Biological Molecules

1. Biological Molecules

2. Food Tests • Benedicts Test-(Reducing Sugars) • Biuret Test-(Protein) • Iodine test-(Starch) • Emulsion test(Lipids) • Non-reducing sugars test

3. 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

4. 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

5. 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

6. 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.

7. 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

8. Monomer – building blocks of biological molecules • Polymer - a chemical compound consisting of repeating structural units (monomers) • Macromolecules – another name for a polymer

9. Carbohydrates • Made of C, H and O • Three types: • Monosaccharide • Disaccharide • Polysaccharide

10. Monosaccharides • Simplest carbohydrates • Glucose, fructose, galactose

11. Glucose • Two types:

12. Glycosidic Bonds

14. Condensation

15. Hydrolysis

17. Polysaccharides

18. Starch • Storage polysaccharide in plants • Made of two substances: • Amylose • Amylopectin

19. Amylose • α glucose molecules with 1-4 links • Coils into a spiral • Held together with hydrogen bonds

20. Amylopectin • α glucose with 1-4 links and 1-6 links • Causes branching chains

22. 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

23. 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

24. Proteins

25. Primary Structure • Monomer – amino acid • Amino acids joined by peptide bonds • Condensation reaction

26. Secondary Structure • Two possible structures: • α helix • β pleated sheet • Held together by hydrogen bonds

27. Tertiary Structure • Secondary structure folded and bonds form between the R chains • Different types of bonds: • Hydrogen bonds • Ionic bonds • Disulphide bridges • Hydrophobic interactions

28. Tertiary Structure Bonds

29. Quaternary structure • More than one tertiary structure joined together.

30. 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

31. 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)

32. Haemoglobin Haem

33. 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.

35. Collagen • Fibrous protein • Three strands plaited together • Very strong

37. Lipids • Made of two parts: • Glycerol • Three fatty acid chains • High energy due to many hydrogen atoms

38. 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.

39. 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

40. 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.

41. Water

42. 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.

43. at approximately 4 °C pure water reaches its maximum density  • Protects aquatic environments

44. 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. 

45. Essay • Describe the characteristics of water. • How do these characteristics enable living organisms to survive.