Eukaryotic organelles

Cellular Organelles and Their Functions

Endoplasmic Reticulum and Golgi Apparatus

• Endoplasmic Reticulum (ER)

  • Responsible for the synthesis of macromolecules, including proteins and lipids.

  • Two types: Rough ER (with ribosomes) for protein synthesis; Smooth ER (without ribosomes) for lipid synthesis and detoxification.

• Golgi Apparatus

  • Receives, modifies, and packages macromolecules produced by the ER.

  • Acts as the shipping center of the cell, sending molecules to their destinations.

Lysosomes

• Function

  • Known as the "garbage disposal" or recycling center of the cell.

  • Contain hydrolytic enzymes that perform hydrolysis to break down waste molecules and macromolecules.

• Enzymatic Action

  • Able to break down large polymers into their monomers (e.g., proteins into amino acids, carbohydrates into monosaccharides).

  • Operate in an acidic environment filled with protons (H+ ions), which is optimal for the enzymes to function.

• Mechanism

  • Merges with food vacuoles to digest engulfed molecules for reuse.

  • Can also digest old or damaged organelles, enabling cellular recycling.

Vacuoles

• General Function

  • Membrane-bound sacs primarily used for storage within the cell.

  • Can store water, nutrients, pigments, or waste.

• Plant vs. Animal Cells

  • Plant Cells: Feature a large central vacuole that can occupy most of the cell's volume; serves critical functions in storage and maintaining turgor pressure.

  • Animal Cells: Typically contain multiple smaller vacuoles.

• Contractile Vacuoles

  • Found in organisms like paramecium to expel excess water, functioning like a sump pump to regulate water content in freshwater environments.

Mitochondria

• Function

  • Known as the "powerhouse of the cell." Major site for ATP (energy molecule) production through the breakdown of glucose.

• Structure

  • Dual membrane structure: an outer membrane and a highly folded inner membrane forming cristae to increase surface area.

  • Contains its own DNA and ribosomes, enabling the synthesis of some proteins independently.

• Importance

  • Critical for cellular respiration and energy transformation, converting stored energy from glucose into ATP that powers cellular activities.

Chloroplasts

• Function

  • Present only in plants, they are responsible for photosynthesis, converting sunlight and carbon dioxide into glucose.

• Structure

  • Similar dual membrane structure like mitochondria, with a third internal membrane called thylakoids, organized into stacks (grana).

  • Stroma is the liquid matrix surrounding the thylakoids, where the Calvin cycle occurs.

• DNA and Ribosomes

  • Contain their own small amount of DNA and ribosomes for protein production necessary for their function.

  • Presence in large quantities in photosynthetic tissues but sparse in non-photosynthetic tissues like roots.

Comparison: Plant vs. Animal Cells

• Both are eukaryotic and possess membrane-bound organelles.

• Key differences express through specific organelles:

  • Plant Cells: Contain chloroplasts and a large central vacuole.

  • Animal Cells: Lack chloroplasts and generally have smaller vacuoles.

• Understanding these differences helps in recognizing how various cells adapt to their functions and environments.