Chapter 4: Carbon and the Molecular Diversity of Life

Organic chemistry

Branch of chemistry based around carbon-containing compounds; carbon's ability to form diverse molecules makes it central to the origin and diversity of life.

Carbon

Element with 6 electrons (2 in the first shell, 4 in the valence shell) that can form up to four covalent bonds, enabling diverse organic molecules.

Hydrocarbons

Organic molecules composed only of carbon and hydrogen.

Isomers

Compounds with the same molecular formula but different structural arrangements or spatial configurations.

Structural isomers

Isomers that differ in covalent arrangement of atoms (connectivity) despite having the same formula.

Cis-trans isomer

A type of stereoisomer where double bonds prevent rotation; substituents can be on the same side (cis) or opposite sides (trans) of the bond.

Enantiomers

Mirror-image isomers that are non-superimposable due to the presence of an asymmetric carbon; same formula, different arrangement.

Functional group

Chemical groups directly involved in chemical reactions; determine properties and typical reactions of molecules.

Hydroxyl group

–OH group; polar due to electronegative oxygen; forms hydrogen bonds with water and helps dissolve compounds (example: alcohol).

Carbonyl group

C=O group; found in ketones and aldehydes (and in sugars as part of carbonyl-containing structures).

Carboxyl group

–COOH group; acts as an acid by donating H+ because the O–H bond is highly polar.

Amino group

–NH2 group; acts as a base and can accept H+ from solution.

Sulfhydryl group

–SH group; two –SH groups can form cross-links that help stabilize protein structure.

Phosphate group

–PO4 group; carries negative charges (–1 within a chain, –2 at the end) and reacts with water to release energy.

Methyl group

–CH3 group; can affect gene expression when attached to DNA or proteins; influences the shape and function of male and female sex hormones.

ATP (adenosine triphosphate)

Adenosine attached to three phosphate groups; main energy currency of the cell, providing energy for cellular processes.