Biology 120 Notes (Part 3) Water

Water - Essential to Life

• Water makes up 60-70% of the human body.

• Water is the most critical molecule for life on Earth.

Why?

• The first reason is because water is a polar molecule.

• The second reason is because it can form hydrogen bonds.

Properties of Water

• Water has a high heat capacity.

• Water has a high heat of vaporization.

• Water is a good solvent.

• Molecules can be hydrophobic or hydrophilic.

• Water molecules are cohesive and adhesive.

• Water has surface tension and capillary action.

• Ice is less dense than liquid water.

• Water expands as reaches 0 degrees Celsius.

The Importance of Organic Molecules

Organic compounds are molecules that contain carbon bonded to hydrogen and other elements.

Why Carbon?

• Carbon is the most versatile atom on Earth.

• The number of valence electrons.

• Carbon is able to form many bonds.

Comparing Inorganic vs. Organic Molecules

• Inorganic molecules are made up of various elements, usually have ionic bonds, are small molecules, and are associated with non-living things.

• Organic molecules are always composed of carbon and hydrogen, always have covalent bonds, are larger molecules, and are associated with living things.

The Carbon Skeleton and Functional Groups

• The carbon chain is the equivalent to a skeleton or backbone.

• Functional groups are attached to the carbon skeleton.

Functional Groups

• H-, N-, O-, P-, and S- contain functional groups found in organic compounds.

• Amino groups act as bases (N.)

• Carboxyl groups act as acids (COO or COOH) which have two oxygens.

• Carbonyl groups have sites that link molecules into more complex compounds (CO or COH) which have one oxygen.

• Hydroxyl groups act as weak acids (OH.)

• Phosphate groups have two negative charges (P.)

• Sulfhydryl groups link together via disulfide bonds (S.)

• An important thing to remember is how “R” equals the carbon skeleton.

• Hydrogen bonds between functional groups help stabilize biological molecules and allows them to perform their biological function.

• Hydrogen bonds connect two strands of DNA together to create the double helix.

• Isomers are organic molecules that have identical molecular formulas but a different arrangement of atoms.