Unit 1 Biology - 1

• Water


  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
  • One atom of oxygen combines with two atoms of hydrogen by sharing electrons; this is covalent bonding
  • The sharing of the electrons is uneven between the oxygen and hydrogen atoms
  • The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms (δ+)
  • This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole
  • When a molecule has one end that is negatively charged and one end that is positively charged it is said to be a polar molecule
  • Water is a polar molecule
• 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
• Hydrogen bonds


  • They are constantly breaking and reforming; this means that water molecules flow past each other in a liquid state
  • They contribute to the many properties water molecules have that make them so important to living organisms
• Cohesion


  The attraction of water molecules to each other
• Adhesion


  The ability of water to form hydrogen bonds with other molecules
• Solvent


  The ability of water to dissolve many ions and covalently bonded polar substances
• Water molecules surround charged particles due to forces of attraction between polar water and the charged particles. The surrounded particles are said to have dissolved
• Carbohydrates


  One of the main carbon-based compounds in living organisms
• Carbon atoms


  • Key to the structure of organic compounds because
  • Each carbon atom can form covalent bonds; this makes the compounds very stable
  • Covalent bonds are so strong they require a large input of energy to break them
  • Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur
  • Carbon atoms 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 carbohydrate; they can join together to make carbohydrate polymers
• Monosaccharides


  • Triose (3C) eg. glyceraldehyde
  • Pentose (5C) eg. ribose
  • Hexose (6C) eg. glucose
• Disaccharides


  Two monosaccharides joined together via condensation reactions
• Glycosidic bond


  The new chemical bond that forms between two monosaccharides when they join to form a disaccharide
• 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
• Starch


  • Stored as granules inside plant cells
  • Plants make glucose during photosynthesis and the molecules of glucose are joined to make the polysaccharide starch
  • Starch is constructed from two different polysaccharides: Amylose and amylopectin
• Glycogen


  The storage polysaccharide of animals and fungi
• Glycogen


  • Highly branched and not coiled
  • Compact which means that much can be stored in a small space
  • Liver and muscles cells have a high concentration of glycogen, present as visible granules; this enables a high cellular respiration rate
• Cellulose is an important polysaccharide but you do not need to know about it in this topic
• Make sure you are clear on the differences between starch and glycogen
• Glucose


  A well known example of a monosaccharide
• Glucose


  • A hexose sugar
  • The six carbons that make up glucose form a ring structure
  • Comes in two forms; alpha (α) and beta (β)
  • The forms of glucose are almost identical; they differ only in the location of the H and OH groups attached to carbon 1
• Alpha glucose


  Has the H above carbon 1 and the OH group below
• Beta glucose


  Has the H below carbon 1 and the OH group above
• Monosaccharides


  The main function is to store energy within their bonds
• The structure of glucose is related to its function as the main energy store for animals and plants
• Glycosidic bond


  A strong covalent bond that forms when two hydroxyl (OH) groups on different monosaccharides interact
• Glycosidic bonds


  • The name depends on the location of the OH groups on the monosaccharides concerned
  • Every glycosidic bond results in one water molecule being released, thus glycosidic bonds are formed by a condensation reaction
• Hydrolysis


  The process of breaking glycosidic bonds by adding water
• Examples of hydrolytic reactions include the digestion of food in the alimentary tract and the breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration
• Disaccharides


  Provide the body with a quick-release source of energy
• Disaccharides


  • Made up of two sugar molecules so they're easily broken down by enzymes in the digestive system into their respective monosaccharides and then absorbed into the bloodstream
  • Due to the presence of a large number of hydroxyl groups, disaccharides are easily soluble in water
  • Just like monosaccharides they are sweet in taste
• Disaccharides


  • Sucrose (table sugar)
  • Maltose
  • Lactose
• Polysaccharides


  May be branched or unbranched
• Sucrose


  A disaccharide formed from a molecule of glucose (left) and a molecule of fructose (right) joined together by a 1,2 glycosidic bond