Ch. 4Carbon and the Molecular

Diversity of Life

A. Overview

• cells 72% water, 25% carbon-based compounds, 2% salts

• Carbon can form large, complex, and diverse molecules because each carbon atom makes 4 stable covalent bonds. • Proteins• Nucleic acids (DNA and RNA)• Carbohydrates• Lipids

CH

H HH

macromolecules

CHONPS

B. Carbon Bonding• Study of carbon-based molecules called organic chemistry• Most organic compounds contain hydrogen as well

CH

H HH

• First organic molecules synthesized on planet proved by Urey-Miller experiment

• Why carbon as the building block?• 4 valence

electrons

Water vapor

H 2NH

3

“Atmosphere”

Electrode

Condenser

Coldwater

Cooled watercontainingorganicmolecules

Sample forchemical analysis

H2O“sea”

CH4

•With 4 valence electrons, carbon can form four covalent bonds with a variety of atoms.• tetravalence makes large, complex molecules possible.•each carbon bonded to four other atoms has a tetrahedral shape.•However, when two carbon atoms are joined by a double bond, the molecule has a flat shape.

tetrahedral

NameMolecular Formula

Structural Formula

Ball-and-StickModel

Space-FillingModel

(a) Methane

(b) Ethane

(c) Ethene (ethylene)

Ethane Propane1-Butene 2-Butene

(c) Double bonds

(d) RingsCyclohexane Benzene

Butane 2-Methylpropane(commonly called isobutane)

(b) Branching

(a) Length

a.Diamondb.Graphitec.Lonsdaleited.Fullerenee.Fullerenef. Fullereneg.Amorphous carbonh.Carbon Nanotube

•Hydrocarbons are organic molecules consisting of only carbon and hydrogen.•Many organic molecules, such as fats, have hydrocarbon components in long hydrocarbon chains.•Hydrocarbons can undergo reactions that release a large amount of energy (i.e. gasoline).

• Hydrocarbons are non-polar, not soluble in H2O, hydrophobic• stable• very little attraction between molecules• gas at room temperature

C. Polymers• Long molecules built by linking repeating building blocks or monomers in a chain • covalent bonds• Put together by dehydration synthesis (remove H2O)

H2O

HO

HO H

H HHO

Dehydration synthesis

• joins monomers by “taking” H2O out• one monomer donates OH– ,other monomer donates H+

• requires energy & enzymes

Condensation reaction

H2O

HO

HO H

H HHO

enzyme

Dehydration synthesis

H2O

HO H

HO H HO H

enzyme

• Digestion uses H2O to breakdown polymers

•reverse of dehydration synthesis•cleave off one monomer at a time•H2O is split into H+ and OH–

•H+ & OH– attach to ends• requires enzymes• releases energy

Hydrolysis

Digestion

D. Functional Groups• Isomers are compounds with the same molecular

formula but different structures and properties:• Structural isomers have different covalent

arrangements of their atoms.• Geometric isomers have the same covalent

arrangements but differ in spatial arrangements.• Enantiomers are isomers that are mirror images of

each other.

(b) Geometric isomers

cis isomer: The two Xs areon the same side.

trans isomer: The two Xs areon opposite sides.

Pentane

(c) EnantiomersL isomer D isomer

Pentane

(a) Structural isomers2-methyl butane

•Enantiomers, mirror image isomers, important in the pharmaceutical industry.•Two enantiomers of a drug may have different effects.•Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules.

Drug

Ibuprofen

Albuterol

Condition

Pain;inflammation

Asthma

EffectiveEnantiomer

S-Ibuprofen

R-Albuterol

R-Ibuprofen

S-Albuterol

IneffectiveEnantiomer

•Distinctive properties of organic molecules depend not only on the carbon skeleton but also on the molecular components attached to it.• A number of characteristic groups are often attached to skeletons of organic molecules. These are called functional groups.

FUNCTIONAL GROUPS MOST IMPORTANT IN LIFE

Hydroxyl group -OHCarbonyl group -C=OCarboxyl group -COOH

Amino group -NH2

Sulfhydryl group -SHPhosphate group -OPO3

2-

Methyl group -CH3