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FTM Exam 2 > Lecture 49: DNA Repair > Flashcards

Lecture 49: DNA Repair Flashcards

1
Q

DNA Damage Consequences

Short term/long term

A

Short term:
1) Reduced proliferation
2) Altered gene expression
30 Cell death = apoptosis

Long Term:

1) Aging
2) Diseases especially cancer

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2
Q

DNA Mutation

Types

A

Process:
Dna damage –> Replication before repair –> repair = mutation

-Induced or spontaneous mutations can occur

Spontaneous mutations:

1) Errors of replication (S-phase):
- Wrong base incorporated by DNA polymerase
- Tautomerism = chemicals can exist as a mixture of two

2) Spontaneous lesions: Chemical changes (Resting cells)

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3
Q

DNA Polymerase

A
  • 5’-3’ polymerase activity

- 3’ to 5’ exonuclease activity

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4
Q

Bloom syndrome

A

-Defect in BLM gene (a DNA helicase enzyme)
DEFECT IN REPLICATION/REPAIR/RECOMB

Characteristics:
-smaller than average
-narrow chin, prominent nose and ears
*facial rash (pigment and dilated blood vessels) upon
exposure to sun
-often get diabetes and have neurological, lung and
immune system deficiencies

-Chromosomal instability = many
chromosomal breaks and sister chromatid exchanges

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5
Q

Dna Frameshift Mutation

A

-Form from slipping of DNA polymerase during replication

-Tend to occur at positions where there are base
repeats

-DNA kinks/loops = not all bases are copied

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6
Q

Spontaneous lesions

Main types

A

-Changes that occur in a resting cell due to the chemical nature of the DNA

Main types:

1) Depurination
2) Deamination
3) Oxidative damage

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7
Q

Depurination

A
  • Spontaneous lesion
  • Breaking of glycosidic bond between base and sugar in purine nucleotides = base lost, sugar-phos intact
  • Can result in mutation if persists
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8
Q

Deamination

A
  • Spontaneous lesion

- loss of amine group from a base

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9
Q

Oxidative damage

A
  • Spontaneous lesion
  • Oxidative products cause production of reactive oxidative cmpds

Effects:

  • Damages cell
  • Adds oxygen group to nucleotide bases
  • Mis-pairing with A and potential transversion
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10
Q

Mutagens

A

-Increase the frequency of “normal” mutations

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11
Q

Ionizing Radiation

A

-High energy particles/rays = cellular damage, even death, DNA damage, heritable mutations

(Ex: X-rays, radiation, radioactive particles)

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12
Q

UV Light

A
  • Generates deleterious products
  • Aka primidine dimers/thymine dimers

-Interfere with normal pairing and block
replication

-Covalent linkages between bases on the
same strand

Example:
-Cyclobutane pyrimidine dimers or
6-4 photoproducts

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13
Q

Indirect Repair

A

1) Nucleotide Excision
- Removes more than a FEW bases around a damaged site

2) Base Excision
- repairs a SINGLE bases by removing it

3) Mismatch Repair
- repairs mismatched bases

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14
Q

Excision Repair Mechanism

A

-Same for all excisions, the specific method accounts for size of repair

1) Recognition of damage
2) Recruit endonucleases
3) Region removed
4) DNA Polymerase fills in gap

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15
Q

Repair mismatched bases

A
  • Post-replicative repair mechanism
  • A form of excision repair
  • Mismatched bases are recognized and excised

Strand discrimination:

  • Prokaryotes= methylation
  • Eukaryotes= methylation and interactions w dna machinery

1) Mismatch missed by proofreading is
recognized by MSH proteins

2) Repair may occur during S-phase (if
missed by proof-reading) or in G2
when genome is scanned for errors

3) Excision of bases around mismatch

4) Repair by re-synthesis
- -MSH genes involved

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16
Q

Repair mismatched bases

Strand discrimination

A
  • Post-replicative repair mechanism
  • A form of excision repair
  • Mismatched bases are recognized and excised
  • Can remove small repeats that tend to expand

Strand discrimination: Figuring out “right” strand to remove

  • Prokaryotes= methylation
  • Eukaryotes= methylation and interactions w dna machinery

1) Mismatch missed by proofreading is
recognized by MSH proteins

2) Repair may occur during S-phase (if
missed by proof-reading) or in G2
when genome is scanned for errors

3) Excision of bases around mismatch

4) Repair by re-synthesis
- -MSH genes involved

17
Q

Hereditary Nonpolyposis Colon Cancer

A
  • May occur when there are mutations in genes encoding mismatch repair proteins MSH2, MLH1, PMS1, PMS2, or MSH6
  • microsatellite instability in tumors = tandem repeats
18
Q

Double stranded breaks

A
  • Type of mutation
  • Dangerous bc loss of genetic info/chrom abnormalities

Fixes:

1) Non-homologous end joining
2) Recombination repair (uses homolog chroms)

19
Q

What happens when errors get through:

Somatic errors

Germline errors

A

Somatic errors (bad for us)

  • Cancer
  • Aging
Germline errors (bad for our kids)
-Genetic disease passed on to offspring
20
Q

How are DNA repair genes vulnerable to mutation?

A

1) Increased error rate
- Bases not repaired correctly

2) Genomic Instability
-Mutations in genes involving resting DNA repair/chrom breaks =destabilization of genome
(Ex: Blooms, XP)

21
Q

Ataxia Telangiectasia

A
  • Defect in ATM gene (11q22-23)
  • Problem w DNA Double-stranded break repair
  • AR disorder
  • Serine-threonine protein kinase with the following:
    1) detecting dna damage
    2) Activating cell cycle arrest and DNA repair proteins (Ex: p53)

Symptoms:

  • Blood shot eye (Ocular telangiectasia)
  • Increased incidence of cancer
  • Affects cerebellum and immune system
22
Q

Triggers of Apoptosis

A

1) Extrinsic Pathway
- Lack of growth factor supply outside the cell
- Caspase 8 and 3

2) Intrinsic Pathway
- Response to genotoxic stress: Radiation, toxins, hypoxia
- Caspase 9 and 3

3) Perforin/Granzyme Pathway
- Mediated by immune system cells: Cytotoxic T cells
- Caspase 10 and 3

23
Q

What does role does p53 play with apoptosis

A
  • Communicates to the cell cycle and helps mediate cell cycle arrest instead of apoptosis
  • Cells harbor mutations in p53 may continue proliferating w DNA damages = accumulation of mutations = cancer progression
24
Q

Intrinsic Apoptotic Pathway

A

DNA damaged –> BAX produced + goes into mitochondria –> BAX releases cytochrome C from mitochondria –> Cleavage activates from a cascade –> Apoptosis

25
Q

Cancer cells exhibit high levels of what proteins?

A
  • High levels of anti-apoptotic proteins (Ex: BCL-2)

- Low levels of pro-apoptotic proteins (p53, BAX)

FTM Exam 2 (25 decks)

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