sickle-cell anemia

1
(No Transcript)
2
(No Transcript)
3
sickle-cell anemia
4
Analogy of the effects of substitution, deletion,
and insertion of one letter in a sentence
composed of three-letter words, demonstrating
point and frameshift mutations.
5
(No Transcript)
6
(No Transcript)
7
Standard base-pairing relationships (a), compared
with anomalous base-pairing that occurs as a
result of tautomeric shifts (b). The long
triangle indicates the point at which the base
bonds to the pentose sugar.
8
NORMAL
RARE FORM
The standard base-pairing relationships compared
with two anomalous arrangements occurring as a
result of tautomeric shifts. The long triangle
indicates the point of bonding to deoxyribose
9
(No Transcript)
10
Standard base-pairing relationships (a), compared
with anomalous base-pairing that occurs as a
result of tautomeric shifts (b). The long
triangle indicates the point at which the base
bonds to the pentose sugar.
11
A T to G C transition mutation as a result of
a tautomeric shift in adenine.
12
A T to G C transition mutation as a result of
a tautomeric shift in adenine.
13
Tautomeric Shift in Adenine Formation of a
T-double bond-A to a C-triple bond-G transition
mutation as a result of a tautomeric shift in
adenine.
14
Formation of a T-double bond-A to a C-triple
bond-G transition mutation as a result of a
tautomeric shift in adenine.
15
MUTAGENS BASE ANALOGS
5-bromouracil (5-BU) in similar in structure to
thymine. In the common keto form, 5-BU
base-pairs normally with adenine, behaving as an
analog of T. In the rare enol form, it pairs
anomalously with guanine, behaving as an analog
of C.
16
In the common keto form, 5-BU base-pairs normally
with adenine, behaving as an analog of T.
17
In the rare enol form, 5BU pairs anomalously with
guanine, behaving as an analog of C.
18
ALKYLATION another way of possible chemical
modifications of bases Conversion of guanine (G)
to 6-ethylguanine by the alkylating agent
ethylmethane sulfonate (EMS) addition of ethyl
on 6th carbon of the base. The 6-ethylguanine,
being an analog of A. base-pairs with thymine
19
MUTAGENIC RADIATION
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
GOOD NEWS

• MUTATIONS CAN BE REPAIRED

24
Direct correction in replication DNA polymerase
proofreads in 3 ? 5 direction

• Synthesis of DNA strand has high rate of
  misincorporations (ERRORS), about 1 in 100,000
  nucleotides! (10-5) with proofreading 99
  repaired still 10-7 with
• Mutations in gene that codes for the proofreading
  subunit ? no proofreading!mutator gene of E.
  coli

25
Mismatch repair (after proofreading, still during
replication)

• AAACCTTGGG
• TTTGGATCCC
• But how to decide which strand is correct?
• In E. coli, DNA methylation of A on template (in
  GATC) strand happens during replication so
  template is in fact temporarily highlighted by
  methylase enzyme
• Repair enzyme recognizes mismatch, makes a
  nick exonuclease degrades a portion Dna pol
  ligase fill the gap

26
Post-replication repair occurs if DNA replication
has skipped over a lesion, such as a thymine
dimer (produced by UV).
27
(No Transcript)
28
Through the process of recombination, the correct
complementary sequence is recruited from the
parental strand and inserted into the gap
opposite the lesion. The new gap that is created
is filled by DNA polymerase and DNA ligase.
29

• DNA ligase working on repair

30
Damaged DNA repaired by photoreactivation repair.
The bond creating the thymine dimer is cleaved by
the photoreactivation enzyme (PRE), which must be
activated by blue light in the visible spectrum.
31
Base-excision repair (BER) accomplished by uracil
DNA glycosylase, AP endonuclease, DNA polymerase,
and DNA ligase. Uracil is recognized as a
non-complementary base, excised, and replaced
with the complementary base (C).
32
Nucleotide-excision repair (NER) of a UV-induced
thymine dimer. In actuality, 13 nucleotides are
excised in prokaryotes and 28 nucleotides are
excised in eukaryotes during repair.
33
Two individuals with xeroderma pigmentosum. The
4-year-old boy on the left shows marked skin
lesions induced by sunlight. Mottled redness
(erythema) and irregular pigment changes in
response to cellular injury are apparent. Two
nodular cancers are present on his nose. The
18-year-old girl on the right has been carefully
protected from sunlight since her diagnosis of
xeroderma pigmentosum in infancy. Several cancers
have been removed and she has worked as a
successful model.
34
Xeroderma pigmentosum, or XP, is an autosomal
recessive genetic disorder of DNA repair in which
the ability to repair damage caused by
ultraviolet (UV) light is deficient. This
disorder leads to multiple basaliomas and other
skin malignancies at a young age. In severe
cases, it is necessary to avoid sunlight
completely. The most common defect in xeroderma
pigmentosum is a genetic defect whereby
nucleotide excision repair (NER) enzymes are
mutated, leading to a reduction in or elimination
of NER.1 Unrepaired damage can lead to
mutations, altering the information of the DNA in
individual cells. If mutations affect important
genes, like tumor suppressor genes (e.g. p53) or
proto oncogenes then this disorder may lead to
cancer. Patients exhibit elevated risk of
developing cancer. Normally, damage to DNA in
epidermal cells occurs during exposure to UV
light. The absorption of the high energy light
leads to the formation of pyrimidine dimers,
namely CPD's (cyclobutane-pyrimidine-dimers) and
6-4PP's (pyrimidine-6-4-pyrimidone
photoproducts). The normal repair process entails
nucleotide excision. The damage is excised by
endonucleases, then the gap is filled by a DNA
polymerase and "sealed" by a ligase.
35
Onset of skin cancers in patients with or without
xeroderma pigmentosum (XP),
36
The Dark Side of the Sun is a 1988 American -
Yugoslavian drama film starring a young Brad Pitt
about a young man in search for a cure for a
dreaded skin disease. It is directed by Bozidar
Nikolic. The footage for the film was shot in
1988 but due to the outbreak of civil war it had
to be abandoned and much footage was lost. It was
eventually released officially in 1997.
37
An insertion sequence (IS), shown in red. The
terminal sequences are perfect inverted repeats
of one another.
38
Site-directed mutagenesis. A single strand of
DNA is isolated and hybridized with a synthetic
oligonucleotide containing a triplet altered to
encode an amino acid of choice. After
semiconservative replication, a different
complementary base pair is present in one of the
new duplexes. Upon transcription and translation,
a mutant protein that was designed in the
laboratory will be produced.
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
Structural organization of a copia transposable
element in Drosophila melanogaster, showing the
terminal repeats.
44
(No Transcript)