Cytoskeleton and Its Components

Cytoskeleton

• A microscopic network of protein filaments and tubules in the cytoplasm
• Consists of three main types of filaments, which are elongated chains of protein:
  • Microfilaments
  • Microtubules
  • Intermediate Filaments
• Supports the cell, gives the cell its shape, and facilitates movement
• Plays important roles in molecule transport and cell division

Microfilaments

• Primarily composed of the protein actin
• Involved in multiple cellular processes, including:
  • Cytokinesis (cytoplasm division)
  • Cell motility
  • Cytoplasmic streaming
  • Muscle contractions
  • Maintenance of cell shape

Microtubules

• Involved in a variety of important cellular processes, including:
  • Chromosome division during cell division
  • Transporting molecules within the cell
  • Maintenance of cell shape
  • Cell motility

Cilia and Flagella

• Flagella are "tails" that propel a cell forward
• Cilia are cellular appendages that allow the cell to move

Intermediate Filaments

• Intermediate in size between microfilaments and microtubules (8-10 nm)
• Composed of various proteins like keratin, vimentin, desmin, and lamin
• Play a crucial role in maintaining cell shape
• Provide structural support by bearing tension

Cell Membrane

• Also known as the plasma membrane
• Encloses the cell and its organelles
• Phospholipids form the basic structure of the cell membrane, creating a lipid bilayer with embedded proteins
• Involved in five key functions:
  • Protects the cell by acting as a barrier
  • Regulates transport of substances into and out of the cell
  • Receives chemical messengers from other cells
  • Acts as a receptor
  • Cell mobility, secretions, and absorptions of substances

Structure of the Cell Membrane

• Contains various components that aid in its function:
  • Channels or transporters: move molecules in one direction
  • Receptors: recognize specific chemicals
  • Cholesterol molecules: keeps the membrane fluid consistent
  • Enzymes: catalyze production of substances
  • Glycoproteins: identify cell type

Phospholipids in the Cell Membrane

• Have a hydrophilic (head) and hydrophobic (tail)
• Hydrophilic head has affinity for water
• Hydrophobic tail repels water
• This interaction of phospholipids with water is crucial for life

Movement Across the Plasma Membrane

• Some molecules can move across the cell membrane without assistance:
  • Water, Carbon dioxide, Ammonia, Oxygen
• Other molecules need different transport mechanisms:

Methods of Molecule Movement into Cells

• Passive transport: moves chemicals from high to low concentration (does not require energy)
• Active transport: moves chemicals from low to high concentration (requires energy, uses protein pumps)
• Endocytosis: movement of large materials into cells
• Exocytosis: movement of large materials out of the cells

Passive Transport

• Moves chemicals down their concentration gradient
• Three types of passive transport:
  • Diffusion
  • Facilitated Diffusion
  • Osmosis

Diffusion

• Movement of molecules from high concentration to low concentration to equalize concentration
• Requires no energy
• Driven by the existing concentration gradient

Facilitated Diffusion

• Passive transport of molecules or ions through specific transmembrane integral proteins
• Does not require energy but needs carrier proteins
• Moves molecules from high to low concentration

Osmosis

• Movement of water across a semipermeable membrane
• Water moves from a dilute solution to a concentrated solution
• Important for water movement in and out of cells

Osmosis vs Diffusion

• Osmosis is the movement of solvent particles (water molecules)
• Diffusion is the movement of particles (like oxygen)

Hypotonic, Hypertonic, and Isotonic Solutions

• Hypotonic: lower solute concentration than the cell, water moves into the cell, causing it to swell
• Hypertonic: higher solute concentration than the cell, water moves out of the cell, causing it to shrink
• Isotonic: equal solute concentration inside and outside the cell, water moves in and out at the same rate, equilibrium

Active Transport

• Moves chemicals against their concentration gradient
• Requires energy to move chemicals from low to high
• Creates a charge gradient across the cell membrane
• Requires protein pumps to move chemicals

Endocytosis

• Movement of large materials into cells
• Three types of endocytosis:
  • Bulk-phase (non-specific)
  • Receptor-mediated (specific)
  • Receptor-mediated endocytosis uses phagocytosis and pinocytosis processes

Receptor-Mediated Endocytosis

• How cells take in specific molecules by binding to receptors on the cell surface

Phagocytosis

• "Cell eating"
• Engulfing large particles or organisms by the cell

Pinocytosis

• "Cell drinking"
• Engulfing dissolved materials by the cell

Exocytosis

• The reverse of endocytosis
• Cell discharges materials
• Vesicle containing the material moves to cell surface
• Membrane of vesicle fuses with cell membrane
• Materials are expelled outside the cell.

Explore the intricate structure and function of the cytoskeleton, including microfilaments, microtubules, and intermediate filaments. Understand how these components support cell shape, movement, and essential cellular processes such as division and transport.