DNA Replication
What model of DNA replication, confirmed by Meselson and Stahl, involves the double helix unwinding so that each old strand serves as a template?
The semi-conservative model
During DNA replication, which strand is synthesized continuously while the other is produced discontinuously as Okazaki fragments?
Leading strand and the Lagging strand
Which DNA repair pathway removes and replaces a single damaged base, such as a deaminated cytosine?
Base-excision repair (BER)
Responsible for the prevention of bond formation between ssDNA
SSB - Single stranded binding proteins
What primary enzyme adds new DNA nucleotides to the template strand and possesses a built-in 3'→5' proofreading ability?
DNA polymerase
In what specific direction must new DNA strands always be polymerized by DNA polymerases?
From 5' to 3'?
Responsible for creating short RNA Primers
Primase
What major repair pathway fixes bulky DNA lesions—such as thymine dimers caused by ultraviolet (UV) light—by removing a short single-stranded oligonucleotide patch?
Nucleotide-excision repair (NER)
Responsable for breaking down hydrogen in double stranded DNA
Helicase
What permanent changes to the DNA sequence would increase dramatically without DNA proofreading and repair mechanisms?
Mutations
The area in which DNA Replication begins
Origin of replication
At the ORI, fork movement goes in what direction?
Both directions
What enzyme seals the final nick in the sugar-phosphate backbone during various excision and ligation repair pathways?
DNA Ligase
What ring-shaped protein is locked around DNA by a clamp loader to keep DNA polymerase securely attached during elongation?
Sliding-clamp protein
What specific enzymatic activity removes a mismatched or incorrectly paired nucleotide right as it is added during replication?
3'→ 5' exonuclease activity
Specific enzyme responsible for relieving winding of single stranded DNA
Topoisomerase I
Why does DNA polymerase only synthesize in the 5' to 3' direction?
DNA Polymerase can only add a nucleotide to the OH- group on the 3' of the existing strand
What is the process that repairs complex DNA damage—specifically double-stranded breaks (DSBs) and single-stranded DNA gaps—using an undamaged homologous sequence as a template?
Homologous recombination (HR)
A component in DNA replication which contains an RNA sequence which helps the concluding of DNA replication
Telomerase
What cellular system scans newly synthesized DNA immediately after replication to fix errors that the DNA polymerase proofreading step missed?
Mismatch repair (MMR)
Essential enzyme that manages DNA tangles, supercoils, and chromosome separation by cutting both strands of the DNA double helix simultaneously
Topoisomerase II
Why are RNA primers used instead of DNA primers?
RNA primers are easier to identify and remove because DNA polymerase I can recognize and replace them with DNA. Additionally, DNA polymerases cannot begin DNA replication on their own, they require an RNA primer to provide a starting point.
What process repairs DNA double-strand breaks by directly ligating the broken ends together without needing a homologous template?
Non-Homologous End Joining (NHEJ)
Enzyme that has both 5' to 3' and 3' to 5' exonuclease activity
DNA Polymerase I
What is the approximate error rate per base pair of DNA replication without proofreading?
1 in every 100,000 base pairs