Exam 3: January 30 - February 3 Flashcards
what are aquaporins?
a protein channel that transports water
water doesn’t diffuse it does osmosis
what is osmosis?
the net diffusion of H2O across a membrane
how does water move during osmosis?
water will move from high to low water concentration
water goes from low solute concentration to high solute concentration
what is osmotic pressure?
the pressure exerted by solutes for water to move across the membrane
what is osmolarity?
total[solutes] in solution
the concentration of solutes is of ALL solutes, there aren’t different osmolarity for different solutes
water goes towards higher osmolarity
what is the osmolarity of 3 mol MgCl2 and 2 mol lc in 1 liter of water
11 mol/1 L
11 Osm
what’s the relationship between [water] and osmolarity?
the bigger the osmolarity means the smaller the amount of water so high osmolarity = low [H2O]
what are the consequences of osmosis?
1) water can move across the membrane through the aquaporins and also slightly through the membrane itself – cholesterol prevents a lot of it but we can still see movement of water
2) change in cell size due to solution: when we put a cell in different osmolarities, we can end up changing how the water is positioned inside of that cell (isotonic and hypertonic and hypotonic solutions)
3) osmotic pressure
what is an isotonic solution?
same concentration of solutes inside and outside of the cell on both sides of the membranes yields no change in volume and there’s no gradient – this only applies for non-penetrating solutes (?) – CO2 and NO2 are penetrative - we want blood to be isotonic with RBC so that our RBC aren’t changing size
what is a hypertonic solution?
there is a higher concentration of np solute outside of the cell than inside the cell: increased [npS] = decreased cell volume because water goes to high osmolarity so the water will leave the cell and the cell will shrink
what’s a hypotonic solution?
there is less solute outside compared to the inside of the cell so the water will go into the cell and the cell will expand
what if the membrane is immobile or if it isn’t semipermeable? what are the consequences in terms of osmotic pressure?
where our membrane is semipermeable (??): some np S – the red balls can’t move across the membrane so the only option we have is to change the volume – water will go towards the higher osmolarity where there’s more solute so we’ll see a shift in water so that the side with higher solute will get bigger so that the two sides match each other now – if the membrane can move to accommodate this, then when this happens there’s no osmotic pressure
what if the membrane is immobile? Then no cell volume change is allowed – now we can’t change the denominator – water still wants to go to higher osmolarity but there isn’t enough space – PV=nRT now comes into play because if we can’t change V but we want to increase n by moving water over to side 2, then there needs to be a larger P – osmotic pressure is when water wants to move to a certain area but there isn’t room for it so there’s a pressure build up that keeps the water back – this only happens when membrane is semipermeable (can’t change the numerator) and when we have an immobile membrane (can’t change the denominator)
what does gating mean?
gating means a channel can either be open or closed
what is carrier mediated transport?
carrier mediated transport are kind of like a revolving door – one side is open and the other is closed –they are not a channel, they’re transporters
our protein will act as a shuttle – the compound that we want to move has to get in there and then you’ll change the shape and get the protein to the other side
will require binding of solute to regulate transport – not the same binding in the chemically gated ion channels where the binding of something else opened to gate but it itself wasn’t what was getting move across
what are the types of carrier mediated transport?
facilitated diffusion and active transport
what is facilitated diffusion?
diffusion with the gradient so no energy cost (figure 3-14)
conformational shape change when it binds causes transport – when you bind something to a protein to ALWAYS get a shape change – you don’t know how big or small the shape change is but nevertheless, there’s a shape change
the transportee regulates the transport
what is specific binding?
only specific things can be transported by specific proteins
what is saturation in terms of facilitated diffusion?
overloading
you can overload these transporters like at na OSU football game - there’s a limit to how fast they can dump things to the other side
what are competitors in terms of facilitated diffusion?
it can be that we’re going to the stadium and there’s a Michigan fan that can’t figure out how to get through the turnstiles – so there can be competitors that get bound there but don’t get moved through and slow the process – an example of this is getting glucose inside of our cells (Glucose transports GLUTs) – there’s more glucose outside than inside so the transporters move it inside your cell
what can you do to hinder facilitated diffusion?
saturation and competitors
what is active transport?
almost always against the gradient - work against diffusion which costs energy because you’re going from high to low concentration
still carrier mediated so still dependent on conformation shape changes caused by transportee binding to the protein and also ATP through the use of equation 1
what are the types of active transport?
primary active transport and secondary active transport
what is primary active transport?
uses ATP directly (ATPase pumps) - ATP is getting broken down comes from “ase” enzyme and they’re making a gradient
one or two things get moved
what’s an example of primary active transport?
Na/K ATPase pump
there’s “naturally” more K inside the cell than outside but how did that happen
pump moves Na against its gradient from inside to outside the cell and puts K into the cell
what are the steps of the Na/K ATPase pump?
1) 3 Na bind
2) shape change
3) ATP breaks down into Pi and energy and ADP
4) energy reorients carrier to the extracellular fluid which also causes us to not be able to hold onto Na anymore
5) 3 Na released into ECF
6) 2 K from ECF bind and there’s a shape change which releases the bound phosphate on the inside of the cell which releases energy and causes us to shape change back to the ICF
7) 2 K released into the inside of the cell
8) Repeat
what is secondary active transport?
uses ATP indirectly
relies of primary facilitated diffusion just like how Krebs cycle relies on ETC
always moves at least two compounds - one of the compounds will always be going with its gradient and the other will be going against it’s gradient so one gradient will be getting bigger and the other will be getting smaller
what’s an example of secondary active transport?
Na/K glucose pump
what are the steps of the Na/K glucose pump?
1) Na binds to transporter in ECF which causes a shape change (Na from diet)
2) shape change allows glucose to bind
3) second binding of glucose causes a shape change the reorients our protein to the ICF and it’ll dump out the Na and glucose (Na i going with its gradient and glucose is going against)
4) after the release, the protein will reorient back to ECF
5) repeat
under what conditions will the Na/K glucose pump work?
will only happen if Na gradient is still there with more Na outside the cell than inside – you’ll only have the sodium gradient if the Na/K ATPase pump is working to create the Na/K gradient
what is cotransport?
both to ECF or both to ICF (Na/glucose transport)
what is counter transport?
one to ECF and the other to ICF
what is vesicle formation?
moves large compounds - not limited by movement through a protein
requires ATP
plasma membrane needs cholesterol associated with it to make vesicles because it provides stiffness and creates bends in PM that have a distinct shape – can’t be fluid or shape won’t form
how are vesicles formed/destroyed?
endocytosis vs exocytosis
intake vs. export
what is endocytosis?
creating a vesicle
endocytosis makes the plasma membrane smaller
intakes things
