2.7 (and part of 7.1) DNA Replication Flashcards
State the function of DNA replication.
To create two identical copies of genetic material for a newly created sister cell.
In what way is DNA replication semi-conservative?
DNA is semi-conservative in that each new strand of DNA contains one of the helices from its parent strand and one newly created strand.
Describe DNA helicase’s structure. State its function.
- 6 globular polypeptides arranged in a donut shape
- Act as an enzyme in unwinding and unzipping the DNA double helix by breaking the hydrogen bonds between bases
What is the role of DNA polymerase in replication?
- DNA polymerase brings free nucleotides into the position where hydrogen bonds could form and, if it is complementary to the strand, the nucleotide binds.
- Once this occurs, DNA polymerase links it to the end of the new strand by covalent bonds between the nucleotides.
In what direction does DNA polymerase add nucleotides?
5’ terminal of the free nucleotide to the 3’ terminal of the existing strand
Why is prokaryotic DNA considered to be naked?
Because, unlike in eukaryotes, it is not associated with histones, which are used to supercoil DNA.
Explain supercoiling of the DNA making reference to histones, nucleosomes, and octamers.
Histone proteins package DNA into nucleosomes, which consist of a core of 8 histones, an octamer, with DNA coiled around them. A short ‘linker’ or ‘spacer’ DNA connects one nucleosome to another. An additional histone, called H1, binds DNA to the octamer.
Why is supercoiling necessary?
- Allows significant lengths of DNA to be greatly compacted, reducing the space needed to house the same amount of DNA.
- Facilitates the packaging of the large genomes that eukaryotes possess.
Distinguish between the leading and lagging strand.
- The leading strand is made continuously following the fork as it opens.
- The lagging strand is made in fragments, moving away from the replication fork.
What is the role of DNA helicase in DNA replication?
Unwinds and separates DNA strands.
What is the role of DNA polymerase in DNA replication?
Links nucleotides together to form a new strand which matches a pre-existing one with covalent bonds.
What is the role of RNA primase in DNA replication?
Adds RNA primers to the parent strands for DNA polymerase to bind to.
What is the role of DNA topoisomerase in DNA replication?
Releases the strain that develops ahead of helicase.
What is the role of DNA ligase in DNA replication?
Connects the gaps between fragments.
Explain the process of DNA replication on the lagging strand, with reference to DNA helicase, RNA primase, primers, DNA polymerase, Okazaki fragments, DNA topoisomerase, and DNA ligase.
- Helicase unwinds and separates the strands of DNA. DNA topoisomerase releases the strain that develops ahead of the helicase. Single-stranded binding proteins keep the strands apart long enough for the template strand to be copied.
- RNA primase creates an RNA primer on the leading strand and many on the lagging strand, which activates DNA polymerase.
- DNA polymerase binds to the primer and and begins adding free nucleotides to the new strand.
- DNA polymerase removes the RNA primers by replacing uracil with thymine.
- DNA ligase then binds together the Okazaki fragments with covalent bonds.
