Lecture 12: DNA Replication Flashcards
In what direction is DNA synthesised?
In the 5’ to 3’ direction.
What direction does the parent strand of DNA run in?
The 3’ to 5’ direction.
What is an origin of replication?
A region on DNA where replication begins. This region is always A - T rich.
Name the structure that forms when hydrogen bonds between bases begin to break?
A replication bubble.
What is the area on either side of the replication bubble called.
The replication fork.
Why does the origin of replication occur in an A-T rich region?
Because A - T only has two hydrogen bonds whereas C - G has three hydrogen bonds. Therefore it is easier to start from here.
Describe why the process of DNA replication is semi-discontinuous.
This is because there is a continuously and discontinuously synthesised strand due to the nature of DNA Polymerase III. The new strand which runs 5’ - 3’ towards the replication fork is synthesised easily. As this is the direction enzyme polymerase III runs in. This stand is referred to as the leading strand and is synthesised continuously. The other stand which runs in 5’-3’ away from the replication fork must be synthesised differently. This strand is the lagging strand and is synthesised discontinuously. Because the strands are synthesised continuously and discontinuously the whole process is called semi discontinuous.
What is an okazaki fragment?
Fragments of nearly synthesised DNA in the lagging strand.
Draw and label the process of DNA replication.
Make sure all enzymes are included, labelled directions of fragments.
What is the purpose of enzyme helicase?
Helicase breaks the hydrogen bonds between complementary bases to ‘unzip,’ the DNA molecule.
In what direction can DNA Polymerase III work?
5’ to 3’ direction.
What is the role of DNA Primase?
Primase has an internal 3’ prime hydroxyl group which can start building a short set of nucleotides to serve as a starting point for DNA replication. Primase drops down an RNA Primer giving which is complementary to the strand parallel to it giving DNA polymerase a 3’ hydroxyl group to work off.
What is the role of DNA Polymerase I?
To remove all the RNA Primers (referred to as RNase activity) and fills the gap with nucleotides from the 3’ end of a neighbouring okazaki fragment.
What is the role of DNA Ligase?
DNA Ligase comes in and joins the okazaki fragments together via phosphodiester linkage.
What does Topoisomerase do?
Topoisomerase works ahead of helicase and unravels the DNA double helix into single strands so that helicase doesn’t end up pulling the strand tight.
