Cell Biology Quiz

Cell Structure and Function

• Cell: The basic unit of life, possessing various organelles and structures.
• Cytoplasm: The gel-like substance filling the cell.
• Cytoplasmic contents: Comprised of organelles, inclusions, and cell matrix.
• Organelles: Specialized structures with specific functions within the cytoplasm.
• Membrane-bound organelles: Mitochondria, Golgi apparatus, lysosomes, endoplasmic reticulum, peroxisomes, and cytoplasmic vesicles.
• Non-membrane-bound organelles: Ribosomes and cytoskeleton.
• Cell membrane (Plasma membrane): A thin, flexible outer layer of the cell that regulates the passage of materials into and out of the cell.
  • 9-10 nm thick
  • Not visible in light microscopy
  • Trilaminar (3 layers) in electron microscopy
• Chemical structure of cell membrane: Composed of lipids (phospholipids and cholesterol), proteins (integral and peripheral), and carbohydrates (glycoproteins and glycolipids).
• Functions of cell membrane:
  • Exchanges of materials
  • Endocytosis (Phagocytosis for solid, Pinocytosis for fluids)
  • Exocytosis
  • Sodium-potassium pump
  • Functions of cell coat

Mitochondria

• Definition:
  • Membrane-bound organelles.
  • Powerhouse of the cell responsible for energy production.
• Structure (L.M.): Rods, granules, filaments
• Structure (E.M.): Rod-shaped or spherical, covered by two membranes.
  • Outer membrane: smooth
  • Inner membrane: forms cristae. Has an inter membranous space.
  • Matrix space: contains DNA, RNA, ribosomes, and proteins.
• Function: Produce ATP (energy).
• Number: Variable depending on cell type and function.

Ribosomes

• Definition:
  • Non-membrane-bound organelles.
  • Sites of protein synthesis.
• Structure (L.M.): Basophilic (RNA containing)
• Structure (E.M.):
  • Small particles, two subunits (large and small)
  • Composed of rRNA and proteins.
  • Formed within nucleolus.
  • Released through nuclear pores
• Function: Protein synthesis.
• Types: Free ribosomes (protein synthesis into cytosol) and attached ribosomes (protein synthesis for secretion or incorporation into membranes).

Endoplasmic Reticulum (ER)

• Types:

  • Rough ER (RER): studded with ribosomes; involved in protein synthesis destined for secretion or membrane incorporation.
  • Smooth ER (SER): lacks ribosomes; involved in lipid synthesis, detoxification, carbohydrate metabolism.

• Structure (EM): Interconnecting tubules and cisternae (flattened sacs) to form a network.

• Function (RER): Protein synthesis, particularly proteins destined for transport or secretion.

• Function (SER): Synthesis of steroid hormones, glycogen metabolism, detoxification of toxins, and regulation of calcium in skeletal muscles.

Golgi Apparatus

• Structure (LM): Pale area near nucleus in routine stains; visible with silver staining
• Structure (EM): Composed of flattened sacs called saccules, transfer vesicles, secretory vesicles
• Function:
  • Chemical modification of proteins synthesized by ER.
  • Packaging of proteins into vesicles (for secretion).
  • Secretion of proteins (vesicles move along cytoskeleton to plasma membrane).
  • Formation of coated vesicles and lysosomes.

Lysosomes

• Definition: Membrane-bound organelles containing hydrolytic enzymes.
• Structure: Round, electron-dense bodies.
• Types:
  • Primary lysosomes: Newly formed lysosomes coming from the Golgi.
  • Secondary lysosomes: Primary lysosomes fused with other vesicles to digest material.
• Function:
  • Phagocytosis of foreign particles/bacteria
  • Pinocytosis & digestion of fluids
  • Digestion/breakdown of old organelles.

Cytoskeleton

• Components: Microtubules, microfilaments, and intermediate filaments.
• Microtubules (25nm): Pipe-like structures, made from tubulin protein.
  • Function: Support cell shape, transport substances, form cilia/flagella/centrioles, mitotic spindle.
• Microfilaments (7 nm ): Thin, contractile filaments (actin).
  • Function: Muscle contraction, support for microvilli, cleavage furrow during cell division.
• Intermediate filaments (10nm): Support cell shape, transmission of forces (smooth muscles), and involved in tumor identification.

Centrioles and Centrosome

• Structure: Paired perpendicular centrioles (made of microtubules).
• Function: Organize microtubules for cell division (mitotic spindles) and basal bodies for cilia.

Cilia

• Definition: Hair-like projections on the cell surface.
• Structure: 9 peripheral microtubule doublets and 2 central microtubules.
• Function: Movement of fluids/substances across the cell surface
• Location: Respiratory system, female reproductive system

Cell Inclusions

• Definition: Non-living materials stored in the cytoplasm.
• Types:
  • Stored food (glycogen, lipids)
  • Pigments (exogenous and endogenous)

Nucleus

• Structure (LM):
  • Number: Single (mononucleated), binucleated, multinucleated, or anucleated.
  • Size: Variable (3-14 µm)
  • Shape: Spherically, oval, kidney-shaped, lobed (segmented), horse-shoe shaped.
  • Staining: Basophilic (due to DNA and RNA).
  • Appearance: Open-face (vesicular) or condensed.
• Structure (EM): Nuclear envelope (membrane), nucleolus, chromatin, nuclear sap.

Chromatin

• Definition: Basophilic material forming chromosomes.
• Structure: Nucleoprotein (DNA + histone proteins)
• Types: Euchromatin (extended, active) and heterochromatin (condensed, inactive).