1. CARBON AND THE MOLECULAR DIVERSITY OF LIFE
CHAPTER 4
CARBON AND THE MOLECULAR DIVERSITY OF LIFE

2. Overview: Carbon—The Backbone of Life
Aside from water, the most biologically important molecules are carbon-based (organic).
Although cells are 70–95% water, the rest consists 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

3. Concept 4.1: Organic chemistry is the study of carbon compounds
A. Organic chemistry is the study of compounds that contain carbon 1. Organic compounds range from simple molecules to colossal ones 2. Most organic compounds contain hydrogen atoms in addition to carbon atoms

4. Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms
Electron configuration is the key to an atom’s characteristics
Electron configuration determines the kinds and number of bonds an atom will form with other atoms

5. A. The Formation of Bonds With Carbon
1. Carbon atom
Atomic number 6 (6 protons, 6 electrons, 6 neutrons)
4 valance electrons
Forms 4 covalent bonds usually with H, O, N, C
Can form large, complex molecules
2. Carbon Dioxide (OCO)
Source of carbon for all organic molecules found in organisms

7. B. Molecular Diversity Arising from Carbon Skeleton Variation
1. Covalent bonds link carbon atoms together in long chains that form the skeletal framework for organic molecules.
2. Carbon skeletons may vary in:
Length
Shape (straight chain, branched, ring)
Number and location of double bonds
Other elements covalently bonded to available sites
3. Variation contributes to complexity and diversity of organic molecules

8. 04_05CarbonSkeletons_A.html

9. C. Hydrocarbons
Hydrocarbons are organic molecules consisting of only carbon and hydrogen
Many organic molecules, such as fats and fossil fuels, have hydrocarbon components
Hydrocarbons can undergo reactions that release a large amount of energy
Hydrocarbon chains are hydrophobic because C—C and C—H bonds are nonpolar.

10. Hydrocarbon

11. D. Isomers
1. Isomers are compounds with the same molecular formula but different structures and properties.
2. Three types of isomers:
a. Structural Isomers
Have different covalent arrangements of their atoms
Number of possible isomers increases as C skeleton size increases
Ex: C5 H13—3 isomers
C8 H18—18 isomers
C20 H42—366,319 isomers
May differ in location of double bonds

12. Structural Isomers

13. b. Geometric isomers
Have the same covalent arrangements but differ in spatial arrangements
Result from the fact that double bonds will not allow the atoms they join to rotate freely about the axis of the bonds
Subtle differences between isomers affects their biological activity

14. Geometric Isomers

15. Are isomers that are mirror images of each other
c. Enantiomers
Are isomers that are mirror images of each other
Can occur when 4 different atoms or groups of atoms are bonded to the same carbon (asymmetric carbon)
Usually one form is biologically active and its mirror image is not
Important in the pharmaceutical industry
Two enantiomers of a drug may have different effects
04_07Isomers_A.html

16. Enantiomers

17. Enantiomer
04_07L_Dopa_A.html

19. Concept 4.3: A small number of chemical groups are key to the functioning of biological molecules
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

20. A. The Chemical Groups Most Important in the Process of Life 1
A. The Chemical Groups Most Important in the Process of Life 1. Functional groups are the components of organic molecules that are most commonly involved in chemical reactions 2. The number and arrangement of functional groups give each molecule its unique properties 3. Functional group replaces an H bonded to the carbon of a hydrocarbon

22. 4. The seven functional groups that are most
4. The seven functional groups that are most important in the chemistry of life:
Hydroxyl group
Carbonyl group
Carboxyl group
Amino group
Sulfhydryl group
Phosphate group
Methyl group

23. Polar group, therefore it makes the molecule attached to water soluble
5. The Seven Functional Groups
a. Hydroxyl Group (-OH)
Consists of a hydrogen atom bonded to an oxygen atom, which is bonded to carbon
H H
| |
H—C—C—OH R—OH
Ethanol  
Polar group, therefore it makes the molecule attached to water soluble
Organic compounds with hydroxyl groups are called alcohols
Names end in –ol

24. Consists of a carbon atom double-bonded to oxygen
b. Carbonyl Group (-CO)
Consists of a carbon atom double-bonded to oxygen
Polar group, therefore it makes the molecule attached to water soluble
Found in sugars
If the carbonyl group is on the end of the carbon skeleton, the compound is an aldehyde 
OH OH O O
| | // //
H—C—C—C R—C
| | \ \
H H H H
Glyceraldehyde 

25. If the carbonyl group is in the internal part of a carbon skeleton, the compound is a ketone
H O H O
| || | ||
H—C—C—C—H R—C—R
| |
H H
Acetone

26. c. Carboxyl Group (-COOH)
Consists of a carbon atom which is both double-bonded to an oxygen and single bonded to the oxygen of a hydroxyl group
Polar group and water soluble
Have acidic properties
Compounds with this group are called carboxylic acids (organic acids)
H O O
| // //
H—C—C R—C
| \ \
H OH OH
Acetic Acid

27. Polar group and water soluble Weak base
d. Amino Group (-NH2)
Consists of a nitrogen atom bonded to two hydrogens and to the carbon skeleton
Polar group and water soluble
Weak base
Organic compounds with this functional group are called amines
H H H
| / /
H—C—N R—N
| \ \
H H H

28. Contain both carboxyl and amino groups
B. Amino Acids
Contain both carboxyl and amino groups
H H O
\ | //
N—C—C
/ | \
H R OH
amino carboxyl

29. Consists of an atom of sulfur bonded to an atom of hydrogen
e. Sulfhydryl Group (-SH)
Consists of an atom of sulfur bonded to an atom of hydrogen
Helps stabilize the structure of proteins
Organic compounds with this functional group are called thiols 
H H
| |
H—C—C—SH R—SH
H H

30. Functional group which is the dissociated form of phosphoric acid
f. Phosphate Group (H3PO4)
Functional group which is the dissociated form of phosphoric acid
Polar group and water soluble
Acid properties
Form organic phosphates
Organic phosphates are important in cellular energy storage and transfer (ATP)
OH OH H O O
| | | || ||
H—C—C—C—O—P—O R—O—P—O-
| | | | |
H H H O O-

31. ATP

32. Consists of a carbon bonded to 3 hydrogens
g. Methyl Group (-CH3)
Consists of a carbon bonded to 3 hydrogens
May be attached to a carbon or to a different atom
Not really a functional group because they are not reactive but may serve as important markers on organic molecules
Can affect expression of genes H /
—C—H \