Carbon and the Molecular Diversity of Life

Introduction to Biological Molecules

Biological molecules are primarily composed of carbon atoms bonded to other elements such as hydrogen, oxygen, nitrogen, sulfur, and phosphorus. The unique properties of carbon allow it to form a wide variety of structures, including straight chains, branched chains, and rings, which are essential for the diversity of life.

• Carbon's Versatility: Carbon can form four covalent bonds, enabling the construction of complex molecules.

• Hydrocarbon Core: Many biological molecules have a hydrocarbon (C-H) core, which can be modified by the addition of functional groups.

• Functional Groups: Specific groups of atoms that confer particular chemical properties to molecules. Each functional group has its own characteristics and reactivity.

Major Functional Groups in Biological Molecules

Functional groups are key to the chemical behavior of organic molecules. They are often attached to the carbon skeleton and determine the properties and functions of molecules.

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

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

• 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): Found in some amino acids; forms disulfide bonds in proteins.

• Phosphate (-PO4): Found in nucleic acids and ATP; involved in energy transfer.

• Methyl (-CH3): Nonpolar; affects gene expression when added to DNA.

Macromolecules

Overview of Macromolecules

Macromolecules are large, complex molecules essential for life. They are polymers, built by linking smaller subunits called monomers through covalent bonds.

• Carbohydrates: Made from monosaccharides (simple sugars).

• Lipids: Not true polymers; composed of various sets of monomers.

• Proteins: Made from 20 different amino acids.

• Nucleic Acids: Made from four types of nucleotides.

Polymerization and Dehydration Synthesis

Polymers are formed by joining monomers through a process called dehydration synthesis (condensation reaction), where a water molecule is removed to form a new bond.

• Dehydration Synthesis: The -OH group from one monomer and an -H atom from another are removed, forming water () and a covalent bond between the monomers.

• Example Equation:

Hydrolysis

Hydrolysis is the reverse of dehydration synthesis. It involves the addition of water to break covalent bonds between monomers, splitting polymers into smaller units.

• Hydrolysis Reaction: Water is added, and the bond is broken, resulting in two separate monomers.

• Example Equation:

Carbohydrates

Structure and Function of Carbohydrates

Carbohydrates are organic molecules that store and transport energy, provide structural materials, and act as signal molecules. They are composed of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1.

• Monosaccharides: Simple sugars with 3-7 carbons (e.g., glucose, fructose, galactose).

• Functional Groups: Contain carbonyl (C=O) and hydroxyl (-OH) groups.

• Isomers: Glucose, fructose, and galactose have the same formula () but different structures.

• Ring Formation: Monosaccharides can exist as straight chains or rings in aqueous solutions.

Disaccharides and Polysaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage (a type of covalent bond), while polysaccharides are long chains of monosaccharide units.

• Disaccharides: Examples include sucrose (glucose + fructose), maltose (glucose + glucose), and lactose (glucose + galactose).

• Polysaccharides: Can be used for energy storage (starch in plants, glycogen in animals) or structural support (cellulose in plants, chitin in fungi and arthropods).

Comparison of Major Polysaccharides

Lipids

Structure and Properties of Lipids

Lipids are a diverse group of hydrophobic molecules that are not true polymers. They are important for energy storage, membrane structure, and signaling.

• Hydrophobic Nature: Lipids are insoluble in water due to their large proportion of nonpolar C-H bonds.

• Types of Lipids: Includes fats, oils, phospholipids, and steroids.

• Fats and Oils: Composed of glycerol and three fatty acids (triglycerides). Fats are solid at room temperature; oils are liquid.

• Saturation: Saturated fats have no double bonds (solid); unsaturated fats have one or more double bonds (liquid).

Phospholipids and Steroids

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

• Steroids: Characterized by four fused carbon rings. Examples include cholesterol, estrogen, and testosterone.

Proteins

Structure and Function of Proteins

Proteins are polymers of amino acids joined by peptide bonds. They perform a vast array of functions in the cell, including catalysis, defense, transport, support, regulation, and movement.

• Amino Acids: The building blocks of proteins; each has a central carbon, amino group, carboxyl group, hydrogen atom, and a variable side chain (R group).

• Peptide Bond: Formed by dehydration synthesis between the amino group of one amino acid and the carboxyl group of another.

Levels of Protein Structure

• Primary Structure: The unique sequence of amino acids in a polypeptide chain.

• Secondary Structure: Local folding into alpha-helices and beta-pleated sheets, stabilized by hydrogen bonds.

• Tertiary Structure: The overall 3D shape of a polypeptide, determined by interactions among R groups (hydrophobic interactions, ionic bonds, hydrogen bonds, disulfide bridges).

• Quaternary Structure: The association of two or more polypeptide subunits to form a functional protein.

Protein Folding and Denaturation

• Chaperone Proteins: Assist in the proper folding of new proteins.

• Denaturation: Loss of protein structure (and function) due to changes in pH, temperature, or ionic concentration. Denatured proteins may lose their biological activity.

Nucleic Acids

Structure and Function of Nucleic Acids

Nucleic acids store and transmit genetic information. There are two main types: DNA and RNA.

• DNA (Deoxyribonucleic Acid): Stores genetic information; double-stranded helix.

• RNA (Ribonucleic Acid): Reads DNA code and directs protein synthesis; usually single-stranded.

Nucleotide Structure

• Nucleotide: The monomer of nucleic acids, consisting of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base.

• Nitrogenous Bases: Purines (adenine, guanine) and pyrimidines (cytosine, thymine in DNA; uracil in RNA).

Base Pairing and Double Helix

• Base Pairing: In DNA, adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C) via hydrogen bonds.

• Double Helix: DNA consists of two antiparallel strands twisted into a helix.

• RNA: Similar to DNA but contains ribose sugar and uracil instead of thymine; usually single-stranded.

Summary Table: DNA vs. RNA

Additional info: These notes expand on the original slides by providing definitions, examples, and context for each macromolecule and their subtypes, as well as clarifying the chemical processes involved in polymerization and hydrolysis.