TAMU BICH 410 - Transmembrane Transport (3 pages)

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Transmembrane Transport

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Transmembrane Transport


Introduction to transmembrane transport

Lecture number:
Lecture Note
Texas A&M University
Bich 410 - Comprehen Biochem I
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F BICH 410 Lecture 25Outline of Last Lecture - Enzyme Regulation- MembranesOutline of Current Lecture - Transport Membraneo Diffusion of molecule from one side to anothero Chemical potential deltaG=RTln[Ad]/[As]o Electric potential= charge of ion x faraday’s constant (96.465) x membrane potentialo Change in free energy= Electrochemical potential= chemical + electrical potentialo membrane potential is the potential inside – potential outside negative= inside negativity greater cytosol= inside if analyzing more than one molecule must multiply by total number if ion moves from inside to out then the sign changes but not if moves from outside to inside- Transporto Mediated- 1. passive mediated/facilitated transport or 2. active transport (requires energy) Facilitated diffusion- proteins help to increase rate of transport- eventually reaches saturation- and can perform uniport, symport, or antiport o Nonmediated- simple diffusion- such as water, steroids, and O2o Channels- transport through pores with high selectivity and can be gated- rapid flux through channels Na, K, Cl K more permeable than N Channels lined with carbonyls which replace water ions around K+ Na is too small to interact with channel 2 K can be in channel at onceo Aquaporins- allow high rate of water transport  Lined with hydrophobic groups allowing fast transport of water because of repulsiono Carrier transport- undergoes structural change- pumps or transporters Glut Transporter- carrier protein- Glut1-4 specific for glucose and Glut5 specific for fructose- critical for glucose transportThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Gated Ion Channels- gating- ligand gated for extracellular ligands ie neurotransmitters or for voltage gated ion channels used in membrane potential Nicotinic acetylcholine receptor- Binding of acetylcholine opens allowing Na in at post synaptic clef Nerve impulses- high Na outside and K inside- neuron stimulation opens channel- Na floods in- depolarization occurs and K channel opens- gate closed preventing equilibriumo Active transport- energy required ATP, light or conc gradient N-K ATPase- ATP drives Na out and K in- Antiport so that three charges exit and two enter- all cells spend a lot of ATP maintaining cytosolic Na and K conc Na-K ATPase- phosphorylation of Asp on transport protein Aspartyl phosphate residue is hydrolyzed when K present Protein is 120 and 35kD Alpha subunit has 10TMD Oubain and digitalis bind to alpha retaining conformation but as Na increases Na-Ca atiport is stimulated and Ca increases in sarcoplasmic reticulum increasingmuscle contraction because of increased release of Ca Playtoxin binds and keeps transporter openo Secondary active transport Ion gradient driven active transport- Na-K atpase generate electrochemical gradients that can drive endergonic processes- Intestinal epithelium cells take up glucose using Na dependent symporto Uptake of glucose is secondary active transport; Na gradient maintained by NA-K ATPase pump- Ca2+-ATPase- increases cytolic Ca and causes responses such as muscle contraction, release of neurotransmitter, glycogen breakdowno Ca four times less concentrated in cytosol than extracellular spaceo Pump is necessary to prevent formation of Ca3(PO4)2o Large gradient difference maintained using active transport of Ca from Plasma Mem. To ER using Ca ATPase pump to keep cytosol Ca levels low- H-K ATPase- gastric mucosa cells secrete HCL at 0.15Mo Secretion of H is accomplished by H-k atpASE o SECRETED PROTONS COE FROM HYDRATION of CO2 by carbonic anhydraseo Gastric fluid =6pH and cytosol=7.4pHo Histamine binds to cell and activates this pumpo Tagamet competes with histamineo Ulcers occur of excess HCL- ATP binding cassette-ABC- transporterso Pump ions, sugars, AA- and can use method of importer or exporter (only Eukarya)o Cystic fibrosis, adrenoleukodystrophy, ect are associated with ABC transport defects Cystic fibrosis transmembrane conductance regulator is the only ABC transporter that functions as ion channel CFTR pumps out Cl and Na and water maintains proper fluidity With disease the pumping does not work and thick mucus

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