Cell Biology: Vacuoles and Nucleus

Cell Organelles and Their Functions

• Central Vacuole: Large storage organelle in plant cells, responsible for maintaining turgor pressure and storage of nutrients.
• Food Vacuole: In organisms like Paramecium, it stores and digests food particles.
• Contractile Vacuole: Expels excess water in single-celled organisms, maintaining osmotic balance.
• Cytosol: Fluid component of the cytoplasm, where metabolic processes occur.

Endomembrane System

• Nuclear Envelope: Connects with rough Endoplasmic Reticulum (ER) and is continuous with smooth ER.
• Rough ER: Synthesizes proteins, has ribosomes on its surface.
• Smooth ER: Synthesizes lipids and detoxifies certain chemicals.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids received from ER into vesicles.
• Lysosomes: Membrane-bound organelles filled with digestive enzymes that digest macromolecules.
• Secretory Pathway: Transport proteins to the plasma membrane for secretion.

Energy-Converting Organelles

• Mitochondria:

  • Powerhouse of the cell; site of cellular respiration producing ATP.
  • Double membrane structure contains its own circular DNA and ribosomes.
  • Compartmentalized into intermembrane space and matrix, where enzymes for respiration are located.

• Chloroplasts:

  • Site of photosynthesis in plants and algae, contains chlorophyll.
  • Also a double membrane organelle with membranous sacs (thylakoids) stacked to form granum.
  • Stroma is the fluid interior where enzymes are located.

Peroxisomes

• Specialized organelles involved in lipid metabolism and detoxification.
• Contains enzymes like oxidases which convert substrates to hydrogen peroxide.
• Peroxidation is neutralized by catalase, breaking down H2O2 into water and oxygen.

Cytoskeleton

• Composed of three types of fibers:
  • Microtubules: Thickest, provide structure and facilitate intracellular transport.
  • Microfilaments (Actin filaments): Thinnest, involved in muscle contraction and cell movement.
  • Intermediate Filaments: Provide mechanical support and stability.
• Functions: Provides cellular structure, aids in cell division, and organizes cell activities by anchoring organelles.

Epithelial Tissue Types

• Simple Columnar Epithelium: Brick-shaped cells, lines the intestines for secretion and absorption.
• Simple Cuboidal Epithelium: Dice-shaped cells found in glands and kidney tubules, specialized for secretion.
• Stratified Squamous Epithelium: Multilayered, rapid regeneration, and protection against abrasion, found in skin and linings.
• Pseudostratified Columnar Epithelium: Appears layered but is a single layer; ciliated in respiratory tract to move mucus.

Specialized Epithelial Glands

• Goblet Cells: Unicellular glands secreting mucus.
• Exocrine Glands: Secrete products through ducts (e.g., sweat and salivary glands).
• Endocrine Glands: Release hormones directly into the bloodstream (e.g., pituitary glands).

Connective Tissue

• Main functions include binding and supporting other tissues, consisting of:

  • Ground Substance: Material that fills spaces between cells.
  • Fibers: Include collagen for strength and elastin for flexibility.
  • Cells: Varied, including blood cells.

• Types of Connective Tissue:

  • Loose Connective Tissue: Most widespread, found throughout the body.
  • Fibrous Connective Tissue: Dense, found in tendons and ligaments connecting muscles to bones and bones at joints.
  • Bone: Mineralized tissue formed by osteoblasts, combining collagen with minerals for hardness.