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Biological Molecules


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Biological Molecules

  1. 1. BIOLOGICAL MOLECULESThe structure of carbohydrates, lipids andproteins and their roles in living organisms ALBIO9700/2006JK
  2. 2. • Molecular biology: the study of structure and functioning of biological molecules• Metabolism: the sum total of all the biochemical reactions in the body• The building blocks of life: – Hydrogen, carbon, oxygen and nitrogen – Monosaccharides, organic bases, amino acids, fatty acids and glycerol ALBIO9700/2006JK
  3. 3. • Macromolecule: ‘giant molecule’• Polymers (cellulose & rubber; polyester, PVC & nylon): macromolecules made up of many repeating subunits that are similar or identical to each other and are joined end to end (polymerisation) – Polysaccharides – Proteins (polypeptides) – Nucleic acids (polynucleotide) ALBIO9700/2006JK
  4. 4. Carbohydrates• Contains carbon, hydrogen and oxygen• General formula: Cx(H2O)y• 3 main groups: – Monosaccharides – Disaccharides – Polysaccharides ALBIO9700/2006JK
  5. 5. Monosaccharides• Sugars (saccharide ~ sweet or sugar)• General formula: (CH2O)n – Molecular and structural formula• Single sugar molecule (mono)• Types: – Trioses (3C) – Pentoses (5C) – Hexoses (6C) ALBIO9700/2006JK
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  7. 7. Ring structures• α-glucose: the form of glucose where the hydroxyl group (-OH) on carbon atom 1 is below the ring• β-glucose: the form of glucose where the hydroxyl group (-OH) on carbon atom 1 is above the ring• Isomers: 2 forms of the same chemical ALBIO9700/2006JK
  8. 8. Roles of monosaccharides in living organisms• Source of energy in respiration (glucose) – Due to large number of carbon-hydrogen bonds which can be broken to release energy• Building blocks for larger molecules – Glucose: make polysaccharides (starch, glycogen and cellulose) – Ribose (a pentose): make RNA and ATP – Deoxyribose (a pentose): used to make DNA ALBIO9700/2006JK
  9. 9. Disaccharides and glycosidic bond• Sugars• Condensation: how 2 monosaccharides join together to form disaccharides• Bridge is called glycosidic bonds• Hydrolisis: addition of water, reverse of condensation (during digestion of disaccharides and polysaccharides)• Both controlled by enzymes ALBIO9700/2006JK
  10. 10. Condensation Hydrolisis ALBIO9700/2006JK
  11. 11. Polysaccharides• Not sugars• Polymers with monosaccharide subunits joined by condensation with glycosidic bonds• Several thousand monosaccharide units join to form a macromolecule• Most important polysaccharides: – Starch – Glycogen Polymers of glucose – Cellulose ALBIO9700/2006JK
  12. 12. • Glucose is converted to storage polysaccharides which are convenient, compact, insoluble molecules• In the form of starch in plants and glycogen in animals ALBIO9700/2006JK
  13. 13. Starch, Glycogen and Cellulose• Starch is a mixture of amylose and amylopectin• Amylose: many 1,4-linked α-glucose molecules form a spring like compact structure• Amylopectin: 1,4-linked α-glucose but shorter chains with branching out due to 1,6 linkages• Starch grains commonly found in chloroplast and in storage organs such as the potato tuber and the seeds of cereals and legumes ALBIO9700/2006JK
  14. 14. Amylose ALBIO9700/2006JK
  15. 15. Amylopectin ALBIO9700/2006JK
  16. 16. Glycogen• No starch in animal cells• Glycogen: amlyopectin-like molecules used as the storage carbohydrates• Glycogen molecules tend to be more branched than amylopectin• They clump together to form granules – liver cells and muscle cells ALBIO9700/2006JK
  17. 17. Glycogen ALBIO9700/2006JK
  18. 18. Cellulose• Most abundant organic molecule (20-40% of the average cell wall)• Structural role (mechanically strong)• Cellulose is a polymer of β-glucose• Hydrogen bonds Microfibrils Fibrils ALBIO9700/2006JK
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  21. 21. • Very high tensile strength (almost equal to steel)• Provide support by making tissues rigid• Responsible for cell expansion during growth• Freely permeable, allowing water and solutes to reach plasma membrane ALBIO9700/2006JK
  22. 22. Lipids• Diverse group of chemicals• Triglycerides – most common type• Commonly fats and oils ALBIO9700/2006JK
  23. 23. Triglycerides• 3 fatty acid + 1 glycerol (condensation)• -COOH group attached to a hydrocarbon tail• Glycerol – alcohol• Glyceride – fatty acid + glycerol (triglyceride) ALBIO9700/2006JK
  24. 24. Condensation ALBIO9700/2006JK
  25. 25. • Insoluble in water but soluble in organic solvent (ether, chloroform and ethanol)• Due to hydrocarbon tail of fatty acids• Non-polar and hydrophobic ALBIO9700/2006JK
  26. 26. Saturated and unsaturated fatty acids ALBIO9700/2006JK
  27. 27. • Unsaturated – do not contain the maximum possible amount of hydrogen• Fatty acids and lipids melt easier due to double bonds• Polyunsaturated - >1 double bond• Monounsaturated - 1 double bond• Animal lipids – saturated (fats)• Plant lipids – unsaturated (oils) ALBIO9700/2006JK
  28. 28. Roles of triglycerides• Energy reserves (richer in carbon-hydrogen bonds than carbohydrates/higher calorific value)• Insulator against loss of heat• Buoyancy• Metabolic source of water ALBIO9700/2006JK
  29. 29. Desert kangaroo rat ALBIO9700/2006JK
  30. 30. Phospholipids• One end is soluble in water• One of the 3 fatty acids is replaced by a phosphate group which is polar• Phosphate group is hydrophilic• Membrane structure ALBIO9700/2006JK
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  32. 32. Proteins• >50% of the dry mass of most cells is protein• Functions: – Essential components of cell membranes – The oxygen-carrying pigment haemoglobin – Antibodies which attack and destroy invading microorganisms – All enzymes – Hair and the surface layers of skin contain the protein keratin – Collagen adds strength to the many tissues, such as bone and the walls of arteries ALBIO9700/2006JK
  33. 33. Amino acids• Basic component of protein• Central carbon atom, amine group (-NH2), carboxylic acid group (-COOH)• R group• 20 different amino acids ALBIO9700/2006JK
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  35. 35. The eight amino acids in the orange area are nonpolar and hydrophobic.The other amino acids are polar and hydrophilic ("water loving").The two amino acids in the magenta box are acidic ("carboxy" group in the side chain).The three amino acids in the light blue box are basic ("amine" group in the side chain). ALBIO9700/2006JK
  36. 36. The peptide bond ALBIO9700/2006JK
  37. 37. • 2 linked amino acids – dipeptide• Many amino acids – polypeptide (macromolecule/polymer)• Ribosomes – sites where amino acids are linked together to form polypeptides• Complete protein may contain one or more polypeptide chain which interact with each other ALBIO9700/2006JK
  38. 38. Primary structure• The types of amino acids contained in the polypeptide chain and the sequence in which they are joined• Enormous number of different possible primary structures ALBIO9700/2006JK
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  40. 40. Secondary structure• Polypeptide chain coils into an α-helix due to attraction between the oxygen of the -CO group of one amino acid and the hydrogen of the -NH group of the amino acid four places ahead of it• This is result of the polar characteristics of the – CO and –NH groups• Sometimes a much looser, straighter shape is formed, called a β-pleated sheet ALBIO9700/2006JK
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  42. 42. Tertiary structure• The secondary structure coils and folds to form 3 dimensional shapes• Four types of bonds involved: – Hydrogen bonds (between R groups) – Disulphide bonds (between 2 cysteine molecules) – Ionic bonds (between R groups containing amine and carboxyl groups) – Hydrophobic interactions (between R groups which are non-polar or hydrophobic) ALBIO9700/2006JK
  43. 43. Tertiary structure ALBIO9700/2006JK
  44. 44. Quaternary structure ALBIO9700/2006JK
  45. 45. Globular and fibrous proteins• Globular protein: protein whose molecules curl up into a ‘ball’ shape (e.g. myoglobin & haemoglobin)• Usually curl up so that their non-polar, hydrophobic R groups point into the centre of the molecule, away from their watery surroundings. The polar, hydrophilic, R group remain on the outside of the molecule• Fibrous protein: long strands, insoluble and have structural roles (e.g. keratin & collagen) ALBIO9700/2006JK
  46. 46. Globular and fibrous proteins e.g. enzymes e.g. keratin and collagen ALBIO9700/2006JK
  47. 47. • Molecular structure and function of haemoglobin as an example of a globular protein• Molecular structure and function of collagen as an example of a fibrous protein ALBIO9700/2006JK
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