biology unit 1

• 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 between the hydroxyl group and the water molecule
• Alpha glucose is used in respiration in plants and animals, this is because the enzymes involved in these processes have active sites complementary to the shape of alpha glucose and not beta glucose
• Beta glucose molecules join to form a polymer called cellulose; this is an essential polysaccharide used in the structure of plants
• 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, e.g. between carbon 1 of one glucose and carbon 4 of another

  
• Common disaccharides


  • Maltose
  • Lactose
  • Sucrose

  
• Lactose


  A disaccharide made from two monosaccharides: galactose and glucose

  
• Lactose is usually found in milk and dairy products
• Lactase


  An enzyme produced by the body that breaks down lactose into monomers
• People with lactose intolerance are unable to produce enough lactase to break down lactose
• In people with lactose intolerance, the undigested lactose stays in the digestive system and is fermented by bacteria, producing gas and symptoms like stomach cramps, bloating and diarrhoea
• There is no cure for lactose intolerance, it is normally controlled by dietary changes and avoiding high lactose foods
• Medication in the form of drops or tablets can be taken to help digest lactose, but must be taken with all meals
• 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

  
• Amylose is shaped like a coiled spring because of the position of the 1,4-glycosidic bonds

  
• Amylopectin


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

  
• Plants store excess glucose in the form of starch, which is a mixture of the polysaccharides amylose and amylopectin
• Glycogen


  A polysaccharide of alpha-glucose that animals use to store excess energy, mainly in the liver and skeletal muscles
• Glycogen has a similar structure to amylopectin but with many more side branches, allowing it to be broken down quickly to release glucose
• Glycogenolysis


  When blood glucose levels drop, glycogen phosphorylase releases glucose-1-phosphate by untangling the alpha 1,4-glycosidic linkages, and glycogen debranching enzyme detaches the branch points to release free glucose
• Glucose-1-phosphate is converted to glucose-6-phosphate, which can enter the glycolytic pathway to be oxidised for energy
• Proteins are large polymers made of long chains of amino acids, and are involved with nearly all cellular functions
• Cells in the body are 50% protein
• Functions of proteins


  • Structural (e.g. collagen, muscle, cell membranes)
  • Enzymes
  • Antibodies
  • Receptors
  • Ion channels
  • Haemoglobin
  • Hormones
  • Buffers
• Amino acids


  The monomers that make up proteins, consisting of a central carbon atom linked to an amine group, a carboxyl group, a hydrogen atom, and a variable side chain (R group)

  
• Humans use 21 different types of amino acids to function and grow
• 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 like disulfide bridges, ionic bonds, and hydrophobic/hydrophilic interactions

  
• Quaternary structure


  Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein
• Proteins can have prosthetic groups, which are non-protein parts essential for the protein's function, like the haem group in haemoglobin
• Globular proteins


  Soluble, roughly spherical proteins like haemoglobin