Lecture Focus Questions; Membrane Transport Flashcards
What are the functions of the Plasma Membrane?
- It is a semi-permeable barrier that separates the extracellular fluid from the cytoplasm
- It is also very thin & flexible
- And it also made of mostly phospholipids that form a bilayer
- It includes other components like cholesterol, proteins, glycoproteins, glycolipids
How do we know that the membrane is a bilayer?
-We know because the area of the monolayer of phospholipids from RBC is 2x the area of the membrane in those cells
How permeable would a Pure Phospholipid Membrane be?
- It would be somewhat permeable to small polar molecules
- But it would be impermeable to large polar molecules
- And very impermeable to ions & other charged molecules
Why can water pass through a membrane easily even though its polar?
-Water can pass through easily because it is small
What does a membrane fitting the Fluid Mosiac Model have?
-The fluidity extends to the proteins embedded in the membrane & their ability to move laterally within the plane of the bilayer
What controls the fluidity of the membrane?
-The chemical structure of fatty acids in the membrane
What would the shape be of a membrane w/ Unsaturated Fatty acids?
-The membrane will be more fluid
What would the shape of a membrane w/ Saturated Fatty Acids?
-It will be less fluid= solid
What is the difference between a long chain and a shorter chain of Fatty Acids?
- The longer chain will make the membrane less fluid
- While the short chain will make the membrane more fluid
If there is a higher concentration of a hydrophobic molecule outside the cell, what will happen?
-The small hydrophobic molecule will enter the cell via simple diffusion & vise versa if there is a greater concentration inside the cell
How to molecules that are permeable to the membrane move?
-They move from regions of high concentration to low concentration by simple diffusion
What is Facilitated Diffusion?
-The diffusion of membrane impermeable molecules is facilitated by the help of integral membrane proteins= carriers or channels
What is the difference between Carriers & Channels?
- Carrier proteins transport molecules one or a few at a time (ferry boats)
- Channel proteins allow many molecules to be transported at once (bridges)
What is the difference between Facilitated Diffusion & Active Transport?
- Facilitated diffusion allows an impermeable molecule to pass through the membrane & requires a favorable concentration gradient
- Active transport can use energy to move molecules against their gradient & allows cells to use energy to create, maintain & strengthen a gradient
How do Carrier Proteins function?
-They must bind to a single molecule substrate or small group of molecules BEFORE transport can occur
How do Channel Proteins function?
-The total rate of transport will be limited by the concentration of the Ion being transported so they will show a linear increase
What are the 3 different types of transporters for active transport?
- Uniporters
- Symporters
- Antiporters
What are Uniporters?
-They transport only a single molecular species in a SINGLE direction
What are Symporters?
- They transport 2 molecules in the SAME DIRECTION
- they also use a gradient of one substance to move another subsance= Coupled transport
What are Antiporters?
- They transport 2 molecules in OPPOSITE DIRECTIONS
- They also use a gradient of one substance to move another substance
What is Osmosis?
-It is the movement of water over a semi-permeable barrier in response to the difference of concentration of solutes on both sides of a membrane
What is an Isotonic Solution?
-It is when the concentrations of both sides of the membranes are the same
What is a Hypertonic Solution?
-It is where the concentration of solutes is higher OUTSIDE the cell causing water to move outside the cell causing it to shrivel up and die
What is a Hypotonic Solution?
-It is where the concentration of solutes is higher INSIDE the cell causing water to move inside the cell causing it to explode
What are the 3 types of specialized junctions between cells?
- Tight junctions
- Anchoring junctions
- Communicating junctions
What are Tight Junctions?
- They provide a water-tight seal between cells= fluid cannot move between the cells that have tight junctions
- Septate junctions are the same but are present in vertebrates
What are Anchoring Junctions?
-They connect one cell to another or connect one cell to the ECM
What are the 3 types of Anchoring Junctions?
- Desmosomes
- Adherens Junctions
- Hermidesmosomes
What are Desmosomes?
- They use cadherin membrane proteins to connect the intermediate filaments to the cytoskeleton of 2 adjacent cells
- They also form points of attachment between cells
What are Adherenes Junctions?
- They use cadherin membrane proteins to connect the actin filaments in the cytoskeleton of 2 adjacent cells
- They can either form points of attachment or bands of attachment between cells
What are Hemidesmosomes?
-They connect the cytoskeleton of a cell to the ECM
What are Communicating Junctions?
- They allow signals & molecules to travel between cells
- They include Gap Junctions in animal cells & Plasmodesmata in plant cells
What are Gap Junctions made of?
-They are made of 2 hexamers of the connexon protein= one in the plasma membrane of each cell that connects the cytoplasm of each cell
What are Plasmodesmata?
-They connect the cytoplasm & the ER of adjacent cells through the membrane & the plant cell wall
