Biological Molecules
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
Carbohydrates Made of C, H and O Three types: Monosaccharide Disaccharide Polysaccharide
Monosaccharides Simplest carbohydrates Glucose, fructose, galactose
Glucose Two types:
Glycosidic Bonds
Condensation
Hydrolysis
Polysaccharides
Starch Storage polysaccharide in plants Made of two substances: Amylose Amylopectin
Amylose α glucose molecules with 1-4 links Coils into a spiral Held together with hydrogen bonds
Amylopectin α glucose with 1-4 links and 1-6 links Causes branching chains
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
Proteins
Primary Structure Monomer – amino acid Amino acids joined by peptide bonds Condensation reaction
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
Tertiary Structure Bonds
Quaternary structure More than one tertiary structure joined together.
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
Haemoglobin The “R” groups on amino acids are sometimes referred to as side chains. Some amino acids have hydrophobic side chains (repelling water), and some have hydrophilic side chains (attracting water)
Haemoglobin Haem
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.
Collagen Fibrous protein Three strands plaited together Very strong
Lipids Made of two parts: High energy due to many hydrogen atoms Glycerol Three fatty acid chains High energy due to many hydrogen atoms
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.
Water
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.
at approximately 4 °C pure water reaches its maximum density Protects aquatic environments
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.
Essay Describe the characteristics of water. How do these characteristics enable living organisms to survive.