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 DNA repair is a collection of processes by
which a cell identifies and corrects damage
to the DNA molecules that encode ...
a permanent (heritable) change in the
DNA sequence
 Substitution, deletion, or insertion of a base
pair.
 Chromosomal de...
DNA Lesions are sites of damage in the base-
pairing or structure of DNA.
They are classified as follows:
 Abasic Site: T...
 Modified Bases: These lesions are caused by
changes to the bases themselves, such as the
methylation of guanine to O6MeG...
 Double-stranded breaks (DSB): The most
lethal sort of lesion, this is where both
strand backbones are broken. This is
ty...
hydrolatic
attack
oxidative
damage
uncontrolled
methylation
DNA frequently suffers from spontaneous alterations and chemic...
G A CT
ds DNA Break Mismatch
Thymidine dimer
AP site
Covalent X-linking
ss Break
C-U deamination
Replication is highly accurate, but not perfect
Molecular Biology of the Gene, 5th Edition
Eukaryotes
MISMATCH REPAIR corrects replication errors
Some replication errors still escape detection: MUTATION
Molecular Biology of the Gene, 5th Edition
MUTATION
REPLICATION E...
If all DNA damage were left
unrepaired, cells would quickly die
due to the accumulation of lethal
mutations and the inhib...
If uncorrected, these changes may result in mutations
DNA repair is a collection of
processes by which a cell identifies
and corrects damage to
the DNA molecules that encode i...
DIRECT REVERSAL
BASE EXCESSION REPAIR
NUCLEOTIDE EXCISION REPAIR
RECOMBITIONAL REPAIR
TRANSLESION DNA SYNTHESIS
a. Photoreactivation
b. Methyltransferase
DIRECT REVERSAL
BASE EXCESSION REPAIR
NUCLEOTIDE EXCISION REPAIR
RECOMBITIONAL REPAIR
TRANSLESION DNA SYNTHESIS
Base Excision Repair and Nucleotide Excision Repair
are the two major pathways for repairing DNA damage
DIRECT REVERSAL
BASE EXCESSION REPAIR
NUCLEOTIDE EXCISION REPAIR
RECOMBITIONAL REPAIR
TRANSLESION DNA SYNTHESIS
DNA damages are repaired by a recombination
mechanism known as sister-strand exchange.
 Homologous (or general)
between t...
DIRECT REVERSAL
BASE EXCESSION REPAIR
NUCLEOTIDE EXCISION REPAIR
RECOMBITIONAL REPAIR
TRANSLESION DNA SYNTHESIS
Error-prone repair
Occurs when the other repairs are
not efficient enough
Translesion synthesis is catalyzed by
a speci...
Translesion DNA
synthesis
Catlyzed by a
specialized class of
DNA polymerases that
synthesize DNA
directily across the
site...
The enzyme is not ‘reading’
sequence information from
the template
Translesion synthesis is often
highly error-prone
DNA damages are repaired by a
recombination mechanism known as sister-
strand exchange.
 Homologous (or general)
between ...
Homologous (or general)
between two homologous DNA sequences
 Site-Specific
between two defined DNA sequence elements
 ...
 Homologous recombination is a type of genetic
recombination in which nucleotide sequences
are exchanged between two simi...
Two distinct mechanisms repair double-strand breaks
Homologous recombination repairs strand breaks
Homologous recombination is crucial for meiosis
IZOMERIZATION OF A HOLLIDAY JUNCTION
 Homologous (or general)
between two homologous DNA sequences
Site-Specific
between two defined DNA sequence elements
 ...
Lysogenic cycle involves integration of phage into the host chromosome by
SITE-SPECIFIC RECOMBINATION
Molecular Biology of...
The insertion of bacteriophage l genome into the host DNA
(recombination sites)
(recombinase)
Types of site-specific recombination
Molecular Biology of the Gene, 5th Edition
the darker red and blue boxes – the recomb...
 Homologous (or general)
between two homologous DNA sequences
 Site-Specific
between two defined DNA sequence elements
...
Unlike elements moving by site-specific recombination, TRANSPOSONS can insert
into any DNA sequence
Molecular Biology of t...
Molecular Biology of the Gene, 5th Edition
Transposons can move with or without duplication
Thank you!

Any queries please write to me on comment
below or email me at
manjuchhetri@gmail.com
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
DNA Damage, Repair and Recombination
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DNA Damage, Repair and Recombination

It content details of DNA Damage, DNA Repair Mechanisms, DNA recombition

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DNA Damage, Repair and Recombination

  1. 1.  DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome.  A failure to repair damaged DNA produces : mutation
  2. 2. a permanent (heritable) change in the DNA sequence  Substitution, deletion, or insertion of a base pair.  Chromosomal deletion, insertion, or rearrangement. Somatic mutations occur in somatic cells and only affect the individual in which the mutation arises. Germ-line mutations alter gametes and passed to the next generation.
  3. 3. DNA Lesions are sites of damage in the base- pairing or structure of DNA. They are classified as follows:  Abasic Site: This is where a base is missing from the DNA (note that the sugar-phosphate backbone is still intact, just the base is missing).  Mismatch: These are caused by replication errors, such as tautomerization, or the spontaneous deamination of cytosine to uracil.
  4. 4.  Modified Bases: These lesions are caused by changes to the bases themselves, such as the methylation of guanine to O6MeG, which base- pairs with thymine, or the UV-induced creation of thymine dimers.  Single-stranded breaks (SSB): This lesion is a nick in the sugar-phosphate backbone of one strand. This is caused by peroxides, Cu++ion, oxygen radicals, or ionizing radiation.
  5. 5.  Double-stranded breaks (DSB): The most lethal sort of lesion, this is where both strand backbones are broken. This is typically caused by ionizing radiation.  Inter strand Crosslinks: This is where there is an actual covalent linkage between the two strands. DNA replication cannot proceed past this point because helicase can’t melt apart the base-pairs for polymerase. This is caused by chemicals such as mitomycin C, cisplatins, and psoralens.
  6. 6. hydrolatic attack oxidative damage uncontrolled methylation DNA frequently suffers from spontaneous alterations and chemical damage
  7. 7. G A CT ds DNA Break Mismatch Thymidine dimer AP site Covalent X-linking ss Break C-U deamination
  8. 8. Replication is highly accurate, but not perfect Molecular Biology of the Gene, 5th Edition
  9. 9. Eukaryotes MISMATCH REPAIR corrects replication errors
  10. 10. Some replication errors still escape detection: MUTATION Molecular Biology of the Gene, 5th Edition MUTATION REPLICATION ERROR (still can be repaired) (a permanent change; can not be repaired)
  11. 11. If all DNA damage were left unrepaired, cells would quickly die due to the accumulation of lethal mutations and the inhibition of essential processes relying on the integrity of DNA (i.e. replication and transcription)
  12. 12. If uncorrected, these changes may result in mutations
  13. 13. DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome.
  14. 14. DIRECT REVERSAL BASE EXCESSION REPAIR NUCLEOTIDE EXCISION REPAIR RECOMBITIONAL REPAIR TRANSLESION DNA SYNTHESIS
  15. 15. a. Photoreactivation b. Methyltransferase
  16. 16. DIRECT REVERSAL BASE EXCESSION REPAIR NUCLEOTIDE EXCISION REPAIR RECOMBITIONAL REPAIR TRANSLESION DNA SYNTHESIS
  17. 17. Base Excision Repair and Nucleotide Excision Repair are the two major pathways for repairing DNA damage
  18. 18. DIRECT REVERSAL BASE EXCESSION REPAIR NUCLEOTIDE EXCISION REPAIR RECOMBITIONAL REPAIR TRANSLESION DNA SYNTHESIS
  19. 19. DNA damages are repaired by a recombination mechanism known as sister-strand exchange.  Homologous (or general) between two homologous DNA sequences  Site-Specific between two defined DNA sequence elements  Transposition between specific DNA element and any DNA site (we will go in details at the end of this slides)
  20. 20. DIRECT REVERSAL BASE EXCESSION REPAIR NUCLEOTIDE EXCISION REPAIR RECOMBITIONAL REPAIR TRANSLESION DNA SYNTHESIS
  21. 21. Error-prone repair Occurs when the other repairs are not efficient enough Translesion synthesis is catalyzed by a specialized class of DNA polymerases, translesion polymerases, that synthesize DNA directly across the damage site.
  22. 22. Translesion DNA synthesis Catlyzed by a specialized class of DNA polymerases that synthesize DNA directily across the site of the damage
  23. 23. The enzyme is not ‘reading’ sequence information from the template Translesion synthesis is often highly error-prone
  24. 24. DNA damages are repaired by a recombination mechanism known as sister- strand exchange.  Homologous (or general) between two homologous DNA sequences  Site-Specific between two defined DNA sequence elements  Transposition between specific DNA element and any DNA site
  25. 25. Homologous (or general) between two homologous DNA sequences  Site-Specific between two defined DNA sequence elements  Transposition between specific DNA element and any DNA site
  26. 26.  Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA.  It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks.  Homologous recombination also produces new combinations of DNA sequences during meiosis.  Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses
  27. 27. Two distinct mechanisms repair double-strand breaks
  28. 28. Homologous recombination repairs strand breaks
  29. 29. Homologous recombination is crucial for meiosis IZOMERIZATION OF A HOLLIDAY JUNCTION
  30. 30.  Homologous (or general) between two homologous DNA sequences Site-Specific between two defined DNA sequence elements  Transposition between specific DNA element and any DNA site
  31. 31. Lysogenic cycle involves integration of phage into the host chromosome by SITE-SPECIFIC RECOMBINATION Molecular Biology of the Gene, 5th Edition
  32. 32. The insertion of bacteriophage l genome into the host DNA (recombination sites) (recombinase)
  33. 33. Types of site-specific recombination Molecular Biology of the Gene, 5th Edition the darker red and blue boxes – the recombinase recognition sequences the black arrows – the crossover regionsrecombination sites
  34. 34.  Homologous (or general) between two homologous DNA sequences  Site-Specific between two defined DNA sequence elements Transposition between specific DNA element and any DNA site
  35. 35. Unlike elements moving by site-specific recombination, TRANSPOSONS can insert into any DNA sequence Molecular Biology of the Gene, 5th Edition (transposon)
  36. 36. Molecular Biology of the Gene, 5th Edition Transposons can move with or without duplication
  37. 37. Thank you!  Any queries please write to me on comment below or email me at manjuchhetri@gmail.com

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