Flashcards in Chapter 11.1 (membrane transport) Deck (51):
What are carriers (transporters)?
physically bind a solute and undergo a conformational change to move the solute across the membrane
Doesn't catalyze conversion of substrate into product
What are the different type of molecules a transporter transport?
There is a different type of transport protein for every solute. Transport may or may not be active
What is transport direction dependent on?
concentration gradient of solute
direction of transport is not fixed
What does transport kinetics follow?
Michaelis Menten kinetics
J=Jmax* Cout/Km + Cout
What is Jflux equal to?
reaction/transport rate at some solute concentration
depending on which direction of transport
What is Jmax?
maximum rate of transport
analogous to Vmax
What will enzymes have like enzymes?
a specific Km for which enzyme they are binding and transporting
What are the units of Km?
What type of concentration dependent flux rate does channels tend to show?
more linear but at high enough concentration gradient flux rate will level off like carriers
What are the different types of carriers?
What is a uniport?
transport a single kind of solute
not specific to a particular solute just similar solutes
What type of transport uniports perform?
Depending on what type of solute it could be
Facilitated diffusion or
What are examples of some uniports?
CA++ ATPase -active uniport
GLUT2- allows 6 differ hexose sugars (facilitated diffusion)
there are any secondarily active transport via uniport
How doe s coupled transport, transport molecules?
must be two different solutes via one protein
at the same time or in a 1-2 cycle
one solute cannot be transported without the other
it is primarily or secondarily active transport
What is a symport?
transport two solute in the same direction
What is an antiport?
Two or more solutes in opposite directions
How does the solutes move across the plasma membrane?
they physically bind to transport protein,
transport protein changes conformation and solute is transported across membrane
What is the Glut family if transporters?
13 members that span the the membrane 12 times a single polypeptide chain
all difference in specificity of solute.
all move solutes down its concentration gradient
What is the Na/glucose cotransporter(symport) found?
epithelium of kidney tubules and small intstines
What must be present in order for Na/glucose symporter to change conformation and transport sodium and glucose?
sodium and glucose both must be present and bound to the transporter for it to change conformation and move them
Where does the Na/glucose usually move sodium and glucose?
into the cell
How does Na/glucose transporter move the solutes across?
potential energy stored in sodium electrochemical gradient is used to move glucose up its concentration gradient
What is a Na+/K+/2Cl- cotransporter?
a symport that uses the sodium electrochemical gradient to drive potassium and Chloride against their electrochemical gradient.
What is the net charge movement of the Na+/K+/2Cl- across the membrane?
it has 2Cl- that cancels the K+ and Na+
Which ion in the Na+/K+/Cl- cotransporter must be concentrated above its above its electrochemical equilibrium?
What is an exchanger?
exchanges solutes in the opposite direction
all solutes must be present
What is an example of a exchanger?
uses Na+ concentration gradient to drive H+ out of the cell.
What is the purpose of the Na+/hydrogen exchanger?
it maintains the cell pH at an a optimum 7.2
HCO3- moving into the cell also helps maintain pH
What are sodium exchangers mostly driven by?
secondarily active transport
using sodium gradient across the membrane
What is the chloride bicarbonate antiporter?
also known as a anion exchanger
uses active transport for ion exchange depending on cell type
What is the Na+/K+ ATPase pump (Na+ pump)?
uses ATP to drive sodium and potassium against their electrochemical gradient via primary active transport
Where are sodium pumps found?
found in all animal cell
important for maintaining the ionic gradients across cell membranes
What does the sodium pump exchange?
3Na+ out of cells 2K+ into cell
pump is electrogenic (creates a charge)
What are concentration of Na+ and K+ in and out the cell?
intracellular High K+ low Na+
extracellular high Na+ low K+
What doe the subunits makeup on a sodium pump?
subunits makeup binding and transporting domains
also have ATPase domain that is the site of phosphorylation
What induces a conformational change in the sodium pump?
phosphorylation/dephosphorylation of the pump that allows movement of the ions across the membrane
What type of active transport is the sodium pump?
primary active transport because ATP is hydrolyzed for each cycle
Describe the action of a sodium pump?
1) PO4- group temporarily binds to pump
2) conformational change is induced
3) allows sodium to be moved from cytoplasm to extracellular fluid
4)pump loses PO4 group and returns to the most energetically stable conformation
5) brings K+ from extracellular fluid into cell
What is the role of the sodium pump?
maintain ion concentration over plasma membranes
present in all animals
How long is the cycle of a sodium pump?
completes one cycle every 10 milliseconds
What blocks the cycle of the sodium pump?
ouabain.- a type of cardiac glycoside
How does ouabain work?
binds to K+ binding site on extracellular side and prevents it from changing conformation
If a solute is moving down its electrochemical gradient what is it?
what is always passive transport?
simple diffusion (non-prtein mediated)
facilitated diffusion via channel
What type of transport is transmembrane flux via a carrier?
may be active or passive
What type of diffusion is a carrier mediate uniport transport when it is passive?
What is active transport ?
some type of energy input to move a solute against its electrochemical gradient
What is primary active transport?
using cellular energy (ATP)- also called pumps
What is secondary active transport?
using stored potential energy (Na+ down its concentration gradient to move a ion against its electrochemical gradient)
ex. sodium glucose cotransporters
what is the sodium gradient across the membrane maintained by?
Na+/K+ ATPase pump (sodium pump)