AS biology new spec biological molecules

Biological molecules

·         Monomers can be linked together to form polymers in polymerisation reactions. E.g. nucleotides to polynucleotides, monosaccharides to polysaccharides and amino acids to polypeptides.

·         Polymerisation is a condensation reaction where water is released. The polymers can be hydrolysed into the monomers using water.

·      1 mole is 6.022 10²³ particles of the substance, this is Avogadro’s constant. A molar solution is 1 mole of the substance in 1 litre of solution. 1 mole is the molecular mass in grams.

·         Carbon readily makes bonds with other carbon so long chains easily form. Carbon containing molecules are organic molecules.

·         Monosaccharides are sweet tasting and soluble, they have the general formula (CH₂O)n. n= 3-7. Examples are glucose, galactose and fructose which are hexose sugars. 5= ribose and deoxyribose.  Glucose has 2 isomers;

·         Reducing sugars are maltose, galactose, fructose, and glucose. They donate electrons. The test for them is the benedict’s test. Benedict’s reagent is an alkaline solution of copper 2 sulphate. When heated the copper 2 gets reduced to copper 1 forming a red copper oxide precipitate.

·         Add 2cm³ of the food sample either in liquid form or ground up with water. Add 2cm³ of benedict’s solution and heat the mixture gently in a boiling water bath fir 5 minutes. If it turns orange brown, a reducing sugar is present. Semi quantitative benedict’s test can be conducted using colour to estimate the amount of reducing sugars.

·         2 monosaccharides join in a condensation reaction to form a disaccharide and water. The bond between the 2 sugars is a glycosidic bond. +  = maltose,   + fructose = sucrose, and   + galactose = lactose.

·         Sucrose and lactose are non-reducing sugars. To test for a non-reducing sugar, you must hydrolyse it. Put 2cm³ of the liquid form food with 2cm³ of benedict’s solution and heat for 5 minutes, it will stay blue. Put another 2cm³ in another test tube with 2cm³ of HCl and put in a boiling water bath for 5 minutes. The acid will hydrolyse the disaccharide. Slowly add sodium hydrogen carbonate to neutralise the acid as benedict’s will not work in acidic conditions. Check the pH is alkaline then add 2cm³ of benedict’s and heat in a water bath or 5 minutes, it will go orange/brown.

·         Polysaccharides are lots of monosaccharides joined together with glycosidic bonds.

·      Starch is a polysaccharide found in plants, it is formed of 200-100,000  monomers. The test for starch is the iodine test. Add 2cm³ of the sample in a test tube add 2 drops of the iodine solution and shake. If starch is present it will go black/blue.

·         There are 2 types of starch; amylose and amylopectin. Amylose is non-branched and is made of around 300 ’s. it is coiled and…