Lipids and Membranes
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18C amino alcohol | sphingosine
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amide linkages of fatty acids to the nitrogen of sphingosine | ceramides
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represent a phosphorus containing subclass of sphingolipids | sphingomyelins
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ceramides with one or more sugars beta-glycosidic linkages at the 1-hydroxyl group | glycosphingolipids
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glycosphingolipids with ONE sugar | cerebrosides
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glycosphinglipids with 2 or more sugars | globosides
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ceramides with 3 or more sugars, one of which is sialic acid | gangliosides
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gangliosides = ceramides with _#_ or more sugars, one of which is ______ | 3; sialic acid
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esters of long chain alcohols with long chain fatty acids | waxes
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highly insoluble lipid found coating animal skin and fur, in leaves of many plants and bird feathers | waxes
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lipid with ether linkage instead of acyl group at C-1 position of glycerol | ether glycerophospholipids
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ether glycerophospholipids with unsaturated alkyl chain (C-2) | plasmalogens
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terpenes are based on ____ structure | isoprene (5C)
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all sterols (incl. cholesterol) are ____-based molecules | terpene
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many _____ are recognized by their characteristic flavors or odors (ex. limonene, citronellal, pinene, menthol) | monoterpenes
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C20 terpenes; include retinal, phytol, and gibberellins | diterpenes
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lanosterol (constituent of wood fat) is example of ____ (terpene) | triterpene
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tetraterpene; carotenoid found in ripe fruit esp. tomatoes | lycopene
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1. initiation point for synthesis of carbohydrate polymers in animals = ____ 2. analogous alcohol of (1) in bacterial systems that consists of 11 ISOPRENE units | 1. dolichol phosphate
2. undecaprenol (AKA bactoprenol)
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delivers sugars from cytoplasm for the synthesis o cell wall components such as peptidoglycans, lipopolysaccharides, and glycoproteins | undecaprenyl phosphate (isoprene)
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____ compounds serve as side chains of Vit. K, the ubiquinones, plastoquinones, and tocopherols (Vit. E) | polyprenyl compounds (isoprene)
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functions as both a hormone and visual pigment of the vertebrate eye | vitamin A
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vitamin A derivative which regulates gene expression in the development of epithelial tissues; isoprene (hormone fxn of Vit A) | retinoic acid
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vitamin A derivative, pigment that initiates the response of rod and cone cells of the retina to light; isoprene (visual pigment fxn of vit A) | retinal
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What activates inactive retinal (Vitamin A1 derivative) to change to functional retinal (pigment for vision)? | VISIBLE LIGHT makes 11C-12C double bond TRANS from cis
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_____ is not itself biologically active, but is converted by enzymes in the liver and kidney to 1,25-dihydroxycholechalciferol, a hormone that regulates CALCIUM UPTAKE in the intestine and CALCIUM LEVELS in kidney and bone | Vitamin D3
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deficiency of vitamin D leads to _____ | defective bone formation
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collective name for a group of closely related lipids called TOCOPHEROLS | Vitamin E
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hydrophobic, associate with the membranes and lipoproteins in blood, collectively called Vitamin E --Biological antioxidants | Vitamin E
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Why are tocopherols (Vit E) considered biological antioxidants? | the aromatic ring reacts with and destroys the most reactive forms of oxygen radicals and other free radicals, protecting unsaturated FA from oxidation and preventing oxidative damage to membrane lipids
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principle symptom of vitamin E deficiency? | fragile erythrocytes
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The aromatic ring of _____ undergoes a cycle of oxidation and reduction during the formation of active PROTHROMBIN, a blood plasma proteolytic protein essential in blood clot formation | Vitamin K
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activated ____ splits peptide bonds in the blood protein fibrinogen to convert it to fibrin, the insoluble fibrous protein that holds blood clots together | prothrombin (formed from Vit K)
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Vit K deficiency leads to ______ | slows blood clotting (can be fatal)
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Coumadin (widely prescribed anticoagulant) and Warfarin (component of rodent poisons) act as _____ | antagonists of Vitamin K in body (so slows/prevents blood clotting)
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stimulates the carboxylation of proteins participating in blood clotting cascade = ___1___ Carboxylation of these coagulation factors is catalyzed by a carboxylase that requires the ___2___ form of (1), molecular oxygen, and CO2 | 1. Vitamin K
2. reduced
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Enzyme targeted by Coumadin and Warfarin? | Vitamin K epoxide reductase (blood clotting requires redox reactions of Vitamin K)
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Steroids: based on a core structure consisting of __ 6-membered rings and __ 5-membered rings, all fused together | 3 6-membered
1 5-membered
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most common steroid in animals and precursor for all other steroids in mammals | cholesterol
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serve many functions in animals incl. salt balance, metabolic function, and sexual function | steroid hormones
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BILE ACIDS = polar derivatives of ____ BILE SALTS = synthesized from ____ and stored in the ____ | cholesterol
synthesized from CHOLESTEROL in LIVER
stored in GALL BLADDER
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Bile = ? | mixture of bile acids, cholesterol, and pigments from breakdown of RBC
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Bile is secreted into the ____ after a fatty meal Function of bile? | small intestine
acts as a DETERGENT emulsifying dietary fats to make them more readily accessible to DIGESTIVE LIPASES
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taurocholic acid = example of ____ | bile acid
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impt precursor for many steroid hormones (incl. testosterone, estradiol, cortisol, aldosterone, prednisolone, prednisone) | cholesterol
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formation of an amide linkage between a FA and a sphingosine produces a _____ | ceramide
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constitute the boundaries of cells and intracellular organelles; also provide a surface where many impt biological reactions such as electron transport, oxidative phosphorylation, electrical activity, and signaling occur | membranes
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T/F Lipids form ordered structures spontaneously in water. | true
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Monomer lipids? | Very few lipids exist as monomers
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How do micelles react to nonpolar solvents? | reverse, tails go to outside
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two ways lipid bilayers can form? | 1. unilamellar vesicles (liposomes)
2. multilamellar vesicles
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Components of the Fluid Mosaic Model? | 1. phospholipid bilayer = fluid matrix
2. bilayer = two-dimensional solvent
3. Lipids and proteins can undergo rotational and lateral mov't
4. 2 classes of proteins: peripheral (extrinsic) and integral (intrinsic)
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Where does cholesterol occur in membrane? | integrated
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how has lipid diffusion (migration of lipids and proteins in the bilayer) been shown? | NMR and EPR as well as fluorescence measurements
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How are proteins and lipids arranged in membrane? | LATERAL ASYMMETRY of both lipids and proteins - they can cluster in the plane of the membrane and are not uniformly distributed
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What might induce phase separations of components of membrane (form liposomes)? | divalent cations such as Ca2+
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membrane protein known to SELF-ASSOCIATE or form clusters in nonrandom formations) | Bacteriorhodopsin forms clusters known a PURPLE PATCHES in membranes of Halobacterium halobium
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Transverse Asymmetry of proteins: Bark Bretscher showed that the ___ of glycophorin is extracellular wherease ____ is intracellular | N-terminus = extracellular
C-terminus = intracellular
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Transverse Asymmetry of lipids: in most cell membranes, the composition of the ____ is different from the _____ | Outer monolayer is different from the inner monolayer
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proteins that move lipids from one monolayer to the other Where do these proteins get energy? | Flippase Proteins
Some are passive and do not require an energy source
Most require energy hydrolysis of ATP (ex. in erythrocytes)
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What type of flippase can generate membrane asymmetries? | Active Flippase (uses ATP hydrolysis)
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Phase transitions in membranes? **only pure lipid systems give sharp, well-defined transition temperatures | Below a certain transition temp - membrane lipids are rigid and tightly packed
Above the transition temp - lipids are more flexible and mobile
**The transition temperature is characteristic of the lipids in the membrane
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What happens to membrane as it is WARMED? | Surface area increases as thickness decreases. Mobility of the lipid chains INC dramatically (goes through phase transition)
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proteins which are NOT strongly bound to membrane, can be dissociated from the membrane by treatment with salt solutions or changes in pH | Peripheral proteins
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proteins that are imbedded in bilayer; can removed only by agents capable of breaking up the hydrophobic interactions within the lipid bilayer itself --often transmembrane but not necessarily --Ex. glycophorin, bacteriorhodopsin | integral membrane proteins
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A single transmembrane segment with globular domains on either end transmembrane segment is ____ (shape) and consists of __#__ hydrophobic amino acids | Glycophorin
alpha helical; 19 AA
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Extracellular portion of glycophorin (transmembrane protein) contains ____ which constitute ______ determinants | oligosaccharides; ABO and MN blood group determinants
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spans the membrane of the human erythrocyte via a single alpha-helical transmembrane segment C-terminus faces _____ N-terminus points to _____ What attaches to the N-terminus? | Glycophorin A
C-terminus faces cytosol of erythrocyte
N-terminus faces extracellular side
Carbohydrates
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a 7-transmembrane-segment (7-TMS) protein --found in purple patches of Halobacterium halobium --consists of 7 transmembrane helical segments with short loops that interconnect the helices --light driven proton pump | Bacteriorhodopsin
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Bacteriorhodopsin = a ____ protein, ___-driven proton pump found in _____ | 7-TMS protein
LIGHT driven proton pump
Purple patches of Halobacterium halobium
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Where are porins found? | in both Gram - bacteria and in mitochondrial outer membrane
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pore-forming proteins (30-50 kD) --general or specific (exclusion limits 600-6000) --most arrange in membrane as trimmers --high homology between various proteins --make beta barrels | Porins
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Most porins arrange in membrane as ____ | trimers
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PORIN from Rhodobacter capsulatus has _____ that transverses the membrane to form the pore | 16-stranded beta barrel
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a relatively new class of membrane proteins; 4 types have been found: -amide-liked myristoyl anchors -thioester-linked fatty acyl anchors -thioether-linked prenyl anchors -glycosyl phosphatidylinositol anchors | Lipid-Anchored Membrane Proteins
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Type of lipid-anchored membrane protein? --always myristic acid --always N-terminal --always a Gly residue that links | Amide-linked myristoyl anchors
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The following proteins are examples of ____: cAMP-dependent protein kinase pp60^sro tyrosine kinase calcineurin B alpha subunits of G proteins gag protein of HIV-1 | amide-linked myristoyl anchors
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amide-linked myristoyl anchors: 1. always ____ acid 2. always __-terminal 3. always a ___ residue that links | 1. myristic acid
2. N-terminal
3. Gly
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N-myristoylation always occurs at _____ | N-terminal glycine residue
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Anchor with broader specificity for lipids - myristat, Palmitate, stearate, oleate all found | Thioester-linked acyl anchors
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The following are examples of _____: G-coupled protein receptors Surface glycoproteins of some viruses Transferrin receptor triggers and signals | Thioester-liked acyl anchors
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S-pamitoylation always occurs at the ____ residues of polypeptide chain. | cysteine
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G-protein coupled receptors, with seven transmembrane segments, may contain one (or two) palmitoyl anchors in thioester linkage to _____ residues in the __-terminal segment of the protein | cysteine; C-terminal
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Anchors: Prenylation refers to linking of "isoprene" based groups --always Cys of CAAX (C=Cys, A=Aliphatic, X=any residue) --isoprene groups include farnesyl (15C, 3 double bond) and gernaylgeranyl (20C, 4 double bonds) gropus | Thioether-linked prenyl anchors
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The following are examples of _____: yeast mating factors p21^ras nuclear lamins | Thioether-linked prenyl anchors
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Proteins containing the C-Terminal sequence CAAX can undergo ____ reactions that place ____ at the CYSTEINE side chain | prenylation
thioether linked farnesyl or geranylgeranyl groups
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_____ is accompanied by the removal of the AAX peptide and the methylation of the carboxyl group of the cysteine residue, which has become the _____ residue | Prenylation; C-terminal
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____ is a small GTP-binding protein involved in cell signaling pathways that regulate cell growth and division --mutations in this are involved in 1/3 of all human cancers --it is dependent on prenylation and the proteolysis of the -AAX motif | RAS
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Because the signaling activity of RAS is dependent on __1__, the reaction itself, as well as the proteolysis of the __2__ motif, and the methylation of the __3__, have been considered targets for development of NEW CHEMOTHERAPY strategies | 1) prenylation
2) -AAX motif (from the C-terminal sequence CAAX, the -AAX is removed)
3) prenylated Cys residue (what is left at the end of the C-terminal after proteolysis)
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Anchors that are more elaborate than the others --always attached to C-terminal residue --Ethanolamine link to an oligosaccharide linked in turn to inositol of PI | Glycosyl Phosphatidyllinositol Anchors
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GPI anchors are always attached to a ____ residue | C-terminal
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The following are examples of _____: surface antigens adhesion molecules cell surface hydrolases | Glycosyl Phosphatidylinositol anchors
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Core of Glycosyl phosphatidylinositol (GPI) = _______ Additional modifications may include FA at the ___ and ___ -OH groups | 3 mannose residues and a glucosamine (elaborate lipid-anchoring group)
inositol and glycerol
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When transported species simply move down its concentration gradient (from high cxn to low cxn) | passive diffusion
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What does a high permeability coefficient signify? | passive diffusion is not the whole story
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Passive diffusion of an UNCHARGED species depends on: | only the concentrations on the two sides of the membrane
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Passive diffusion of a CHARGED species depends on: | 1. CONCENTRATION of particle Z
2. CHARGE of particle Z
3. ELECTRICAL DIFFERENCE across the membrane (delta psi)
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How does facilitated diffusion occur? | solutes only move in the thermodynamically favored direction but proteins may facilitate transport increasing the rates of transport
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2 impt distinguishing features of facilitated diffusion? | 1. Solute only flows in favored direction
2. Transport displays saturation kinetics
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How does energy input drive active transport processes? | Energy source and transport machinery are coupled so that solutes can flow against thermodynamic potential.
Energy source may be ATP, light or a concentration gradient.
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SODIUM PUMP: large protein (120kD and 35kD) 1) maintains intracellular ___ low and ___ high 2) Crucial for all organs but esp. ___ and ___ 3) ATP hydrolysis drives ___ out and ___ in | 1) Na low & K high
2) neural tissue and brain
3) Na+ out & K+ in
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SODIUM PUMP: 1) Alpha subunit has 10 transmembrane ____ with a large cytoplasmic domain 2) ATP hydrolysis occurs via _____ 3) _____ inhibit by binding to outside | 1) helices
2) E-P intermediate
3) cardiac glycosides
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For sodium pump what moves in and out per ATP? | 3 Na+ out and 2 K+ in
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osteoclasts vs osteoblasts? | **Bone material undergoes ongoing remodeling.
OsteoCLASTS tear down bone tissue
OSTEOBLASTS build it back up
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How do osteoclasts function? | by secreting acid into the space between the osteoclast membrane and the bone surface. Acid dissolves the Ca-phosphate matrix of the bone.
**It is all driven by an ATP proton pump in the membrane
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Proton pumps cluster on the ruffled border of ____ and function to pump protons into the space between the cell membrane and the bone surface. ____ ____ concentration in this space dissolves the mineral matrix of the bone | osteoclast cells
High proton concentration
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a member of a "superfamily" of genes/proteins that appear to have arisen as a "tandem repeat" --defeats efforts of chemotherapy --recognizes a broad variety of molecules and transports them out of the cell using the hydrolytic energy of ATP | MDR ATPase (AKA the P-glycoprotein) - an organic molecule pump
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MDR ATPase: this multidrug transporter is postulated to have _#_ transmembrane alpha-helices and _#_ ATP binding sites **Some of cytotoxic drugs are transported by MDR ATPase (Colchicine, Vinblastine, Adriamycin, and Vincristine) | 12 transmembrane alpha-helices (HUGE!)
2 ATP binding sites
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How is amino acid and sugar transport driven by ion gradients? | SECONDARY ACTIVE TRANSPORT
Does not use ATP directly, but uses the gradient of other compounds ---> Symport and Antiport
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Symport vs antiport (2* active transport) | Symport = ion and the AA or sugar are transported in the same direction across the membrane
Antiport = ion and transported species move in opposite directions
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