Flashcards in Membrane Transport of Small Structures: Ch.11 Deck (42):
Lipid bilayer is permeable to...
1) hydrophobic molecules (CO2, O2, N2, benzene)
2) small uncharged polar molecules (H20, urea, glycerol)
Describe the diffusion of molecules through the lipid bilayer. (concentration)
-goes from high concentration to low concentration (down the concentration gradient)
-the more hydrophobic/non-polar the molecule, the faster the diffusion across the lipid bilayer
Lipid bilayer is impermeable to...
1) large uncharged polar molecules (glucose, sucrose)
2) ions/charged molecules (Na+, K+, H+, etc.)
What kind of molecules do multipass transmembrane proteins transport?
-transport polar and charged molecules (ions, sugars, AAs, nucleotides)
Each transport protein is ______
(transport specific class of molecules)
What is the resting membrane potential?
-the cell is more negative on the inside than the outside
-positive has the greatest motive force because -ve on inside attracts +ve on outside
__________ + __________ = electrochemical gradient
concentration gradient + membrane potential (electric gradient) = electrochemical gradient
What is active transport?
-goes against electrochemical gradient
What are the three types of active transport?
1) coupled transporters: one molecule down gradient; second molecule against gradient
2) ATP-driven pumps (ATPases): ATP hydrolysis, moves molecules against gradient
3) light-driven pumps (bacteria): light energy, moves molecules against gradient
Describe transporter proteins.
-bind to specific solute and transport it across membrane
-undergo conformational change
What is a uniporter?
-one molecule; passive transport down electrochemical gradient
-direction of transport is reversible
ex. GLUT uniporters
What are two functions of GLUT uniporters?
-transports glucose down electrochemical gradient
-works in both directions (glucose in or out of cell)
What are the similarities and differences between symporters and antiporters?
-both involve two molecules (transported molecule and co-transported ion)
-symporters: molecules move in SAME direction
-antiporters: molecules move in OPPOSITE direction
Na+/glucose symporter: Na+ down the electrochemical gradient provides the energy to move...
-glucose against the concentration gradient
What does cooperative binding of Na+ and glucose lead to?
-conformational change in the protein
What pH is required for cytosol and lysosomes? And what maintains cytosolic pH?
cytosol: neutral pH
lysosomes: acidic, low pH
-Na+ driven antiporters maintain cytosolic pH
What happens to excess H+?
-leaks into cell
-produced by acid forming reactions
Which way do Na+ and H+ molecules move? Which is the co-transported ion and the transported ion?
-Na+ moves with the electrochemical gradient into the cell (co-transported ion)
-H+ moves against the electrochemical gradient out of the cell (transported ion)
Does transporter activity increase or decrease with the Na+/H+ exchanger/antiporter? What happens to the pH?
increases; pH drops/acidifies
How is the Na+ electrochemical gradient maintained?
-the Na+/K+ pump (transport ATPase)
Where do the two transporters get their energy?
-use energy stored in the Na+ electrochemical gradient to move other molecules against their electrochemical gradients
Give examples of the following:
4. P-type ATPase
1. GLUT uniporter
2. Na+/glucose symporter
3. Na+/H+ exchanger
4. Na+/K+ pump
P-type pump gets _________ (hint: uses energy)
phosphorylated (ATP to ADP + Pi)
Which way does Na+ and K+ move?
Na+ out of cell, K+ into cell
-both move against electrochemical gradients
What are the two functions of Na+ gradient?
1. transports nutrients into cells
2. maintains pH and cell volume
Transport proteins work together to transfer glucose from the ______ to the _______
intestines; blood stream
What is a tight junction?
-a barrier to prevent the mixing of membrane proteins from the basolateral and apical domains
Intestinal epithelial cells:
-transport proteins are restricted by ______
-apical membrane contains ______
-basolateral plasma membrane contains _____ and _____
-GLUT 2 uniporter and Na+/K+ pump
What are the three types of ATP driven pumps?
1. P-type pump
2. F-type and V-type proton pump
3. ABC transporter
What are the differences between F-type and the V-type ATPases?
F-type: ATP synthase uses the H+ electrochemical gradient to produce ATP; used in mitochondria, chloroplasts and bacteria
V-type: H+ pump uses ATP to pump H+ against the electrochemical gradient into organelles; used in lysosomes and plant vacuoles
What is the ABC transporter and what does it do?
ATP Binding Cassette: pumps small molecules across membranes; each member contains two ATPase domains; not selective
Describe channel proteins.
-hydrophilic/aqueous pore across membrane; most are selective (e.g. ion channels)
Passive transport involves _____ interactions with solute and _____ transport by channels than transporters because...
several molecules pass through when open
Ion channels are found in what three things?
animals, plants and microorganisms
What are the two types of ion channels?
1. non-gated: always open; K+ moves out of cell; plasma membrane of animal cells (e.g. K+ leak channels)
2. gated: chemical or electrical signal required for channel opening
What is the importance of the membrane potential?
-used by symporters and antiporters to carry out secondary active transport (animals and plants)
-action potentials in nerve cells (animals)
How is the membrane potential generated? (two ways)
1. K+ leak channel: outward flow of K+ (major role in membrane potential)
2. Na+/K+ pump: 3 Na+ ions out, 2 K+ ions in (10% of membrane potential)
What are the two principles of the membrane potential?
1. ion in solution are present in pairs since each needs a counter ion
outside: Na+, Cl-
cytosol: K+, Cl- and cell's fixed anions
2. ions diffuse from high concentration to low concentration (K+ leak channel)
What is the net result of the membrane potential?
-more positive outside the cell (Na+, K+)
-more negative inside the cell (Cl- and fixed anions)
What does the resting membrane potential have a high concentration of in the cytosol?
-high concentration of K+ in cytosol: outward flow of K+
-balanced by repulsion to excess (+) on outside and attraction to excess (-) on inside
What are the 4 types of gated ion channels?
1. voltage-gated: change in voltage across membrane
2. mechanically-gated: mechanical stress; opens if PM is stretched
3. ligand-gated: extracellular ligand (neurotransmitters)
4. ligand-gated: intracellular ligand (ion, nucleotide)