5: DNA cell damage and Repair Flashcards
Why can DNA easily be damaged?
because the DNA bases are planar carbon rings –> easily chemically activated and then
- be reactive, react with other molecules
- are chemically similar –> can be transfered into one another
What is Deamination in the process of modification of an AA?
What does it lead to?
The loss of one amine group of a DNA base (often converted to keto group)
- can lead to mutation via conversion of
- cytosin to uracil (essentially thymine)
- adenine to hypoxanthine
- guanine to xanthine
- and 5-methyl cytosine to thymine.
What are “other chemical modificatios” of DNA?
What do they lead to?
Many reacgtions, often induced by free radicals or hyper-reactive oxygen molecules (byproducts of normal motabolism or can be produced by ionising radioation)
Leading to
- formation of double-bonds
- methylation, alkylation of DNA bases
- adduct formation
What is photodamage?
How does it change the DNA?
intra-strandal change by UV light being absorbed by the DNA bases
- UV light activates and causes
- pyrimindien dimer (often thyamine dimers)
- driver in skin cancer
What are the different modifications/damages that can occur in DNA change?
- Deamination
- other chemical modification
- methylation
- alkylation
- adduct formation
- photodamage
What is the consequence a Base-mismatch in the DNA?
There will be a bulge in DNA –> will be used to find the site of damage and repair of the DNA
How does Radiodamage modifies the DNA
It can sometimes break the phospho-diester bonds–> leading to gap in DNA
- also used to find the site of damage and repair
Overall spoken: What causes DNA damage?
- Carcinogens
- dietary
- lifestyle
- environmental
- occupational
- medical
- endogenous
- Radiation
- ionizing
- solar
- cosmic
Why is DNA damage problematic?
Damage can lead to mutation –> mutations can lead to cancer
- damaging DNA is an important strategy in cancer therapy (might lead to apoptosis)
Explain how polycyclic aromatic hydrocarbons might lead to DNA damage?
Where are they found?
- Common environmental pollutants
- Formed from combustion of fossil fuels
- Formed from combustion of tobacco
E.g. Benzo(a) pyrene (B(a)P)
- itself it nor carcinogenic but gets activated by metabolism (highly carciongenic)
- Forms DNA adduct when activated
Name an example of a food-born carcinogen and how it could cause cancer
Aflatoxin B1– >formed by fungi on grains and peanuts
- metabolism converts it into carcinogen
- activation–> highly reactive
- adduct formation
How does UV radioation cause cancer?
UV radiation might induce
- Pyrimidine (thymine) dimers
- mutation
- melanoma
Explain how ionizin radioation can cause DNA damage
- Generates free radicals in cells
- Includes oxygen free radicals
- super oxide radical: O2•
- hydroxyl radical: HO•
- Includes oxygen free radicals
- Possess unpaired electrons
- electrophilic and therefore seek out electron-rich DNA
Explain the effects of free radicals on the cell
They attack the DNA and cause:
- Double and single strand breaks
- Apurinic & apyrimidinic sites
- Base modifications
- ring-opened guanine & adenine
- thymine & cytosine glycols
- 8-hydroxyadenine & 8-hydroxyguanine (mutagenic)
Why is DNA repair so important?
What are its physiological capacities?
There is a lot of DNA damage going on all the time needs to be repaired to not cause cancer
–> normally: cell has a lot higher capcity to repair than damage happens