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Unformatted text preview: CHEM 350: Introduction to Biological Chemistry!
"Brian Lee, Ph.D.
"Ofﬁce: Neckers 146G or 324
"Hours: 9:30am to 10:30am or by appointment!
/online.siu.edu! 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.
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) (http://www.siu.edu/~fao/jobs/)!
Undergraduate Assistantships (http://www.siu.edu/~fao/jobs/)!
McNair Scholars Program (http://www.siu.edu/~mcnair)!
REACH Awards Competition (http://www.siu.edu/~reach/) (due Jan 30th)!
Undergraduate Scholarships (due Jan 31st)!
Chemistry Majors see Department website!
Science Majors see College of Science website!
• 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− ]
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− ]
( )( ) KW = Keq 55.5M = [H+ ][OH− ] "
( −16 )( ) "Ion product of water!
‐14 2 KW = 1.8x10 M 55.5M = [H ][OH ]=
= ‐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!
Acid=can donate a proton!
Base= can donate a hydroxide ion!
Acid= can donate a proton!
Base= can accept a proton!
↔ H + A [H+ ][A− ]
Keq = Ka =
‐ logKa CH3COOH and CH3COOconjugate acid-base pair! Equilibrium constants for !
ionization reactions are also !
called ionization or dissociation !
Measurement of acid strength Polyprotic acids can donate multiple protons! Buffers: !
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:!
have a optimum pH. !
On either side of
the optimal pH,
activity declines.! Water is a functional component of enzymes, such as
Water lines the proton
Cytochrome f couples
electron ﬂow to proton
Protons are transported
by hopping from one
water molecule to
another.! Water can also be a
reactant within the
Water participates in
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