DNA replication Flashcards
Why is DNA a unique molecule?
Because it can reproduce itself exactly
When does replication of DNA take place?
Before mitosis
What does replication ensure?
That each daughter cell has a full chromosome complement
What is the first stage of DNA replication?
Hydrogen bonds between vase pairs break allowing the two strands to separate (unwind and unzip). This is controlled by an enzyme. The bases are now exposed at a Y-shaped replication fork.
What is the second stage of DNA replication?
The DNA nucleotides bind (by hydrogen bonds) to their complementary partners of the template strand at the 3’ end
What is the third stage of DNA replication?
The enzyme DNA polymerase beings about the formation of sugar-phosphate bonds between the nucleotides
What are the limitations of DNA polymerase?
It can only add nucleotides to a pre-existing chain (where there is a primer). Primers are replaced by DNA in the final new DNA strand
What is a primer?
A short series of nucleotides at the 3’ end of the parental DNA to be replicated.
What direction does synthesis occur?
Occurs in a 5’ to 3’ direction on the new strand
What are the two strands in DNA replication called?
Leading and lagging strands
What can the replication of the leading strand be described as?
Continuous
What can the replication of the lagging strand be described as?
Discontinuous
Why is the synthesis of DNA on the lagging strand discontinuous?
Because DNA polymerase can only add nucleotides to the 3’ end of a growing strand (the lagging strand starts on a 5’ end)
How must the lagging strand be replicated?
In fragments each starting at the 3’ end of a primer
What are the fragments in the lagging strand called?
Okazaki fragments
