Lesson 2

• Organelles found in the cytoplasm include:

  • Ribosomes
  • Endoplasmic Reticulum
  • Golgi Apparatus
  • Secretory Granules
  • Lysosomes
  • Mitochondria
  • Peroxisomes
• Ribosomes:

  • Consist of small and large subunits
  • Formed in the nucleus (nucleolus) and exported to the cytoplasm
  • Small subunit has highly folded rRNA chain associated with proteins
  • Large subunit has three other rRNA molecules and basic proteins
  • Functions in protein synthesis
  • Engage in protein synthesis by binding to mRNA to form polyribosomes or polysomes
  • Bound ribosomes produce proteins for secretion, plasma membrane, and lysosomes
  • Free ribosomes produce proteins used within the cell
• Endoplasmic Reticulum:

  • A convoluted membranous network extending from the nucleus throughout the cytoplasm
  • Rough ER is involved in the production of membrane-associated proteins and proteins for secretion
  • Smooth ER lacks bound polyribosomes and performs functions like synthesis of phospholipids, detoxification, and calcium regulation
• Golgi Apparatus:

  • Series of elongated, flattened saclike membranous structures
  • Modifies, packages, and sorts materials from the ER
  • Forms secretory vesicles and lysosomes
• Secretory Granules:

  • Formed as vesicles in the Golgi apparatus
  • Contain a concentrated form of the secretory product
  • Zymogen granules contain digestive enzymes
• Lysosomes:

  • Spherical-shaped membrane-bound organelles formed from the Golgi apparatus
  • Contain about 40 different hydrolytic enzymes
  • Sites of intracellular digestion and turnover of cellular components
• Peroxisomes:

  • Smaller, spherical-shaped membrane-bound organelles
  • Contain oxidative enzymes like oxidases and catalase
• Mitochondria:

  • Double membrane-bound organelles containing circular DNA
  • Synthesize ATP during cellular respiration
  • Mitochondrial matrix contains enzymes for oxidation of pyruvate and fatty acids
• Inclusions in the cell:

  • Temporary structures containing accumulated metabolites or substances
  • Include lipid droplets, glycogen granules, zymogen granules, pigment granules, crystals, and dust particles
• Lipid Droplets:

  • Accumulations of lipid in adipocytes and other cells
• Glycogen Granules:

  • Aggregates of the carbohydrate polymer glucose stored in cells
  • Visible as periodic acid-Schiff (PAS) positive material in liver cells
• Pigment Deposits:

  • Melanin: dark brown granules protecting cells from UV radiation
  • Lipofuscin: pale brown granules found in stable nondividing cells
  • Hemosiderin: dense brown aggregate of denatured ferritin proteins with bound iron