Chapter 4—Carbon and the

Molecular Diversity of Life

Carbon Skeletons and their

Attachments

I. The Importance of Carbon

• Living Organisms: • 70-95% Water

• 5-30% Carbon-based compounds

• Carbon accounts for the large diversity found in

biological molecules • Carbon backbones attached to H, O, N, S, & P

• Organic Chemistry • Branch of chemistry that studies carbon compounds

– small → large molecules

» i.e. CH4 or CO2 vs. proteins with 1,000s of atoms

Simple Organic Molecules

Valences of Organic Molecules

Carbon = Most Versatile Building

Block

Carbon has 4 valence electrons (1/2 full)

fills its valence shell by sharing e- with other atoms

forming 4 covalent bonds

Carbon = intersection or branching point for

molecules = lots of versatility of structures

Variations in Carbon Skeletons

Diversity of Carbon Skeletons =

Diversity of Organic Molecules

• Carbon chains form the skeletons of organic molecules

• Vary in: – Length

– Arrangement (i.e. straight, branched, rings)

– Location of single & double bonds

– Other elements bonded to the skeleton (functional groups)

• Hydrocarbons—

– Consist of only C & H – Example: petroleum (fossil fuel)

Hydrocarbons in Living Organisms

Hydrocarbons

are:

Nonpolar

Hydrophobic

Store large

amounts of

energy

Isomers = Diversity of Organic

Molecules

Isomers—

Same molecular formula

Different structure or

arrangement

Different properties

3 Types of Isomers

• Structural Isomers— • Covalent arrangements of atoms differ (single &

double bonds)

• Geometric Isomers— • Same covalent bonds, different arrangement of

atoms

• Enantiomers— • Molecules are mirror images of each other

(―right or left handed‖)

• Usually one is biologically ‗active‘ and the other is ‗inactive‘

Enantiomers

Organisms are

sensitive to

small changes

in architecture

Emergent

property—

Change

arrangement

of atoms →

change

function of

molecule

II. Functional Groups

• Specific arrangement of atoms

• Attached to carbon skeleton

• Usually involved in chemical reactions

• All are hydrophilic, increase solubility

• Each type exhibits characteristic behavior

Sexuality has a biological basis

Sex and sexuality is based on carbon chemistry

Variations in functional

groups along carbon

skeletons = major

source of molecular

diversity

Organic compounds in

cells usually contain 2

or more functional

groups