Ch2-120123 - CHEM 350: Introduction to Biological...

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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 ( (due Jan 30th)! Undergraduate Scholarships (due Jan 31st)! Chemistry Majors see Department website! Scholarships.pdf! Science Majors see College of Science website!! Assignments! •  Read Chapter 3 ! "Nucleotides, Nucleic Acids and Genetic Information! •  Chapter 3 Problems! •  Help Desk ! "Tuesday 6:30-7:30pm in Neckers 218! "Thursday 5:00-6:00pm in Neckers 410! Water has a tendency to ionize.! "H+ associates with water to "form a hydronium ion.! "The H-bonding between water ! "molecules makes transfer of ! "H+ from one water molecule to "another instantaneous.! Ionization of Water at equilibrium! H2O ↔ H+ + OH− 

 Described by the equilibrium expression! [H+ ][OH− ] Keq = [H2O] 

 Equilibrium constant is 1.8 x 10-16 M! In pure water at 25°C, [H2O] = 55.5 M and is much larger than the concentration of ions, therefore it can be considered constant.! [H+ ][OH− ] Keq = 55.5M 

 ( )( ) KW = Keq 55.5M = [H+ ][OH− ] " 

 ( −16 )( ) "Ion product of water! ‐14 2 KW = 1.8x10 M 55.5M = [H ][OH ]= 

 ‐log[H+ ] 

 ‐ pOH
 = ‐log[OH ] 

 + − Because the concentrations of H+ and OH-! ions are too small to work with, Sorensen! proposed a more practical quantity called! pH known as the Sørensen equation! KW = [H+ ][OH− ]= 
 € Weak Acids and Bases! Arrhenius: ! Acid=can donate a proton! Base= can donate a hydroxide ion! Brønsted-Lowry definition:! Acid= can donate a proton! Base= can accept a proton! + − H 

 ↔ H + A [H+ ][A− ] Keq = Ka = [HA] 


 ‐ logKa CH3COOH and CH3COOconjugate acid-base pair! Equilibrium constants for ! ionization reactions are also ! called ionization or dissociation ! constants, Ka! Measurement of acid strength Polyprotic acids can donate multiple protons! Buffers: ! aqueous systems that resist changes in pH upon addition of acid or base. ! They are a mixture of weak acids and their conjugate bases. ! Henderson-Hasselbalch Equation! Given:! Solve for [H+]:! Negative log on both sides:! Henderson-Hasselbalch Equation which describes the shape of a titration curve:! Acetic acid has a pKa of 4.76. What is the pH of a solution containing 10 mM acetic acid and 100 mM sodium acetate (the conjugate base of acetic acid)?! A.  pH = 1.00! B.  pH = 3.76! C.  pH = 4.76! D.  pH = 5.76! E.  pH = 10.00! pKa indicates! the useful buffering! range for a weak! acid (or base).! Optimal buffering range! is ±1 pH unit around the ! pKa value.! Polyprotic acids have 3 pKa values and 3 buffer ranges! Enzymes and pH:! Enzyme reactions have a optimum pH. ! On either side of the optimal pH, their catalytic activity declines.! Water is a functional component of enzymes, such as cytochrome f.! Water lines the proton channel.! Cytochrome f couples energetically favorable electron flow to proton transport.! Protons are transported by hopping from one water molecule to another.! Water can also be a reactant within the cell.! Water participates in hydrolysis and condensation reactions! ...
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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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