BCH 4053 HOUR TEST 1 NAME _____________________
June 7, 1996
Points
(12) 1. Draw a titration curve for the dipeptide
His.Arg on the graph below. Locate and
identify the points on the curve corresponding
to pK1, pK2, pK3 and pK4. Calculate the
approximate pI value and locate its position on
the curve. Indicate the pH region on the graph
in which less than 10% of the histidine side
chain is charged.
þ
13 Ãþ
³ pI =
12 Ãþ
³
11 Ãþ
³
10 Ãþ
³
9 Ãþ
³
8 Ãþ
³
7 Ãþ
pH ³
6 Ãþ
³
5 Ãþ
³
4 Ãþ
³
3 Ãþ
³
2 Ãþ
³
1 ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
1 2 3 4
equivalents of base ----->
(8) 2. The phosphate concentration in blood is about 2 mM. If the pH of
blood is 7.4,
(a) what are the two major protonated species present?
(b) what fraction of the phosphate is H2PO4-?(Note: I'm looking for
fraction, not ratio). (pK1=2.2; pK2=7.2; pK3=12.7)
(15) 3. Given the following data on four different proteins:
Protein M.W.(x10-3) D pI
myoglobin 16.9 11.3 7.0
catalase 221.6 4.3 5.6
cytochrome c 13.4 11.4 10.6
serum albumin 68.5 6.1 4.8
Assume all proteins have partial specific volumes of about 0.73 ml/g.
Indicate in the blanks the protein(s) with the indicated behavior.
________________________ (a) Difficult to separate on gel-filtration.
________________________ (b) Elutes first from a DEAE column at pH 7.4.
(i.e., an anion exchange column).
________________________ (c) Elutes first from a carboxymethyl cellulose
column at pH 5.0. (i.e., a cation exchange
column).
________________________ (d) Migrates fastest on electrophoresis in SDS.
________________________ (e) Migrates to the anode (positive electrode)
on electrophoresis at pH 6.0.
(10) 4. You have stock solutions of 0.1 M formic acid and 0.1 M sodium
formate. You want to make one liter of a 0.02 M formate buffer at
pH 4.3. The pK of formic acid is 3.8. What volume of each stock
solution, and what volume of water should be mixed to produce the
buffer?
(15) 5. Using both the three- and one-letter abbreviations, list amino acids
whose side chains:
(a) contain a hydroxyl group:________________________________________
(b) contain an amide group:__________________________________________
(c) contain an aromatic group:_______________________________________
(d) contain sulfur:__________________________________________________
(e) contain branched aliphatic hydrocarbons:_________________________
(12) 6. Explain the role of each of the following reagents in sequencing a
protein:
(a) cyanogen bromide
(b) dithiothreitol
(c) iodoacetate
(d) performic acid
(9) 7. For the following three tripeptides:
A. Lys.Phe.Ala B. Asp.Ser.Thr C. Leu.Ile.Trp
Predict:
(a) The order of elution from a reversed-phase HPLC column with the
eluting buffer at pH 2.
First:______ Second:______ Third:______
(b) The order of elution from a cation exchange column, starting
with an eluting buffer of pH 4.
First:______ Second:______ Third:______
(b) The direction of migration of each in an electrophoresis
experiment at pH 7.
Towards cathode (negative electrode):_____________
Towards anode (positive electrode):______________
(6) 8. Fill in the following blanks with à helix or disordered to represent
the primary conformation of the indicated synthetic polypeptide at
the indicated pH.
Polypeptide pH 3 pH 7 pH 11
polyglutamate __________ _________ __________
polylysine __________ _________ __________
(8) 9. Predict whether each of the following changes would increase or
decrease the binding affinity of oxygen to hemoglobin (i.e., increase
or decrease the fraction of hemoglobin containing bound oxygen).
_______ Binding of carbon monoxide to a few of the hemoglobin sites. (CO
binds to the heme iron in place of oxygen).
_______ Lowering the [H+] in the blood.
_______ Acclimation to high altitudes.
_______ Binding of carbon dioxide to hemoglobin.
(5) 10. Below is a graph which plots the è and psi angles of peptide backbone
conformations in a peptide chain. Such a graph is called a
180 ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ _________________________ map.
³ y ³
³ ³ Identify the letter or letters in
³ ³ the map which correspond to the
³ ³ following set of è, psi angles:
³ ³
psi 0 ³ w ³ _____ right handed à-helix
³ x ³
³ ³ _____ á-sheet structure
³ z ³
³ ³ _____ generally not accessible
³ ³
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è 180