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Chapter 3
BIOCHEMISTRYWater
Carbon CompoundsMolecules 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