DNA synthesis and repair Flashcards
What biological systems is DNA replication employed in?
To make new (identical) copies of chromosomes for cell division (Growth)
To help maintain continuity of genetic information (Reproduction)
Continuous surveillance of DNA and its repair
Define overwound
B-form DNA that has more than 10.4 base pairs per turn of the helix.
Define underwound
B-form DNA that has fewer than 10.4 base pairs per turn of the helix.
How does supercoiling Affect the structure of DNA?
Supercoiling occurs only in “closed” DNA with no free ends.
The coiling of a closed duplex DNA in space so that it crosses over its own axis.
What are the enzymes that are required for DNA replication?
DNA helicases - disruption of hydrogen bonds between the two strands and separate DNA by “unzipping” mechanism
Topoisomerase - elimination of all the topological links between the two strands and to facilitate unwinding (swivel motion)
Primase –synthesizes RNA primer to initiate DNA replication
DNA Polymerase – Synthesis of a new strand of DNA complementary to the template DNA
DNA Ligase – facilitates joining of DNA strands by the formation of phosphodiester bonds
When does DNA replication occur?
replication initiates when a protein complex binds to the origin and melts the DNA there
What is the process of Subcomplexes?
A clamp loader places the processivity subunits on DNA, where they form a circular clamp around the nucleic acid.
Β2-ring dimer makes the holoenzyme highly processive.
At least one catalytic core is associated with each template strand
What is required to start DNA synthesis?
Priming
What provides priming?
The priming end can be provided by an RNA primer, a nick in DNA, or a priming protein.
Define a Nuclease
Nucleases are enzymes that degrade nucleic acids; they include DNases and RNases and can be categorized as endonucleases or exonucleases.
Define Endonuclease
endonuclease cleaves a bond within a nucleic acid
Define Exonuclease
exonuclease removes bases one at a Mme by cleaving the last bond in a polynucleotide chain
What is the role of Helicase and single-strand binding protein
Replication requires a helicase to separate the strands of DNA using energy provided by hydrolysis of ATP
A single-stranded DNA binding protein is required to maintain the separated strands.
Priming of replication on double-stranded DNA always requires a helicase, SSB, and primase.
DnaB is the helicase that unwinds DNA for replication in E. coli. Lewin
Define replication forks
DNA polymerases make a copy of the DNA using one strand as a template
Ancillary Enzymes: DNA Gyrase cut and unwind the DNA (unravels supercoiling)
Explain Topoisomerase as a cancer target
Doxorubicin is a chemotherapy medication used to treat cancer which targets topoisomerases
As cancer cells are rapidly dividing, they are replicating their DNA and topoisomerases are needed
Therefore this drug affects the cancer cells more than the other cells of the body.
