Study Notes: The Cell (BIO 121, Campbell - Chapter 6)

Chapter 6: The Cell

Structural Organization of Prokaryotic and Eukaryotic Cells

The cell is the fundamental unit of life, and cells are classified as either prokaryotic or eukaryotic based on their structural organization. Understanding these differences is essential for studying cell biology.

• Prokaryotic Cells: Lack a true nucleus and membrane-bound organelles. Their genetic material is located in a region called the nucleoid.

• Eukaryotic Cells: Possess a true nucleus enclosed by a nuclear envelope and various membrane-bound organelles.

• Size Comparison: Prokaryotic cells are generally smaller (1-10 μm) than eukaryotic cells (10-100 μm).

• Advantages of Small Cell Size:

  • Higher surface area-to-volume ratio, facilitating efficient exchange of materials.

  • Faster cellular processes due to shorter diffusion distances.

Example: Escherichia coli is a typical prokaryotic cell, while animal and plant cells are eukaryotic.

Microscopy in Cell Biology

Microscopy is essential for visualizing cells and their components. Different types of microscopes are used in biology, each with specific advantages and limitations.

• Light Microscopy: Uses visible light to illuminate specimens. Suitable for observing living cells and tissues.

• Electron Microscopy: Uses beams of electrons for much higher resolution. Includes Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM).

• Advantages and Disadvantages:

  • Light microscopes allow observation of living cells but have lower resolution.

  • Electron microscopes provide detailed images of cell ultrastructure but require fixed (dead) specimens.

Example: TEM is used to study internal cell structures, while SEM provides 3D images of cell surfaces.

Eukaryotic Cell Structure: Membranes and Organelles

Eukaryotic cells are characterized by compartmentalization, with various organelles performing specialized functions.

• Plasma Membrane: Selectively permeable barrier that regulates entry and exit of substances.

• Cell Membrane vs. Cytoplasm vs. Cytosol:

  • Cell Membrane: Outer boundary of the cell.

  • Cytoplasm: Region between the plasma membrane and nucleus, containing organelles.

  • Cytosol: Fluid portion of the cytoplasm.

• Major Organelles and Their Functions:

  • Nucleus: Stores genetic material (DNA).

  • Rough and Smooth Endoplasmic Reticulum (ER): Protein and lipid synthesis.

  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

  • Mitochondria: Site of cellular respiration and energy production.

  • Lysosomes: Digestive organelles containing hydrolytic enzymes.

  • Transport Vesicles: Move materials between organelles.

Example: Animal cells contain lysosomes, while plant cells have large central vacuoles.

Cytoskeleton and Cell Motility

The cytoskeleton provides structural support and enables cell movement. It consists of different types of protein filaments.

• Microfilaments: Composed of actin; involved in cell shape and movement.

• Intermediate Filaments: Provide mechanical strength.

• Microtubules: Hollow tubes made of tubulin; involved in organelle movement and cell division.

• Extracellular Matrix (ECM): Network of proteins and carbohydrates outside the cell, providing structural support.

• Motility Structures:

  • Cilia: Short, hair-like structures for movement or fluid transport.

  • Flagella: Long, whip-like structures for cell locomotion.

• Centrioles: Organize microtubules during cell division.

Example: Human respiratory tract cells use cilia to move mucus; sperm cells use flagella for movement.

Plant vs. Animal Cells: Structural Differences

Plant and animal cells share many features but also have distinct differences, especially in their structural components and organelles.

• Cell Wall: Present in plant cells, providing rigidity and protection; absent in animal cells.

• Central Vacuole: Large organelle in plant cells for storage and maintaining turgor pressure.

• Chloroplasts: Site of photosynthesis in plant cells; absent in animal cells.

• Lysosomes: Common in animal cells; plant cells use vacuoles for similar digestive functions.

• Organelle Comparison Table:

Organelle	Plant Cell	Animal Cell
Cell Wall	Present	Absent
Central Vacuole	Present (large)	Absent or small
Chloroplasts	Present	Absent
Lysosomes	Absent (vacuole serves similar function)	Present

Example: The central vacuole in plant cells stores nutrients and waste products, while lysosomes in animal cells digest cellular debris. *Additional info: The notes have been expanded with definitions, examples, and a comparison table for clarity and completeness.*