecules.

Carbohydrates are large molecules made from one or more sugars (e.g. both Starch and Glycogen are both polymers of Glucose)

Proteins are polymers of Amino Acids

Lipids are made from one glycerol molecule and three fatty acid molecules joined together.

Food Group and their Function


Lipids (fats & oils)

Used as a long-term energy store (much easier to store than carbohydrates). Also have a role in protection and insulation.

Carbohydrates

Made from single sugars or chains of sugars. They are used in respiration to provide energy.

Proteins

Broken down into amino acids, which our body absorbs and assembles into new proteins. The proteins are used for growth and repair.

Fibre

Regulates bowel movement. Sloughs off old lining of intestine.

Water

Essential as a solvent for chemical reactions (e.g. cytoplasm), heat loss (e.g. transpiration), transport (e.g. blood) etc

Vitamins and Minerals

Essential for the normal function of some enzymes and proteins e.g. Fe2+ is an essential part of Haemoglobin and Mg2+ is part of Chlorophyll

scool.gif

Enzymes:


- Are proteins
- Are biological catalysts (speed up chemical reactions)
- Are specific to one particular Substrate
- Are affected by temperature and pH
- Are not used up in the reaction they catalyze

enzyme prods.GIF
Factors affecting enxyme activity
1. Initially, raising the temperature increases the rate of reaction.
2. However, after the optimum temperature is reached the enzyme begins to change shape and the active site stops being able to bind to the substrate.
3. The enzyme becomes denatured and stop working (the rate of reaction is zero at this point).

enzyme temp.GIF

1. Initially, increasing the pH increases the rate of reaction.
2. However, after the optimum pH is reached the enzyme begins to change shape and the active site stops being able to bind to the substrate.
3. The enzyme becomes denatured and stops working (the rate of reaction is zero at this point).

enzyme ph.GIF

You need to be able to recall an experiment you have done that explores the effect of temperature on enzymes. An example is the enzyme Catalase, which breaks Hydrogen peroxide into Water and Oxygen;

2H2O2 ---> O2 + 2H2O

Catalase is found in potatoes. Therefore, putting potato chips into peroxide will produce O2. The rate of reaction is, therefore, proportional to the volume of O2 given off. Changing the temperature will alter the volume (i.e. initially increase it, reach an optimum, then decrease quickly as the Catalase becomes denatured).

scool.gif