Peroxisomes are tiny powerhouses that protect cells from harmful substances and break down fats. These organelles are crucial for detoxification and energy production, working alongside other cellular structures to keep things running smoothly.

Specialized organelles like endosomes, vacuoles, and lysosomes handle specific tasks within cells. The cytoskeleton, a network of protein filaments, provides structure and helps move organelles around, ensuring everything stays organized and functional.

Peroxisomes and Specialized Organelles

Structure and function of peroxisomes

• Peroxisomes are small, spherical organelles bound by a single membrane
  • Contain enzymes involved in oxidative reactions such as catalase and oxidases (hydrogen peroxide, fatty acids)
• Function in the breakdown of fatty acids through beta-oxidation
  • Produce acetyl-CoA which can be used in the citric acid cycle for energy production (ATP)
• Detoxify harmful substances such as alcohol and hydrogen peroxide ($H_2O_2$)
  • Catalase converts $H_2O_2$ into water and oxygen preventing cellular damage (oxidative stress)
• Synthesize bile acids (liver function) and plasmalogens, a type of phospholipid (cell membrane component)
• Involved in the glyoxylate cycle in plants and some microorganisms
  • Allows the conversion of fatty acids into carbohydrates (glucose, energy storage)

Peroxisomes in cellular metabolism

• Peroxisomes play a crucial role in protecting cells from oxidative stress
  • Detoxify reactive oxygen species (ROS) and other harmful compounds (free radicals)
  • Prevent cellular damage and maintain cell viability (apoptosis, necrosis)
• Essential for lipid metabolism, particularly the breakdown of very long chain fatty acids (VLCFAs)
  • VLCFAs cannot be processed by mitochondria and require peroxisomal beta-oxidation (C22 and longer)
• Disorders in peroxisomal function, such as Zellweger syndrome, can lead to the accumulation of toxic substances and impaired lipid metabolism
  • May result in neurological disorders, liver dysfunction, and other health issues (adrenoleukodystrophy, Refsum disease)

Specialized organelles and functions

• Endosomes are membrane-bound organelles involved in the sorting and transport of materials within the cell
  1. Early endosomes receive materials from the plasma membrane via endocytosis (receptor-mediated, pinocytosis)
  2. Late endosomes mature from early endosomes and fuse with lysosomes for degradation (hydrolytic enzymes)
  3. Recycling endosomes return some materials back to the plasma membrane (receptors, membrane components)
• Vacuoles are large, membrane-bound organelles found in plant and fungal cells
  • Plant vacuoles store water, ions, and various molecules such as pigments and enzymes (anthocyanins, aleurone grains)
  • Maintain cell turgor pressure and play a role in plant growth and development (cell elongation, stomatal movement)
  • Fungal vacuoles are involved in storage, pH regulation, and waste disposal (polyphosphates, amino acids)
• Lysosomes are specialized organelles containing hydrolytic enzymes for the degradation of cellular waste and foreign materials
  • Maintain cellular homeostasis by recycling nutrients and removing damaged organelles (autophagy)

Cytoskeleton for cellular organization

• The cytoskeleton is a network of protein filaments that provides structure, support, and movement within the cell
• Consists of three main types of filaments: microfilaments (actin), intermediate filaments, and microtubules
• Microtubules are involved in organelle movement and positioning
  • Motor proteins such as kinesins and dyneins transport organelles along microtubules (anterograde, retrograde)
  • Microtubules help maintain the distribution and organization of organelles within the cell (endoplasmic reticulum, Golgi apparatus)
• Microfilaments (actin filaments) are involved in short-range organelle movement and anchoring
  • Myosin motor proteins interact with actin filaments to facilitate organelle transport (vesicle trafficking)
• The cytoskeleton plays a crucial role in cell division, particularly in the formation and function of the mitotic spindle
  • Microtubules attach to chromosomes and separate them during mitosis and meiosis (anaphase, telophase)
• Cytoskeletal elements also contribute to cell polarity and the maintenance of cell shape
  • Intermediate filaments provide mechanical strength and resistance to shear stress (keratin, vimentin)