Human biology

• Monosaccharides


  The simplest carbohydrates, monomers that can bond together to form disaccharides and polysaccharides

  
• Properties of monosaccharides


  • Soluble in water
  • Form crystals
  • Taste sweet
• Glucose


  The main source of energy for many organisms, a hexose monosaccharide with the formula C6H12O6

  
• Alpha (α) glucose


  • OH group at carbon 1 is below the plane of the ring
  • Used in respiration in plants and animals

  
• Beta (β) glucose


  • OH group on carbon 1 is above the plane of the ring
  • Joins to form the polymer cellulose, an essential structural component in plants

  
• Disaccharide


  Two monosaccharides bonded together by a glycosidic bond, formed through a condensation reaction

  
• OH group on carbon 1

  Is above the plane of the ring
• Glucose molecules


  Are polar and soluble in water because hydrogen bonds can form in between the hydroxyl group and the water molecule

  
• Alpha glucose is used in respiration in plants and animals
• Alpha glucose and beta glucose have different functions as well as structures

  
• Beta glucose molecules join to form a polymer called cellulose

  
• Disaccharide


  Formed when two monosaccharides bond together during a condensation reaction, where water is eliminated

  
• Glycosidic bond


  A new covalent bond formed when two monosaccharides bond together

  
• Common disaccharides


  • Maltose
  • Lactose
  • Sucrose

  
• Lactose


  A disaccharide made from two monosaccharides: galactose and glucose

  
• Lactase


  An enzyme that breaks down lactose into monomers so they can be absorbed into the bloodstream
• People with lactose intolerance are unable to produce enough lactase to break down lactose
• Lactose stays in the digestive system and is fermented by bacteria in people with lactose intolerance
• Lactose intolerance causes symptoms such as stomach cramps, bloating and diarrhoea
• Polysaccharide


  Polymers of monosaccharides, consisting of thousands of monosaccharide monomers bonded together

  
• Amylose


  A polysaccharide composed of unbranched chains of glucose monomers connected by alpha 1,4 glycosidic linkages

  
• Amylopectin


  A polysaccharide consisting of 1,4 glycosidic bonds and also 1,6 glycosidic bonds, forming a branched structure

  
• Glycogen


  A polysaccharide of alpha-glucose, similar in structure to amylopectin but with more side branches

  
• Glycogenolysis


  Glycogen breakdown, coordinated by glycogen phosphorylase and glycogen debranching enzyme
• Glucose-1-phosphate from glycogenolysis is converted into glucose-6-phosphate, which can enter the glycolytic pathway

  
• Amino acids


  The monomers of proteins, consisting of a central carbon atom linked to an amine group, a carboxyl group, a hydrogen atom and variable side chains
• Elements in amino acids

  • Carbon
  • Oxygen
  • Hydrogen
  • Nitrogen
• Proteins


  • Large polymers made of long chains of amino acids, involved with nearly all cellular functions
  • Structural proteins like collagen provide mechanical support and tensile strength
  • Globular proteins like enzymes and haemoglobin play a vital role in biological processes
• Primary structure


  The specific sequence of amino acids that forms a polypeptide chain

  
• Secondary structure


  The polypeptide chain forms spirals (alpha helices) and sheets (beta sheets), held together by hydrogen bonds

  
• Tertiary structure


  The alpha helices and/or beta sheets are folded to form a compact globular molecule, held together by intramolecular bonds

  
• Quaternary structure


  Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein
• Peptide bond


  A covalent bond formed between the carboxyl group of one amino acid and the amino group of another

  
• Alpha helix


  A right-handed coiled formation in the secondary structure of a protein, held together by hydrogen bonds

  
• Beta pleated sheet


  The folding of the primary structure into parallel polypeptide chains, held together by hydrogen bonds

  
• Disulphide bridges


  Covalent bonds formed between two sulphur atoms in the R groups of cysteine and methionine
• Ionic bonds


  Bonds formed between oppositely charged R groups, such as aspartic acid and lysine
• Hydrophobic and hydrophilic interactions

  Amino acids with hydrophobic R groups are found in the centre of the protein, while those with hydrophilic R groups are on the outside

  
• Prosthetic group


  The non-protein part of a protein structure that is essential for its functioning, e.g. haem in haemoglobin
• Glycoproteins


  Carbohydrates covalently attached to amino acid R groups, with functions such as structure, reproduction, immune response, hormone and cell protection