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Living organisms are predominantly composed of carbon-based chemicals.
Carbon's unique ability allows it to form diverse, complex molecules, the foundation of organic compounds.

Organic Compounds: Compounds that contain carbon.
Four main classes of biologically significant molecules:
- Carbohydrates
- Lipids
- Proteins
- Nucleic acids
Carbohydrates, lipids, and proteins can form macromolecules, which are massive compounds made of smaller units (monomers).

Versatility: Carbon can form four covalent bonds with various elements, determining its bonding capability.
Tetrahedral Geometry: When forming bonds, carbon adopts a tetrahedral shape unless involved in double bonds, leading to planar arrangements.

Simple Molecules: Illustrations of molecules like methane (tetrahedral) and ethene (flat due to double bonds) demonstrate how bonding affects shape.
Valences: Carbon's covalent bonding abilities are showcased through its compatibility with numerous elements.
Carbon can form chains or cycles, leading to a vast diversity of organic molecules, impacting length, branching, and the presence of double bonds.

Hydrocarbons: Composed entirely of carbon and hydrogen; many lipids include hydrocarbon components, and they can release substantial energy during reactions.

Isomers: Compounds that share the same composition but differ in structure and properties.
- Structural Isomers: Variations in atomic arrangements.
- Cis-Trans Isomers: Configurations that arise due to double bonds.
- Enantiomers: Mirror-image compounds often with distinct biological activities.

Functional Groups: Groups of atoms within molecules that determine chemical properties, modifying hydrocarbons.
Key Moieties:
- Hydroxyl (-OH): Found in alcohols, soluble in water.
- Carbonyl (C=O): Key feature in sugars and other molecules.
- Carboxyl (-COOH): Found in organic acids, important for metabolism.
- Amino (-NH2): Basic group in amino acids, critical for proteins.
- Phosphate (-PO4): Important in energy transfer (ATP).
- Methyl (-CH3): Alters the properties of biological molecules.

ATP (Adenosine Triphosphate): Accounts for a major source of energy, facilitating various cellular processes by releasing energy upon hydrolysis.

Polymers: Long molecules made from repeating subunits (monomers).
The synthesis and breakdown of polymers occur via dehydration synthesis (forming polymers) and hydrolysis (breaking down polymers), often facilitated by enzymes.
Polymers exhibit vast diversity based on their constituent monomers and linkages.

Monosaccharides: Simple sugars acting as building blocks for larger carbohydrates (polysaccharides).
Polysaccharides: Include storage types like starch and glycogen as well as structural types like cellulose.
Structural and storage polysaccharides differ in shape and function: starch is helical while cellulose is linear, influencing digestibility and utility.

Lipids: Diverse group that lacks true polymers; characterized by their hydrophobic nature and functional importance.
Fats: Composed of glycerol and fatty acids. Types include saturated (solid at room temperature) and unsaturated (liquid).
Phospholipids: Key components of cell membranes, featuring hydrophilic heads and hydrophobic tails, self-organizing into bilayers in water.
Steroids: Include cholesterol, important for membrane structure but can impact health at high levels.

Proteins: Comprise a majority of cellular mass, involved in diverse functions from movement to signaling.
Amino Acids: Building blocks linked by peptide bonds to form polypeptides; properties are determined by their side chains (R groups).
Protein Structure: Organized into four levels: Primary, Secondary, Tertiary, and Quaternary, each influencing the protein's function.
Denaturation: Loss of protein structure can occur due to changes in environmental conditions, leading to inactivity.

Nucleic Acids: DNA and RNA serve as vehicles of genetic information.
DNA: Double helix structure, essential for heredity and providing instructions for protein synthesis.
RNA: Single-stranded; plays roles in translating genetic code into functional proteins.
Polynucleotides: Chains of nucleotides connected by phosphodiester linkages.

Human Genome Project: Significant advancement in sequence analysis, offering insights into gene functions and related disorders.
Bioinformatics: Combines biology with computational tools to manage genomic data.
Comparative Genomics: Studies gene similarities across species to investigate evolutionary relationships.

Genetic sequences' similarities between individuals and species provide insight into evolutionary kinship, underlying the processes of common descent.