MOL100 - Lecture 1: Cells and the Molecules of Life

Core Concepts of Molecular Biology

The (Macro-) molecules of Life

• Proteins (Covered in more detail in lectures 2-5)

  • Most abundant macromolecules in cells.

  • Chains of 20 different amino acids.

  • The sequence (order) of amino acids dictates the protein's 3-dimensional structure (primary, secondary, tertiary, and sometimes quaternary levels) (further discussed in lecture 3).

  • Functions:

  • Enzymes: Catalysis of chemical reactions (e.g., Amylase breaking down starch into glucose) (further discussed in lecture 4).

  • Structural proteins: Form structures like filaments of the cytoskeleton, essential for regulating cell shape and intracellular transport.

  • Numerous other functions exist, including transport, signaling, and immune response.

• Nucleic Acids (Covered in more detail in lectures 2, 7-8)

  • DNA (deoxyribonucleic acid):

  • Composed of four different nucleotides: A (Adenine), G (Guanine), T (Thymine), and C (Cytosine).

  • Two DNA strands intertwine to form a double helix.

  • The two strands are complementary: A always binds to T, and C always binds to G.

  • This complementarity is crucial for making copies of DNA, which is essential for heredity (arvelighet) (further discussed in lecture 9).

  • DNA encodes information for proteins (further discussed in lecture 8).

    • Genes: Functional units located on the DNA strand.

    • Transcription: DNA is transcribed into RNA (ribonucleic acid).

    • Messenger RNAs (mRNAs): Are translated into proteins.

    • Coding sequence: Determines which specific amino acids are incorporated into the protein.

    • Regulatory sequences: Control when and where an RNA is produced.

    • Non-coding RNAs: Some RNAs are not translated into proteins but have other functions.

• Phospholipids (Covered in more detail in lectures 2, 9)

  • Amphipathic molecules: Possess both hydrophilic (water-loving) and hydrophobic (water-fearing) properties.

  • Hydrophilic head: Charged, containing phosphorous.

  • Hydrophobic tail: Made of fatty acid chains.

  • In aqueous (watery) solutions, phospholipids self-arrange into bilayered (two-layered) membranes.

  • The hydrophilic heads face outwards towards the aqueous environment.

  • The hydrophobic tails face inwards, forming the core of the membrane.

  • Cellular membranes (biomembranes):

  • Contain numerous proteins and other lipids (e.g., cholesterol).

  • Crucially surround aqueous liquids to separate the cell's interior from its external environment.

  • Also generate distinct compartments within cells (further discussed in lecture 7).

• Polysaccharides (Saccharides/Sugars) (Covered in more detail in lecture 2)

  • Polymers of monosaccharide units.

  • Functions: Energy storage (e.g., starch in plants, glycogen in animals), structural components (e.g., cellulose in plant cell walls, chitin in fungi and arthropods).

Cells as Fundamental Units of Life

• Living organisms are organized hierarchically: molecules \to cells \to organisms \to ecosystems.

• Cells can be broadly classified into two main types: Prokaryotic cells and Eukaryotic cells.

  • Prokaryotic cells: Simpler, lack a membrane-bound nucleus and other organelles (e.g., bacteria, archaea).

  • Eukaryotic cells: More complex, possess a membrane-bound nucleus and various organelles (e.g., animal, plant, fungal cells).

Common Ancestry of Cells

• All living organisms share a common ancestral cell.

• A phylogenetic tree illustrates these evolutionary relationships.

• Due to this shared evolutionary origin, many fundamental features and molecules are conserved across all cells.

• This conservation allows us to