DLA #8: DNA Packaging Flashcards
Prokaryotic DNA is packaged into a
Nucleoide
What proteins and enzymes allow for Prok. DNA to be packaged into a nucleoide
1) HU proteins
2) DNA Topoisomerase-l
3) DNA Gyrase (Topoisomerase - ll)
Describe a nucleoide
HU proteins wrapped around with supercoiled prok. DNA
Negative supercoiling occurs in order to
Relieve torsional strain from underwond DNA
Positive supercoiling occurs in order to
Relieve strain form overwound DNA
What happens during DNA replication and transcription
Negative and Positive supercoiling.
Why is postive super coiling very bad during DNA replication/transcription
Can hinder its process
How does negative supercoiling affect DNA replication
It promotes strand seperation
Ciprofloxacin is
a drug that inhibits DNA gyrase
What does Topoisomerase-l do
- Makes a single covalent bond and w/ DNA and breaks the phosphodiester bond. Then it reattaches the phosphodiester bond after a rotation.
- Has exonuclease and ligase activity
What does DNA Gyrase (Topoisomerase II) do
Attaches covalently to both stands of a DNA helix, breaks the helix, and allows another helix to pass through.
Requires ATP
What is the function of telomerase
During DNA replication there is an interesting event at the lagging strand.
At the lagging stand, there is a 3’ overhang. (B/C we can’t place a primer)
We want to eliminate that overhang and form the telomere.
Telomerase extend the overhang at the leading stand in a 3’ to 5’ syntheis
The addition of an RNA primer is then added to the lagging stand to finish the synthesis of the lagging strand and form a complete telomere
******USING RNA AS A TEMPLATE TO SYNTHESIZE NEW DNA
What does DNA methylation do to the genome of DNA
Tags it for proteins to alter histones. Allows for formation of heterochromatin
Explain the steps of heterochromatin formation
1) Dnmt3 methylates DNA (cytosine)
2) MCP2 recruits HDAC1
3) HDAC1 Deacytlates histones
4) Heterochromatin is formed
