Bio

• Water


  The medium of life
• Water


  • Liquid water is thought to have existed on earth for more than 4 billion years
  • Water makes up more than 70% of the earth's surface
• Hydrogen bonds


  Consequence of the polar covalent bonds within water molecules
• Formation of hydrogen bonds in water

  1. Water molecules can associate via weak hydrogen bonds

  2. Hydrogen bonds are transitory in nature – they constantly form, break and re-form
• Cohesion of water molecules

  • Due to hydrogen bonding
  • Gives cohesive forces great strength
• Adhesion of water


  • Water molecules tend to stick to other molecules that are charged or polar
  • Adhesive forces bond water to surfaces
• Capillary action


  Caused by the combination of adhesive forces causing water to bond to a surface and the cohesive forces bonding water molecules together
• Solvent properties of water

  • Water can dissolve many organic and inorganic substances that have charged or polar regions
  • Polar attraction of water molecules can interrupt intramolecular forces and result in dissociation of atoms
• Metabolic reactions happen most readily in solutions of water
• Cells are mostly water therefore diffusion into and out of them happens most easily if the substance is in solution
• Soluble substances such as sucrose can be easily transported around the plant in the phloem
• Hydrophilic


  Substances that are chemically attracted to water
• Hydrophilic substances


  • Glucose
  • Amino acids
• Blood plasma consists mainly of water (95%) plus dissolved substances which it transports
• Hydrophilic


  Substances that water adheres to, e.g. cellulose
• A space filling molecular diagram of glucose showing the positive and negative charges
• Solvent properties of water

  Linked to its role as a medium for metabolism and for transport in plants and animals
• Blood plasma


  Consists mainly of water (95%) plus dissolved substances which it transports
• Glucose


  Polar molecule hence freely soluble, carried by the blood plasma
• Amino acids


  Positive and negative charges (due to the amine and acid groups) therefore soluble in water, R group varies and determines the degree of solubility, carried by the blood plasma
• Sodium Chloride


  Ionic compound, freely soluble in water, dissolving to form sodium ions (Na+) and chloride ions (Cl-), carried in the blood plasma
• Oxygen


  Non-polar molecule, due to the small size it is soluble in water but only just, water becomes saturated with oxygen at relatively low concentrations, as temperature increases the solubility of oxygen decreases, at body temperature very little oxygen can be carried by the plasma, too little to support aerobic respiration, hemoglobin in red blood cells carry the majority of oxygen, hemoglobin has 4 binding sites for oxygen
• Hydrophobic


  Molecules that do not have negative or positive charges and are nonpolar, all lipids are hydrophobic including fats and oils, hydrophobic molecules dissolve in other solvents such as propanone (acetone)
• Fats


  Large, non-polar molecules, insoluble in water, they are carried in blood inside lipoprotein complexes (in the plasma)
• Cholesterol


  Molecules are hydrophobic, apart from a small hydrophilic region at one end, this is not enough to make cholesterol dissolve in water, they are carried in blood in lipoprotein complexes (in the plasma)
• Lipoprotein complex


  Outer layer consists of single layer of phospholipid molecules, hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water, the hydrophobic hydrocarbon tails face inwards and are in contact with the fats, cholesterol molecules are positioned in the phospholipid monolayer - hydrophilic region facing outwards, proteins are also embedded in the phospholipid layer
• Physical properties of water

  • High specific heat capacity, high heat of vaporisation, high heat of fusion, these properties are due to many hydrogen bonds that need to be formed or broken to change the temperature or state of water, therefore the temperature of water remains relatively stable, water is used by leaves as a coolant, the heat lost from leaves for evaporation prevents them overheating
• Viscosity of water


  • Measure of the items resistance to flow and is related to how much energy is required to change its shape, more viscous than air
• Thermal conductivity of water

  • Measure of how well heat is able to be transferred through a substance from regions of hot to cold, water has high thermal conductivity compared to other liquids and air
• Buoyancy of water


  • The force that counteracts the force of gravity, the high density of water creates high buoyancy enabling less dense materials to float, cold water is more dense so sinks to the bottom, air is less dense than water so less buoyant
• Black throated loon found in the Scottish highland lochs (summer) and sheltered coasts in winter, ringed seal found in the cold arctic water, rarely come to land but stay where there are pack ice and ice floes, it maintains a stable body temperature with a thick layer of fat/blubber
• Initially Earth consisted of a surface of hot molten magma unable to form or maintain water, over a long period of time the surface cooled down, during this time asteroids struck the surface of the earth bringing hydrated minerals that released water
• Hydrated minerals


  Solid minerals that have molecular bonds with water molecules
• All bodies of water consists of two forms: normal water (more common) and heavy water - consisting of an isotope of hydrogen with a neutron, the ratio of normal to heavy water hydrogen is similar to those found on many asteroids
• Goldilocks zone


  Habitable position in relation to the sun, to support life a planet must have water and therefore exist in an area of the solar system that allows water to exist in a liquid state
• Requirements for a planet to support life

  • Distance for ideal temperature to maintain liquid water, atmosphere to prevent water escaping and protect against harmful radiation, planetary size to create sufficient gravitational pull
• Relatively few features are shared by all viruses: small, fixed size; nucleic acid (DNA or RNA) as genetic material; a capsid made of protein; no cytoplasm; and few or no enzymes.
• Viruses


  • Highly diverse in their shape and structure
  • Genetic material may be RNA or DNA, which can be either single- or double-stranded
  • Some viruses are enveloped in host cell membrane and others are not enveloped
• Virus examples


  • bacteriophage lambda
  • coronaviruses
  • HIV
• Lytic cycle of a virus

  1. Attachment to host cell

  2. Entry

  3. Replication of viral genome

  4. Transcription of virus mRNA and protein synthesis

  5. Maturation and assembly of viruses

  6. Release from host cell