Carbon is the “backbone” of all life
- Enters biological systems by plants using CO2
- Organic compounds have C and H
- Has a valence of 4 and commonly covalently bonds to C, H, O, N
- Although atoms are connected in a molecule, they want to be as far away from each other as possible
- Double bonds - each line is a shared pair of electrons

Hydrocarbons - ONLY C and H
- Petroleum
- Not prevalent in living organisms, but there are regions on larger molecules that are composed of hydrocarbons (IE - fats)

Isomers - Same number of atoms of the same element but in different structure. Three types.
1. Structural isomers - differ in covalent arrangement of their atoms, also can change location of a double bong
2. Geometric isomers - same covalent partnerships. Double bond prevents any rotation of the bonded carbons.
- Cis - Attached atoms of the same type are on the same side
- Trans - Attached atoms of the same type are on the opposite side
3. Enantiomers - mirror images of each other (left vs. right hand). Can have drastic differences in biological effect

Functional groups - Parts of the molecule involved in chemical reactions. You need to know the following functional groups - all of them are in common in biological systems and all are hydrophilic.

1. Hydroxyl - an -OH connected to a C chain (NOT the same as OH-)
- Alcohols - IE - ethanol (alcoholic beverages)
- Polar, dissolved organic compounds

2. Carbonyl - C connected to an O by a double bond (=CO)
- Ketones - IE - acetone (group is found in the middle of a C chain)
- Aldehydes - IE - Propanol (end of the C chain)

3. Carboxyl - the O is double bonded to C which is bonded to a hydroxyl group (-OH)
- Carboxylic acids - IE - acetic acid (vinegar)
- Can lose/regain the H on the hydroxyl

4. Amino - NH2
- Amines - IE - Glycine (amine and carboxyl - amino acid)
- Acts as a base

5. Sulfhydryl - SH
- Thiols - IE - Ethanethiol
- Can help stabilize protein shape

6. Phosphate - A phosphate connected to 4 O, one of the O is connected to the C chain, and two of the O carry a negative charge.
- Organic phosphate can carry energy between organic molecules

- ATP (adenosine triphosphate)
- When ATP is “broken” the products are ADP (adenosine diphosphate), an inorganic phosphate, and energy