Biological Molecules and Their Functions

Small Molecules in Cells

  • Overview of Small Molecules:
    • Atoms form small molecules, which are crucial for biological functions.
    • Key classes of small molecules include organic and inorganic molecules, primarily derived from a handful of elements.

Carbon Compounds in Cells

  • Importance of Carbon:

    • Nearly all cellular molecules are carbon-based.
    • Carbon's bonding ability:
    • Small size and four outer shell electrons allow for four covalent bonds.
    • Links to other carbon atoms (C–C bonds) to form extensive rings and chains.
    • Organic vs. Inorganic:
    • Organic molecules contain carbon; inorganic molecules do not (e.g., water).

  • Functional Groups:

    • Specific combinations of atoms that influence molecular properties:
    • Methyl (-CH3)
    • Hydroxyl (-OH)
    • Carboxyl (-COOH)
    • Carbonyl (-C=O)
    • Phosphoryl (-PO4)
    • Amino (-NH2)
    • Understanding these groups aids in deciphering life’s chemistry.

Sugars: Energy Sources and Polysaccharides

  • Monosaccharides:

    • Simplest sugars with general formula (CH₂O)n.
    • Example: Glucose (C6H12O6).

  • Carbohydrates:

    • Sugars and larger molecules form carbohydrates.
    • Isomers (same formula, different structures) and optical isomers (mirror images) are prevalent.

  • Functions of Sugars:

    • Energy source (e.g., glucose breakdown releases energy).
    • Storage forms (glycogen in animals, starch in plants).
    • Structural roles:
    • Cellulose (plant cell walls, polysaccharide of glucose).
    • Chitin (fungal cell walls, insect exoskeletons).

  • Polysaccharides and Oligosaccharides:

    • Can have complex branching structures.
    • Component of glycolipids and glycoproteins in cell membranes, aiding in cell recognition and protection.

Fatty Acids and Lipid Membranes

  • Fatty Acid Structure:

    • Comprises a long hydrocarbon chain (hydrophobic) and a carboxyl group (hydrophilic).
    • Amphipathic molecules have both hydrophobic and hydrophilic regions.

  • Lipid Types:

    • Includes triacylglycerols and phospholipids.
    • Phospholipids are crucial for cell membranes, forming lipid bilayers that isolate cellular contents.

  • Cell Membrane Structure:

    • Composed of phospholipids, glycolipids, and other lipids, contributing to selective permeability.

Amino Acids: Building Blocks of Proteins

  • Structure of Amino Acids:

    • Contain a carboxylic acid group (-COOH), an amino group (-NH2), and a variable side chain (R).

  • Types of Amino Acids:

    • 20 standard amino acids, each with distinctive properties based on side chains.

  • Optical Isomers:

    • Amino acids exist as L- and D-forms, where L-forms are found in proteins.

  • Functions of Amino Acids:

    • Amino acids contribute to protein functionality.
    • Side chains can influence polarity, charge, and hydrophilicity/hydrophobicity.

Nucleotides: Subunits of DNA and RNA

  • Nucleotide Structure:

    • Compromised of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and a phosphate group.

  • Types of Bases:

    • Pyrimidines (C, T, U) and purines (A, G).

  • Functions of Nucleotides:

    • ATP as a primary energy carrier; synthesis of macromolecules during metabolism.
    • Role of nucleotides in encoding genetic information in DNA and RNA.

  • Nucleic Acids:

    • DNA: Double-stranded; stable, long-term genetic storage.
    • RNA: Usually single-stranded; more transient in function, involved in protein synthesis.

  • Base Pairing:

    • A-T (or U) and G-C pairing supports hereditary functions and evolution.