DNA & Replication Flashcards
Nucleoside
5C sugar bonded to a nitrogenous base
Nucleotide
Nucleoside + 1 to 3 phosphates attached
Which histone protein stabilizes the nucleosome?
H1
DNA coiled around histone protein
Nucleosome
DNA and its associated histones
Chromatin
Dense, transcriptionally silent DNA
Heterochromatin
Less dense, transcriptionally active DNA
Euchromatin
Telomeres contain a high content of what two nucleotides? Why?
GC, to prevent DNA from unraveling
How many origins of replication in Eukaryotes vs. Prokaryotes?
Euk - multiple per chromosome
Pro - one per chromosome
Enzyme responsible for unwinding DNA during replication
Helicase
Stabilize unwound template strands to prevent reannealing or degradation
SSB’s (single stranded binding proteins)
Enzyme responsible for the synthesis of short RNA primer in 5’ –> 3’ direction to start replication on each strand
Primase
Enzyme responsible for actual synthesis of new DNA strands
DNA Polymerase
What DNA pol is used in eukaryotes vs. prokaryotes?
Euk - DNA pol alpha, sigma, and epsilon
Pro- DNA pol III
What is the enzyme responsible for removing primers in prokaryotes, and what type of activity does it exhibit?
DNA polymerase I (5’ to 3’ exonuclease)
What is the enzyme responsible for removing RNA primers in eukaryotes, and what type of activity does it exhibit?
RNase H (5’ to 3’ exonuclease)
What polymerases fill in the gaps left behind when RNA primers are removed in eukaryotes and prokaryotes?
Euk - DNA pol sigma
Pro - DNA pol I
What enzyme is responsible for joining of Okazaki fragments?
DNA ligase
What enzyme is responsible for removal of positive supercoils ahead of advancing replication forks?
DNA topoisomerases (DNA gyrase)
Enzyme responsible for synthesis of telomeres?
Telomerase
Proto-oncogenes
name given to oncogenes before mutation
What kind of proteins do oncogenes primarily encode?
Cell-cycle related proteins
Name of genes that code for proteins that reduce cell cycling or promote DNA repair
Tumor suppressor genes
T/F: tumor suppressor genes can also lead to cancer
True
What enzyme is responsible for proofreading?
DNA polymerase
During proofreading activity, how does DNA polymerase discriminate between the parent and daughter strands?
By level of methylation: parent strand has existed for longer time period and thus is more heavily methylated
DNA composed of nucleotides from two different sources
Recombinant DNA
What is the name of the enzyme machinery (and the genes that encode these enzymes) in the G2 phase of cell cycle which detects and removes errors introduced in replication that were missed during S phase of cell cycle?
Mismatch repair
genes = MSH2 and MLH1 in eukaryotes
and MutS and MutL in prokaryotes
What kind of damage does UV light cause in DNA?
induces formation of dimers between Thymine residues which interferes with DNA replication and normal gene expression and disorts the DNA double helix
How is DNA damage induced by UV light repaired?
Nucleotide excision repair (NER) mechanism which uses an excision endonuclease along with DNA polymerase and DNA ligase to cut-and-patch Thymine dimers
Thermal energy absorption leads to what kind of DNA damage?
Cytosine deamination and conversion to Uracil
What kind of damage does base-excision repair fix and how?
Fixes nondeforming DNA lesions (such as cytosine deamination) by removing affected base & leaving behind an AP site which is recognized by an AP endonuclease that functions to remove and replace affected base
