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Food Tests
Benedicts Test-(Reducing Sugars) Biuret Test-(Protein) Iodine test-(Starch) Emulsion test(Lipids) Non-reducing sugars test
Benedict’s Test
Add 2cm3 of the sugar solution to a test-tube, and then an equal volume of Benedict’s solution. Bring to the boil in a water-bath.
Result: Turns green, then yellowish, then may form brick-red precipitate.
Basis: The Cu++ ions in the copper sulphate in Benedict’s are reduced by the sugar to insoluble Cu+ which precipitates out
Biuret Test
Add equal quantities of test solution and potassium hydroxide and mix. Add two drops of copper sulphate, and mix
Result: Mauve or purple colour slowly develops
Basis: Nitrogen atoms in the peptide chain form a purple complex with the Cu++ ions
Iodine Test
Add a few drops of potassium iodide solution to the test solution and mix
A blue/black colouration develops
A polyiodide complex forms with the starch molecules
Emulsion test
Add equal quantities of the suspected lipid and absolute ethanol in a test tube. Shake vigorously to dissolve. Add an equal quantity of cold water.
Result: A cloudy white suspension
Lipids are insoluble in water, so adding water to a solution of the lipid in alcohol results in an emulsion of tiny lipid droplets in the water which look white as they reflect light.
Non Reducing Sugars
Add 2cm3 sucrose solution to a test-tube. Add 1cm3 dilute sulphuric acid. Boil for one minute, and then carefully neutralize with sodium bicarbonate. (take care, as it will effervesce). Carry out Benedict’s test
The acid hydrolyses the sucrose (breaks the glycosidic bond) making two monomer molecules (glucose and fructose), which are reducing sugars
Monomer – building blocks of biological molecules
Polymer - a chemical compound consisting of repeating structural units (monomers)
Macromolecules – another name for a polymer
Glycogen
Storage in animals and fungi
α glucose molecules with 1-4 links and 1-6 links
Forms a branching chain
Held together with hydrogen bonds
Cellulose β glucose with 1-4 links Adjacent molecules in the chain are flipped 180
degrees Hydrogen bonds form between different chains
forming a bundle of microfibrils
Secondary Structure
Two possible structures: α helix β pleated sheet
Held together by hydrogen bonds
Tertiary Structure
Secondary structure folded and bonds form between the R chains
Different types of bonds: Hydrogen bonds Ionic bonds Disulphide bridges Hydrophobic interactions
Haemoglobin
Globular protein 4 tertiary structures joined together Two alpha chains (141 aa), and two beta
chains (146 aa) Each chain has a haem (containing an iron
atom) group attached This is used to bond the oxygen
Some amino acids have hydrophobic side chains (repelling water), and some have hydrophilic side chains (attracting water)
The “R” groups on amino acids are sometimes referred to as side chains.
Haemoglobin
On the four polypeptide chains that make up the haemoglobin, amino acids with hydrophobic side chains point inwards, helping to hold the molecule together
Amino acids with hydrophilic side chains point outwards, making the haemoglobin molecule soluble.
Haemoglobin
Saturated and unsaturated
Saturated fats have no carbon to carbon double bonds, they are solid at room temperature
Unsaturated fats have one or more carbon to carbon double bonds. These form kinks in the fatty acid chains and so they are liquids at room temperature.
Phospholipids
Polar region is the phosphate group and it allow it to be soluble in water – hydrophillic
The non-polar fatty acid chains are insoluble in water - hydrophobic
Structure and function
Their insulating properties keep mammals warm.
They contain twice the stored energy of carbohydrates, gram for gram.
They are used in the formation of cell-surface membranes.
In aquatic mammals, the fat is less dense than water, so it acts as a buoyancy aid.
Properties of water
High specific heat capacity High heat of vaporisation
both of which are a result of the extensive hydrogen bonding between its molecules.
These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.
Universal solvent Water molecules stay close to each other
(cohesion), due to the collective action of hydrogen bonds between water molecules. Leading to high surface tension.
Water also has high adhesion properties because of its polar nature.