DNA Replication Flashcards
Give the two transfer of genetic information
- inheritance (via copied DNA) = replication
- expression (via RNA) = transcription
Give information on DNA replication
The mechanism by which DNA makes a copy of itself during cell division and proof reads it to maintain fidelity.
An exact copy of DS (double stranded) DNA is made during DNA replication.
Takes place in specialised regions of the cell.
Is a result of the interaction of many proteins.
The proteins involved are usually clustered together in the nucleus of a cell and we can think of this cluster as a replication factory.
In a factory, DNA strands are copied.
DNA replication
What happens during mitosis?
Why is DNA replication need prior to division?
What phase takes replication take place?
- Cells mitosis and meiosis, cells divide to form two daughter cells and each daughter cells need its own copy of the DNA
- Needed to that each of the dividing will receive a genome
- S phase
Give information on semi-conservative replication
DS DNA unwinds (DNA helicase enzyme).
Each strand of the original DS DNA molecule serves as a template for a new strand.
An exact copy of the parent molecule is made.
The new strands are called daughter cells.
Half of the strands will be the original strands and one parental strand
Explain the concept of the replication factory
The DNA template is passed through the proteins of the replication factory.
The DS DNA first has to be split into single strands. This requires the hydrogen bonds between the two strands to break.
Both of the strands now act a template for new strands.
Each of the template strands is copied and becomes half of the new DS DNA.
Explain how DNA polymerase works
DNA polymerase synthesises DNA.
In 5’-3’ direction.
Adds complementary dNTP’s to the 3’ position of the sugar-phosphate backbone.
Synthesis of DNA by incorporation. of dNTPs results in the release of pyrophosphate.
Numerous proteins are needed before DNA polymerase can copy DNA.
DNA polymerase cannot start a new strand by can extend the strand.
There are 8 main proteins in DNA replication. Try to name them and give brief detail
- Helicase - 6 proteins arranged in a ring which unwinds the DNA into 2 individual strands
- Topoisomerase - releases supercoils in DNA
- Single stranded binding proteins - tetramers which bind to the SS DNA so they can no longer anneal back together
- Primase - an RNA polymerase which makes short RNA primers
- DNA polymerase III - claw shaped enzyme that copies DNA 5’ to 3’
- The sliding clamp - helps the DNA polymerase hold onto the strand while it is copying
- RNaseH - removes the RNA polymers
- DNA ligase - links the strands together (phosphodiester bond)
What must happen for the 2 parental strands to be replicated?
They must be serrated in a small region called the ‘origin of replication’. Replication proceeds in a biodirectional manner from here.
How many regions of origin in bacteria? eukaryotes?
What types of DNA replicate differently?
Bacteria - one unique site of replication but eukaryotes have more than one.
Circular and linear DNA
What unwinds the DNA at the replication fork?
What coats the DNA to prevent is annealing back?
What will be the feature of the two strands which have unwound?
Helicase
Single stranded binding proteins
Antiparallel to each other, complementary
What does DNA polymerase need to start copying?
Explain this
DNA-RNA hybrid
A primer is a short nucleic acid sequence that provided a starting point for DNA synthesis.
The enzyme primase synthesises short RNA primers, about 10 bases, which bind to DNA and form a short DS DNA:RNA hybrid.
After DNA synthesis, the RNA primers are removed.
What is a problem with DNA replication?
DNA polymerase can only synthesise DNA in the 5’ to 3’ direction.
Explain the idea of discontinous replication
One strand is replicated continuously.
The other strand is replicated discontinuously i.e. in short fragments which are then ligated later on.
What old and new strands are in a leading strand?
A lagging strand?
Leading = old 3’, new 5’
Lagging = old 5’, new 3’
Why are gaps left in the lagging strand?
How are these gaps removed?
Replication is in the opposite direction to DNA polymerase movement.
DNA is synthesised in segments on the lagging strand.
RNA primers sit between the fragments, DNA polymerase 1 removes the RNA primers and DNA ligase forms the missing phosphodiester bonds.
