MIT Department of Biology
7.014 Introductory Biology, Spring 2005
Recitation Section 20
April 25-26, 2005
Immunology
A. Antibody production
Shown below is a schematic of the production of a heavy chain polypeptide for an antibody. At the top
is the chromosomal arrangement found in an immature B cell, at the bottom is shown the heavy chain
polypeptide.
V segments
D segments
J segments
constant segment
= intron regions
1. Label the process indicated by each arrow. Choose the one best option for each from:
protein processing
transcription
translation
transduction
DNA ligation
DNA rearrangement
RNA splicing
RNA ligation
2. Indicate on the diagram below where you would expect to find each of the following components:
promoter
Transcription terminator
start codon
stop codon
3. Indicate on the diagram below the variable and the constant region of the heavy chain
polypeptide.
1
An activated B cell undergoes cell division and produces many daughter cells. Some daughter cells will
function as B cells, some will function as plasma cells and other will become memory cells.
4. Assume that an activated B cell undergos somatic mutation and produces two different B cells
each with a slightly altered version of the antibody. This event occurs early in the immune
response (i.e. when antigen was present in the organism). Mutation A makes the antibodyantigen interaction stronger, mutation B makes the antibody-antigen interaction much weaker.
i) Would you expect memory cells derived from the original activated B cell?
__
__
ii) Would you expect memory cells derived from the daughter B cell with mutation A (antibodyantigen interaction stronger)?
__
__
iii) Would you expect memory cells derived from the daughter B cell with mutation B (antibodyantigen interaction much weaker)?
__ __
Explain your answers.
B. Immunology and Immunizations
The varicella zoster virus (VZV) is the infectious agent that results in chickenpox, a common childhood
illness that causes itchy red spots on the skin. Contracting VZV as a child is relatively benign, but can
present serious health issues when contracted as an adult.
1. How does a VZV infected cell signal the immune system? How are the infected cells specifically eliminated from the body?
2. Over the course of a lifetime, the average person is exposed to VZV many times, yet usually
only displays symptoms once. What is the immune system mechanism that results in lifetime
resistance?
As of September 1999 any child entering kindergarten must have had chickenpox or received a new
vaccine against VZV.
3. Present an argument in support of this vaccination campaign.
4. Present an argument opposed to this vaccination campaign.
2
C. Immunology and Central Dogma
Shown below is a diagram of the interaction of an antibody molecule with an antigen
(phosphorylcholine).
Phosphorylcholine
_
OH
O
Arg 52
P
_
O
O
CH2
Tyr 33
Trp 104
CH 2
CH 3
+N
Glu 58
CH 3
CH 3
Asn 90
Glu 35
Heavy Chain of antibody
1. Indicate the strongest type of interaction that occurs between the amino acids
Phosphorylcholine molecule. Phosphorylcholine and Arg 52 listed and the
Phosphorylcholine and Tyr 33
Phosphorylcholine and Glu 35
Phosphorylcholine and Trp 104
2. Each of the following mutations alters the binding of the antigen to the antibody. Explain in
terms of the change in interactions why the binding of the Phosphorylcholine to the antibody has
remained the same, been made stronger, or been made weaker.
mutation in antibody
binding of antibody to phosphorylcholine
1
Trp 104 -----> Leu 104
same
2
Arg 52 -----> Lys 52
stronger
3
Glu 35 -----> Gln 35
weaker
4
Tyr 33 -----> Phe 33
weaker
3. Can any of these mutations be due to a single base pair substitution?
If so, give one possibility.
3
The Genetic Code
U UUU
UUC
UUA
UUG
C CUU
CUC
CUA
CUG
A AUU
AUC
AUA
AUG
G GUU
GUC
GUA
GUG
U
phe
phe
leu
leu
leu
leu
leu
leu
ile
ile
ile
met
val
val
val
val
C
ser
ser
ser
ser
pro
pro
pro
pro
thr
thr
thr
thr
ala
ala
ala
ala
UCU
UCC
UCA
UCG
CCU
CCC
CCA
CCG
ACU
ACC
ACA
ACG
GCU
GCC
GCA
GCG
A
tyr
tyr
STOP
STOP
his
his
gln
gln
asn
asn
lys
lys
asp
asp
glu
glu
UAU
UAC
UAA
UAG
CAU
CAC
CAA
CAG
AAU
AAC
AAA
AAG
GAU
GAC
GAA
GAG
UGU
UGC
UGA
UGG
CGU
CGC
CGA
CGG
AGU
AGC
AGA
AGG
GGU
GGC
GGA
GGG
G
cys
cys
STOP
trp
arg
arg
arg
arg
ser
ser
arg
arg
gly
gly
gly
gly
U
C
A
G
U
C
A
G
U
C
A
G
U
C
A
G
STRUCTURES OF AMINO ACIDS
at pH 7.0
O
O
C
H
C
H
CH 3
ALANINE
(ala)
C
H
C
CH 2 CH 2 CH 2
N
H
CH 2 SH
O
H
N
C
O
+
C
H
H
CH 2
NH 3
+
N
C
H
O
C
S
CH 3
H
C
C
CH 2
H
C
O
H
CH 3
NH OH
+ 3
THREONINE
(thr)
H
H
C
CH 2
C
H
H
H
H
O
O
NH 3
+
H
CH 2
CH 2
H
C
C
H
O
O
C
CH 2
OH
NH 3
+
H
TYROSINE
(tyr)
OH
SERINE
(ser)
C
H
CH 2
NH 3
+
PROLINE
(pro)
H
N
TRYPTOPHAN
(trp)
C
N
H +
H
NH 3 +
O
O
CH 2
C
H
H
C
O
O
H
CH 2 CH 2 CH 2 CH 2
LYSINE
(lys)
C
CH 2
C
NH 3
+
CH 3
PHENYLALANINE
(phe)
O
H
CH 3
LEUCINE
(leu)
H
O
C
C
NH 3
+
NH 3
+
O
O
C H
GLYCINE
(gly)
H
C
H
CH 2 CH 3
H
NH 3
+
O
C
CH 2 CH 2
METHIONINE
(met)
C
C
C
NH 2
O
O
O
O
NH 3
+
H
C
H
GLUTAMINE
(glN)
O
C H
O
C
O
C
NH 3
+
ISOLEUCINE
(ile)
C
H
-
NH 3 CH 3
+
H
HISTIDINE
(his)
O
O
-
ASPARTIC ACID
(asp)
O
CH 2 CH 2
O
NH 3
+
O
C
O
CH 2 C
C
NH 2
C
H
GLUTAMIC ACID
(glu)
CYSTEINE
(cys)
C
C
NH 3
+
NH 3
+
H
CH 2 CH 2
H
ASPARAGINE
(asN)
O
C
O
O
C
C
O
NH 2
+
C
CH 2 C
C
NH 3
+
O
O
C
H
C
H
NH 2
O
O
C
ARGININE
(arg)
O
O
O
NH 3
+
NH 3
+
O
O
O
H
H
C
CH 3
C
NH 3 H
+
CH 3
VALINE
(val)
4