B1.2 Proteins

• Amino acids


  Monomers used to make proteins
• Proteins


  • Complex macromolecules
  • Composed of one or more chains of amino acids
  • Play an important role in many biological processes
• Amino acid structure

  • Amine Group (NH2)
  • Carboxyl group (COOH)
  • Alpha Carbon (C)
  • R Group
• Condensation reactions forming dipeptides


  1. Amino acids join together

  2. Peptide bond formation

  3. Water molecule released
• Peptide bond


  Formed when the carboxyl group of one amino acid reacts with the amino group of another amino acid
• Dipeptide


  Molecule consisting of two amino acids joined by a single peptide bond
• Oligopeptide


  Molecule composed of a few (typically 2-20) amino acids
• Polypeptide


  Longer chain of amino acids, typically longer than 20 residues, but not yet a fully functional protein
• 1. terminal


  Free amino group not involved in the peptide bond
• 1. terminal


  Unbound carboxyl group
• Polypeptide formation


  1. Occurs in the ribosome

  2. Can be found in the cytoplasm or on the rough endoplasmic reticulum
• Each time an amino acid joins the growing polypeptide strand, a new peptide bond is formed and a water molecule is released
• Sources of amino acids


  • Plant cells
  • Animal cells
• Essential amino acids


  Amino acids that your body cannot produce and must obtain from food
• Non-essential amino acids


  Amino acids that can be produced by the body from other amino acids or by the breakdown of proteins
• Non-essential amino acids are important to have but not required
• Vegans need to consume a variety of plant-based foods to ensure they get all essential amino acids
• Most plants are incomplete proteins, lacking one or more essential amino acids
• Monosaccharides


  Simple sugars classified by the number of carbon atoms they contain
• Types of monosaccharides

  • Pentoses
  • Hexoses
• Pentoses


  • Ribose
• Hexoses


  • Glucose
  • Galactose
  • Fructose
• Fructose


  A type of sugar naturally found in fruits
• Galactose


  A type of sugar commonly found in dairy products
• Glucose


  The most common monosaccharide found in nature and an important source of energy for many organisms
• Properties of glucose

  • Has two isomers
  • Is soluble
  • Is stable
  • Can be oxidised
• Formation of isomers


  Orientation of hydroxyl group
• Alpha-glucose


  Isomer of glucose with –OH group oriented downwards
• Beta-glucose


  Isomer of glucose with –OH group oriented upwards
• Difference in orientation between alpha-glucose and beta-glucose


  Plays a critical role in the formation of polysaccharides
• Polysaccharides formed from glucose


  • Starch
  • Glycogen
  • Cellulose
• Starch


  The primary storage form of glucose in plants
• Amylose


  A linear polysaccharide made up of glucose monomers linked through alpha-1,4-glycosidic bonds
• Amylopectin


  A highly branched polysaccharide made up of glucose units linked through alpha-1,4-glycosidic bonds and occasional alpha-1,6-glycosidic bonds
• Starch structure


  • Coiled structure
  • Compact due to polymerisation
  • Relatively insoluble
• Glycogen


  The primary storage form of glucose in animals
• Glycogen structure


  • Branched polymer
  • Highly compact
  • Coiled structure
• Cellulose


  A complex polysaccharide composed of beta-glucose molecules, essential for plant cell walls
• Cellulose structure


  • Forms straight chains
  • Cross-linked microfibrils
  • Provides tensile strength
• Glycoproteins


  Proteins with one or more carbohydrates attached, playing roles in cell signalling and communication