Lecture Notes on Cells

Overview of Cells

• Cells are the smallest living units of an organism.
• All cells share three common features:
  • Cell Membrane: Separates the cell’s interior from the environment.
  • Cytoplasm: Jelly-like fluid within the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

1. Eukaryotic Cells

   • Have organelles (e.g., nucleus, specialized parts).
   • More advanced and complex (e.g., plant and animal cells).

2. Prokaryotic Cells

   • Lack a nucleus and membrane-enclosed organelles.
   • Genetic material is not contained within a nucleus.
   • Always unicellular (e.g., bacteria).

Organelles Overview

• Definition: Specialized parts of a cell with unique functions ("little organs").

Nucleus

• Control center of the cell.
• Contains DNA (genetic material).
  • Chromatin: Tangled DNA inside the nuclear membrane.
  • Condenses into chromosomes during cell division.
• Contains a nucleolus, where ribosomes are made.

Ribosomes

• After leaving the nucleus, ribosomes synthesize proteins.
• Either float in cytoplasm or attach to Endoplasmic Reticulum (ER).
  • Types of ER:
    • Rough ER: Has ribosomes attached.
    • Smooth ER: No ribosomes.

Golgi Apparatus

• Receives proteins/materials from ER in vesicles.
• Customizes proteins by folding them or adding materials (lipids, carbohydrates).

Vacuoles

• Sac-like structures for storing materials (e.g., central vacuole in plants stores water).

Lysosomes

• Garbage collectors for damaged/worn-out cell parts.
• Contain enzymes to break down cellular debris.

Mitochondria

• Powerhouse of the cell.
• Produce ATP through cellular respiration for energy.
• More mitochondria in cells that require more energy.

Cytoskeleton

• Maintains cell shape.
• Composed of:
  • Microfilaments: Thread-like protein structures.
  • Microtubules: Thin hollow tubes.

Chloroplasts

• Found in photoautotrophic organisms (e.g., plants).
• Site of photosynthesis; contains chlorophyll (green pigment).

Cell Wall

• Present in plant cells for shape, support, and protection.
• Animal cells do not have a cell wall.

Unique Structures in Some Cells

• Cilia: Microscopic hair-like projections in respiratory tract cells.
• Flagella: Tail-like structures for movement (e.g., some bacteria, sperm cells in humans).

Summary

• Eukaryotic Cells: Have nucleus and membrane-enclosed organelles (plants and animals).
• Prokaryotic Cells: Unicellular, lack nucleus and organelles.
• All cells possess: cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria; only plant cells have chloroplasts.