Fluid Mosaic Model: Cell Membrane

• The Fluid Mosaic Model describes the cell membrane as a flexible, oily bubble with floating proteins.
• The cell membrane is not solid, and it allows substances to move in and out, protecting the cell.
• Plasma membrane exhibits selective permeability, controlling the entry and exit of substances like a selective gatekeeper.
• Proteins in the cell carry out diverse functions.

Fluid Mosaic Model

• The image illustrates the Fluid Mosaic Model, emphasizing its structure and function.
• The phospholipid bilayer forms the membrane, appearing as yellow/orange lines.
• Membrane proteins, depicted as purple structures embedded in the bilayer, facilitate transport and communication.
• Cholesterol, represented by small yellow structures, contributes to membrane stability.
• Blue fibers represent the extracellular matrix, offering structural support outside the membrane.
• The cytoskeleton or microfilaments (orange strands) maintain the cell's shape from the inside.
• The diagram illustrates how the cell regulates entry and maintains its shape.
• Nonpolar O2 can easily pass through the phospholipid bilayer.
• Small nonpolar molecules diffuse from high to low concentration.
• Transport proteins enable specific ions or molecules to enter the cell, like selective gatekeepers for cells that are nonpolar and needs help.
• Some membrane proteins function as enzymes, potentially grouped to perform sequential reactions.
• Attachment proteins link to the extracellular matrix and cytoskeleton, aiding membrane support and coordinating internal and external changes.
• Receptor proteins act as cellular antennas, capturing signals like hormones or messages and relaying them by activating other molecules inside the cell.
• Junction proteins create intercellular junctions, connecting adjacent cells like bridges, allowing them to function as a unit.
• Glycoproteins serve as nametags, facilitating cell recognition and communication.
• Diffusion occurs as particles spread out evenly in an available space.
• Diffusion across a cell membrane doesn't require energy, known as passive transport.
• Molecules naturally disperse to fill space equally.
• Molecules move down the concentration gradient from high to low concentration without energy.
• Equilibrium is achieved when molecules are evenly distributed on both sides.
• Osmosis involves water diffusion across a selectively permeable membrane.
• Permeable means that something can pass through something.
• Water can permeate the membrane, but solutes (dissolved substances) cannot.
• Water will move to the side with more solute until solute levels are balanced through osmosis.
• Water balance between cells and their surroundings is vital for living organisms.
• Tonicity is the ability of a solution to cause a cell to gain or lose water.
• Cells shrink in a hypertonic solution.
• Cells swell in a hypotonic solution.
• Animal cells thrive in isotonic solutions, while plant cells become flaccid (droopy) due to insufficient water, causing the cell membrane to shrink from the cell wall.

Cell Reactions to Water Levels

• Hypotonic solutions (more water than solute) cause animal cells to lyse (burst) and plant cells to become turgid (swell).
• Isotonic solutions (equal water and solute) result in normal cells (plant cells may be slightly droopy/weak).
• Hypertonic solutions (more solute than water) cause animal cells to shrivel (shrink) and plant cells to plasmolyze (shrivel).
• Water movement balances solute levels, which affects cell shape and function.
• Transport proteins facilitate molecule passage across the cell membrane, easing diffusion without energy use.
• Hydrophobic substances diffuse across the hydrophobic cell membrane easily.
• Polar or charged substances struggle to cross the hydrophobic interior of the cell membrane.
• Transport proteins aid polar or charged molecule passage through facilitated diffusion, which does not need energy input.
• Facilitated diffusion requires no energy and depends on the concentration gradient.
• Substances diffuse across the membrane down their concentration gradients with the help of transport proteins, requiring no energy input.
• Water traverses cells through aquaporins, special protein channels.
• Facilitated diffusion is when a transport protein assists a specific molecule in crossing the cell membrane without energy.
• Active transport uses energy to move a solute against its concentration gradient.
• ATP provides the energy for most active protein molecules.
• Cells transport large molecules in or out via vesicles.
• Exocytosis expels large molecules from the cell.
• Endocytosis brings large molecules into the cell.
• Vesicles (small sacs) transport large molecules, merging with the cell membrane to facilitate entry or exit.
• Endocytosis involves cell intake of large molecules by engulfing them in a vesicle, including phagocytosis and receptor-mediated endocytosis.
• Phagocytosis, or "cell eating," involves a cell engulfing a particle by wrapping its membrane around it, forming a vacuole.
• Receptor-mediated endocytosis employs membrane receptors for specific solutes, where a cell engulfs a particle by wrapping its membrane around it, forming a vesicle.
• Phagocytosis (cell eating ) the cell engulfs large particles by wrapping its membrane around them, forming a food vacuole
• Receptor - mediated endocytosis - the cell uses receptors to grab specific molecules, which are then brought inside a coated vesicle.