BIO 1140 Lecture Notes - Lecture 30: Dna Ligase, Dna Supercoil, Primase

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Mon, March 21-Lecture 19 DNA replication part 1
Slide 8
How often does replication occur? Depending on the cell, sometimes all the time or sometimes
NEVER. How often does transcription occur? All the time.
Slide 9
They didn't have any data in terms of the distance between each ring of the DNA. Like a winding
staircase, going from one step to the next (how much distance between each step). Until they got
Rosalind Franklin's data (saw it without her knowing), gave them actually measurements, data,
and size. All of a sudden the structure was solved. There is only one possible arrangement. She
shot x-ray beams at DNA, had a defraction pattern.
Slide 11
On the sugar, each Carbon is numbered. The 5th carbon outside the ring still counts. Phosphate is
attached to 5th carbon. The nitrogenous base is bound to the 1st carbon. The hydroxyl group is
essential, only place in can bring in an additional nucleotide. This is why elongation is
ALWAYS 5' to 3'. Same thing for RNA, difference is only one strand.
Slide 12
In each eukaryotic cell, must fit all DNA into a nucleus. Millions or billions of base pairs (2m
long) into a nucleus 6um in diameter.
Slide 12
How to organize it? Accessibility, fit it into the space. Use proteins called histomes, wrap the
DNA around the histories, 1st level of saving space. This structure is a nucleosome, leave a little
bit of space (linker). Then take two nucleosomes and wrap them together. Can then fit lots into a
small space, but have them still be easily accessible. Solenoid is multiple nucleosomes wrapped
together.
Slide 13
Cell division- whenever you divide a cell, the end product is exactly the same. Splitting the
membrane isn't complicated, organelles aren't much of a problem. DNA- must make a copy.
Replication happens BEFORE mitosis- must happen adequately so that you have an exact copy
when you go through mitosis.
Slide 16
Watson and Crick actually predicted that it was semi-conservative, but this experiment proved it
years later. Nitrogen because the nitrogenous bases all contain nitrogen, ensures that any
difference observed isn't due to a difference in amounts of nitrogen in each base (they all have
the same amount of N). Can track using centrifugation. The conservative model could
technically work, but that is a lot of management of this large molecule inside the nucleus. This
experiment demonstrates that this doesn't actually work. Understand and explain this
experiment*
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