Download gln.val.tyr.ala lys.arg.glu.trp met.his.leu.asp cys.pro.gly.asn F-A-D

BCH 4053
July 1, 1998
(10)
1.
HOUR TEST 2
NAME_____________________
Given the following data on three different proteins:
Protein:
hemoglobin
Molecular Weight (M)
Diffusion Coefficient (D)
Isoelectric pH (pI)
64,500
6.9
6.8
chymotrypsinogen
23,250
9.5
9.5
urease
482,000
3.5
5.0
Page
Points
1
2
3
4
____
____
____
____
Total
______
Indicate in the blanks which of the three proteins will:
____________________
(a)
Elute first from a gel filtration column.
____________________
(b)
Elute first from a diethylaminoethyl cellulose ion exchange
column.
____________________
(c)
Have the smallest frictional coefficient (f).
____________________
(d)
Migrate fastest upon electrophoresis in sodium dodecyl sulfate
(SDS).
____________________
(e)
Migrate fastest to the anode in a native electrophoresis
experiment at pH 6.0.
(6)
2.
Describe two methods of cleaving disulfide bonds in proteins prior to sequencing.
(12)
3.
Underline the following peptides which are negatively charged at pH 7.0. Circle each amino
acid which is aromatic.
gln.val.tyr.ala
lys.arg.glu.trp
met.his.leu.asp
cys.pro.gly.asn
F-A-D-S
M-I-C-K
BCH 4053 --Hour Test 2
Page 2
Name________________________
(10)
4.
You have isolated an octapeptide with the amino acid composition
(Lys2, Asp, Tyr, Phe, Gly, Ser, Ala)
Reaction of the intact peptide with FDNB yields DNP-alanine. Cleavage with trypsin yields
peptides with compositions
(Lys, Ala, Ser) and (Gly, Phe, Lys) plus a dipeptide.
Reaction with chymotrypsin releases free aspartic acid, a tetrapeptide with composition (Lys,
Ser, Phe, Ala) and a tripeptide with composition (Gly, Lys, Tyr). What is the sequence?
(Explain your reasoning).
(4)
5.
In the Edman degradation of a peptide, the peptide first reacts with phenylisothiocyanate
under ______________ (acid or alkaline?) conditions; the amino acid at the _____________
(amino terminal or carboxyl terminal?) is then removed in _______________ (acid or
alkaline?) conditions, and the resulting amino acid derivative, known as a
___________________, is analyzed by chromatography.
(5)
6.
Peptides can be specifically cleaved at methionine by reaction with _________________
(name the reagent). Draw the complete structure of two peptides formed by cleavage of
His.Met.Thr.Asp
with this reagent, indicating the predominant charge on all protonatable groups if the two
peptides were in solution at pH 7.0.
BCH 4053 --Hour Test 2
(4)
7.
Page 3
Name________________________
Following are and angles of two peptide secondary structures. Identify which is the
alpha helix and which is the beta sheet.
(phi) angle
(psi) angle
secondary structure
- 57o
-47o
________________
-139o
+135o
_________________
(3)
8.
What is meant by a motif when referring to protein structure?
(6)
9.
The conformation of deoxyhemoglobin is called the T conformation, and that of
oxyhemoglobin is called the R conformation. Identify which of these conformations:
_____ binds 2,3-bisphosphoglycerate
_____ is stabilized by salt bridges between the alpha and beta subunits
_____ is favored by raising the pH
(6)
10.
Fill in the following blanks with -helix or disordered to represent the primary
conformation of the indicated synthetic polypeptide at the indicated pH.
Polypeptide
(4)
11.
pH 3
pH 7
pH 11
polyglutamate
_______
_______
_______
polylysine
_______
_______
_______
Fetal hemoglobin has two subunits replacing the two subunits of hemoglobin A. The
chains have a serine in one position where the chains have a histidine, in a region next
to the central cavity of hemoglobin.
(a)
Does fetal hemoglobin bind oxygen more tightly or less tightly than hemoglobin
A?
______________
(b)
How does this amino acid substitution account for the different binding affinity of
fetal hemoglobin?
BCH 4053 --Hour Test 2
(5)
12.
13.
14.
15.
galactose
galactose
________________ (b)
(4)
16.
17.
ribose
threose
ribulose
ribose
mannose
erythrose
-D-galactose and -D-galactose
D-threose and D-erythrose
-D-mannose and -L-mannose
________________ (d)
-D-glucose and -D mannose
Lactose is a disaccharide found in milk.
(a)
Draw the structure of lactose, using the Haworth projection.
(b)
Is lactose a reducing sugar? Why or why not?
Circle each of the following terms which is a correct description of the disaccharide
sucrose:
furanoside
18.
dihydroxyacetone
________________ (c)
-fructoside
(3)
glyceraldehyde
Identify the following pairs as enantiomers, epimers, or anomers. More than one term
may apply to a pair.
________________ (a)
(4)
ribose
Circle the following monosaccharides which are epimers of D-glucose.
fructose
(4)
fructose
Circle the following monosaccharides which are pentoses.
fructose
(5)
Name________________________
Circle the following monosaccharides which are aldoses.
glucose
(5)
Page 4
ketal
hemiacetal
-glucoside
pyranoside
reducing sugar
-galactoside
Ribitol is a sugar alcohol formed by reducing the aldehyde group of ribose to an alcohol.
What is the structural relationship between L-ribitol-1-phosphate and D-ribitol-5-phosphate?