Ch10-120302 - CHEM 350 Introduction to Biological Chemistry Brian Lee Ph.D [email protected] Office Neckers 146G or 324 Phone 453-7186 Hours 9:30am

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Unformatted text preview: CHEM 350: Introduction to Biological Chemistry Brian Lee, Ph.D. [email protected] Office: Neckers 146G or 324 Phone: 453-7186 Hours: 9:30am to 10:30am or by appointment Website: https:/ / Textbook (required, U.S. edition only) Fundamentals of Biochemistry, 3rd Ed., Voet, Voet & Pratt. Study Guide (recommended) Student Companion to Fundamentals of Biochemistry, 3rd Ed. Help Desk Tuesday 6:30 to 7:30 pm in Neckers 218 Thursday 5:00 to 6:00 pm in Neckers 410 Announcements Undergraduate Research Opportunities Research for credit (such as CHEM 396 or CHEM 496) Student worker ($8.00 per hour) ( Undergraduate Assistantships ( McNair Scholars Program ( REACH Awards Competition ( Summer Research Experiences for Undergraduates (REU) Deadline for SIUC REU Program is March 7th For other REU programs, search the National Science Foundation site: Students must contact the individual sites for information and application materials. NSF does not have application materials and does not select student participants. A contact person and contact information is listed for each site. Assignments Read Chapter 10 Membranes Transport Chapter 10 Problems Student Companion site for Voet, Voet & Pratt Third Midterm Exam, Wednesday March 28th Chapters 10-13 Help Desk Tuesday 6:30 to 7:30 pm in Neckers 218 Thursday 5:00 to 6:00 pm in Neckers 410 Grades are posted on SIU Online Exam 2 – raw score (4 pts per question) Curved Exam 2 – no curve, yet A sample Exam 2 with answers marked is posted. Appeals for exam grading due Friday before Spring Break Your appeal must be in writing and describe either: 1) Why your answer is correct. 2) Why the answer key is incorrect. Donald Voet • Judith G. Voet • Charlotte W. Pratt Electrochemical Potential Movement of solutes across a permeable membrane depends on the difference in chemical potential and electrical potential. [ A]in Gt = RT ln + ZA [ A]out Gibbs Free energy depends on the concentration gradient and the membrane potential across the membrane. = membrane potential ( VM) Thermodynamics defines the driving force of transport: The membrane is a kinetic barrier to transport. [ A]in Gt = RT ln + ZA [ A]out Kinetics defines the pathway for transport: kB T kt = e h G± RT G‡ is the free energy of activation derived by transition state theory. Analogous to activation energy in Arrhenius equation. Transporters provide a pathway to lower barrier Functional Classification of Membrane Transport 1) Non-mediated transport - simple diffusion 2) Me diated transport a) passive-mediated transport - facilitated diffusion b) active transport - coupled to exergonic process [ A]in Gt = RT ln + ZA [ A]out 2. 1. Simple Diffusion 6. 3. Membrane Transport 5. 4. Mediated Membrane Transport Structural Classification 1) Channels helix type channels barrel porins pore forming toxins 2) Porters - uniporter - symporter - antiporter other porters 3) ATP driven transporters 2. Facilitated Diffusion 1. 6. 3. Membrane Transport 5. 4. Glucose transporter: GLUT1 mediates passive transport (flow from high to low concentrationfacilitated diffusion). Model of glucose transport Transport Kinetics Sout + T1 k1 Sout • T1 k4 Sin + T2 k2 k3 Sin • T2 Saturation Binding Kinetics* Vmax [ S ]out V0 = K t + [ S ]out * derivation in chapter 12 Saturation curve Double reciprocal plot Facilitated diffusion: Chloride-bicarbonate exchanger Cotransport system: coupled transport is obligatory. Movement of ions in opposing directions: antiport No change in charge differential, so no change in membrane potential Remember that both H+ and Cl- w ill stabilize the T state of hemoglobin Facillitated Diffusion or Passive-Mediated transport 1. 2. 6. 3. Primary Active Transport Membrane Transport 5. 4. Active transport: solute is transported from low to high concentration, against a concentration gradient (endergonic). This process is coupled to an exergonic process to be favorable. Active transporters, P-type ATPases: Na+K+ ATPase: The process of mo ving 3 Na+ o ut for every 2 K+ moving in creates a net separation of charge across the membrane. Gibbs Free Energy of Transport Transport of Na+ and K+ against a concentration gradient [ Na + ]out [K + ]in Gt = RT ln [ Na + ]in [K + ]out (150 mM )(140 mM ) Gt = (8.315 J/mol)(298 K) ln = 15.1 kJ/mol (12 mM )(4 mM ) Membrane potential contributes to Gibbs free energy [ Na + ]out [K + ]in Gt = RT ln +Z + + [ Na ]in [K ]out Z is the ion charge and is Faraday’s constant Gt = 15.1 kJ/mol + (1)(96.48 kJ/mol)(0.1 V) Gt = 15.1 kJ/mol + 9.6 kJ/mol = 24.7 kJ/mol Mechanism of Na+ and K+ transport Phosphorylation induces change in transporter conformation. Dephosphorylation shifts transporter back to original conformation Transport cycle for Na+/K+ ATPase (P-type ATPase) Na+ triggers phosphorylation K+ triggers dephosphorylation Note: inorganic phosphate is released inside the cell Figure 10-17 Cardiac Glycosides Inhibitors of Na+/K+ ATPase Forces cardiac Na+/Ca2+ antiport system to reduce Na+ concentration. Increases intracellular Ca2+ which is stored in SR. Extra Ca2+ is released during muscle contraction, increases force of cardiac muscle contraction. Sarcoplasmic Reticulum Ca2+ ATPase (P-type ATPase) stores intracellular calcium in the lumen of the en doplasmic reticulum N domain (binds ATP) P do main (phosphorylation) A domain (actuator) mediates structural changes During transport cycle, the N domain tips by 20° bringing ATP binding site close to Asp351 and the A domain twists 90 degrees. Transport cycle for Ca2+ ATPase (P-type ATPase) Ca2+ is a second messenger for cellular functions: -muscle contraction -neural signaling High concentrations of Ca2+ bind to Pi and precipitate in the cytoplasm. Note: inorganic phosphate is released inside the cell Inside and outside refer to the ER lumen. F-type ATPase/ATP synthase: Catalyzes the transmembrane passage of protons, against the concentration gradient and against the membrane potential, driven by ATP hydrolysis. Reversibility of F-type ATPases ABC transporters: (ATP Binding Cassette) ATP-dependent that pump various molecules against a concentration gradient. P-glycoprotein (multidrug transporter) cancer therapy resistance. Open cavity binds hydrophobic molecule. ATP drives change in conformation. Extracellular surface is hydrophilic. 1. 6. 2. 3. Membrane Transport 4. Secondary Active Transport 5. Active transport: solute is transported from low to high concentration, against a concentration gradient (endergonic). This process is coupled to an exergonic process to be favorable. Secondary Active Transport - Lactose Permease (LacY) Symport - lactose and protons, obligatory cotransport Lactose is transport against a concentration gradient, driven by the favorable proton gradient and the membrane potential. Oxidation of metabolites drives the proton pump. Energy is stored in the proton gradient. Secondary Active Transport - Lactose Permease (LacY) Figure 10-23 Secondary Active Transport - Lactose Permease (LacY) inward - low affinity outward - high affinity LacY can interconvert between inward and outward facing conformations only when both lactose and a proton are bound. Lactose can only bind to the opened face of LacY. The inward facing low affinity state allows release of lactose. Secondary active transport cycle for Lactose Permease Figure 10-22 Multiple Transporters can be Coupled Together Glucose-Na+ symport brings glucose in from the intestine. Na+ concentration is regulated by Na+/K+ ATPase. GLUT1 uniport delivers glucose to the blood stream. 1. 2. 3. 6. Membrane Transport 5. Ion Channels 4. Passive mediated transport (facilitated diffusion) Ion selective channels – often coupled to other transporters Extremely efficient - diffusion limited rate of transport. Selective filter mechanism distinguishes ions for transport. KcsA structure from Roderick MacKinnon K+ Channel-high selectivity for K+ homotetramer w ith 45 Å channel selectivity filter (3 Å) 10 Å cavity hydrated cyto plasmic anionic tunnel K+ Channel (KcsA) high selectivity for K+ Due to electrostatic repulsion only positions 1,3 and 2,4 are occupied at a given time 1 2 3 4 Selectivity Filter only showing backbone carbonyls of two subunits Selection filter has the signature sequence TVGYG which strips away water molecules and binds to K+ ions with carbonyl oxygens. Only K+ can coordinate all 4 carbonyl oxygens. Na+ would only bind 2. Lower affinity for Na+ gives 10,000 fold selectivity. ...
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This note was uploaded on 03/26/2012 for the course CHEM 350 taught by Professor Lee during the Spring '08 term at SIU Carbondale.

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