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