Biology AS

• Water is the medium in which all metabolic reactions take place in cells and in which all substances are transported around the body
• Water


  Composed of atoms of hydrogen and oxygen
• Covalent bonding

  One atom of oxygen combines with two atoms of hydrogen by sharing electrons

  
• Dipole


  Separation of charge due to the electrons in the covalent bonds being unevenly shared
• Polar molecule


  A molecule that has one end that is negatively charged and one end that is positively charged
• Hydrogen bonds


  Weak bonds that form between the positive and negatively charged regions of nearby water molecules as a result of the polar nature of water

  
• Water


  • Cohesive
  • Good solvent
• Carbohydrates are one of the main carbon-based compounds in living organisms
• Carbon atoms

  • Key to the structure of organic compounds because they can form covalent bonds, making the compounds very stable
  • Can form covalent bonds with oxygen, nitrogen and sulfur
  • Can bond to form straight chains, branched chains, or rings

  
• Monomers


  Small, single subunits that can bond with many repeating subunits to form large molecules, or polymers
• Polymerisation


  The process of monomers bonding to form polymers
• Types of carbohydrates


  • Monosaccharides
  • Disaccharides
  • Polysaccharides

  
• Monosaccharides


  The monomers of carbohydrates; they can join together to make carbohydrate polymers

  
• Monosaccharides


  • Triose (3C) e.g. glyceraldehyde
  • Pentose (5C) e.g. ribose
  • Hexose (6C) e.g. glucose

  
• Disaccharides


  Two monosaccharides joined together via condensation reactions

  
• Glycosidic bond


  The new chemical bond that forms between two monosaccharides

  
• Disaccharides


  • Maltose
  • Sucrose
  • Lactose

  
• Polysaccharides


  Carbohydrate polymers; repeated chains of many monosaccharides joined by glycosidic bonds in a condensation reaction

  
• Starch


  The storage polysaccharide of plants
• Amylose


  An unbranched, helix-shaped polysaccharide in starch with 1,4 glycosidic bonds

  
• Amylopectin


  A branched polysaccharide in starch with 1,4 and 1,6 glycosidic bonds

  
• Alpha (α) glucose


  Has the hydrogen above carbon 1 and the OH group below

  
• Beta (β) glucose


  Has the hydrogen below carbon 1 and the OH group above

  
• Glycosidic bond


  A strong covalent bond that forms between two hydroxyl (OH) groups on different monosaccharides
• Glycosidic bonds can link monosaccharides together to form polysaccharides such as amylopectin

  
• Polysaccharides


  Large molecules made up of many monosaccharides joined together
• Polysaccharides


  • May be branched or unbranched
  • May be straight or coiled
• Being branched


  Increases the rate at which a polysaccharide can be broken down
• Polysaccharides


  • Cellulose
• Being coiled


  Makes a molecule more compact and suitable for storage
• Polysaccharides


  • Amylose in starch

  
• Amylose


  Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules

  
• Amylopectin


  A branched molecule containing 1,4 glycosidic bonds between α-glucose molecules and 1,6 glycosidic bonds

  
• The branches in amylopectin


  Result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage

  
• Glycogen


  Highly branched and not coiled, contains both 1,4 and 1,6 glycosidic bonds

  
• The branching in glycogen


  Provides more terminal glucose molecules which can either be added to or removed by hydrolysis, allowing quick storage or release of glucose

  
• Liver and muscle cells have a high concentration of glycogen, present as visible granules, enabling a high cellular respiration rate
• Starch


  The storage polysaccharide of plants, stored as granules in plastids
• Types of Carbohydrate


  • Starch
  • Glycogen

  
• All organisms need to exchange gases with their environment, e.g. Aerobic respiration requires oxygen and produces carbon dioxide as a waste product, Photosynthesis requires carbon dioxide and produces oxygen as a waste product