W2: Lesson 2.1 Flashcards
What energy is used to move materials across a membrane in simple/passive diffusion?
- uses (charge difference across membrane) concentration gradient/electrochemical gradient to move materials across membrane. High con’t. flows to low concentration.
- b/c it is following concentration gradient it does not require any energy to perform. No ATP
Characterize Na+, Ca++, and K+, H+ ion concentrations within and outside a typical cell.
Na+: higher outside a cell than inside (10-30x higher)
Ca++: extremely low inside cells (10-20 fold lower exist inside than outside cell)
K+: Higher inside the cell than it is outside the cell.
H+: higher inside the cell than outside = pH of cell is lower than that of the environment
What energy source is used to move glucose into cells, and what protein is required?
- coupled transport using active carrier protein
- high extracellular concentration of Na+ is used by cells to transport glucose into the cell (even though glucose concentrations are already higher w/in the cell than outside)
- facilitated diffusion for Na+ and active transport for glucose
Would you expect the membrane permeability of glucose, CO2, H2O, and Ca++ to be high or low
Glucose: large, uncharged, polar, molecule = less likely to move across than CO2 and H20
CO2: small, uncharged, non polar, hydrophobic molecule = highest permeability
H2O: polar, uncharged molecules w/no net charge, hydrophilic = can move across membrane
Ca++: charged ions = impermeable
Organize in order of low permeability to high permeability:
sucrose(large polar), glycerol(small polar), O2, Mg2+
Mg2+ < sucrose < glycerol < O2
Organize in order of high permeability to low permeability:
large uncharged polar molecules, ions, hydrophobic molecules, small uncharged polar molecules
hydrophobic molecules > small uncharged polar molecules > large uncharged polar molecules > ions (w/charge)
What is an electrochemical gradient?
combination of charge and concentration gradient
If there’s a (+) ion outside the membrane and the membrane is uncharged, what will determine the movement of the ion?
-the concentration difference of the ion alone
If the interior of the membrane is (-), and the ion outside the cell is a (+) ion will this attract or repel the ion?
-attracting the positive ion and transfer of the positive ion across the membrane will be enhanced
If external membrane is negative charged, and interior is positive, will this attract the + ion inside and across the membrane?
Will be less likely to transport or will be inhibited
what three states can a membrane channel be in?
open
closed
inactivated
what are the two proteins in facilitated diffusion?
- channel forming protein
- carrier protein
What are the differences between channel forming proteins and carrier proteins?
Channel: simple pores, formed by beta barrel integral membrane proteins. Porin allows small molecules to travel through. Some always open but can be closed or inactive
Carrier: these proteins actually change their shape between two or more states in a way that allows the movement of molecules through them. Others will rotate or move from one face of the lipid bilayer to the other
Discuss the ability of different transport mechanisms to be saturated. What is the mechanistic basis for whether a transport mechanisms is or is not saturable?
if transport depends on the # of transport proteins to transport then there is a maximal transport rate (Vmax) and it is said to be saturated.
Saturation vs. Unsaturation depends on the relationship between concentration gradient and movements of solute.
In simple diffusion: there’s a linear relationship between the con’t gradient and the rate of molecule movements across membrane. The greater the con’t gradient the faster solutes will move across membrane usually w/no limit. this relationship is said to be non saturable
in facilitated diffusion: con’t gradient provides energy needed to make facilitated diffusion to work, however, the solute molecules have to wait around unit a membrane protein becomes available in order for it to traverse the membrane. Increasing the amount of solute on one side of the membrane doesn’t change the # of transmembrane proteins and therefore there’s an upper limit to how fast a protein can perform it’s function. Speed of movement across membrane has a curve that flattens out, as the concentration difference goes up, past some limit. this is said to be saturable
Describe in detail an example of a coupled transport, providing components of the system and what they do
when carrier proteins move two different types of solutes across the membrane together this is know as coupled transport. If both solutes are going in the same direction this is known as symport. If two solutes are moving in opposite directions this is know as antiport.
an example of coupled transport would be Na+/Glucose symporter. Cells use the high extracellular concentration of sodium to transport glucose into the cell (which glucose con’t are aleady higher inside than outside; moving from low to high against it’s concentration gradient). This symport will undergo a change from state A to B if both sodium and glucose are bound to it, and it only goes back from state B to A if neither are attached to it. Otherwise the protein would simply act as a sodium uniport.
The association of glucose with state A isn’t common, but the carrier protein is going to wait until both glucose and sodium are attached before it changes to the state B.
what force drives water across cell membranes? and how do different types of cells deal with this.
Osmosis drives water across cell membrane. Unlike con’t grad. which moves from high to low. Water follows from a location of low solute concentration to a high con’t.
Animal cells/multicellular cells/bacteria use Na+/K+ pumps (pump 3 Na+ out of cell and 2 K+ into cell) to regulate osmolarity as this equilibrates osmotic pressure across membrane
Plant cells are prevented from swellin by their rigid walls and can tolerate osmotic differences across their plasma membranes, internal turgor pressure builds up which at equilibrium forces as much water as enters
Protozoa avoid becoming swollen with water by periodically extruding water from a special contractile vacuoles
What are ionophores?
- Ionophores are a special group of lipid soluble proteins
- involved in moving charged ions across membranes and disrupt ion gradients
- can be channel forming proteins or carrier proteins
- they are passive transporters and only facilitate the movement of ions from one are to another area in an area of high concentration to an area of low concentration.
Why is calcium so low inside cells?
-one of the reasons for very low con’t of free calcium inside cells is the use of high energy phosphate molecules, like ATP for cell energy. Higher con’t of free calcium inside cells would probably cause the formation of calcium phosphate, which crystallizes
