Ultra Structure of Cell

Introduction to Cells

• Cells are the basic structural and functional units of life.
• Organisms can be unicellular (e.g., most bacteria) or multicellular (e.g., humans).

Cell Functions

• Cells can vary in shape and function, such as:
  • Secretion (e.g., enzymes)
  • Storage of sugars or fats
  • Memory and intelligence (e.g., brain cells)
  • Contraction (e.g., muscle cells)
  • Protection (e.g., skin cells)
  • Defense (e.g., white blood cells)

History of Cell Study

• Anton Leeuwenhoek invented the microscope in the late 1600s, first observing cells.
• Light microscopes have limited resolution compared to electron microscopes.

Basic Cell Organization

• All cells contain:
  1. Cell membrane: separates the interior from the exterior.
  2. DNA-containing region: holds instructions for life processes.
  3. Cytoplasm: semi-fluid containing the cell's machinery.

Types of Cells

• Prokaryotic Cells:
  • No internal membranes or organelles.
  • DNA is loose in the cytoplasm.
  • Surrounded by a rigid cell wall; sometimes a polysaccharide capsule.
  • Use flagella for movement.
  • Exhibit diverse internal metabolic systems.
• Eukaryotic Cells:
  • Larger and more complex than prokaryotes.
  • Contain organelles with specific functions.
  • DNA enclosed in a nucleus.

Eukaryotic Cell Components

• Organelles include:
  • Cell membrane
  • Nucleus
  • Endoplasmic reticulum (smooth and rough)
  • Golgi apparatus
  • Lysosomes
  • Peroxisomes
  • Mitochondria
  • Cytoskeleton
  • Special plant organelles like chloroplasts and central vacuole

Cell Membrane

• Composed of a phospholipid bilayer with embedded proteins.
• Functions as a selective barrier.
• Involved in cell recognition and transport.

Transport Across Cell Membrane

• Passive transport: moves substances down the concentration gradient without energy.
• Active transport: requires energy (ATP) to move substances against the gradient.
• Bulk transport: for large quantities via endocytosis and exocytosis.

Nucleus

• Contains DNA, organized into chromosomes.
• Site of RNA transcription and ribosome production (nucleolus).

Endoplasmic Reticulum (ER)

• Rough ER: studded with ribosomes; synthesizes proteins.
• Smooth ER: synthesizes lipids; detoxifies chemicals.

Golgi Apparatus

• Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

Lysosomes and Peroxisomes

• Lysosomes: contain digestive enzymes for waste breakdown.
• Peroxisomes: break down fatty acids; generate hydrogen peroxide.

Vacuoles

• Large central vacuole in plant cells for storage and maintaining cell structure.

Ribosomes

• Site of protein synthesis, found on rough ER or floating in cytoplasm.

Plant-Specific Organelles

• Chloroplasts: sites of photosynthesis; contain chlorophyll.
• Cell wall: provides rigidity and protection, made of cellulose.

Mitochondria

• Powerhouse of the cell; site of ATP production.
• Contains its own DNA, similar to bacterial DNA.

Quick Review

• Control center: Nucleus
• Cell boundary: Cell membrane
• Organelles absent in animal cells: Cell wall, central vacuole, chloroplasts
• Photosynthesis organelle: Chloroplasts
• ER: Endoplasmic reticulum

These notes summarize the key points about the ultra structure of cells, including the differences between prokaryotic and eukaryotic cells, the functions of various organelles, and the specific structures found in plant versus animal cells. Understanding these concepts is crucial for comprehending cellular biology and the molecular processes that sustain life.