Bioscience Foundations - Week 3: Cells

Week 3 - Cells Overview

  • Definition of Cells: Smallest units of life, with ~50-100 trillion cells in humans and ~250 different cell types.
  • Cell Theory: 1) Cells are the smallest unit of life. 2) All organisms consist of one or more cells. 3) Cells arise from other cells.

Plasma Membrane

  • Structure: Double layer of phospholipids (hydrophilic heads, hydrophobic tails), embedded proteins; referred to as the fluid mosaic model.
  • Functions:   - Physical barrier separating ICF from ECF.   - Selective permeability for substance transport.   - Communication and cell recognition via membrane proteins.

Membrane Proteins

  • Varieties include integral proteins (for transport, communication) and peripheral proteins (support).
  • Roles of Proteins: Transport, signal transduction, enzymatic activity, attachment to cytoskeleton, and cell-cell joining.

Transport Mechanisms

  • Passive Transport: No energy required, substances move down concentration gradient (e.g., diffusion, osmosis).
  • Active Transport: Requires energy (ATP) to move substances against concentration gradient (e.g., primary, secondary transport).
  • Vesicular Transport: Movement of large particles via vesicles (endocytosis and exocytosis).

Osmosis and Tonicity

  • Osmosis: Diffusion of water through a selectively permeable membrane; influenced by solute concentration.
  • Tonicity Types: 1) Isotonic (equal concentrations), 2) Hypertonic (higher concentration outside), 3) Hypotonic (lower concentration outside).

Cytoplasm and Organelles

  • Cytoplasm: Site of metabolic activities, includes cytosol, organelles, and inclusions.
  • Organelles: Specialized compartments, e.g., mitochondria (ATP production), ribosomes (protein synthesis), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (transport and modification of proteins).

Nucleus

  • Function: Control center; houses genetic material; coordinates protein synthesis.
  • Structure: Nuclear envelope, nucleoli, chromatin.

Cell Cycle

  • Composed of Interphase (G1, S, G2) and Mitotic Phase (Mitosis and Cytokinesis); essential for growth and repair.