FCELL- DNA synthesis Flashcards
describe DNA synthesis and its coordination with the cell cycle
replication origin is recognised by an initiation complex
DNA at the origin unwinds to form a replication bubble and allows access to the replication
DNA synthesis occurs in S phase
bacterial cells have less DNA so can divide quicker compared to mammalian cells
cell cycle - mitosis, G1 (cells prepare to replicate), S (synthesis), G2 (DNA and cells are prepared for condensation into chromosomes)
how is bacterial replication different to eukaryotic replication
in bacteria - chromosome is circular
single phase of replication
results in unwinding of parental strands to begin - generates a replication bubble - replication forks are generated when the parental strand unwinds - replication in bacteria is bidirectional
eukaryotic cells - DNA helix has multiple replication bubbles - over time replication forks move away from bubble making the bubble larger - results in the synthesis of two daughter strands
describe the properties of DNA polymerase to ensure DNA synthesis occurs with high fidelity
add nucleotides 3OH end of the growing DNA chain - meaning they can only work in 5’ - 3’ direction
helix = two strands copied differently
utilises A-T, C-G base pairing
requires a DNA template, primer, dNTP building blocks and Mg2+ ions
proof reading edition function
leading strand synthesis = continuous copying
lagging strand is synthesised in a discontinuous way - okazaki fragments
differentiate the different types of enzymes required for DNA replication
telomerase - synthesise DNA at the end of the chromosome
DNA polymerase Delta - lagging strand - needs primer - makes the DNA - nucleases ligase the okazaki fragments together
DNA polymerase alpha - lays the primer
DNA polymerase epsilon - copies leading strand
topoisomerase remove the supercoils ahead of the DNA replication forks
how does the failure to correct DNA synthesis errors lead to cancer
defects in mismatch repair genes are involved in cancer
incorrectly repaired nucleotides will become permanent
mutations after the next cell dicision - become established - cell no longer recognises them as an errors
incorrect DNA sequence will be used as a template for future DNA synthesis - leading to the error occurring in all future division
cells begin to accumulate mutations as they divide - if enough mutation accumulates = cancer
how is DNA synthesis an important target for chemotherapy
if you prevent DNA synthesis = no more cancerous DNA
what DNA synthesis inhibitors are used in bacteria
ciprofloxacin, levofloxacin, novobiocin
gyrase inhibitors
what DNA synthesis is important in antitumor therapy
etoposide
doxorubicin
mitoxantrone
these are topo II inhibitors
what DNA synthesis inhibitors are important in antiviral treatment
AZT and others
reverse transcriptase inhibitors
