CHAPTER 2
THE CHEMISTRY OF LIVING THINGS

All Matter Consists of Elements Made of Atoms

•Atoms, the smallest functional unit, consist of:

•Protons: positive charge, have mass

•Neutrons: no charge, have mass

•Electrons: negative charge, have no discernable mass

Elements of Living Organisms

Isotopes

•Same element, same atomic
number = same number of protons and electrons

•Different number of
neutrons = different weight

Radioisotopes

•Are unstable (varies with isotope)

•Emit energy (radiation)

•Emit particles

Ions

•Differ in number of electrons

•Cations – have lost one or more electrons (- charges), have a net + charge

•Anions – have gained one or more electrons (- charges) have a net - charge

Atoms Combine to Form Molecules

•Joining atoms – creating bonds - requires energy

•Electrons may be transferred or shared as bonds are created

Three Types of Chemical Bonds

Life Depends on Water

•Water molecules are polar (regions of + and – charge)

•Water is liquid at body temperature

•Water can absorb and hold heat energy

Two Important Biological Functions
of Water

•Water is the biological solvent

•Water helps regulate body temperature

Water Keeps Ions in Solution

The Importance of Hydrogen Ions

•Acids are proton (hydrogen ion) donors, bases
accept hydrogen ions

•pH Scale = hydrogen ion concentration

•Buffers: minimize pH change

•Carbonic acid and bicarbonate act as one of
body’s most important buffer pairs

The pH Scale

The Organic Molecules of Living Organisms

•Carbon, the building block of living things:

•Comprises 18% of body by weight

•Forms four covalent bonds

•Can form single or double bonds

•Can build micro- or macromolecules

Carbon Can Bond in Many Ways

Making and Breaking Biological Macromolecules: Dehydration Synthesis and Hydrolysis

Dehydration Synthesis is the Reverse of Hydrolysis

•Dehydration synthesis

•Removes equivalent of a water molecule to link molecular units

•Requires energy

•Hydrolysis

•Adds the equivalent of a water molecule to break apart macromolecules

•Releases energy

Carbohydrates are Used for Energy and Structural Support

•Oligosaccharides: short chains of monosaccharides

•Disaccharides: sucrose, fructose, lactose

•Polysaccharides: thousands of monosaccarides
joined in chains and branches

•Starch: made in plants; stores energy

•Glycogen: made in animals; stores energy

•Cellulose: undigestible polysaccharide made in plants for structural support

Carbohydrates are Composed of Monosaccharides

Lipids: Insoluble in Water

•Triglycerides: energy storage molecules

•Fatty acids: saturated and unsaturated

•Saturated fatty acids havc no double bonds, are solid at room temperature, are typical of animal fats

•Unsaturated fatty acids have double bonds, are liquid at room temperature, are typical of plant oils

•Phospholipids: cell membranes

•Steroids: carbon-based ring structures

•Cholesterol: used in making estrogen and
testosterone

Proteins: Complex Structures Constructed of Amino Acids

•Structure

•Primary: amino acid sequence

•Secondary: describes chain’s orientation in space; e.g., alpha helix, beta sheet

•Tertiary: describes three-dimensional shape created by disulfide and hydrogen bonds

•Quaternary: describes proteins in which two or more tertiary protein chains are associated

Structure and Function of Nucleic Acids

•Functions

•Store genetic information

•Provide information used in making proteins

•Structure

•Nucleotides consist of a phosphate group, a sugar, and a nitrogenous base

•DNA structure is a double helix: two associated strands of nucleic acids

•RNA is a single-stranded molecule

Structure of DNA and RNA

•DNA: double-stranded

•Sugar: deoxyribose

•Nitrogenous bases: adenine, thymine, cytosine, guanine

•Pairing: adenine-thymine and cytosine-guanine

•RNA: single-stranded

•Sugar: ribose

•Nitrogenous bases: adenine, uracil, cytosine, guanine

•Pairing: adenine-uracil, cytosine-guanine

Structure and Function of Adenosine Triphosphate (ATP)