General Biology: Carbon Chemistry, Biomolecules, and Macromolecules

Carbon and the Molecular Diversity of Life

Introduction to Carbon Chemistry

Carbon is a fundamental element in biological molecules due to its unique ability to form four covalent bonds, allowing for a diversity of stable and complex structures. This versatility underpins the molecular diversity essential for life.

• Organic Chemistry: The study of carbon-containing compounds, especially those found in living organisms.

• Hydrocarbons: Molecules consisting entirely of carbon and hydrogen; important as energy sources and structural components.

• Electron Configuration of Carbon: Carbon has four valence electrons, enabling it to form up to four covalent bonds with other atoms.

• Carbon Skeletons: The chain or ring structures formed by carbon atoms, which can vary in length, branching, and ring formation.

Example: Methane (CH4), ethane (C2H6), and benzene (C6H6) all have different carbon skeletons.

Isomers

Isomers are compounds with the same molecular formula but different structures and properties. The diversity of isomers increases the complexity and functionality of organic molecules.

• Structural Isomers: Differ in the covalent arrangement of atoms.

• Cis-trans Isomers: Differ in spatial arrangement around double bonds.

• Enantiomers: Mirror images of each other, important in biological systems due to enzyme specificity.

Example: Glucose and fructose are structural isomers (C6H12O6).

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity. They are key to the function of biological molecules.

• Hydroxyl (-OH): Alcohols; increases solubility in water.

• Carbonyl (C=O): Found in aldehydes and ketones.

• Carboxyl (-COOH): Acts as an acid; found in amino acids and fatty acids.

• Amino (-NH2): Acts as a base; found in amino acids.

• Sulfhydryl (-SH): Important in protein structure (disulfide bonds).

• Phosphate (-PO42-): Involved in energy transfer (e.g., ATP).

• Methyl (-CH3): Affects gene expression and molecular shape.

Example: The carboxyl group in acetic acid (vinegar) gives it acidic properties.

ATP: Adenosine Triphosphate

ATP is the primary energy carrier in cells. It consists of an adenine base, a ribose sugar, and three phosphate groups. The hydrolysis of ATP releases energy for cellular processes.

• ATP vs. ADP: ATP (adenosine triphosphate) has three phosphate groups; ADP (adenosine diphosphate) has two. The removal of one phosphate group from ATP releases energy.

Equation:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Macromolecules: Structure and Function

Polymers and Monomers

Most biological macromolecules are polymers, long chains made from repeating units called monomers. The formation and breakdown of polymers involve dehydration synthesis and hydrolysis reactions.

• Polymer: A large molecule made of repeating monomer units.

• Monomer: The basic building block of a polymer.

• Dehydration Synthesis: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding water.

Equation (Dehydration Synthesis):

$\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

Four Major Classes of Biomolecules

Biological macromolecules are classified into four main groups, each with distinct structures and functions.

• Carbohydrates: Serve as fuel and building material.

• Lipids: Hydrophobic molecules including fats, phospholipids, and steroids.

• Proteins: Perform a wide range of functions due to their diverse structures.

• Nucleic Acids: Store, transmit, and express hereditary information.

Carbohydrates

Types and Functions

Carbohydrates are sugars and polymers of sugars. They are classified based on the number of sugar units.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides; can be storage or structural.

Storage Polysaccharides: Starch (plants), glycogen (animals).

Structural Polysaccharides: Cellulose (plants), chitin (fungi and arthropods).

Lipids

Types and Functions

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids. They play roles in energy storage, membrane structure, and signaling.

• Fats (Triglycerides): Composed of glycerol and three fatty acids.

• Fatty Acids: Can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol).

Example: Olive oil contains unsaturated fatty acids; butter contains saturated fatty acids.

Proteins

Structure and Function

Proteins are polymers of amino acids and perform a vast array of functions in cells, including catalysis, structure, transport, and signaling.

• Amino Acids: The monomers of proteins; 20 different types exist.

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

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet).

  • Tertiary: Overall 3D shape.

  • Quaternary: Association of multiple polypeptides.

• Denaturation: Loss of protein structure and function due to environmental changes.

Example: Hemoglobin is a quaternary protein that carries oxygen in blood.

Nucleic Acids

DNA and RNA

Nucleic acids store and transmit genetic information. DNA and RNA are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA (Deoxyribonucleic Acid): Double-stranded; stores genetic information.

• RNA (Ribonucleic Acid): Single-stranded; involved in protein synthesis and gene regulation.

• Nucleotides: Building blocks of nucleic acids; composed of a pentose sugar, phosphate group, and nitrogenous base.

• Nitrogenous Bases: Adenine (A), Thymine (T, in DNA), Uracil (U, in RNA), Cytosine (C), Guanine (G).

Example: The sequence of bases in DNA encodes genetic instructions for building proteins.

Macromolecule	Monomer	Bond Type	Main Function
Carbohydrate	Monosaccharide	Glycosidic linkage	Energy storage, structure
Lipid	Glycerol & Fatty acids	Ester bond	Energy storage, membranes
Protein	Amino acid	Peptide bond	Catalysis, structure, transport
Nucleic Acid	Nucleotide	Phosphodiester bond	Genetic information

Additional info: Some details, such as the full list of functional groups and the specific figures referenced, were inferred or expanded for completeness and clarity.