Unit 3: The Plasma Membrane & Membrane Potential Flashcards
True or False- All cells have both an internal and external plasma membrane.
False.
-All cells must only have an external membrane.
What type of molecules easily diffuse across the plasma membrane?
-small, non-polar, or uncharged molecules.
What are Trans-membrane proteins?
Exist within the plasma membrane and act as channels that allows for specific transport of molecules from the ECF to the ICF.
What is the purpose of Cholesterol within the membrane?
Contributes to the fluidity of the membrane.
Describe the fluid mosaic model
Proteins (icebergs) afloat in the sea of lipids.
Restricted by the cytoskeleton
What are Channel Proteins?
Highly selective canals that allow for the passage of certain molecules.
*Only ions pass through these channels.
What are Carrier Proteins?
-Allow for specific binging of molecules to proteins across the barrier that could not be done on their own.
What are Docking- Marker Acceptors?
-Located on the inner membrane surface, and bind to docking markers of secretory vesicles in a “Lock-in-key” fashion.
What are Membrane Bound Enzymes?
-Surface located proteins that control chemical reactions within the cell
What are Receptor Sites?
-Recognize and bind molecules on the plasma membrane.
What are Cell Adhesion Molecules (CAMS)?
- Proteins that extend from the outer cell membrane that form loops that grip to connective tissues which interlace cells.
- Can become signalling molecules.
- ->Integrins, cadherins
What are Glycoproteins?
Important for cell’s to self-recognize.
*Carbohydrate containing markers which allow the cell to recognize it’s own cells as self.
What composes and holds together tissues?
-Cells, but also glue-like substances of fibrous proteins such as extracellular matrix! (biological glue)
What are the properties of collagen?
-Forms cable like fibres or sheets that give the cell tensile strength.
What are the properties of elastin?
-Protein within the ECM that is prominent in cells that stretch.
What are the properties of fibronectin?
-Promotes cell adhesion’s and keeps the cell in place.
What are desmosomes?
-Act like “spot rivets” that anchor 2 cells together so they are adjacent, but not touching. Glycofilaments attach these cells like string woven together.
What are tight junctions?
-Form fluid-tight seals between cells.
Join the lateral edges of epithelial cells so matter MUST pass through the cells and not around them.
–>Prevent undesirable leaks.
What are Gap junctions?
Link of 2 adjacent cells by connexon tunnels.
What are communication junctions?
Allow for the passage of ions and molecules without entering the cells extracellular fluid.
- Abundant in cardiac/ smooth muscle.
- NO passage of large molecules.
What are the two means of passive forces across the permeable plasma membrane?
- Diffusion down a concentration gradient.
2. Diffusion down an electrical gradient.
PASSIVE Diffusion moves from?
High concentration to low concentration.
What is Net Diffusion?
- The total number of molecules that move in both directions of the concentration gradient.
ex. -3 left, +7 right = 4
Fick’s Law of Diffusion?
Magnitude of gradient, permeability of membrane, surface area over where diffusion occurs, molecular weight of the substance and distance of diffusion.
Where do ions move in an electrical gradient?
-To the sides of opposite charge.
What is an Electrochemical gradient?
-Occurs with both an electrical and chemical gradient occur at once.
What are aquaporins?
Channels that allow for the passage of water through the plasma membrane.
Define Osmosis.
-Water moves from areas of low concentration to high concentration.
What is hydrostatic pressure?
-Pressure exerted by a large volume of water compared to a smaller volume of water. This difference in pressure moves water to the smaller volume side.
What is osmotic pressure?
-A measure of the tendency for water to move into a cell, based on the concentration gradient and non-penetrating solutes.
Osmotic pressure vs. hydrostatic pressure relationship.
-Greater concentration of solute= less volume of water= greater drive of water into the cell= higher drive of pressure to stop osmotic flow
What is Tonicity?
- The effect the solution has on cell volume (shrinks, swells or stays the same
- Determined by solute concentration.
What is an isotonic solution?
Solution has no impact on cell volume.
What is a hypotonic solution?
Low concentration of solutes in solution= high volume of water in solution compared to cell, leads to cell swelling due to high volumes of water entering the cell.
What is a hypertonic solution?
High concentration of solutes in solution= low volume of water in solution= cell shrinking (water moving out to environment)
Explain carrier mediated transport?
- Carrier proteins REVERSE the shape of the plasma membrane after binding of specific molecules to allow molecules to transfer from the ECF to the ICF.
- Change in plasma membrane conformation.
What is carrier mediated transport regulated by?
- Specificity of binding
- Saturation- A limited # of binding sites
- Competition for binding
What is the Transport Maximum ? (Tm)
- The maximum number of molecules that can bind carriers at once.
- Until Tm is reached, more substrate can be carried over.
What is Facilitated Diffusion?
-carrier mediated transport that occurs passively, from areas of high to low concentration.
What is Active Transport?
- carrier mediated transport that occurs “uphill”; areas of low to high concentration.
- After phosphorylation on the low concentration side, the membrane is flipped so that the molecule is on the high concentration side. REQUIRES ATP
How does the hydrogen ion pump work in the body?
-In specialized stomach muscles to transport H+ into the stomach lumen with the release of HCl.
How does the Na/ K Pump work?
2 K+ moves from the outside to the inside, and 3 NA+ moves from the inside to the outside. This makes the outside of the membrane more positive and the inside more negative, making the inside negative.
What is Vesicular Transport?
Transport of large particles into the cells ICF without touching the cells ECF as it passes through the tunnel.
Exocytosis Mechanism
-Membrane enclosed vesicles bind to the cell surface and open contents up to the cell exterior.
Endocytosis Mechanism
-Membrane enclosed vesicles bind to the cell surface, creating a pinch. This encloses material into the cell.
Materials may be further treated:
1. Degraded by lysosomes in the ICF.
2. Released to the exterior by ECF.
What is membrane potential?
- Separation of charges across the membrane or to a difference in the relative number of cations and anions in the ICF and ECF.
- Potential is measured in volts (mV’s)
Resting Membrane Potential?
- When excitable tissues are at rest.
- 70mV is the resting membrane potential, meaning there is more sodium outside the cell than potassium inside, making it negative inside.
- It’s normal to have more sodium outside and more potassium inside the cell.
K+ Equilibrium potential (Ek+) ?
Potassium will exit the cell and enter the ECF until it reaches a membrane potential of -90 mV.
- Potential is usually closer to EK+ due to the membranes greater permeability to potassium.
- ->Potassium leaves cell until it reaches -90mV (equilibrium potential- meaning it won’t allow any more potassium to leave at this level)
- Only ever approaches membrane potential
Na + Equilibrium potential (ENa+) ?
Sodium channels open and sodium ions move into the cell, until the membrane potential reaches +60mV.
*Won’t reach chemical equilibrium–> at +60mV the cell is positive enough to repel anymore entry of sodium ions from entering.
How does the Na+/K+ pump counteract leaks?
All passive leaks are counteracted by active pumping.
-If sodium continuously leaks into the cell, potassium will counteract it by moving out of the cell.
