Plasma Membranes Flashcards
Role of cell membranes
Separate all contents from exterior environment, or separate organelles from cytoplasm
Why is permeability important to cells
Due to permeability, substances can pass through. Some very small molecules simply diffuse through the cell membrane in between structural molecules, some dissolve in lipid layer, others pass through protein channels
Do not let all substances pass through: partially permeable
Roles of membranes at cell surface
-Protection
-Fixed environment
-Transportation
-Cell signalling and reception
Role of membranes within cells, and give some examples
-Separate organelles from cytoplasm
-Nuclear envelope: separates nucleoplasm from cytoplasm
-Permanent Vacuole
What is cell communication?
-Occurs when chemical bind to receptor molecules on the plasma membrane, and cause a response within the cell
-stay in contact with environment and adjacent cells
-cells over 1m apart need to communicate so body functions effectively
Examples of receptor molecules and the chemical signal they are specific for
Insulin receptor on liver cell: Insulin
Auxin receptor on meristem cells: Auxin
FSH receptor on cells of ovary: FSH
CDA receptor on T cells: HIV
Simple diffusion
The movement of particles from a region of high concentration to an area of low concentration of that particle, down a concentration gradient. No metabolic energy is required, only non-polar and small molecules pass through
Facilitated diffusion
Movement of molecules from an area of high concentration of that molecule to an area of low concentration of that molecule across a partially permeable membrane via protein channels or protein characters. No metabolic energy is required
How does diffusion occur across the cell membrane?
- As phospholipids vibrate, small gaps appear. CO2 and O2 are small enough to get through. Water is unusual but also gets through.
Steroid hormones dissolve through lipid bilayer - Polar molecules or charged ions can not interact with hydrophobic tails so enter via water filled protein channels
- Some molecules are too large for the water filled pores. Require a specific, transmembrane carrier protein (eg, glucose)
What does passive mean in terms of diffusion?
No metabolic energy [ATP] is required
How does temperature affect diffusion?
Results in more kinetic energy, so more diffusion
Losing heat means less/slower diffusion
How does distance affect diffusion?
Thicker the membrane, the slower the diffusion
How does surface area affect diffusion?
More diffusion across larger surface area
Specialised cells for absorption have extension to surface membranes, increase SA
How does the size of the molecule affect diffusion?
Smaller ions/molecules diffuse more rapidly than large molecules
How does the concentration gradient affect diffusion?
Steeper the gradient, the faster the diffusion to side of fewer molecules down the gradient
What is endocytosis?
Process by which the cell surface membrane engulfs material, forming a small sac (or ‘endocytic vacuole’) around it
What is exocytosis?
Exocytosis is the process by which materials are removed from, or transported out of, cells
Why are endo and exocytosis needed?
larger quantities of materials that might need to cross the membrane, can’t pass through it
processes require energy input and are therefore forms of active transport
What is osmosis?
The diffusion and net movement of water across a partially permeable membrane, and no energy is required, and is from a region of high water potential to an area of low water potential
What is net movement?
The overall movement of water molecules
down a water potential gradient. Some water will flow back the other way
What is water potential?
The measure of the ability of water molecules to move freely in a solution OR the relative tendency of water to move from one area to another
What is an isotonic solution?
Solute concentration/water potential inside a cell or tissue is equal to the solute concentration outside, in the surrounding environment
Equilibrium
What is a hypotonic solution?
Water potential of solution is higher than the cells. Water moves into the cell
What is a hypertonic solution?
Water potential of solution is lower than that of the cell. Water moves out of the cell
