Page 266 - Color Atlas of Biochemistry

Mutation and repair 257

A. Mutagenic agents

1. Ionizing Alkylating Reactive
radiation compounds methyl
group
CH 3

O NH C O UV HNO 2 α, β, γ [CH ] O N
3
C radi- X
N C CH ation R NO
R CH 3 3. Methylnitrosamine
O NH O
C C
N C Desami- Free
R CH CH 3 nation radicals Epoxide
2. Thymine dimer

O
Deletions CH
or HC
insertions C H
due to HO H C
faulty
recombination OH
Formation Base Spon- Chemical 4. Mutagenic
of exchange taneous modificaton derivative of
pyrimidine C U loss of of bases benzo(a)pyrene
dimers A I bases

B. Effects C. Repair mechanisms

· G TA C CT · Thymine dimer
· CAT G G A ·
HNO 2 Base a a
exchange
Excision
endonuclease Photo-
· GTAUCT · lyase
· C ATGGA ·
4.1.99.3
Replication
b Light
· GTACCT · · GTAUCT · b
· C ATGGA · ·C AT A GA ·
Defect-
binding
Normal Replication protein
c
· G TAT C T · 2. Photoreactivation
· C ATAGA ·
c
Single-strand
Permanent binding
change DNA poly- proteins a Replication
merase
1. Point mutation

Insertion b
d
· GCTACCT ·
· C C AT G GA · DNA ligase

· GTACCT · · GCTACCT ·
· CATGGA · · CGATGGA ·
e Repaired DNA
·· Val-Pro- ·· -Ala-Thr-X ·· c

2. Frameshift mutation 1. Excision repair 3. Recombinational repair

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme
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