Chapter 1 - DNA replication Flashcards
When does DNA replication occur?
During interphase
What does the enzyme DNA helicase do?
DNA helicase breaks the hydrogen bonds between nitrogen bases, and separates the strands
What do single-strand binding proteins do?
- Binds to each strand of the separated DNA
- prevents from from rejoining (reannealing)
- Forms replication fork
Describe the replication fork
- Can be multiple replication forks
- Replication can happen in multiple place (speeds up process)
What are single strands after they have been fully separated?
Templated
What are the limitations of DNA polymerase?
- Needs a free 3’ OH end to start the replication process
- Can only replicate from 5’ to 3’ direction
What does RNA primase/primer do?
- Short sequence of RNA nucleotides called a primer
- Allows DNA polymerase to start the whole process
What does DNA polymerase do?
- Adds complementary nucleotides, starting at 3’ end of primer
- Sliding clamp helps to move
- At the end, goes back and checks nucleotides
What are each of the DNA strands called?
Leading strand and Lagging strand
Describe the leading strand
The leading strand replicates the DNA continuously
Describe the lagging strand
The lagging strand is synthesised discontinuously in chunks of nucleotides called Okazaki fragments.
Why does the lagging strand have to be built in Okazaki fragments?
Have to build in chunks because DNA polymerase only moves from 5’ to 3’
What does Nuclease do?
Removes primers and fills in the gaps with complementary nucleotides
What does DNA ligase do?
Joins the sections of DNA into a single long strand
Why is a DNA considered semi conservative?
Because it is made up of one original parental strand and one replicated strand
