Chapter 3 BIOCHEMISTRY Water Carbon Compounds Molecules of Life

 Objectives: 1.Describe the structure of a water molecule. 2.Explain how water’s polar nature affects its ability to dissolve substances. 3.List two of water’s properties that result from hydrogen bonding. Water 3-1

Polarity  Hydrogen and oxygen atoms share electrons to form covalent bonds  Oxygen atom pulls electrons from hydrogen toward its nucleus  Electrical charge of H2O is uneven  Oxygen is slightly negative, hydrogen slightly positive

 Because water is polar it is effective in dissolving many substances  Water dissolves:  Other polar substances (sugars and some proteins)  Ionic compounds (sodium chloride NaCl) Water as a Solvent

 Ionic compounds dissolved in water tend to dissociate into ions.  This frees up ions to participate in many biological reactions  Sodium Ions and Chloride ions are essential to muscle contractions and transmission of nervous impulses Water as a Solvent Cont.

 Polar water molecules are attracted to each other  This attraction is called a Hydrogen Bond.  The hydrogen atom in one molecule forms a hydrogen bond with the region of negative charge on another molecule.  Hydrogen bonds are weak, and can be easily broken. Hydrogen Bonding

 Cohesion – attractive force between particles of the same kind.  Adhesion – attractive force between unlike substances.  Capillarity - Adhesion and cohesion together enable water molecules to move upward through narrow tubes against gravity. Cohesion and Adhesion

 Water must gain or lose a large amount of energy for its temperature to change.  Waters ability to absorb large amounts of energy helps keep cells at an even temperature, despite changes in the environment.  Maintaining homeostasis! Temperature Moderation