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.