Cell Biology - Key Concepts

Cell Biology - Lecture 2: Cell Components

Learning Objectives

  • Identify the main components of cells
  • Explain the functions of key organelles in cells
  • Explain the process of protein production in cells
  • Understand projections from the surface of the cells and their functions
  • Explain how cells are bound together and the different types of junctions

Main Components of Cells

  • Plasma membrane
  • Nucleus
  • Cytoplasm:
    • Cytosol
    • Organelles
    • Cytoplasmic inclusions
    • Cytoskeleton

Plasma Membrane

  • Structure:
    • Outer boundary of the cell.
    • Composed of a lipid bilayer (with polar and non-polar regions) and proteins.
    • Highly dynamic and fluid.
    • Components:
    • Polar heads (water-soluble)
    • Non-polar tails (lipid-soluble)
    • Cholesterol and membrane-associated proteins.

Nucleus

  • Function:
    • Control center of the cell via DNA.
  • Components:
    • Nuclear Envelope:
    • Double membrane structure with nuclear pores.
    • Nucleolus:
    • Produces ribosomes.
    • Chromatin:
    • DNA associated with histone proteins.

Endoplasmic Reticulum (ER)

  • Smooth ER (SER):
    • Tubular network involved in steroid synthesis, cholesterol synthesis, and drug metabolism.
    • Site for lipid synthesis.
  • Rough ER (RER):
    • Studded with ribosomes where protein synthesis occurs.
    • Composed of cisternae (sheets).

Protein Synthesis and Transport

  • Process Overview:
    1. Protein synthesis occurs in the Rough ER.
    2. Proteins are transported to the Golgi apparatus for processing.
    3. Proteins exit either within lysosomes or secretory granules.

Golgi Apparatus

  • Function:
    • Modifies, sorts, and packages proteins for secretion or use inside the cell.
  • Lysosomes:
    • Contains enzymes that digest unwanted molecules.
  • Cis and Trans Faces:
    • The sides of the Golgi apparatus that face the ER and plasma membrane, respectively.

Mitochondria

  • Function:
    • Provides energy for the cell in the form of ATP (adenosine triphosphate).
  • Structure:
    • Outer and inner membranes forming cristae to increase surface area.

Cytoplasmic Inclusions

  • Includes various components like:
    • Pigments (e.g., melanin in skin cells).
    • Glycogen (e.g., in liver cells).
    • Lipid droplets (e.g., in fat cells).

Cell Projections

  • Microvilli:
    • Increases surface area for absorption.
  • Cilia:
    • Involved in motility and moving materials along cell surfaces.
  • Both projections consist of microtubules and microfilaments for structural support.

Cell-Cell Connections

  • Close interactions between adjacent cell membranes that help:
    • Prevent the passage of substances between cells.
    • Promote communication and structural integrity.
  • Types of Junctions:
    1. Tight Junctions:
    • Impermeable junctions preventing passage between cells.
    1. Desmosomes:
    • Anchor cells together for strength and support.
    1. Gap Junctions:
    • Connexins form channels for communication between adjacent cells.