Term
| The main components of biological membranes are...? |
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Definition
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Term
| what is the ratio of proteins to lipids in the cell membrane? |
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Definition
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Term
| Some membranes contain also sugar residues bound to...? |
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Definition
| lipids (glycolipids) or proteins (glycoproteins). |
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Term
| what are the main types of membrane lipids? |
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Definition
| phospholipids, cholesterol, glycolipids (gangliosides), sphingolipids (?) |
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Term
| what mobility do membrane lipids express? |
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Definition
| lateral diffusion, rotation, flexion, and (rarely) |
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Term
| what are the types of phospholipids? |
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Definition
| phosphatidylcholine(PC), sphingomyeling(S), phospatidylserine(PS), phosphatidlyethanolamine(PE) |
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Term
| how are phosphlipids distributed in the cell membrane? |
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Definition
| PC and S are mainly in the outer bilayer. PE and PS are mainly in the inner monolayer. |
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Term
| what is phosphatidylinositol and what does it do? |
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Definition
| an additional phospholipid present in minimal amount serves as a substrate for production of signaling molecules such as prostaglandins, prostacyclins, IP3 (inositol triphopshate), and DG (diacylglycerol) |
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Term
| what determines the fluidity of the membrane? |
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Definition
| the length of fatty acid in phospholipids and the number of unsaturated bonds. (find out which way each one influences fluidity) |
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Term
| what is the effect of cholesterol on the cell membrane? |
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Definition
| It decreases the fluidity and permeability of the membrane, but increases its stiffness, mechanical stability and flexibility. |
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Term
| where are glycolipids in the cell membrane and what do they do? |
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Definition
| Are present in the outer monolayer of the cell membrane and in some of the intracellular membranes. In the former they participate in the formation of the cell coat (glycocalyx). |
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Term
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Definition
| islands of sphingolipids ad cholesterol, about 50nm in diameter. They include specific transmembrane proteins (GPI-anchored proteins and fatty aices anchored proteins) |
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Term
| membrane lipids are responsible for...? |
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Definition
| the cells very existence, the fluidity, self sealing high electric resistance and limited permeability (allow transport of gases such as O2, CO2, N2, lipid soluble molecules such as urea, ethanol, steroid hormones, and of some water). |
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Term
| what are the different types of membrane proteins? |
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Definition
| integral or peripheral (therefore they are classified on the degree of their binding to the lipid bilayer) |
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Term
| what are integral proteins? |
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Definition
| proteins which can not be isolated from the membrane without its disruption. |
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Term
| what are the types of integral membrane proteins? |
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Definition
*transmembrane proteins (both single and multiple pass)
*proteins anchored to the outer monolayer via glycosyl phsphatidylinositol (GPI)
*proteins associated with the inner monolayer via covalently attached fatty acid |
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Term
| what are peripheral proteins? |
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Definition
| they are non-covalently linked to the integral membrane proteins (and also to polar groups of lipids) and can be found on both external and cytoplasmic faces of the membrane. |
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Term
| describe the motility of proteins? |
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Definition
| lateral diffusion and rotation |
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Term
| how is diffusion of proteins restricted? |
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Definition
| by their size, their attachment to the membrane/cell skeleton, and tight cell junction |
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Term
| According to their function membrane proteins can be classified as? |
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Definition
| structural, enzymatic, receptor proteins, and transport proteins |
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Term
| what are the types of transport proteins? |
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Definition
| carrier proteins, channels, and pumps |
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Term
| what are membrane proteins responsible for in terms of functions of the membrane? |
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Definition
| selective transport, binding of hormones, signal transduction |
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Term
| peripheral membrane proteins include...? |
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Definition
| spectrin, fodrin, alfa actinin, dystrophin, TW 260/240 (terminal web) |
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Term
| what do proteins of the membrane skeleton do? |
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Definition
| preserve integrity of membrane, regulate mobility of protein, enable mechanical deformation of the cell, participate in preservation of asymmetry within the lipid bilayer. |
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Term
| how does simple diffusion take place? |
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Definition
| takes place via lipidic phase of the membrane (thru the hydrophobic part?) for lipid soluble, uncharged molecules such as glycerol, urea, benzene, ethanol and gases CO2, NO2, O2, as well as via protein channels (for water and ions) |
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Term
| describe facilitated diffusion? |
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Definition
| requires participation of protein carriers which bind transported solute in a specific manner on one side of membrane and release on the other. Transport efficiency decreases upon saturation of all binding sites and can be blocked by competitive or noncompetitive inhibitors. (down concentration gradient!) |
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Term
| describe active transport? |
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Definition
| (against a conc. gradient), requires participation of protein carrier and supply of energy. Energy may derive either from simulatneous hydrolysis of ATP (direct active transport) or from ion gradient (indirect active transport or ion-driven transport). Proteins responsible for direct active transport posses properties of ATPases (enzymes are responsible for ATP hydrolysis) and are called pumps. |
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Term
| all transport proteins are...? |
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Definition
| multipass transmembranes proteins |
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Term
| why are transport proteins essential? |
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Definition
| they are essential for passage of polar molecules (including sugars, amino acids and ions) which can hardly pass the lipid bilayer. |
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Term
| how is transport of a given molecule achieved? |
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Definition
| by a conformational change of the respective transport protein |
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Term
| channels and carrier proteins transport substances how? |
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Definition
| they transport substances down their concentration gradient (simple diffusion or facilitated transport) |
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Term
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Definition
| they use energy from ATP for a transport against the concentration gradient (direct or indirect active transport) |
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Term
| transport via proteins may involve...? |
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Definition
| uniport, cotransport (symport, antiport) |
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Term
| give an example of a uniporter? |
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Definition
| glucose transporters (GLUT) present in every cell. In insulin sensitive cells (muscular fibers, fat cells) transport of glucose across the membrane can be regulated by the hormone induced insertion of the transporter into the membrane and its subsequent withdrawl) |
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Term
| which cells are equiped with protein transporting amino acids? |
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Definition
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Term
| give an example of a symporter |
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Definition
| sodium dependent glucose transporter (SGLT): in cell responsible for glucose resorption from external fluid (epithelial cells of small intestine and of kdney proximal tubules) |
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Term
| give an example of an antiporter? |
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Definition
| Cl-/HCO3- anion exchanger-particulary important in the membrane of erythrocytes |
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Term
| what are water channels? aka? |
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Definition
| aquaporins AQPs, samll hydrophobic transmembrane proteins elective for water and (some) for glycerol. They areexpressed in cells involved in water transport:... |
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Term
| what are the different types of AQP? |
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Definition
AQP1: kidney proximal tubule, hepatocytes, RBCs
AQP2: terminal segment of the distal tubule and collecting duct
AQP 3 and 4: in basolateral cell surface of epithelia in GI tract, brain, spinal cord. |
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Term
| where is the sodium potassium pump present? |
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Definition
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Term
| how does the Na+K+ATPase pump work? |
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Definition
| Binding of Na+ to the cytoplasmic domain activates ATP-hydrolysis with concomitant phosphorylation of that protein. Phosphorylation leads to conformational change which results in the relase of Na+ to the extracellular space and exposes binding site for K+. Binding of K+ causes dephosphorylation of the proteins and its return to the former conformation which leads to the release of K+ on the cytoplasmic site. 3 ions of Na+ are removed from the cell and 2 ions of K+ are pumped into the cell per every cycle of the pump. |
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Term
| what is the sodium potassium pump responsible for? |
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Definition
| creating sodium gradient across the membrane |
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Term
| what does the sodium gradient enable? |
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Definition
| regulation of cell volume, Na+ driven trasport of substances (ex: glucose), regulation of intracellular pH and Ca 2+ level, conduction of electric signals (in nerve and muscular tissue) |
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Term
| how are channels and carrier proteins different? |
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Definition
| unlike the carrier proteins, channels do not bind the transported substance and are about 1000x more efficient in transport |
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Term
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Definition
constituitively opened
regulated (gated) |
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Term
| which leaflet is cholesterol on? |
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Definition
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Term
| which leaflet is glycolipids on? |
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Definition
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Term
| what is cholesterol composed of? |
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Definition
| a polar head group, a rigid steroid ring structure, and a more fluid region |
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Term
| how is the cell membrane assymetric? |
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Definition
| the phospholipid arrangement is asymmetric, the electric charge is assymetric, and glycolipids are only on the outside |
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Term
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Definition
| is a network of polysaccharides that project from cellular surfaces, e.g. those of bacteria. It serves to protect the bacterium by creating capsules, or allows the bacterium to attach itself to inert surfaces |
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Term
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Definition
| These specialized membrane microdomains compartmentalize cellular processes by serving as organizing centers for the assembly of signaling molecules, influencing membrane fluidity and membrane protein trafficking, and regulating neurotransmission and receptor trafficking. |
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Term
| role of lipids in biological membranes? |
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Definition
*make the membrane
*enable self-sealing of the membrane
*influence fluidity of the membrane
determine permeability of the membran
*regulate function of some membrane proteins
serve as precursors for biologically active molecules |
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Term
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Definition
| it is a heterodimer of intertwined alpha and beta chains |
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Term
| what are the functions of the membrane skeleton? |
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Definition
*preserves integrity of membrane
*regulates mobility of proteins
*enables mechanical deformation
*participates in preservation of asymmetry within lipid bilayer |
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Term
| how are channels or pores within the lipid bilayer made? |
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Definition
| by putting hydrophilic amino acids on the inside of the channel...(ex: leucine in hydrophobic so it is bonded to serine which is hydrophilic and makes up the inside of the pore) |
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Term
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Definition
Na+/suger
Na+/amino acid
Na+/Cl-
Na+/K+/2 Cl-
Na+/H2PO4- |
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Term
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Definition
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Term
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Definition
| the apical surface (where glucose conc. is high) |
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Term
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Definition
| baso-lateral membrane (where glucose conc. is low) |
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Term
| anion exchangers make the cell...? |
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Definition
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Term
| what ion transporters are in the parietal cell? |
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Definition
Cl-/HCO- exchanger
H+/K+ ATPase
Cl- channel protein
K+ channel protein |
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Term
| AQPs are possible targets for drugs blocking? |
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Definition
water in
Hypertension
brain swelling
regulation of intraocular and intracranial pressure |
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Term
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Definition
a lipid-soluble molecule, usually synth. by microogranisms to transport ions across the lipid bilayer of the cell membrane.
*they disrupt transmembrane ion concentration gradient, req-d for the proper functioning and survival of microorganisms, and thus have antbiotic properties (they are used to incr. permeabilility of biological membranes to certain ions) |
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Term
| what are the types of ionophores? |
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Definition
mobile ion carrier: bind to a particular ion, shielding its charge from the surrounding environment, and thus facilitating its crossing of the hydrophobic interior of the lipid membrane.
channel formers, introduce a hydrophilic core into the membrane, allowing ions to pass thru while avoiding contact w/ the membrane's hydrophobic interior |
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Term
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Definition
gramicidin: allows inorganic monovalent cations (H+,Na+, K+) to travel thru cell membrane unrestricted, thereby destroying the ion gradient between the cytoplasm and the extracellular environment
*valinomycin, selective for K+ ions over Na+ ions w/in the cell membrane. Facilitates movement of K+ DOWN conc. gradient (and therefore OUT of cell)
*A23187 (mobile ion carrier) form stable complexes w/ divalent cations, used to incr. intracellular Ca2+ levels |
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Term
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Definition
gramicidin: allows inorganic monovalent cations (H+,Na+, K+) to travel thru cell membrane unrestricted, thereby destroying the ion gradient between the cytoplasm and the extracellular environment
*valinomycin, selective for K+ ions over Na+ ions w/in the cell membrane. Facilitates movement of K+ DOWN conc. gradient (and therefore OUT of cell)
*A23187 (mobile ion carrier) form stable complexes w/ divalent cations, used to incr. intracellular Ca2+ levels |
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