A fork copies 12000 base pairs of a chromosome…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A fork copies base pairs of a chromosome. The lagging strand is made as Okazaki fragments. Assume that all the fragments are the same length.
- In a bacterium the fragments have nucleotides. How many fragments are there?
- How many joints does DNA ligase make in the bacterium?
- In a eukaryote the fragments have nucleotides. How many fragments are there?
Need a reminder? The key ideaShow
A DNA polymerase adds nucleotides only to a 3′ end, so a new strand grows 5′ to 3′. The leading strand is made in one piece. The lagging strand is made as Okazaki fragments, which DNA ligase joins. An origin starts two forks, and the copying takes .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Length nucleotides on the lagging strand, fragments of or nucleotides.
Plan. Divide, then take one away for the joints.
Step 1. (a) fragments.
Step 2. (b) Neighbouring fragments are joined, so there are joints.
Step 3. (c) fragments.
Answer: fragments; joints; fragments.
Check. The eukaryote has five times as many fragments as the bacterium, because its fragments are five times as short.
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