Cell membrane Functions: contains cell contents, controls what enters and exits a cell
Fluid mosaic model: the membrane is flexible like a fluid and has a variety of molecules. Like the variety of tiles in a mosaic
Phospholipids: form a double layer surrounding a cell; composed of a charged phosphate group, glycerol, and two fatty acid chains; tail is nonpolar (not charged).
head: hydrophilic (water loving)
tails: hydrophobic (water fearing)
Other molecules: cholesterol strengthens membranes, proteins aid cell identification and movement of molecules across membranes and cell signaling, carbohydrates aid cell identification
Selective permeability: allows some materials to cross; aka semipermeable and selectively permeable; enables a cell to maintain homeostasis; molecules can cross in a variety of ways
Receptors: detect a signal molecule and perform an action in response
Ligand: is a molecule that acts as a signal when it binds to a receptor.
Intracellular receptor: located inside a cell; binds to molecules and allows them to cross the membrane
Membrane receptor: located in the membrane; binds to molecules than cannot cross the membrane
RECAP VIDEO ON THE MEMBRANE
Section 3.4
Passive transport: the movement of molecules across down a concentration gradient through a
membrane without energy (ATP) input from the cell
Examples:
1. Diffusion: movement of molecules from high concentration to low concentration.
[High] --> [Low]
2. Osmosis: movement of water from higher to lower concentration
Recap
How do different solutions affect cells?
** hypertonic solution has a higher concentration of dissolved particles than a cell. This means water concentration is higher inside the cell than outside. Thus, water flows out of the cell, causing it to shrivel or even die.
**isotonic solution to a cell if it has the same concentration of dissolved particles as the cell.Water molecules move into and out of the cell at an equal rate, so the cell’s size remains constant.
**hypotonic solution has a lower concentration of dissolved particles than a cell. This means water molecules are more concentrated outside the cell than inside. Water diffuses into the cell. If too much water enters a cell, the cell membrane could potentially expand until it bursts.
3. Facilitated Diffusion: diffusion of molecules across the membrane with help from proteins; requires NO ATP
Gummy Bear Lab
Gummy Bear Lab Sheet
Section 3.5
**Most active transport proteins use energy from the breakdownof ATP (IS ENERGY)
Video Recap
Examples:
Endocytosis: process of taking in liquids or larger molecules into a cell by engulfing in a vesicle; requires energy
Exocytosis: process of releasing substances out of a cell by fusion of a vesicle with the membrane requires energy
Phagocytosis: is a type of endocytosis in which the cell membrane engulfs large particles.
Phagocytosis: is a type of endocytosis in which the cell membrane engulfs large particles.
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