Membrane Transport (msbiochem)

  1. 1. What was extremely important in the development of the cell?

    2. What then had to happen?

    3. What are the 2 major components of the cell membrane?

    4. What is unique about phospholipid molecules?

    5. Can water molecules penetrate PL bilayer?

    6. Are membranes & proteins dynamic or rigid?
    1. Development of membranes ---> encapsulation of NAs, proteins, polysaccharides, etc.

    2. Cells had to develop pathways to import nutrients and export wastes through semi-permeable membrane

    • 3. Phospholipid bilayer & integral membrane
    • proteins

    4. Amphipathic molecules - w/ polar and non-polar regions

    5. Rarely

    6. Both are dynamic (NOT RIGID)
  2. 1. How does lipid bilayer impede entry/export of hydrophilic substances?

    2. What, then, is the transport rate for hydrophilic substances? 

    3. How do hydrophilic substances enter otherwise? (1) How so? (2 steps)

    4. What compounds are seen in the phosphatidyl choline bilayer? (5)
    1. Energy barrier

    2. Essentially 0

    3. Through alternative pathways provided by proteins. These parts are amphipathic, creates recognition site for substrate --> provides low-energy pathway for substance to pass through membrane.

    4. C, N, O, H2O, P
  3. What do energy diagrams look like with transporter and without transporter?
    Image Upload 1
  4. 1. What does a cell need to do to survive? 6

    2. What has made this more complicated?
    • 1. Important metabolic substrates
    • 2. Export wastes
    • 3. Maintain cell volume
    • 4. Energy generation (involves membranes)
    • 5. Build & degrade proteins, nucleic acids, etc.
    • 6. Reproduce

    2. Performing these actions in a non-infinite ocean of EC fluid becomes more complex
  5. 1. What are primary active transporters?
    2. What is a common example?
    3. What is EC fluid composition like? What does it take to maintain this fluid composition?
    4. What are the concentrations of K+ and Na+ in and out of cell?
    5. What happens when Na+ - K+ ATPase works?
    6. Where are ion gradients in the cell essential?
    • 1. Couples energy use (hydrolysis of ATP) to transport molecules across a membrane.
    • 2. Na+-K+ ATPase
    • 3. High Na+ outside and high K+ inside - our recapitulation of ocean that primordial cells originated from. Creating this concentration gradient requires energy

    4. K+ 140 mM - 5 mM; Na+ 10 mM - 140 mM

    5. ATP--> ADP while 3 Na+ exits while 2K+ enter

    6. In all cells in body
  6. Describe mechanism of Na-K transport with ATPase (6)
    • 1. Transporter binds 3 Na+ from inside cell
    • 2. ATP is hydrolyzed --> ADP + Pi
    • 3. Phosphorylation favors P-EnzII formation of transporter
    • 4. Transporter releases 3 Na+ to the outside, while binding 2 K+ outside of cell
    • 5. Transporter is dephosphorylated, inducing conformational changes favoring Enz
    • 6. Transporter releases 2K+ inside

    Image Upload 2
  7. 1. What are other forms of primary active transporters? (3)

    2. Describe each in detail
    1. Ca2+ ATPase; K+ H+ ATPase, H+ ATPase

    • 1. Ca2+ ATPase hydrolyzes ATP while poumping out Ca2+ --> helps maintain low IC Ca2+ environment.

    2. K+ H+ ATPase pumps 1 proton for 1 K+, allows stomach to acidify stomach environment.

    3. H+ ATPase pumps 3 protons for every ATP hydrolyzed - important for acidification of IC organelles (endosomes pH = 6, lysosomes pH =4)
  8. 1. What is facilitated transport? Another name? (2)

    2. What is the name for the proteins involved? What is a famous example?

    3. Do they use ATP directly? Do they use energy at all?

    4. What drives facilitated transport? How are substrates kept in cell?

    5. What is a critical aspect of these transporters?
    1. Form of passive transport facilitated by transporter proteins down a concentration/electrochemical gradient. Facilitated diffusion or alternative access model.

    2. Facilitative transporters or UNIPORTERS. GLUT transporters.

    3. No, but may or may not use energy source at all.

    4. Concentration on one side of membrane is greater than other side, bc transporters can go both ways. Glucose is phosphorylated to keep it in the cell (not in kidney)

    5. They are specific for the substrate - GLUTS will only transport glucose.
  9. 1. Define secondary active transporters

    2. How do they differ from facilitated transporters?
    1. Transporters that use energy indirectly from primary active transporters stored from their concentration gradients to move substrates in opposite directions.

    2. Secondary active transporters definitely use residual energy - it is a FORM of facilitated transport, but facilitated transport moves substrates down their concentration gradient, while secondary active transporters CAN move substrates against concentration gradient.
  10. 1. Symporters vs. Antiporters? vs.  Uniporters?
    2. Name examples of symporters (2) and antiporters (3)?
    1. Symporters couples energy of substrates moving along concentration gradient to move substrate against their concentration gradient in same direction.

    • Antiporters - couples energy to move substrates similarly, but in opposite directions.Image Upload 3
    • 2. Na+-glucose, Na, Cl, K+

    • Na+-H+, 3Na+ - 2Ca2+, Cl-HCO3
    • Image Upload 4
  11. 1. Define transmembrane ion channels.

    2. How many ions can travel through per second?

    3. How do transmembrane ion channels differ?
    1. Transmembrane ion channels (TIC) allow ions to flow down (ONLY DOWN, NOT UP) electrochemical gradient at high rate w/ incredible specificity.

    2. 10^8

    3. Ion selectivity  (very selective!) and control of gating. Depending on whether ion channels are open or closed --> ions can get to where they need to go.

  12. 1. Define channels

    2. Define transporters

    3. Define uniporter

    4. Secondary active

    5. Define pump
    1. Channels - allows uncoupled flow of ions or other substrates down electrochemical gradient

    2. Transporters - allow movement of substrates across a membrane, it may involve coupled transport. Translocation rates are orders of magnitude slower than channels

    3. Uniporter - facilitates transport of substance down electrochemical gradient (i.e., facilitated glucose transporter) facilitated diffusion only

    4. Secondary active - sym-or anti-porters/co-countertransporters - one substrate moving down its electrochemical gradient may drive uphill movement of another substrate (i.e., Na+ coupled glucose cotransporter).

    5. Pump - ATP driven transporter, primary active transporter.
  13. 1. What problem did evolution of multicellular organisms create?

    2. What were the solutions? (2)

    3. What is needed to maintain solution?
    1. Not all cells had free access to ocean for uptake of metabolic substrates and export of wastes

    2. Create personal ocean/EC fluid that could be circulated to contact all cells aka blood.

    3. Must make sure that composition and volume of blood stays constant (function of all organs is to maintain and circulate fluid)

    • Heart - pumps fluid through circulatory system
    • Blood vessels - conduit for fluid

    Kidney - filters out waste products in EC fluid

    Liver & intestine - import metabolic substrates into fluid

    Brain - coordinates activity of all these actions.
  14. 1. Define epithelium

    2. What are the two sides of the epithelium? 3 descriptions for each.

    3. What is a tight junction? What do they control? How can they vary?

    4. What does golgi do?

    5. How do microvilli associate with apical side of epithelium?

    6. Which side is usually larger? Apical or basolateral?

    7. What is the role of tight junctions? Tight vs. leaky? What is it important for?
    1. Purely cellular, avascular layer covering all free surfaces (cutaneous, mucous and serous) including glands and other structures derived from them. It is the layer that separates interior of body from external world. EXAMPLE: INTESTINAL LINING

    2. External/lumen side (apical membrane); internal/blood side (basolateral membrane)

    3. Closely associated areas of adjacent cells formed by interactions bt transmembrane proteins forming a virtually impermeable barrier to fluid.

    They control flow of substances from external world to internal world; can vary in "tightness" to allow different materials through.

    4. Golgi determines whether to send certain proteins to apical side or basolateral side.

    5. Microvilli increase surface area of apical side

    6. Basolateral

    7. Sometimes small molecules can pass through leaky tight junctions, but both types prevent entry of larger proteins/molecules. Prevents absorption of intact proteins from intestine. Allergy-inducing molecules can enter via leaky junctions --> to have effect.
  15. 1. Define vectorial transport

    2. Difference b/t transcellular and paracellular transport?

    3. What is needed to accomplish vectorial transport?  2

    4. What is the mechanism needed for vectorial transport?

    5. Example of vectorial transport?
    1. Transport of ion/molecule across membrane in a specific direction.

    2. Transcellular - ion/molecule moves across cell while paracellular transport moves between cells.

    3. (1) Permeability pathways and (2) driving force to make transport directional.

    4. Place different transporters in the apical and basolateral membranes. One energy dep transporter and one passive (facilitated) transport or channel. PUMP LEAK MECHANISM

    5. Intestinal glucose absorption
  16. Describe vectorial transport of glucose in intestine. (3 steps)

    What is another example of vectorial transport?
    1. High sodium and low glucose in intestinal lumen

    2. APICAL MEMBRANE: transporters 2 Na+ down concentration gradient and 1 glucose up CG into cell via Na+ coupled glucose transporter (SGLT) 2ndary active transport

    3. BASOLATERAL MEMBRANE: glucose diffuses down CG into EC fluid and can be absorbed into blood via facilitated transport

    Basically, you go from low concentration to high concentration to low concentration to absorb glucose liberated in intestine.

  17. 1. What are the two families of glucose transporter proteins? What kind of transporters are they?

    2. What is the insulin-stimulated glucose transporter? Why isn't it more ubiquitous?

    3. How does body regulate GLUT 4 transporters? (1)

    4. Describe mechanism of GLUT 4  (5)
    1. GLUT (12 membrane spanning segments - facilitated/passive transporters) and SGLTs (11 membrane spanning segments - Na+ coupled secondary active)

    2. GLUT 4 (muscle, fat, heart). Bc other organs do not want to rely on insulin to uptake glucose - they want a continuous source of glucose.

    3. Through insulin - endocytosis mechanism


    (1) GLUT 4 stored within cell in membrane vesicles

    (2) Insulin binds to IR --> vesicles move to surface and fuse w/ plasma membrane increasing # of GLUT 4 in plasma membrane

    (3) Insulin levels drop, GLUT 4 is removed from plasma membrane by endocytosis --> forms small vesicles

    (4) Smaller vesicles fuse with larger endosome

    (5) Patches of endosome enriched w/ glucose transporters bud off to become small vesicles to go to surface when insulin levels rise again.
  18. 1. How do epithelia pump water?

    2. What is the mechanism of intestinal Cl- induced fluid secretion?

    3. What is the main point of regulation of the above?

    4. Describe mech of regulation when this is on (cAMP)

    5. When it's off (cAMP)

    6. When it's back on again (cAMP)

    7. cGMP
    1. Pumps salt and water follows osmotically (salt goes from BL blood side to apical side)


    1. BL side: Na-K-Cl cotransporter (brings in Na, 2 Cl, K+) AND Na-K ATPase (3Na+ out, 2 K+ in) and K+ ion transporter (1 K+ out)

    2. Cl- flows across cell from BL side to apical side, creating negative potential charge on apical side.

    3. Na+ ions follow Cl-, moving through leaky tight junctions from BL to apical side (paracellular)

    4. H2O follows Na+ transcellularly through water channels in protein.

    Summary: transcellular movement of Cl-, paracellular movement of Na+, transcellular movement of H2O.

    3. Apical chloride channel

    4. Activated by phosphorylation by protein kinase (cAMP-dep kinase A or membrane-bound cGMP-dep kinase).-(1) Phosphorylation of channel --> (2) activation & opens channel --> (3) allows Cl-ions to pass through --> (4) Na+ passes through --> (5) water follows.

    5. Dephosphorylation --> Cl- can't leave --> [Cl-] builds up --> no more entry of Cl-

    6. Then, (1)  hormone comes along, stimulating secretion --> (2) binds to basolateral receptor --> (3) activating G protein --> (4) activates adenylate cyclase (BL membrane): ATP --> cAMP. (5) Binds to PKA, (6) phosphorylates Cl-channel, then as (7) chloride drops, (8) Cl-enters, and (9) water can move again.

    7. Guanylate cyclases-C (apical membrane) activated can activate cGMP which activates PKG (which can also regulate pathway similarly).

    Basically, phosphorylated = active.

    Image Upload 5
  19. 1. How many episodes of diarrhea per year? Split between what?

    2. What is the 2nd largest cause of infant mortality in developing world? What is death caused by? how many deaths for children under < 5 years old?

    3. Medical costs of diarrhea in US? Deaths/year? What has dropped hospitalized diarrhea cases by 30%?
    1. 1.5 billion; 1/3 viruses, 1/3 Ecoli, 1/3 other (cholera/salmonella)

    2. Diarrhea, dehydration, 1.3 million deaths

    3. > $ 1 billion; 300-400 deaths/year; health grades
  20. 1. What are the two main pathological causes for diarrhea?

    2. Why?
    1. cholera toxin and E.coli heat labile enterotoxin

    2. A subunit of structure ADP-ribosylates alpha subunit of G protein (turning G protein on forever) while B subunit is involved in binding & translocation of A-subunit into cytoplasm.
  21. Describe mechanism of cholera toxin/heat labile E. coli enterotoxins

    What about E.Coli?

    How do these stop?
    • 1. Cholera/E.coli toxin binds to surface
    • 2. A fragment enters cell
    • 3. ADP ribosylates G protein (covalent) activating adenylate cyclase irreversible
    • 4. Activates cAMP
    • 5. Activates PKA
    • 6. Phosphorylates and opens Cl- channel constituitively UNREGULATED.

    EColi is heat-resistant --> bc of disulfide bonds, as long as product recools, it will reform.

    E.coli activates guanylate cyclase --> activates GTP --> cGMP --> activates PKG --> p'lates and activates Cl- channel.

    Massive diarrhea washes away STa BUT NOT CHOLERA, terminating signaling from entertoxins.
  22. 1. What has WHO created for therapy against diarrhea-induced dehydration?

    2. Glucose's role

    3. What is better tolerated?

    4. What is the problem of using these packets in third world countries?

    5. Physiological basis of oral rehydration therapy? (2)
    1. 1 quart H2O, 1/2 tsp table salt, 8 tsp sugar.

    2. Glucose is important bc it encourages absorption of Na+. (1) High sugar drives absorption of sodium through sodium-coupled glucose transporter. (2) Sweet-taste receptors are in intestinal cells on apical surface. Glucose binds to sweet taste receptors, increasing activity and # of glucose transporters in intestines.

    3. Lower osmolarity solution (245 mosm/L vs. 311 mOsm/L)

    4. Often, these packets have to be mixed with 1 L of H2O --> source of pathogens.
  23. How are chemical gradients a form of potential energy? (4)

    Where is this seen? 2
    1. Energy is stored in transmembrane ion gradients

    2. Takes energy to create gradients

    3. If there is a leak, it takes energy to maintain gradients

    4. Energy in ion gradients can be captured by transport proteins (i.e., mitochondria).

    • --------
    • Mitochondria & chloroplasts - chemiosmotic ATP generation.
  24. Describe how energy stored in proton gradient can create ATP in mitochondria & chloroplasts (4)
    1. ETC pumps protons out of mitochondria, creating proton gradient across mitochondrial membrane

    2. Protons come back down through ATPase through gradient.

    3. Ionic gradient is used to create covalent bond in phosphorylation of ADP --> ATP

    4. ATP synthase is agnostic as to whether it hydrolyzes or synthesizes ATP --> w/o H+ gradient, it will hydrolyze ATP into ADP.
  25. 1. What usually occurs in sweat generation?

    2. What happens in cystic fibrosis? Sweat glands

    3. What happens in cystic fibrosis? Pancreas (3)

    4. What happens in lungs? (3)

    • 1. Sweat gland transports Na+ and Cl- into gland
    • 2. Water follows Na+ and Cl - osmotically
    • 3. Duct has both chloride and sodium channels - Na+ runs down concentration gradient out of gland
    • 4. Cl - follows bc of charge differential (impermeable to water) and low [salt] (<60 mmol) water is sweated out.

    • -----
    • 2.

    • 1. Defect in chloride channel
    • 2. Chloride cannot be resorbed from sweat gland
    • 3. High [Cl-] in sweat

    • -----
    • 3.

    • 1. CF kids can't secrete Cl- FROM pancretic ducts
    • 2. Can't secrete fluid into pancreatic ducts
    • 3. Proteolytic enzymes are stuck in pancreas --> destroying pancreas.

    • ----
    • Lungs:

    • 1. Can't secrete chloride to have water follow
    • 2. Mucus develops
    • 3. Bacterial infections ensue
  26. 1. What is the genetic basis for cystic fibrosis?

    2. What do drugs do?

    3. When are transporters bad?

    4. What is the moral of the above?
    1. Mutation of cystic fibrosis transporter regulator (CFTR) gene causing deletion --> Cl- channels don't traffic out of endoplasmic reticulum and can't be used.

    2. Drugs cause perfectly folded protein to go to cell surface, allowing Cl- to exit cells!

    3. ABC Bacterial Multidrug Resistance Transporter - MDR proteins recognize hydrophobic cations (to interact with DNA to break it down) cells simply open, pump drugs out, and drugs don't work.

    4. Transporters can be good or bad, depending on the circumstances.
Card Set
Membrane Transport (msbiochem)
ms biochem exam 1