1. Molecular Biology 2.2 Water

2. Discuss: Why is water called “the primary molecule of Life”?

3. WATER Water molecules are polar and hydrogen bonds form between them. Animation The hydrogen and oxygen atoms in a water molecule are held together by polar covalent bonds Due to an uneven sharing of electrons, the oxygen has an overall partial negative charge and the hydrogen atoms a positive.

4. WATER Water molecules are polar and hydrogen bonds form between them. Animation Water has a bent shape This means that the two hydrogens form a positive “pole” and the oxygen forms a negative “pole” Positively charged particles will attract negatively charged particles.

5. WATER Water molecules are polar and hydrogen bonds form between them. Animation A “hydrogen bond” is a force that forms when a hydrogen atom in one polar molecule is attracted to a slightly negative atom of another polar covalent bond. This is a weak intermolecular bond. However, there are so many in water that they give water unique properties.

6. PROPERTIES OF WATER Cohesion and Adhesion Each water molecule bonds with 4 others in a tetrahedral arrangement. As a result, water is cohesive water molecules “cling” to each other in groups. Water is also adhesive water molecules “cling” to other surfaces. Why is this important to living organisms?

7. PROPERTIES OF WATER Cohesion: Capillary Action: water will move against gravity up xylem from roots to shoots. Surface Tension: the surface of water is strong enough to support insects Adhesion: Aids in the absorption of CO 2 in cell walls

8. PROPERTIES OF WATER Thermal properties Specific Heat Capacity Specific Heat Capacity Water has a high specific heat It can give off or absorb heat with minimal change in temperature. Why would this be important to living organisms?

9. PROPERTIES OF WATER Thermal properties Specific Heat Capacity Specific Heat Capacity Many organisms are adapted to a narrow range of conditions. The slow heating and cooling of water lessens the risk of death due to extreme temperature fluctuations. Animation

10. PROPERTIES OF WATER Thermal properties Latent Heat of Vapourization Latent Heat of Vapourization Water has a high latent heat of vapourization It has the ability to absorb a lot of heat before the molecules will separate to become a gas Why would this be important to living organisms?

11. PROPERTIES OF WATER Thermal properties Latent Heat of Vapourization Latent Heat of Vapourization It takes a lot of energy to make water evaporate, it is thus a good coolant evaporating water removes a lot of heat energy from the organism

12. PROPERTIES OF WATER Thermal properties Boiling Point Boiling Point Water has a high boiling point It can remain in the liquid state at a high temperature Why would this be important to living organisms?

13. PROPERTIES OF WATER Thermal properties Boiling Point Boiling Point Water remains as a liquid from 0-100°C in most habitats on Earth

14. PROPERTIES OF WATER Solvent Properties Water molecules surround and isolate solute molecules. Water is able to dissolve polar solutes easily. Ionic substances with dissociate in water. Why would this be important to living organisms?

15. PROPERTIES OF WATER Solvent Properties Dissolves most substances involved in living processes, such as oxygen, carbon dioxide, glucose, amino acids (components of proteins), and sodium chloride (salt)

16. PROPERTIES OF WATER Solvent Properties These can be carried in the circulatory systems of animals or through xylem and phloem in plants through the water in soil or aquatic habitats.

17. PROPERTIES OF WATER Solvent Properties Membranes and biological surfaces are wet allowing molecules to dissolve, including gases, so they can diffuse through more easily. Example: lungs are wet allowing for oxygen diffusion into the bloodstream.

18. PROPERTIES OF WATER Solvent Properties All metabolic reactions (reactions in living things) occur in solution – the reactants are dissolved. Dissolved particles move around and diffuse. Moving particles are likely to collide with one another leading to a reaction.

19. Solvent properties table (p. 49) Aqueous Solution LocationCommon Reactions CytoplasmFluid inside cell but outside organelles Glycolysis/protein synthesis reactions NucleoplasmFluid inside nuclear membrane DNA replication/transcription StromaFluid inside chloroplastLight-independent reactions of photosynthesis. Blood plasmaFluid in arteries, veins and capillaries Loading and unloading of respiratory gases/clotting

20. OTHER PROPERTIES OF WATER Water is dense Expands when it freezes Able to diffuse across the cell membrane

22. Video http://www.youtube.com/watch?v=H8WJ2KENlK0