Human Biology: Cells and Their Functions

Introduction to Cell Biology

• Welcome back to BIOS 150: Human Biology

• Entering Week 2: Discussion on cells

• Objectives for the class

  • Introduction to cells: their study and history

  • Overview of Cell Theory

  • Key cellular structures: plasma membrane, cytoplasm, organelles

  • Cellular division: Mitosis and Meiosis

  • Cellular imbalances and their effects on homeostasis including cancer

Defining the Cell

• Definition: The smallest living unit carrying out all life's functions

• Living organisms made of cells; even unicellular organisms fulfill this criterion

• Non-living entities like viruses and prions, despite impacting biology significantly

• Human body comprises approximately 37 trillion cells (37,000,000,000,000 cells)

  • Sharing characteristics: plasma membrane, cytoplasm, DNA

• Importance of studying cells

  • Connection with various diseases including:

  • Sickle Cell Disease: abnormally shaped red blood cells impede oxygen transport

  • Neuropathies: disruption in nerve cell signaling

  • Cancer: uncontrolled cellular growth leading to tissue invasion

Cytology: The Study of Cells

• Etymology: "Cyto" (cell) + "-ology" (study)

• Essential for fields: pathology, oncology, genetics

• Historical perspective: Robert Hooke's discovery in the 1600s

  • Use of microscopes to observe cells - led to observation of cork cells

• Key figures in cell study:

  • Robert Hooke

  • Schwann and Schleiden: development of Cell Theory

  • Rudolf Virchow: "Omnis cellula e cellula" - cells come from pre-existing cells

Cell Theory

• Three significant principles of Cell Theory:

  • All living organisms are composed of cells (unicellular or multicellular)

  • Cells are the basic units of structure and function in living organisms

  • Essential functions performed include energy production, growth

  • All cells arise from pre-existing cells, disproving spontaneous generation

  • Significant shift in medical understanding aiding health outcomes and healing processes

Basic Structure of Cells

• Common to various cell types, including eukaryotic cells:

  • Plasma Membrane: semi-permeable barrier regulating substance passage

  • Cytoplasm: gel-like substance where organelles reside

  • Nucleus: control center housing DNA, guiding cellular function

Plasma Membrane

• Description: Protective barrier, selectively permeable

• Composition:

  • Phospholipid Bilayer: Contains hydrophilic (water-loving) heads and hydrophobic (water-repellant) tails

  • Channel proteins: Allow selective passage of molecules

  • Carrier proteins: Transport specific molecules across the membrane

  • Receptor proteins: Detect and respond to signals

  • Cholesterol: Provides stability and flexibility of the membrane

  • Carbohydrates: Act as identification tags for cell surface recognition

Cellular Transport Mechanisms

• Passive Transport: Does not require energy; substances move from high to low concentration

  • Types of passive transport:

  1. Diffusion: Movement of small/nonpolar molecules

  2. Osmosis: Diffusion of water through selectively permeable membranes

  3. Facilitated Diffusion: Larger or charged molecules assisted by proteins

• Active Transport: Requires energy (usually ATP); substances move against their gradient

  • Includes:

  1. Endocytosis: Engulfing substances into the cell

  2. Exocytosis: Expelling substances out of the cell

     • Types of Endocytosis:

     • Phagocytosis (cell eating of large particles),

     • Pinocytosis (cell drinking of fluids),

     • Receptor-mediated Endocytosis (specific molecule intake)

Cytoplasm and Organelles

• Components of Cytoplasm:

  • Cyto: Meaning ‘cell’, Cytosol: Liquid component with electrolytes and nutrients

  • Organelles: Specialized structures fulfilling individual functions

  • Nucleus: Regulation of cellular activities and genetic information management

    • DNA: Contains instructions for function, growth, and protein production

    • Nucleolus: Produces ribosomes

  • Endoplasmic Reticulum (ER):

    • Rough ER: Contains ribosomes; modifies and folds proteins

    • Smooth ER: Synthesizes lipids and detoxifies harmful substances

  • Golgi Apparatus: Modifies, sorts, and packages proteins for delivery

  • Lysosomes: Breakdown waste material, bacteria, and cellular debris

  • Mitochondria: Powerhouse of the cell; ATP production through cellular respiration

    • Contains own DNA, maternal inheritance

Cell Division

• Importance of Cell Division:

  • Growth, healing processes, and tissue maintenance

• Phases of the Cell Cycle:

  • Interphase: Preparation for division; includes G1 (growth), S (DNA synthesis), G2 (final preparations)

  • Mitosis: Dividing the nucleus (Phases: Prophase, Metaphase, Anaphase, Telophase) and Cytokinesis (cytoplasm division)

• Meiosis: Special type of cell division for gametes; results in non-identical cells with half the chromosome count

  • Goals: Genetic variation through crossing over and reduction of chromosome number:

  • Haploid (23 chromosomes) vs Diploid (46 chromosomes)

Impacts of Abnormal Cell Division

• Cancer: Result of uncontrolled cellular division due to DNA mutation

  • Types of cancers: Vary based on affected cell types

  • Environmental causes: Carcinogens, radiation exposure, infections, and inherited traits

  • Normal vs Cancer Cells: Comparison showing growth, signaling mechanisms, anchorage dependence, and response to apoptosis

• Consequences of Errors in Division:

  • Insufficient cell division leading to poor healing, tissue damage

  • Genetic disorders from faulty replication, chromosome separation errors (e.g., Down syndrome)

Conclusion

• Emphasizes the interconnectedness of cellular function, structure, and human health

• Importance of understanding cellular mechanisms in healthcare and disease management

• Future studies will build on the foundation laid in this segment regarding cellular biology and its implications for health.