Lecture Notes on Cells

Overview of Cells

• Smallest living units of organisms
• All cells have:
  • Cell membrane: separates cell from environment
  • Cytoplasm: jelly-like fluid inside the cell
  • DNA: genetic material of the cell

Categories of Cells

1. Eukaryotic Cells

   • Have organelles (e.g., nucleus)
   • More complex and advanced
   • Found in plants and animals

2. Prokaryotic Cells

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

Organelles

• Special parts of a cell with unique functions

Nucleus

• Control center of the cell
• Contains DNA
• Chromatin: tangled form of DNA
• Chromosomes: condensed DNA during cell division
• Contains nucleolus: where ribosomes are made

Ribosomes

• Synthesizes/makes proteins
• Can be free in cytoplasm or attached to Endoplasmic Reticulum (ER)

Endoplasmic Reticulum (ER)

• Membrane-enclosed passageway for transporting materials
• Rough ER: has ribosomes attached
• Smooth ER: lacks ribosomes

Golgi Apparatus (Golgi Body)

• Receives proteins from ER
• Customizes proteins (folds and adds materials like lipids or carbohydrates)

Vacuoles

• Sac-like structures for storage
• Central vacuole in plant cells stores water

Lysosomes

• Garbage collectors of the cell
• Contains enzymes to break down damaged cell parts

Mitochondria

• Powerhouse of the cell
• Produces ATP during cellular respiration
• More mitochondria in cells needing more energy

Cytoskeleton

• Maintains cell shape
• Composed of microfilaments and microtubules

Chloroplasts

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

Cell Wall

• Present in plant cells outside the cell membrane
• Provides shape, support, and protection
• Not found in animal cells

Unique Structures in Some Cells

• Cilia: hair-like projections in human respiratory tract cells, helps in trapping particles
• Flagella: tail-like structure for movement, present in some bacteria and sperm cells

Summary

• Eukaryotic cells: have nucleus and organelles (plants and animals)
• Prokaryotic cells: unicellular, no nucleus or membrane-enclosed organelles
• All cells share a cell membrane, cytoplasm, and genetic material
• Chloroplasts in plant cells; both plant and animal cells have mitochondria.