Biological molecules

• Biological molecules


  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic Acids
• Carbohydrates


  Molecules consisting only of carbon, hydrogen and oxygen. They are long chains of sugar units called saccharides.
• Types of saccharides


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Monosaccharide


  Single sugar monomer
• Disaccharide


  Two monosaccharides
• Polysaccharide


  Many monosaccharides
• Glycosidic bonds


  Bonds formed in condensation reactions that join monosaccharides to form disaccharides and polysaccharides
• Glucose


  A monosaccharide containing six carbon atoms, the main substrate for respiration
• Glucose isomers


  • Alpha glucose
  • Beta glucose
• Ribose


  A monosaccharide containing five carbon atoms, a component of RNA
• Deoxyribose


  An isomer of ribose that lacks the OH group on the second carbon of the sugar ring, a component of DNA
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen


  The main energy storage molecule in animals, formed from many molecules of alpha glucose joined by 1,4 and 1,6 glycosidic bonds, has a large number of side branches
• Starch


  The energy storage molecule in plants, a mixture of amylose (unbranched chain of glucose molecules joined by 1,4 glycosidic bonds) and amylopectin (branched molecule of glucose molecules joined by 1,4 and 1,6 glycosidic bonds)
• Cellulose


  A component of plant cell walls, composed of long, unbranched chains of beta glucose monomers joined by 1,4 glycosidic bonds, forms microfibrils that provide structural support
• Lipids


  Biological molecules only soluble in organic solvents
• Types of lipids


  • Saturated lipids
  • Unsaturated lipids
• Saturated lipids


  Lipids that only contain carbon-carbon single bonds, found in animal fats
• Unsaturated lipids


  Lipids that contain carbon-carbon double bonds, found in plants
• Intermolecular forces


  Weaker in unsaturated lipids, resulting in a lower melting point
• Triglycerides


  Lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions, used as energy reserves
• Phospholipids


  Lipids with one fatty acid substituted by a phosphate-containing group, form a bilayer in the cell membrane with hydrophilic heads and hydrophobic tails
• Amino acids


  The monomers from which proteins are made, contain an amino group, a carboxyl group, and a variable R group that determines the chemical properties
• Peptide bonds


  Bonds formed in condensation reactions that join amino acids to form dipeptides and polypeptides
• Levels of protein structure

  • Primary
  • Secondary
  • Tertiary
  • Quaternary
• Primary structure


  The linear sequence of amino acids in the polypeptide chain, held together by peptide bonds
• Secondary structure


  The folding of the polypeptide chain into alpha helices or beta pleated sheets, held together by hydrogen bonds
• Tertiary structure


  The 3D folding of the secondary structure into a complex shape, determined by hydrogen bonding, ionic bonding, and disulfide bridges
• Quaternary structure


  The 3D arrangement of more than one polypeptide
• Types of proteins


  • Fibrous
  • Globular
• Fibrous proteins


  • Long parallel polypeptides, very little tertiary/quaternary structure, occasional cross-linkages, insoluble, used for structural purposes
• Globular proteins


  • Complex tertiary/quaternary structures, form colloids in water, many uses e.g. hormones, antibodies
• Ionic bonding


  Salt bridges, form between oppositely charged groups on the R groups
• Disulphide bridges


  Covalent bonds between sulphur atoms in cysteine
• Not all proteins have all levels of structure
• Types of proteins


  • Fibrous
  • Globular
• Fibrous proteins


  • Long parallel polypeptides
  • Very little tertiary/quaternary structure - mainly secondary structure
  • Occasional cross-linkages which form microfibrils for tensile strength
  • Insoluble
  • Used for structural purposes
• Globular proteins


  • Complex tertiary/quaternary structures
  • Form colloids in water
  • Many uses e.g. hormones, antibodies
• Fibrous protein


  • Collagen
• Collagen


  • High tensile strength due to large number of hydrogen bonds in the structure
  • Molecules are made up of three distinct α-chains which form a triple gamma helix
  • Multiple of these helices link together to form fibrils and strong collagen fibres
  • Forms the structure of bones, cartilage and connective tissue
  • Main component of tendons which connect muscles to bones