Molecular Biochemistry Week 3 Flashcards
Name differnt types of damage that can affect DNA
- Environmental damage:
Chemical agent and radiation - spontaneous damage
Name the 2 reasons for mutations
- Uncorrected replication errors
- DNA damage from : oxidative deamination, radiation and chemical agents
Name the 3 different types of mutations
- point mutation
- Insertion
- Deletion
What is point mutation
When one base is substituted with another
What is insertion
When one or more nucleotides are added
What is deletion
When one or more nucleotides are removed
Explain the process for general DNA repair
- Damaged or mismatched DNA is removed
- DNA polymerase then fills in the gaps using the undamaged strand as a template
- DNA ligase then seals the new strand into the DNA
Name the key enzymes involved in general DNA repair processe
Endonuleases
Exonucleases
DNA polymerase
DNA ligase
Name 4 differnt types of DNA Repair mechanisms
- Nucleotide excision repair (NER)
- Base Excision Repair (BER)
- Mismatch Repair (MMR)
- Transcritpion- Coupled Repair (TCR)
Explain the function of the DNA repair mechanism nucleotide Excision Repair (NER) + what it is used for
Removes a group of nucleotides including the damaged ones
- used for bulky lesions like Uv-induced damage
Explain the function of the DNA repair mechanism Base excision repair (BER) and what it uses
- Creates and AP site , which is then cut and repaired
- uses glycosylase to remove a damaged base
Explain the function of the DNA rapid mechanism - Mismatch repair
- It fixes mismatched base pairs from replication errors
Explain the the DNA repair mechanism- Transcription coupled repair (TCR)- when it is triggered
- Triggered when transcription machinery detects DNA damage in active genes
Cytosine can be deaminated to form what
Uracil
Bases can be lost through what?
- Through hydrolysis of the sugar-phosphate backbone
Deaminating agents like nitrous acid converts these to what?
- Cytosine -
-Adenine-
-Guanine
-cytosine- Uracil
-Adenine- Hypoxanthine
-Guanine- Xanthine
Name an alkylating agent
- Dimethyl sulfate
What is the purpose of Base excision repair(BER)
-Fixes small, non bulky lesions
Explain the full process in BER + enzymes starting with Glycosylase
- Steps:
Glycosylases remove abnormal bases → leaves AP sites (apurinic/apyrimidinic).
AP endonucleases cut near the AP site (5’ side).
Lyase removes the sugar-phosphate remnant.
DNA pol I fills the gap.
DNA ligase seals the strand.
What doe Uv light cause
- Pyrimidine dimers
What is the function of the Uv light
-Block DNA polymerase, stopping replication
What is the purpose of Nucleotide Excision Repair (NER)
- Removes bulky lesions like T-T dimers or large chemical adducts
Explain all the steps in NER including enzymes starting from (uvrABC)
Steps:
1.UV-specific endonuclease (uvrABC) cuts both sides of the dimer.
Damaged fragment is excised.
DNA pol I fills in the gap.
DNA ligase seals it.
Explain the full process of Mismatch repair in DNA
-Mismatch Repair Steps:
Recognition of mismatch.
Endonuclease cuts the strand.
Exonuclease removes the error and nearby nucleotides.
DNA polymerase fills the gap using the sister strand as a template.
DNA ligase seals the strand.
