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Chapter 3Carbon and

the Molecular Diversity of Life

You Must Know

• The properties of carbon that make it so important.

• The role of dehydration reactions in the formation of organic compounds and hydrolysis in the digestion of organic compounds.

Importance of Carbon

Valences of the major elements of organic molecules

Hydrogen(valence 1)

Carbon(valence 4)

Nitrogen(valence 3)

Oxygen(valence 2)

• Critically important molecules of all living things fall into four main classes– Carbohydrates– Lipids– Proteins– Nucleic acids

• The first three of these can form huge molecules called macromolecules

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Molecular Diversity Arising from Variation in Carbon Skeletons

• Carbon chains form the skeletons of most organic molecules

• Carbon chains vary in length and shape

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Hydrocarbons

Concept 3.2: Macromolecules are polymers, built from monomers

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• A dehydration reaction occurs when two monomers bond together through the loss of a water molecule

The Synthesis and Breakdown of Polymers

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Figure 3.6a

Unlinked monomerShort polymer

Longer polymer

(a) Dehydration reaction: synthesizing a polymer

Dehydration removesa water molecule,forming a new bond.

• Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction

The Synthesis and Breakdown of Polymers

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Figure 3.6b

(b) Hydrolysis: breaking down a polymer

Hydrolysis addsa water molecule,breaking a bond.

The Diversity of Polymers

• Each cell has thousands of different macromolecules

• Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species

• An immense variety of polymers can be built from a small set of monomers

HO

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The Chemical Groups Most Important to Life

• Functional groups are the components of organic molecules that are most commonly involved in chemical reactions

• The number and arrangement of functional groups give each molecule its unique properties

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Figure 3.5Chemical Group

Hydroxyl group ( OH)

Compound Name Examples

Alcohol

Ketone

Aldehyde

Methylatedcompound

Organicphosphate

Thiol

Amine

Carboxylic acid,or organic acid

Ethanol

Acetone Propanal

Acetic acid

Glycine

Cysteine

Glycerolphosphate

5-Methyl cytosine

Amino group ( NH2)

Carboxyl group ( COOH)

Sulfhydryl group ( SH)

Phosphate group ( OPO32–)

Methyl group ( CH3)

Carbonyl group ( C O)

The seven functional groups that are most important in the chemistry of life:

You need to memorize these.