Chapter 2: DNA Replication and Repair Flashcards
What is the key function of Polymerase?(Specific)
Enzymes taht synthesize nucleic acids by forming phosphodiester(PDE) bonds.
What are Nuclease(Exonuclease & Endonuclease)?
Enzymes that hydrolyze PDE bonds
What are three key difference of DNA Polymerase & RNA polymeras e functions?
Requires dNTP / NTP
Proofreading acitivty(3’ to 5’ exonuclease) / No
RNA primer required / No
X binds to the single-stranded portion of each DNA strand, preventing them from reassociating and protecting them from degradation by nucleases. What is X
Single-stranded DNA binding protein(SSB).
- What are two anticancer agents that acts by inhibiting DNA gyrase(topoisomerase II).
- Name three specific drugs.
- When could it be used as treatment?
- Quinolones and fluoroquinolones
- Levofloxacin, Ciprofloxacin, Moxifloxacin
- gonorrhea, upper & lower urinary tract
What is Telomerase
It is an enzyme in eukaryotes used to maintain the telomeres. It contains short RNA template complementary to the DNA telomere sequence, as well as telomerase reverse transcriptase activity(hTRT). telomerase activity is present only embryonic celss, germ cells, and stem cells, but not in somatic cells.
Inappropriately present in many cancer cells, contributing to their unlimitied replication
During Steps in DNA replication, there should be a removal of RNA primers. What kind of enzyme does Prokaryotic cells and Eukaryotic cells use to remove RNA primers, replace RNA to DNAs?
Prokaryotic cells use DNA polymerase I while Eukaryotic cells use DNA polymerase alpha + delta
(in prokaryotic cells, DNA synthesis occurs by DNA polymerase III, and removal & replacement of RNA occurs by DNA polymerase I)
(While Eukarytic cells synthesize with DNA polymerase a, d, and removal of RNA primers with RNAase H, replacemnet of RNA with DNA with DNA polymerase d)
What are three drugs that can inhibit DNA synthesis by reverse transcriptase in retrovirus?
AZT, ddC, ddL
Name three tumer suppressor genes related to DNA repairing.
- p53 gene: encodes a protein that prevents a cell with damaged DNA from entering the S phase.
- Li fraumeni syndrome & many solid tumors. - ATM gene: encodes a kinase essential for p53 activity.
- ataxia telangiectasia: hypersensitivity to x-rays and predispotion to lymphomas. BRCA-1 & BRCA 2 - retinoblastoma Rb gene
- Rb & p53 controls entry into S-phase
Which repair mechanism is used when Ultraviolet light causes DNA damage?
Nucleotide excision repair
- UV induces thymine dimers in DNA, which interferes with DNA replication and normal gen expression
What causes base excision repair to happen?
Cytosine deamination
- converts cytosine to uracil.
When does mismatch repair occur, and what are key genes?
Mismatch repair occurs on G2 phase.
MSH2, MLH1
A 6-year-old child was brought to the clinic because his parents were concerned with excessive lesions and blistering in the facial and neck area. The parents noted that the lesions did not go away with typical ointments and creams and often became worse when the child was exposed to sunlight. The physician noted excessive freckling throughout the child’s body, as well as slight stature and poor muscle tone.
Sx) extreme sensitivity to sunlight, skin freckling, ulcerations, and skin cancer
Dx) Xeroderma pigmentosum
- Occurs because of the deficiency of excision endonuclease(Nucleotide excision repair)
- Patients with the disease should avoid exposure to any source of UV light
X results from a mutation in one of the genes(hMLH1 or hMSH2) encoding enzymes.
In patient with X, cells from the resected tumor show microsatellite instability
Microsatellites: di, tri- and tetranucleotide repeats dispersed throughout the DNA, usually in noncoding regions
Hereditary Nonpolyposis colorectal cancer(Lynch syndrome)
For example, TGTGTGTG may occur at paricular locus. If cells lack mismatch repair, the replicated DNA will vary in the number of repeats at that locus
