THE BASIS OF LIFE

I. Matter consists of chemical elements in pure form and in combinations called compounds

A. An element is a substance that cannot be broken down to other substances by chemical reactions

1. Each element consists of a certain kind of atom that is different from those of other elements based on the number of protons

2. Atoms with more or fewer neutrons than protons are isotopes (these decay spontaneously, giving off particles and energy = radioactive)

3. Atoms with more or fewer electrons than protons are ions

B. A compound is a substance consisting of two or more elements combined in a fixed ratio

II. Electron arrangement is involved with energy storage and release and chemical bonding

A. Electrons are arranged in shells, or energy levels

1. Electrons closest to the nucleus have the lowest potential energy

2. Energy added to an atom excites electrons, that is they are moved to outer shells, increasing their potential energy

3. Energy is released as kinetic energy when electrons revert to inner shells

B. The formation and function of molecules depend on chemical bonding between atoms

1. Covalent bonds are the strongest type of bonda. Electrons are shared by atomsb. Energy is stored in covalent bonds and

released when molecules are brokenc. ATP is an example of a biologically important

covalent compound2. Ionic bonds are formed by attractions between

anions (negative ions) and cations (positive ions)a. Ionic compounds are often saltsb. In solution ionic compounds break into ions

3. Hydrogen bonds are a type of weak bond formed by attractions between polar molecules

C. Shape is everything - the shape of a molecule, as dictated by chemical bonds, precisely determines molecular function

III. Macromolecules A. Carbohydrates

1. The simplest form of carbohydrate is a monosaccharide with a C:H:O ratio of 1:2:1; eg. glucose and fructose

2. Two monosaccharides bonded together is a disaccharide; eg. maltose and sucrose

3. More than two is a polysaccharide; eg. glycogen, cellulose, chitin, lactose, etc.

B. Lipids1. Include fats, oils, waxes, steroids2. All are hydrophobic, at least at one end3. Triglycerides are made of a glycerol molecule

with three chains of fatty acids4. Phospholipids have two chains of fatty acids and

a phosphate group; cell membranes are double layer of phospholipids

III. MacromoleculesC. Proteins

1. Made of chains of combinations of 20 amino acids called polypeptides

2. Protein shape determines functiona. Primary structure is the unique sequence of

amino acids in a proteinb. Secondary structure is the folding or coiling of

amino acids in a repeat formation; helical or pleated sheets

c. Tertiary structure is the overall three-dimensional shape of a protein; weak bonds such as hydrogen bonds responsible for shape

d. Quaternary structure is the result of two or more protein subunits

3. Functions include enzymes, structure, hormones, cell membrane receptors, immune system, etc.

Protein primary structure

Protein secondary structure

Protein tertiary structureProtein quaternary structure

III. MacromoleculesD. Nucleic acids store and transmit hereditary information

1. Deoxyribonucleic acid (DNA)a. Subunits called nucleotides

1) Backbone molecules are sugar plus a phosphate

2) Nitrogenous bases; Adenine, Thymine, Cytosine, Guanine (ATCG)

b. Nucleotides arranged in a double helix1) Two antiparallel nucleic acids2) Bases attached by hydrogen bonds in

predictable pairs: A & T, C & G2. Ribonucleic acid (RNA)

a. Single strands of nucleic acidsb. Different form of sugarc. Thymine replaced by uracil (U)