Terms in this set (79)
What is Carrier Mediated Transport ?
Movement of substances across the plasma membrane by protein carrier molecules.
What are protein carrier molecules?
integral membrane proteins
When are protein carrier molecules used?
when molecules attempting to cross the membrane cannot cross or cross too slow.
where are protein carrier molecules found?
embedded in the lipid bilayer
How do protein carrier molecules assist with molecule transport?
they have a receptors for molecules, once molecule bind it promotes a conformational change in the protein carrier and the molecule crosses.
Does a channel form when using protein carrier molecules?
What are the four properties of mediated transport?
As the concentration of the transported substance is in creased what happens to the rate of transport with time?
It begins to approach a maximum due to the presence of a fixed number and limited number of transporters in the membrane.
What does Tm stand for?
Maximum transport rate for carrier mediated transport.
How are carrier molecules specific?
each carrier molecule bind to only a select group of substances.
What is an example of how specificity is expressed?
amino acids are transported by different transporters than is glucose.
Transporters show high degree of what ?
What is an example of how transporters express a high degree of specificity?
D-glucose is easily transported vs. L-glucose.
Is specificity an absolute for transporters?
it is not, glucose transporter in RBC membrane prefers glucose but also transports other sugars such as mannose.
Why can structurally related molecules compete for a transporter?
because specificity is not absolute.
What happens to the transport rate when two substances are competing for the same transporter?
The presence of the second decreases the transport of the first.
What can causes inhibition in protein mediated transport?
substances that are not structurally related to the transported ion or molecule
What is an example of a transport inhibition by non molecule related substances?
Metabolic poisons inhibit ATPases which stops the production of ATP
How else can a pump be inhibited?
By specific blockers
What is an example of a pump inhibition?
Na-K ATPase is inhibited by cardiac glycoside - dioxin or Quabain
Where does cardiac glycoside dioxin bind on the Na-K ATPase?
bind with high affinity on the extracellular side of the pump which has a high affinity for K+, binding of extracellular K+ competitively inhibits digoxin binding.
what is a clinical aspect of extracellular K+ binding?
-competitive inhibition of digoxin binding -Hypokalemia potentiates digitalis toxicity.
What is facilitated diffusion?
Protein carrier- mediated transport of substance down its concentration gradient.
How is facilitated diffusion different from net diffusion?
it is mediated by a carrier, not by water concentration.
Does facilitated diffusion require energy?
How is the transport described in facilitated diffusion?
DOWN a concentration gradient, and bidirectional.
what causes a conformational change during facilitated diffusion?
the binding of the substance to be transported
What is an example of facilitated diffusion?
glucose transport across skeletal muscle cells
Define Active transport
protein carrier-mediated transport of substances AGAINST a gradient
What does active transport require?
How is active transport different that facilitated diffusion?
Active transport transports substances against their gradient and requires energy, while facilitated diffusion does not require energy and transports substances down their concentration gradient.
How is active transport described under physiological conditions?
it is unidirectional and against a gradient
What are the two types of active transport systems?
Primary active transport and secondary active transport
define primary active transport
ATP hydrolysis DIRECTLY supplies energy to transporter (pump )
what is another name for the pump?
ATPases and an example of that is Na-K pump or Na-K ATPase
define secondary active transport system
energy for transport is not provided directly by ATP hydrolysis, ATP is provided indirectly by using the existing gradient of an ion to drive the transport.
Which is the most common ion gradient used for secondary active transport ?
What must occur for the secondary active transport to function?
Both the driving ion and the substance being transported must simultaneously occupy the transporter.
What are the common names for transporters?
What is a transporter which transports only one substance at a time called? Which type of transport is it a part of?
Uniport, facilitated diffusion
What is another name for cotransport?
How does symport transport function? Which type of transport does it support?
carrier has sites for driving ion and at least one other substance. Secondary active transport only
what are some examples of cotransport?
Na+ cotransport of amino acids
Na+ cotransport of glucose
What is another name for countertransport?
how do antiport exchangers work?
carrier has a site for driving ion and for at least one other substance. All sites must be occupied for transport to occur. Ion and substance are moved in opposite directions across the membrane.
What are some examples of antiport exchangers?
Na+ -Ca2+ exchanger
Na+ - H+ exchanger
Which exchanger uses the Na+ gradient to extrude Ca2+ from the cell?
How many Na+ ions enter the cell for each Ca being extruded?
Na+ -Ca2+ exchanger
3 Na ions enter the cell for each Ca ion extruded.
What is an example of an electrogenic exchanger.
Na+ -Ca2+ exchanger
Which exchanger responds when pH is falling and how?
Na+ - H+ exchanger extrudes H+ from the cell in response to falling pH.
What are the other transporters found in our cells? There are 5 mentioned in the notes
What do we use to transport Ca2+ in our cells?
Most cells have an intracellular concentration of Ca2+ equal to what?
0.1 MicroMolar or less, very small amount of free Ca2+ inside our cells.
What are the two Ca-ATPases? What and how do they pump substances?
SERCA (Sarcoplasmic and Endoplasmic Reticulum Calcium ATPases)
PMCA (Plasma Membrane Calcium ATPases)
-pump H+ and Ca in opposite directions
What is the location and function of SERCA Ca-ATPases?
located on the membrane of intracellular organelles
actively sequester Ca2+ in intracellular stores such as sarcoplasmic reticulum and skeletal muscle.
Which pump plays a major role in lowering intracellular Ca levels?
PMCA (Plasma Membrane Calcium ATPases)
How does PMCA pump function?
inactive at physiological calcium levels
as calcium rises, it combines with calmodulin forming CAM
CAM binds to pump increasing affinity for Calcium
as calcium fall, calcium and calmodulin dissociate and pump becomes inactive
What activates the PMCA?
high calcium levels when it combines with Calmodulin to for CAM
What type of transporter is on the parietal cells of the gastric mucosa?
H+ - K+ ATPase which transports H+ into gastric lumen and K+ into parietal cells
What is an Anion Exchanger?
exchanges extracellular univalent anion for an intracellular one.
Which exchanger plays an important role in CO2 handling in the body ?
Chloride-bicarbonate exchanger specifically in red blood cells.
What function does the Cl- and HCO3- exchanger play ?
prevents cytosol from becoming too basic.
Which transporter is found on the nonepithelial cells and basolateral membranes of some epithelial cells?
What is the function of the Na-K-2Cl transporter ?
one function is to regulate cell volume by increasing intracellular Na, K, and Cl.
How do ATP-Binidng Cassettes work?
all bind ATP, some act as primary active transporters, some hydrolyze ATP but do not use the energy for transport, and in others ATP binding regulates ion channels.
What are the various ATP-Binidng Cassette transporters?
Which transporter is involved in transport of phospholipids and cholesterol out of macrophages?
What is a multidrug resistant transporter?
Where are MDR subfamily found ?
in liver, kidney and GI tract cells
What is the function of MDR subfamily transporters?
Primary active transporters that extrude cationic drugs and metabolites from cells.
What is the clinical importance of MDR subfamily transporters?
in cancer patient, because they pump anticancer drugs out of cancer cells rendering the cells resistant to the drugs.
Has a Cl- channel found in apical membrane of many epithelial cells , such as the GI tract, duct of liver, pancreas and salivary glands which subfamily transporter is this?
Cystic fibrosis transmembrane regulator
What are the two ways in which ATP regulates the function of CFTR's Cl- channel ?
1.the channel contains a regulatory domain with sites that must be phosphorylated for channel function.
2. the channel also has two nucleotide binding domains to which the ATP must bind for channel function.
The phosphorylation of regulatory sites result from what?
from an elevation of cAMP which then activates a protein Kinase A that phosphorylates the sites.
What are the two nucleotide domains to which ATP must bind for Cl- channel to function?
NBD1 and NBD2, both must bind.
How does Cl- move through the CFTR?
moves into the cell or out of the cell down the Cl- electrochemical gradient.
Which transporters are used in response to RVI ?
1. Na-H exchanger
What occurs when the Na-H exchanger is activated as a result of RVI?
1. Na-H exchanger, increases Na+ uptake and alkalizes cytoplasm activating Cl-HCO3 exchanger.
2.Na-K ATPase extrudes Na+ in exchange for K+ resulting in net increase in KCl
Which transporters are used in response to RVD ?
activation of K-selective or Cl-selective channels
What is the primary mechanism in response to RVD?
-moves K+ and Cl- out of the cell
-activation of K-selective or Cl-selective channels since in many cells the electrochemical gradient of these ions is outward, there is a new efflux of these ions
-activation of K-Cl countertrasnport
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