Chapter 2 Flashcards
(41 cards)
What is semiconservative replication?
when parental strands are used as template for synthesis of a new complementary strand
What are the properties of bacterial replication?
- single origin of replication
- bidirectional process –> two identical circular molecules of DNA
What are the properties of eukaryotic replication?
- multiple origins of replication
- bidirectional replication produces two identical linear mocelcules of dsDNA (sister chromatides)– in nucleas during S phase
What is a polymerase?
enzyme that synthesizes nucleic acids by forming a phosphodiester bond (PDE)
What is a nuclease? What are the two types?
enzymes that hydrolyze PDE bonds
- exonuclease: remove nucleotides from 5’ or 3’ end
- endonucleases: cut within the nucleic aicd and release nucleic acid fragments
What are the two types of exonucleases?
- 3’ exonuclease: proofreading of DNA polymerase, S phase
- 5’ exonuclease = removes RNA primer, S phase
What is the difference between DNA and RNA synthesis?
- DNA polymerase binds to RNA primer (laid down by primase)
RNA doesn’t require a primer
- DNA uses dNTP nto dNMP as substrate (PPi released)
RNA uses NTP as substrate (PPi released)
- DNA polymerases proofread (3’–>5’ exonuclease) = high fidelity
RNA polymerase doesn’t proofread = low fidelity
- DNA contains thymine
RNA contains uracil
What are the similarities of DNA and RNA synthesis?
- DNA and RNA polymerase read template 3’–>5’
- DNA and RNA synthesized 5’–>3’
- newly synthesized strand is complementary and antiparallel to template strand
- Pyrophosphate (PPi) released during reaction
Steps of DNA replication.
- base sequence of origin of replication recognized
- helicase breaks hydrogen bonds
- single-stranded DNA binding protein (SSB) prevents strands from reassociating and protects them from degredation
- primase makes short RNA primer
- DNA polymerase III syntehsizes DNA (leading strand v. lagging strand and Okazaki fragments)
- RNA primers removed by RNAase H and DNA polymerase fills the gaps
(in prokaryotes, DNA polymerase I removes primer (5’ exonuclease) and makes new DNA
- DNA ligase seals nicks between Okazaki fragments
- DNA gyrase (DNA topoisomerase II) inserts negative supercoils
What does DNA topoisomerase II do?
removes positive supercoils ahead of advancing replication forks
Work in G1 cells
What drugs block the action of topoisomerases?
Quinolones, Fluoroquinolones: most active against aerobic gram-negative bacteria
ex. Nalidixic acid: kills bacteria by inhibiting DNA gyrase
Levofloxacin, Ciprofloxacin, Moxifloxacin
Treats: gonorrhea, upper and lower urinary tract infections
Why don’t drugs that inhibit prokaryotic topoisomerase II (gyrase) also inhibit eukaryotic topoisomerase II?
these enzymes have the same catalytic properties but different biochemistry
What drug inhibits eukaryotic topoisomerase II?
Etoposide, teniposide: antineoplastic
Anticancer agents
What are the side effects and why?
Don’t affect most cells becuase they are in G0 phase
Cells that are in G1 phase acted on and lead to side effects
Ex. Hair loss, digestive problems
What are telomeres?
repetitive sequences at the ends of linear DNA molecules in eukarytoic chromsomes
shortened with each round of replication (aging of cells)
What is a telomerase?
enzyme that maintains telomeres
short RNA template complementary to DNA telomere sequence and telomerase reverse transcriptase activity
Where are telomerases present?
embryonic cells, fetal cells, cetain adult stem cells
not present in adult somatic cells
cancer cells–contributing to unlimited replication
What is the action of the HIV drug AZT?
incorporated into DNA and causes chain termination
HIV has reverse transcriptase that is DNA polymerase but doesn’t have proofreading activity
What are the side effects of AZT?
AZT inhibits reverse transcriptase activity of HIV but also reverse transcriptase activity of telomerase in G1 stage cells
Which cells have increase telomerase activity?
Cancer cells, normal embryonic cells
What is a disease with decreased telomerase activity
**Progeria **
Rapid aging in children
What are the tumor suppressor genes?
p53, ATM, BRCA 1 and 2 and Rb
What is the action of p53?
encodes a protein that prevents cell with damaged DNA from entering S phase
What is Li Fraumeni syndrome?
inactivation or deletion of p53
causes many solid tumors
