Notes on Cell Biology and Membrane Functions

Key Concepts in Cell Biology

  • 6.1 Biologists use microscopes and biochemistry to study cells

    • Microscopes extend human vision to study cells, including Light Microscopes (LM) and Electron Microscopes (EM).
    • Tremendous advancements have been made since the first microscopes in the late 1500s.
    • Parameters for microscopy include magnification, resolution, and contrast.

  • 6.2 Eukaryotic cells have internal membranes that compartmentalize their functions

    • Eukaryotic cells contain organelles that perform specific functions, each enclosed by membranes.
    • The plasma membrane acts as a selective barrier; cells can differ widely in structure and function.
    • Cells can range in size but are generally around 1 – 100 μm.

  • 6.3 The eukaryotic cell's genetic instructions are housed in the nucleus and carried out by the ribosomes

    • The nucleus contains the cell's DNA and conducts gene expression through ribosomes.
    • Ribosomes can be free in the cytoplasm or bound to the endoplasmic reticulum, where they perform protein synthesis.

  • 6.4 The endomembrane system regulates protein traffic and performs metabolic functions

    • The endomembrane system includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles, which collaborate in the synthesis and transport of proteins and lipids.
    • Smooth ER synthesizes lipids and detoxifies molecules, while rough ER assists in protein synthesis.

  • 6.5 Mitochondria and chloroplasts change energy from one form to another

    • Mitochondria are the sites for cellular respiration, converting energy from nutrients to ATP.
    • Chloroplasts conduct photosynthesis in plants, converting solar energy into chemical energy.
    • Evidence supports the endosymbiont theory regarding the evolution of mitochondria and chloroplasts.

  • 6.6 The cytoskeleton is a network of fibers that organizes structures and activities in the cell

    • The cytoskeleton provides mechanical support, helps maintain cell shape, and facilitates cell motility.
    • Composed of microtubules, microfilaments, and intermediate filaments, each part has distinct functions and characteristics.
    • Microtubules guide vesicle movement, while microfilaments play crucial roles in muscle contraction and cell shape changes.

  • 6.7 Extracellular components and connections between cells help coordinate cellular activities

    • Plant cells have cell walls made from cellulose, while animal cells secrete an extracellular matrix (ECM) made of glycoproteins for communication and support.
    • Cell junctions, such as tight junctions and gap junctions, enable communication and connection between adjacent cells.

  • 6.8 A cell is greater than the sum of its parts

    • Cellular processes integrate various components, enabling complex behaviors and functions.
    • The interdependence of cellular organelles shows how structure and function work together in cellular biology.

Microscopy and Cell Study

  • Microscopy: Used to visualize cells; advances in techniques like light and electron microscopy have significantly enhanced understanding of cell structure.
  • Cell Fractionation: A process that separates cellular components for study, allowing correlation between function and structure

Techniques for Cell Study

  • Light Microscopy: Allows up to 1,000x magnification, limited to details above 0.2 μm.
  • Electron Microscopy: Offers greater resolution (0.002 nm) for studying organelles (SEM, TEM).

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells: Lacks nucleus, no membrane-bound organelles (e.g., bacteria).
  • Eukaryotic Cells: Contains a true nucleus and membrane-bound organelles (e.g., plant and animal cells).
  • Both types share basic features like plasma membrane and ribosomes, but differ in structure and complexity.

Cellular Functions

  • Transport Mechanisms: Passive transport (diffusion, facilitated diffusion) vs. active transport (requires energy) for moving substances across membranes.
  • Specific transport proteins (channel, carrier) facilitate the movement of ions and large molecules through the membrane.
  • Importance of membrane fluidity influenced by temperature and lipid composition in maintaining proper function.

Review: Important Concepts

  • Membrane Composition: Fluid mosaic model emphasizing phospholipid bilayer and embedded proteins for selective permeability.
  • Carbohydrates attached to membranes serve as recognition sites and are critical in cell-cell interactions.
  • Endocytosis and Exocytosis: Mechanisms for bulk transport into and out of cells play essential roles in cell function and communication.