Pre-Med Club BBQ ,

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Pre-Med Club BBQ , TODAY _at_ 4pm _at_
Marine Park . Come join the fun, eat free food,
and make new friends!!! Also, at the BBQ there
will be sign up sheets for volunteer
opportunities for Make A Difference Day
(Saturday, Oct. 28th from 8am-1pm ) Also at
the BBQ, sign up to buy a WWU Pre-Med Club
T-shirt!!! If you did not receive an Ocotber
Events Calender, you can pick one up at the
Chemistry Office.
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Exam W 10/11 Review Session?

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Stryer Fig. 3.11 Phe absorbs a little as well.
This phenomenon is the basis of one method to
determine protein concentration in a
non-destructive manner using Beers Law.
Beer
Beer
Beer
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Stryer Fig.3.13
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Stryer Fig. 3.20
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Basic Amino Acids
?
?
?
?
Stryer Fig.3.14
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Figure 4-9 Greek lettering scheme used to
identify the atoms in the glutamyl and lysyl R
groups.
Page 71
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Acidic AAs
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?
?
Stryer Fig.3.16
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Figure 4-22 Some uncommon amino acid residues
that are components of certain proteins.
Page 77
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Figure 4-23 Some biologically produced
derivatives of standard amino acids and amino
acids that are not components of proteins.
Page 77
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Ionic properties of amino acids impart ionic
properties to proteins

• in general these are SURFACE properties (i.e.
  charged sidechains are on solvent-exposed outside
  of folded structure)
• affect protein-ligand binding (e.g. DNA-binding
  proteins) or catalysis
• average charge on protein is an important
  consideration in the design of a purification
  process

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Table 4-1 (left) Covalent Structures and
Abbreviations of the Standard Amino Acids of
Proteins, Their Occurrence, and the pK Values of
Their Ionizable Groups.
Page 66
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Table 4-1 (right) Covalent Structures and
Abbreviations of the Standard Amino Acids of
Proteins, Their Occurrence, and the pK Values of
Their Ionizable Groups.
Page 67
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Figure 4-6 Titration curve of glycine.
Page 70
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This is IMPORTANT!!!

• If pH pKa, then A- HA
• then deprotonated protonated
• If pH lt pKa, then A- lt HA
• then deprotonated lt protonated
• If pH gt pKa, then A- gt HA
• then deprotonated gt protonated

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pKa3
pKa2
pKa1
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Using Henderson-Hasselbalch

• at pH values 3 pH units from pKa the group is
  essentially fully deprotonated or fully
  protonated, so the average charge 0 or 1.
• at pH pKa the group is 50 protonated, thus it
  carries an average charge 0.5
• H-H equation can be used to calculate the average
  charge on any ionizable group at any pH.

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You should be able to determine the net charge
on any amino acid at any pH.
What is the net charge of glu at pH 6?
Determine charge on each ionizable group
? carboxyl -1 ? carboxyl -1 ? amino 1
Net charge is -1.
If youre within 1 pH unit of a pK, you must
calculate the charge with the HH equation.
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What is the net charge on his at pH 6.8?
? carboxyl -1 ? amino 1
Net charge 0.14
Imidazole N ?
Imidazole N 0.14
Which form has the charge?
pH pK log A/HA
HA
6.8 6.0 log A/HA
xHA HA 1 0.14 A
HA 6.3 1
0.8 log A/HA 6.3 A/HA
DOES THIS MAKE SENSE?
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Isoelectric Point pI
pI pH at which a molecule has 0 net charge
For amino acids with no ionizable R groups, pI
pK1 pK2 2
For all others, you must determine which 2 pKs
determine the pI by inspection.
What is the pI for asp?
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Other Properties of Amino Acids

• Stereochemistry (all biosynthetic proteins made
  up of L-isomer)
• Hydropathy (partitioning between polar and
  nonpolar solvents as indicator of polarity)
• these two properties are major determinants of
  peptide conformation

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Figure 4-7 Titration curves of the enzyme
ribonuclease A at 25C.
Page 71
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Bloody Fact

• If 1 mL of 10 N HCl is added to 1 liter of saline
  solution at pH 7.0, the pH will decrease to
  roughly pH 2.
• If 1 mL of 10 N HCl is added to 1 liter of blood
  plasma at pH 7.4, the pH will decrease to pH
  7.2.
• Why? Blood is buffered (in this case by the
  H2CO3/HCO3 system).

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Figure 4-3 Condensation of two a-amino acids to
form a dipeptide.
Page 68
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Figure 4-8 The tetrapeptide Ala-Tyr-Asp-Gly.
Page 71
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Stryer Fig.3.19
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Stryer Fig.3.20
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Glutathione
?-E-C-G
2 Glut-SH
Glut-S-S-Glut 2H 2e-
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