Plasma Membrane

Plasma Membrane

• It's a formation of microscopic lipids and proteins joined together to form an external boundary of the cytoplasm in a cell or enclosed vacuole.
• + Regulates the passage of molecules coming through the cytoplasm.

Function

• Marks the boundary of the cytoplasm in a cell
• Provides shape and support
• Controls the entry and exit of materials (e.g. molecules)
• Identifies the cell (glycoprotein markers - reason for this?)
• Provides receptor sites for chemical messgaes (e.g. hormones)
• Has some enzymes - facilitate chemical reactions

Functions of Membrane Proteins

• Transport -> Receptors for signal transduction -> Attachment to the cytoskeleton and extracellular matrix (ECM) -> Enzymatic activity -> Intercellular joining -> Cell-cell recognition

Tight Junction

• Prevents molecules passing through intercellular space (plasma membrane)

Desmosomes

• Binds adjacent cells together and helps form internal tension-reducing network of fibres.

Gap Functions

• Allows ions and small molecules to pass through one cell to the next for intercellular communication.

Membrane Transport

• PASSIVE - Does NOT require ATP energy for material transport
• The reason why it does not require ATP because it's a concentration gradient, which is a natural substance that can naturally move from a high to low concentration.
• ACTIVE - Does require ATP energy for material transport

Passive

• Diffusion
• - Movement of a substance from a high to low concentration.
• EXAMPLE: Fart gas goes throughout a room and then concentrates to one given area, which is low in concentration.
• Filtration
• - Movement of a substance through a membrane of pressure.
• EXAMPLE: In the kidney they filter positive and negative nutrients that can be used as fuel for cells. The negative nutrients go through the urinary system to be eliminate.
• Simple Diffusion
• - Movement of a fat soluble (molecule) that can simply travel through the phospholipid bilayer.
• These are small lipid soluble substance that can be diffused directly between phospholipids which is a movement from a high to low concentration, that requires no energy showing that it's a Passive transport examples of this are oxygen and carbon dixoide molecules.

Passive

• Facilitated Diffusion
• - When substances are transported across cell membranes by means of a protein carrier.
• Carrier-mediated facilitated diffusion
• - Protein carrier that changes the shape of a protien
• Channel-mediated facilitated diffusion
• - Channel protein that selects ons based on their size and charge
• Large and non-liquid soluable substance e.g. Glucose, Amino Acids, etc; that mediated by a protein carrier or channell to get across the Plasma Membrane is a movement from a high to low concentration.

Osomosis

• - Diffusion of solvent through a protein channel or lipid bilayer
• When water movement mediated by a protein channell to get across a semi-permeable membrane. Is a movement from high to low water concentration. No energy required for this movement.

Membrane

• Permeable to water
• Impermeable to solutes
• Solute molecules are prevented from moving. Moving water by osmosis. Volume increases in the compartment with the higher osmoiarity.