1. Biology ( )
Biological Molecules
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2. Starch is a polymer of glucose.
The Carbohydrates
Carbohydrates are polymers of simple sugars such as glucose. The bonds can be broken by enzymes which release the simple sugars.
Starch is a major source of carbohydrate in the diet and it is eventually digested into much smaller glucose molecules.
Starch is a polymer of glucose.
Amylose
Amylopectin

3. Classification of Carbohydrates
Sugars
Polysaccharides
Monosaccharides
Disaccharides
Storage
Structural
Monosaccharides are single sugar units that include:
Glucose
Fructose
Disaccharides are
double sugar units that include:
Sucrose
Maltose
Lactose
Glycogen
and Starch
are storage carbohydrates.
Animal cells store glucose as glycogen and plant cells store glucose as starch
Cellulose and Chitin
are important structural carbohydrates.
Plant cells walls are made of cellulose. Chitin is found in the exoskeletons of arthropods.
Glucose
Glycogen

4. The Nature of Carbohydrates
Carbohydrates are compounds of great importance in both the biological and commercial world.
They are used as a source of energy in all organisms and as structural materials in membranes, cell walls and the exoskeletons of many arthropods.
All carbohydrates contain the elements carbon (C), hydrogen (H) and oxygen (O) with the hydrogen and oxygen being present in a 2 : 1 ratio.
The general formula of a carbohydrate is:
Cx(H2O)y
EXAMPLES
The formula for glucose is C6H12O6
The formula for sucrose is C12H22O11

5. Test for Reducing Sugar
All the monosaccharides (e.g. glucose) and many of the disaccharides are classed as reducing sugars.
Benedict’s test is used to determine the reducing properties of the different sugars.
Benedict’s solution is a turquoise/blue solution.

6. Test for Reducing Sugar
A solution containing equal quantities of food solution and Benedict’s solution are placed in a boiling tube and heated in a water bath for several minutes.
A change of colour through green, then yellow to ‘brick red’ indicates the presence of a reducing sugar such as glucose.
The ‘brick red’ colour is the definitive result.

7. Test for Reducing Sugar
When a Benedict's test is performed on pure solutions of glucose and sucrose (table sugar), the following results are obtained...
Sucrose
Result
Glucose
Sucrose is a
non-reducing sugar
Glucose is a
reducing sugar

9. Test for Starch
When iodine in potassium iodide solution is added to starch, the iodine molecules pack inside the starch molecules to give a blue-black colour.
When iodine reacts with the starch in this piece of potato, the blue-black colour develops.

10. The Proteins
Proteins are polymers of amino acids such as alanine and glycine. The bonds can be broken by enzymes which release the simple amino acids or peptides (consist of two or more amino acids).

11. Protein Structure
Protein molecules are made up many different amino acid monomers linked together. Amino acids join together by a condensation reaction (produces water) to form a dipeptide.
Amino acid 1
Amino acid 2
Dipeptide +
Water
Then, by successive condensation reactions, the chain of amino acids grows into a tripeptide, then a polypeptide and ultimately a protein.
Polypeptide

12. Basic Amino Acid Structure
All amino acids have a common structure, and the key to the condensation reaction itself, is the amino and carboxylic acid groups.
Basic structure of an amino acid
Variable group
amino group
carboxylic acid group

13. Protein Structure - The Peptide Bond
Two amino acids can join together by a condensation reaction...
Two
Amino
Acids
CONDENSATION -H2O
Peptide bond

14. Genes and Protein Synthesis
The specific protein made, and its function, depend on:
the types of amino acid it contains, and
the sequence in which the amino acids occur along the molecule
Polypeptides 1 and 2 have the same amino acids in the chain, but they are in a different order, and so the proteins they eventually become part of will be different.
The small difference could be all that is different between pig and human insulin.
Polypeptide 2
Polypeptide 1
Ultimately, the sequence of amino acids in a specific protein is coded for by the sequence of bases (triplet code) in the DNA, which makes up the gene.

15. The formula for insulin is:
The Nature of Proteins
Proteins are compounds of great importance in both the biological and commercial world.
This large group of molecules are found as structural materials in cellular membranes, enzymes, antibodies, some hormones (e.g. insulin), fibrin (blood clotting) actin & myosin (muscle fibres).
All proteins contain the elements carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) most have traces of sulphur.
The formula for insulin is:
C256H381N65O79S6
Insulin

16. Test for Protein (Biuret test)
A purple/violet colour indicates the presence of a protein
protein
A solution of the material to be tested is placed in a test tube.
A little sodium hydroxide solution is added to clear the solution.
A small amount of weak copper sulphate solution is added down the side of the test tube.

17. The Lipids (Fats and Oils)
Fats and oils (lipids) are made from fatty acids and glycerol. Lipids are a rich source of energy for respiration, and are also used in connective tissue such as fat cells for insulation purposes.

18. The Lipids (Fats and Oils)
Glycerol
Three
fatty acid
molecules
-3H2O Condensation Reaction
Triglyceride
Ester bond
One molecule of glycerol and three fatty acid molecules make one molecule of fat (triglyceride) and three molecules of water.

19. Saturated & Unsaturated
This is a saturated fatty acid molecule - it is easier to write its formula as...
General formula for a
saturated fatty acid.
Double bond
Unsaturated fatty acid:
less saturated with
hydrogen atoms (more double bonds).

20. Test for Lipid - Emulsion Test
The material to be tested is placed in a test tube.
Approximately 2cm3 of ethanol is added and the tube is shaken.
The ethanol layer is poured off into a second test tube.
Approximately 2cm3 of water is added to the ethanol.
A milky emulsion confirms the presence of a fat or oil

21. Test for Lipid - Paper Test
This is a simple test used to detect fats and oils in food. Paper stays translucent when fats or oils are absorbed - even after drying.

22. Copyright © 2006 SSER Ltd. and its licensors. All rights reserved
Copyright © 2006 SSER Ltd. and its licensors. All rights reserved. All graphics are for viewing purposes only.