Cell Biology: Lysosomes and Cytoskeleton

Lysosomes

• Lysosomes are organelles found in animal, protoctist, and fungal cells. They are rare in plant cells.
• Lysosomes act as the "recycling center" of the cell, breaking down waste materials and cellular debris.

Cytoskeleton

• The cytoskeleton is a network of protein filaments that provides structural support, helps maintain cell shape, and facilitates movement within the cell.
• It consists of three main components:
  • Microfilaments: Actin-based filaments responsible for cell movement and changes in cell shape.
  • Microtubules: Tubulin-based hollow tubes that provide structural support, serve as tracks for organelle movement, and form the centriole.
  • Intermediate filaments: Rope-like structures composed of various proteins that provide structural support and maintain cell shape.

Centriole

• The centriole is a cylindrical structure composed of nine microtubule triplets arranged in a characteristic pattern.
• Centrioles are involved in cell division, forming the spindle fibers that pull chromosomes apart during mitosis and meiosis.

Cilia and Flagella

• Cilia and flagella are hair-like projections from the cell surface that aid in movement.
• Cilia are short and numerous, while flagella are longer and fewer.
• Both structures have a "9+2" arrangement of microtubules, with nine microtubule doublets surrounding a central pair.

Plant Cell Structures

• Plant cells have several distinctive structures, including a cell wall, chloroplasts, and a large central vacuole.
• The cell wall provides structural support and protection for the plant cell.
• Chloroplasts are the sites of photosynthesis, converting light energy into chemical energy.
• The large central vacuole stores water, maintains turgor pressure, and helps regulate cell shape.

Tissues

• Tissues are groups of similar cells working together to perform a specific function.
• There are four main types of tissues in animals: epithelial, connective, nervous, and muscle.

Epithelial Tissue

• Epithelial tissue covers the surfaces of the body and lines internal organs.
• It consists of closely packed cells with little intercellular space.
• Epithelial tissue is avascular, meaning it lacks blood vessels.
• It is classified based on cell shape and the number of cell layers.

Connective Tissue

• Connective tissue supports, binds, and protects the body.
• It is characterized by cells dispersed in a matrix of extracellular material.
• Types of connective tissue include bone, cartilage, blood, and adipose tissue.

Nervous Tissue

• Nervous tissue is responsible for conducting nerve impulses.
• It consists of neurons (nerve cells) and neuroglia (support cells).
• Neurons transmit signals through electrical and chemical means.

Muscle Tissue

• Muscle tissue is responsible for movement.
• There are three types: skeletal, cardiac, and smooth.
• Skeletal muscle is voluntary and responsible for body movement.
• Cardiac muscle is involuntary and found only in the heart.
• Smooth muscle is involuntary and found in the walls of organs like the digestive and urogenital tracts.

Transport Mechanisms

• Active transport involves the movement of molecules against their concentration gradient, requiring energy.
• The sodium-potassium pump is an example of active transport, moving sodium and potassium ions across the cell membrane against their concentration gradients.
• Vesicle transport involves the movement of large molecules in membrane-bound sacs called vesicles.
• Endocytosis is the process of bringing substances into the cell through vesicle formation.
• Exocytosis is the process of releasing substances from the cell by fusing vesicles with the plasma membrane.

Biological Molecules

• Carbohydrates, lipids, proteins, and nucleic acids are the four major classes of biological molecules.
• Carbohydrates serve as energy sources and structural components.
• Lipids are important for energy storage, insulation, and membrane structure.
• Proteins have diverse functions, including enzymes, structural support, and transport.
• Nucleic acids store and transmit genetic information.