Cell Structure Quiz

Cell Structure

• Ribosomes: Small particles (15-20 nanometers).
• Types of Ribosomes:
  • Attached ribosomes: Attached to endoplasmic reticulum (rER) for secretory protein formation.
  • Free ribosomes: Located freely in the cytoplasm for cytoplasmic protein formation.
• Ribosome Structure: Composed of ribosomal RNA and proteins. Formed of two subunits (small and large), both made in the nucleolus.
• Centrosome: Non-membranous organoid, a spherical pale area near the nucleus. Contains two cylindrical centrioles surrounded by a pale centrosphere.
• Centriole Structure: Formed of microtubules (9 peripheral triplets).
• Centrosome Function:
  • Acts as a center for mitotic spindle formation during cell division.
  • Serves as the basal body for cilia.
• Cytoskeleton:
  • Components: Microtubules, microfilaments, intermediate filaments.
  • Functions:
    • Maintains cell shape
    • Stabilizes cell attachments
    • Plays a role in cell motility
    • Plays a role in cell division
• Microtubules Structure: Rigid, thin, tubular structures (25 nm diameter.) The wall is composed of protein units called tubulin.
• Microtubules Function:
  • Determine cell shape
  • Intercellular transport
  • Form mitotic spindle in cell division, centrioles, basal bodies, and axoneme of cilia.
• Microfilaments Structure: Very thin structures (5 nm diameter) made of actin molecules.
• Microfilaments Function: Involved in cellular movement and cellular contraction, as seen in muscle cells.
• Intermediate Filaments Structure: About 10 nm thick. Many types, differing based on chemical composition. Provides physical support and stability to cells and tissues.

Cytoplasmic Inclusions

• Substances in the cytoplasm due to cell product accumulation; not involved in cellular activities.
• Types:
  • Stored food (e.g., glycogen, fat)
  • Pigments (e.g., melanin, hemoglobin)
  • Crystals
• Stored Food (e.g., glycogen, fat):
  • Glycogen is stored in large amounts in liver and muscle cells, visible with PAS staining.
  • Fat is stored in fat cells (adipocytes) and stained with Sudan black stain.
• Pigments:
  • Exogenous Pigments: Enter the body from outside (e.g., carotenoids from food, dust, tattoo pigments).
  • Endogenous Pigments: Formed inside the cell (e.g.,
    • Hemoglobin: Important for respiration, gives red color to tissues
    • Hemosiderin: From hemoglobin breakdown
    • Melanin: Skin, hair, and iris pigment
    • Lipofuscin: Residual body pigment)

Self-Exam Questions

• Question 1: Which organelles are formed of two subunits? Answer: Ribosomes
• Question 2: Which organelle acts as a center for mitotic spindle formation? Answer: Centrosomes
• Question 3: Which structures are NOT part of the cytoskeleton? Answer: Myosin filaments
• Question 4: In which organs is glycogen present in large amounts? Answer: Muscles and liver
• Question 5: Which is NOT an endogenous pigment? Answer: Tattoo