Carbon and the Molecular Diversity of Life: Study Notes

Chapter 3: Carbon and the Molecular Diversity of Life

Concept 3.1: Carbon atoms can form diverse molecules by bonding to four other atoms

Carbon is a unique element in biology due to its ability to form four covalent bonds, allowing for a vast diversity of organic molecules. This property is fundamental to the complexity and variety of life.

• Organic Compounds: Molecules containing carbon atoms bonded to other elements, especially hydrogen, oxygen, and nitrogen.

• Electron Distribution Diagram: Carbon has 6 electrons, with 4 in its outer shell, allowing it to form up to 4 covalent bonds.

• Frequent Partners: Hydrogen, oxygen, and nitrogen are the most common elements bonded to carbon in organic molecules.

• Carbon Skeletons: The backbone of organic molecules, which can vary in length, branching, and ring formation.

• Hydrocarbons: Organic molecules consisting entirely of carbon and hydrogen. They are hydrophobic due to nonpolar C-H bonds.

Isomers: Molecules with the same molecular formula but different structures.

Definition	Example
Isotope	Carbon-12 and Carbon-14
Isomer	Glucose and Fructose

• Functional Groups: Specific groups of atoms within molecules that determine chemical reactivity and properties. Examples include hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups.

Structure	Hydroxyl	Carbonyl	Carboxyl	Amino	Sulfhydryl	Phosphate	Methyl
Example	Alcohols	Aldehydes/Ketones	Acids	Amino acids	Cysteine	ATP	Methylated DNA

• ATP (Adenosine Triphosphate): Releases energy when converted to ADP and inorganic phosphate: $\text{ATP} \rightarrow \text{ADP} + \text{P}_i$

Concept 3.2: Macromolecules are polymers, built from monomers

Macromolecules are large molecules essential for life, constructed from smaller units called monomers. The four major classes are carbohydrates, lipids, proteins, and nucleic acids.

• Polymer: A long molecule consisting of many similar or identical building blocks (monomers) linked by covalent bonds.

• Monomer: The repeating unit that serves as the building block of a polymer.

• Macromolecule: A large molecule formed by the polymerization of monomers.

• Dehydration Synthesis: The process by which monomers are joined to form polymers, releasing water: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: The process by which polymers are broken down into monomers by the addition of water.

Concept 3.3: Carbohydrates serve as fuel and building material

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components in cells.

• Monosaccharides: Simple sugars with the general formula $\text{C}_n\text{H}_{2n}\text{O}_n$. Example: Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$).

• Pentose Sugar: Five-carbon sugar, e.g., ribose ($\text{C}_5\text{H}_{10}\text{O}_5$).

• Hexose Sugar: Six-carbon sugar, e.g., glucose.

• Functional Group: All sugars have a carbonyl group ($\text{C}=\text{O}$).

• Glycosidic Linkage: Covalent bond formed between two monosaccharides by a dehydration reaction.

Type of Polysaccharide	Examples
Storage	Starch (plants), Glycogen (animals)
Structural	Cellulose (plants), Chitin (fungi, arthropods)

• Cellulose: A structural polysaccharide in plant cell walls; humans cannot digest it due to lack of appropriate enzymes.

Concept 3.4: Lipids are a diverse group of hydrophobic molecules

Lipids are nonpolar molecules that include fats, phospholipids, and steroids. They are hydrophobic and serve as energy storage, structural components, and signaling molecules.

• Fats: Composed of glycerol and three fatty acids. Formation involves dehydration synthesis, releasing three water molecules.

• Saturated Fat: Fatty acids with no double bonds; solid at room temperature.

• Unsaturated Fat: Fatty acids with one or more double bonds; liquid at room temperature.

• Phospholipids: Consist of a glycerol, two fatty acids, and a phosphate group. They form the bilayer of cell membranes, with hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a carbon skeleton consisting of four fused rings. Examples include cholesterol and hormones.

Concept 3.5: Proteins include a diversity of structures, resulting in a wide range of functions

Proteins are polymers of amino acids and perform a vast array of functions in living organisms, including catalysis, structure, transport, and regulation.

• Amino Acid Structure: Central carbon atom bonded to an amino group, carboxyl group, hydrogen atom, and R group (side chain).

• Peptide Bond: Covalent bond formed between the amino group of one amino acid and the carboxyl group of another via dehydration synthesis.

• Levels of Protein Structure:

  1. Primary: Sequence of amino acids.

  2. Secondary: Local folding into alpha helices and beta sheets stabilized by hydrogen bonds.

  3. Tertiary: Overall 3D shape formed by interactions among R groups.

  4. Quaternary: Association of multiple polypeptide chains.

• Protein Functions: Enzymes, structural support, transport, signaling, movement, defense.

Type of Protein	Function
Enzyme	Catalyzes biochemical reactions
Structural	Provides support (e.g., collagen)
Transport	Moves substances (e.g., hemoglobin)
Signaling	Hormones and receptors
Defense	Antibodies

Category	Common Elements
Nonpolar	Hydrocarbon side chains
Polar	Hydroxyl, amide, or sulfhydryl groups
Electrically charged	Acidic (carboxyl) or basic (amino) groups

• Dehydration Synthesis: Joins amino acids to form polypeptides, releasing water.

• Polypeptide: A chain of amino acids linked by peptide bonds.

Concept 3.6: Nucleic acids store, transmit, and help express hereditary information

Nucleic acids, such as DNA and RNA, are polymers of nucleotides that store and transmit genetic information in cells.

• Nucleotide: Consists of a phosphate group, a five-carbon sugar, and a nitrogenous base.

• DNA: Double-stranded helix that stores genetic information.

• RNA: Single-stranded molecule involved in protein synthesis and gene regulation.

Additional info: Some explanations and examples have been expanded for clarity and completeness, including definitions, chemical structures, and biological significance.