CONSERTS OF Rab®GY

Chapter 3: CHAPSTRUCTURE AND FUNCTION

1. Overview of Cellular Structure
  • Cells are the fundamental building blocks of all living organisms.
  • Despite diversity among cells from different organisms, such as (a) nasal sinus cells, (b) onion cells, and (c) Vibrio tasmaniensis bacterial cells, all cells exhibit certain common structural characteristics. These characteristics include cellular membranes, cytoplasm, and genetic material organized as DNA.
2. Microscopy Techniques
2.1 Light Microscopes
  • Most light microscopes used in college biology labs can magnify cells up to approximately 400 times.
  • They are particularly useful for viewing prepared slides of cells and tissues.
2.2 Dissecting Microscopes
  • Dissecting microscopes have a lower magnification than light microscopes and are utilized to examine larger, three-dimensional objects, such as tissues.

3. Bacterial Cells: Observations

  • Figure 3.3 depicts Salmonella bacteria:
    • (a) Viewed under a light microscope.
    • (b) Scanning electron micrograph illustrating Salmonella (in red) invading human cells.
  • Such observations emphasize the significance of cellular interactions, particularly in pathogenic contexts.
4. Uterine Cervix Cells
  • Figure 3.4 illustrates uterine cervix cells obtained from a Pap smear:
    • Normal cells on the left.
    • Cells afflicted by human papillomavirus on the right.
5. Prokaryotic vs. Eukaryotic Cells
  • Figure 3.5 shows the generalized structure of a prokaryotic cell.
  • Additionally, comparisons of different types of cells and their sizes can provide insight into their respective functions, as shown in Figure 3.6.
6. Cell Structure: Animal vs. Plant Cells
  • Figure 3.7 highlights the structure of:
    • (a) A typical animal cell.
    • (b) A typical plant cell.
  • Notable differences include the presence of a cell wall in plant cells and the various organelles specific to each type.
7. Plasma Membrane Structure
  • Figure 3.8 describes the plasma membrane as a phospholipid bilayer with embedded proteins, in which other components such as cholesterol and carbohydrates might also be included.
  • The composition of the membrane is vital for its function in regulating the entry and exit of substances.
8. Cytoskeleton Components
  • The cytoskeleton is key to cell structure and function, being composed of:
    • Microfilaments.
    • Intermediate filaments.
    • Microtubules.
  • These components serve functions ranging from support to intracellular transport (illustrated in Figure 3.9).
9. The Nucleus and Its Envelope
  • The nuclear envelope, depicted in Figure 3.10, forms the outer boundary of the nucleus. It consists of two phospholipid bilayers—an outer membrane and an inner membrane—differentiating it from the single phospholipid bilayer of the plasma membrane.
10. Golgi Apparatus
  • The Golgi apparatus, visible in a transmission electron micrograph of a white blood cell (Figure 3.11), appears as a stack of semicircular flattened rings, often accompanied by vesicles that play roles in transport and modification of cellular products.
11. Mechanisms of Pathogen Destruction
  • Figure 3.12 illustrates how a macrophage engulfs a pathogenic bacterium. The bacterium is enclosed in a vesicle that fuses with a lysosome for digestion.
12. The Endomembrane System
  • The endomembrane system plays a pivotal role in modifying, packaging, and transporting lipids and proteins (Figure 3.13).
13. Mitochondrial Structure
  • A detailed view of a mitochondrion shows its inner and outer membranes, cristae, and mitochondrial matrix, which are essential for energy production, as depicted in Figure 3.14.
14. Chloroplast Structure
  • Figure 3.15 presents the chloroplast's simplified diagram, including the outer membrane, inner membrane, thylakoids, grana, and stroma, all crucial for photosynthesis.
15. Extracellular Matrix
  • The extracellular matrix is a network of substances secreted by cells, as illustrated in Figure 3.16, contributing to tissue structure and signaling.
16. Types of Intercellular Connections
  • Four types of cellular connections are identified:
    • (a) Plasmodesmata: channels between adjacent plant cells.
    • (b) Tight junctions: junctions that bind adjacent animal cells closely together to prevent passage between them.
    • (c) Desmosomes: connections that join two animal cells.
    • (d) Gap junctions: channels that facilitate communication between animal cells (illustrated in Figure 3.17).
17. Fluid Mosaic Model of the Plasma Membrane
  • The plasma membrane is described by the fluid mosaic model, which accounts for the dynamic structure formed by a mix of phospholipids, cholesterol, proteins, and carbohydrates (Figure 3.18).
18. HIV Infection Mechanism
  • HIV targets and binds to CD4 receptors on T cells, facilitating its entry and infection of the host cell, as seen in Figure 3.19.
19. Diffusion and Osmosis
  • Diffusion: The process of substances moving through a permeable membrane along the concentration gradient from high to low concentration (Figure 3.20).
  • Osmosis: A specific type of diffusion involving water movement from areas of higher to lower water concentration, restricted by a selectively permeable membrane (Figure 3.21).
20. Osmotic Pressure and Cell Shape
  • The osmotic effects on red blood cells are categorized based on the tonicity of the solution: hypertonic, isotonic, and hypotonic (Figure 3.22).
21. Turgor Pressure in Plant Cells
  • Turgor pressure within plant cells correlates with the surrounding solution's tonicity, impacting cell shape and structure (Figure 3.23).
22. Electrochemical Gradients
  • Electrochemical gradients arise due to concentration and electrical differences across a membrane, influencing cellular processes (Figure 3.24).
23. Sodium-Potassium Pump Function
  • The sodium-potassium pump is a vital mechanism for moving potassium and sodium ions across the plasma membrane, crucial for maintaining cellular homeostasis (Figure 3.25).
24. Types of Endocytosis
  • Three forms of endocytosis are identified:
    • (a) Phagocytosis: the cell membrane engulfs a particle, forming a vacuole.
    • (b) Pinocytosis: the cell membrane forms a vesicle around fluid.
    • (c) Receptor-mediated endocytosis: specific uptake of substances through receptor binding on the membrane (illustrated in Figure 3.26).
25. Exocytosis Mechanism
  • Exocytosis involves vesicles migrating to the plasma membrane, where they bind and release their contents to the outside of the cell (Figure 3.27).