1. Carbon and the Molecular Diversity of Life
Chapter 4:
Carbon and the Molecular Diversity of Life

2. Overview: Carbon: The Backbone of Life
Living organisms consist mostly of carbon-based compounds
Carbon is unparalleled in its ability to form large, complex, and diverse molecules
Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds
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3. Life is based on carbon

4. Organic Molecules and the Origin of Life on Earth
Stanley Miller’s classic experiment demonstrated the abiotic synthesis of organic compounds
Experiments support the idea that abiotic synthesis of organic compounds, perhaps near volcanoes, could have been a stage in the origin of life
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5. Inquiry Could organic compounds have been synthesized abiotically on the early Earth?
EXPERIMENT
In 1953, Stanley Miller simulated what were thought to be environmental conditions on the lifeless, primordial Earth. As shown in this recreation, Miller used electrical discharges (simulated lightning) to trigger reactions in a primitive “atmosphere” of H2O, H2, NH3 (ammonia), and CH4 (methane)—some of the gases released by volcanoes.
RESULTS
A variety of organic compounds that play key roles in living cells were synthesized in Miller’s apparatus.
CONCLUSION
Organic compounds may have been synthesized abiotically on the early Earth, setting the stage for the origin of life. (We will explore this hypothesis in more detail in Chapter 26.)

6. Hydrocarbons
Hydrocarbons are organic molecules consisting of only carbon and hydrogen
Many organic molecules, such as fats and carbohydrates, have hydrocarbon components
Hydrocarbons can undergo reactions that release a large amount of energy
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7. The role of hydrocarbons in fats
(a) A fat molecule
(b) Mammalian adipose cells
100 µm
Fat droplets (stained red)

8. Isomers
Isomers are compounds with the same molecular formula but different structures and properties
Structural isomers have different covalent arrangements of their atoms
Cis-trans isomers have the same covalent bonds but differ in spatial arrangements
Enantiomers are isomers that are mirror images of each other
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9. (a) Structural isomers
Three types of isomers H
CO2H
CH3
NH2 C X
(a) Structural isomers
(b) Geometric isomers
(c) Enantiomers
L isomer
D isomer

10. The pharmacological importance of enantiomers
L-Dopa
(effective against Parkinson’s disease)
D-Dopa
(biologically inactive)

11. Oliver Sachs discovered a major role for L-dopa in the treatment of Parkinson-like diseases.

12. Effective Enantiomer Ineffective Enantiomer Pain; inflammation
Figure 4.8
Effective
Enantiomer
Ineffective
Enantiomer
Drug
Condition
Pain; inflammation
Ibuprofen
S-Ibuprofen
R-Ibuprofen
Figure 4.8 The pharmacological importance of enantiomers.
Albuterol
Asthma
R-Albuterol
S-Albuterol

13. The Chemical Groups Most Important in the Processes of 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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14. A comparison of functional groups of female (estradiol) and male (testosterone) sex hormones
CH3 OH HO O
Estradiol
Testosterone
Female lion
Male lion