Chapter 4 - Carbon and The Molecular Diversity of Life 1
Chapter 4 - Carbon and The Molecular Diversity of Life 1
Chapter 4 - Carbon and The Molecular Diversity of Life 1
Life
Objectives:
1. Explain the difference between vitalism and mechanism.
2. Explain how carbon’s electron configuration accounts for its ability to form large,
complex, and diverse organic molecules.
3. Describe how carbon skeletons may vary, and explain how this variation
contributes to the diversity and complexity of organic molecules.
4. Describe the basic structure of a hydrocarbon and explain why these molecules are
hydrophobic.
5. Distinguish among the three types of isomers: structural, geometric, and enantiomer.
Misconceptions:
1. Students often misunderstand the interaction of hydrophobic molecules and water.
Many students think that individual oil and water molecules repel each other.
Explain to students that individual hydrocarbon molecules are attracted to water
molecules, but with a force much less than the attraction of water molecules to
each other.
2. Students find it difficult to understand the differences among structural isomers,
geometric isomers, and enantiomers. Three-dimensional models, or pictures of
such models, are very useful tools in discussion of these terms.
Notes:
B. Functional Groups:
Objectives:
1. Name the major functional groups found in organic molecules. Describe the basic
structure of each functional group and outline the chemical properties of the
organic molecules in which they occur.
Notes:
1. Functional groups are involved in chemical reactions and contribute to the molecular
diversity of life.
• The components of organic molecules that are most commonly involved in chemical
reactions are known as functional groups.
• If we consider hydrocarbons to be the simplest organic molecules, we can view functional
groups as attachments that replace one or more of the hydrogen atoms bonded to the carbon
skeleton of the hydrocarbon.
• Each functional group behaves consistently from one organic molecule to another.
• The number and arrangement of functional groups help give each molecule its unique
properties.
• As an example, the basic structure of testosterone (a male sex hormone) and estradiol (a
female sex hormone) is the same.
• Both are steroids with four fused carbon rings, but they differ in the functional groups
attached to the rings.
• These functional groups interact with different targets in the body.
• There are six functional groups that are most important to the chemistry of life: hydroxyl,
3
carbonyl, carboxyl, amino, sulfhydryl, and phosphate groups.
• All are hydrophilic and increase the solubility of organic compounds in water.
• In a hydroxyl group (—OH), a hydrogen atom forms a polar covalent bond with an oxygen
atom, which forms a polar covalent bond to the carbon skeleton.
• Because of these polar covalent bonds, hydroxyl groups increase the solubility of organic
molecules.
• Organic compounds with hydroxyl groups are alcohols, and their names typically end in -ol.
• A carbonyl group (>CO) consists of an oxygen atom joined to the carbon skeleton by a
double bond.
• If the carbonyl group is on the end of the skeleton, the compound is an aldehyde.
• If the carbonyl group is within the carbon skeleton, then the compound is a ketone.
• Isomers with aldehydes versus ketones have different properties.
• A carboxyl group (—COOH) consists of a carbon atom with a double bond to an oxygen
atom and a single bond to the oxygen of a hydroxyl group.
• Compounds with carboxyl groups are carboxylic acids.
• A carboxyl group acts as an acid because the combined electronegativities of the two adjacent
oxygen atoms increase the dissociation of hydrogen as an ion (H+).
• An amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and the
carbon skeleton.
• Organic compounds with amino groups are amines.
• The amino group acts as a base because the amino group can pick up a hydrogen ion (H+)
from the solution.
• Amino acids, the building blocks of proteins, have amino and carboxyl groups.
• A sulfhydryl group (—SH) consists of a sulfur atom bonded to a hydrogen atom and to the
backbone.
• This group resembles a hydroxyl group in shape.
• Organic molecules with sulfhydryl groups are thiols.
• Two sulfhydryl groups can interact to help stabilize the structure of proteins.
• A phosphate group (—OPO32−) consists of a phosphorus atom bound to four oxygen atoms
(three with single bonds and one with a double bond).
• A phosphate group connects to the carbon backbone via one of its oxygen atoms.
• Phosphate groups are anions with two negative charges, as two protons have dissociated from
the oxygen atoms.
• One function of phosphate groups is to transfer energy between organic molecules.
• Adenosine triphosphate, or ATP, is the primary energy-transferring molecule in living cells.
2. These are the chemical elements of life.
• Living matter consists mainly of carbon, oxygen, hydrogen, and nitrogen, with smaller
amounts of sulfur and phosphorus.
• These elements are linked by strong covalent bonds.
• Carbon, with its four covalent bonds, is the basic building block in molecular architecture.
• The great diversity of organic molecules with their special properties emerges from the
unique arrangement of the carbon skeleton and the functional groups attached to the skeleton.
Key Terms 4
adenosine triphosphate enantiomer isomer
(ATP) functional group organic chemistry
amino group geometric isomer phosphate group
carbonyl group hydrocarbon structural isomer
carboxyl group hydroxyl group sulfhydryl group
Word Roots
carb- = coal (carboxyl group: a functional group present in organic acids, consisting of a
carbon atom double-bonded to an oxygen atom and a hydroxyl group)
enanti- = opposite (enantiomer: molecules that are mirror images of each other)
hydro- = water (hydrocarbon: an organic molecule consisting only of carbon and
hydrogen)
iso- = equal (isomer: one of several organic compounds with the same molecular formula
but different structures and, therefore, different properties)
sulf- = sulfur (sulfhydryl group: a functional group that consists of a sulfur atom bonded
to an atom of hydrogen)
thio- = sulfur (thiol: organic compounds containing sulfhydryl groups) .