Tertiary Structure of DNA Flashcards
Where is the DNA double helix stored? (for prokaryotes and eukaryotes)
The DNA double helix is packaged into different chromosomes.
In prokaryotes these are often closed, circular stretches of DNA
In eukaryotes, these are more often linear stretches of DNA.
How is DNA compacted into chromosomes?
Through being in the tertiary structure.
What is the length of an E.coli chromosome (in linear form) relative to the length of an E.coli cell?
1.7mm chromsome relative to a cell which is 2 microns.
What is the first stage of DNA compaction?
DNA supercoiling.
Why does DNA need compacting?
Because DNA molecules tend to be very large and have to packed into a very small volume (eg. eukaryotic nucleus).
What is DNA supercoiling?
When the axis of the DNA double helix is coiled in on itself and forms a new helix, superhelix normally called a super coil.
How is supercoiling induced?
By the seperation of the two DNA strands the strain caused this results in supercoiling.
What structures can supercoiling occur in?
Only in closed structures - bacterial chromosomes and plasmids are circular so therefore closed.
Eukaryotic DNA are also closed as they form loops and their ends are held together by proteins.
What does an greater number of supercoils cause?
Increased torsion
What would cause a untwisting to release supercoils?
A break in either of the strands.
What is an open or closed molecule with no supercoils called?
Relaxed.
What are the two ways DNA can be supercoiled?
Negatively and positvely
Which way is most naturally occurring DNA supercoiled?
Negatively.
What is negatively supercoiled DNA said to be?
Underwound
Which way does negatively supercoiling twist DNA?
In the opposite direction to the turns of a right handed helix.
