CH. 2 | Cells: The Living Units

Define cell, its basic activities, and its three major regions.

Cell

• The smallest living unit in the body

  • Functions:
    → Obtain nutrients and essential substances from body fluids
    → Use nutrients to make molecules in order to survive
    → Dispose of waste
    → Maintain its shape and integrity
    → Replicate itself
    
    

Cell’s 3 Major Regions

• Plasma Membrane

  • Outer boundary

• Cytoplasm

  • Internal, contains most organelles

• Nucleus

  • Surrounded by the cytoplasm, controls cellular activities

Describe the composition and basic functions of the plasma membrane.

Plasma Membrane

• Composition / Structure

  • The Fluid Mosaic Model

    • A bilayer of lipid molecules with protein molecules embedded within it
      
      

• Phospholipid (most abundant)

  • Each molecule has:

    • Polar “head” — charged, attracted to water, and lines the inner and outer faces of the membrane

    • Nonpolar “tail” — uncharged, avoids water, lines up in the center
      
      

• Other Lipids

  • Glycolipids — Sugar groups that are attached to about 10% of the outer lipid molecules (“sugar fats”)

  • Cholesterol — Makes the membrane more rigid and increases its impermeability to water and water-soluble molecules
    
    

• Proteins

  • Two distinct types:

    • Integral Proteins

      • Firmly embedded in or attached to the lipid bilayer

      • Most are transmembrane proteins — span the entire width of the membrane, protruding from both sides

    • Peripheral Proteins

      • Loosely attached to the membrane surface

      • Forms a network of filaments that supports the membrane from its cytoplasmic side (without them, the membrane would tear easily)
        
        

• Glycocalyx (Cell Coat)

  • Short chains of carbohydrates attach to integral proteins → forms glycoproteins

  • These sugars project from the external cell surface → forming the glycocalyx

    • Function of the Glycocalyx

      • Sticky — Helps bind cells together

      • Biological marker — Each cell type has a unique sugar pattern, allowing cells to recognize each other

      • i.e., a sperm recognizes an egg cell by the distinctive composition of its glycocalyx

Structure of a generalized cell

Explain the different processes used to move across the plasma membrane.

Describe the structure and cellular activity of each organelle: ribosomes, endoplasmic reticulum, golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeleton, centrosome, and centrioles.

Describe the role of each of the three parts of the nucleus in the control of cellular activities: the nuclear envelope, the nucleolus, and chromatin.

List the phases of the cell life cycle, and describe a key event of each phase.

Name specific cell types, and relate their overall shape to their specific functions.