DNA replication Flashcards
What are the 2 main stages of cell division?
- Nuclear division- the process where the nucleus divides and there are 2 types -mitosis and meiosis.
- Cytokinesis - follows on from nuclear division and it’s the process where the whole cell divides.
What happens before cell division?
The DNA must be replicated to ensure that all the daughter cells have the genetic information to produce the enzymes and other proteins that they need.
What are the 4 requirements needed for semi-conservative replication to take place?
- The 4 organic bases - A, T, C, G must be present.
- Both strands of the DNA molecule act as a template for the attachment of these nucleotides.
- Enzyme DNA polymerase.
- Source of chemical energy is required.
What happens in the process of semi-conservative replication?
1) The enzyme DNA helicase breaks the hydrogen bonds formed between the bases.
2) So the double helix separates into its 2 strands and unwinds.
3) Each exposed polynucleotide strand then acts as a template to which complementary free nucleotides can come and bind by specific base pairing.
4) Nucleotides are joined together in a condensation reaction by enzyme DNA polymerase which forms a phosphodiester bond between adjacent DNA nucleotides, forming a new strand which pairs with the original strand.
5) Each of the new molecules will contain one strand from the parent molecule and one newly synthesised strand. So each new molecule has half of the original strand, therefore, it is named to be semi-conservative replication.
What is the conservative model?
It suggests that the original DNA molecule remained complete and a separate daughter DNA copy was built up from new molecules of deoxyribose, phosphate and organic bases. When the 2 molecules are produced, one would be made from completely new material and one would be from the total original material.
Name the part of the DNA molecule that contains nitrogen.
Nitrogenous bases.
How was the semi-conservative model tested?
Scientists got some bacteria and grew them in nitrogen containing medium.
They grew them in a heavy N15 medium, then transferred into a light N14 medium and evaluated the result after 2 generations.
The results showed that the parent strand has split into 2 daughter cells with half the strand containing N15 and half containing N14 then those 2 daughter cells produced the 2nd generation with 2 molecules with half N15 and half N14 while the other 2 molecules only containing N14.
This suggested that in DNA replication, the parent cells are split into 2 strands and then recombined.
Explain why, after one generation, all the DNA is made up of an equal mixture of N14 and N15?
Every DNA molecule consists of one heavy strand from the parent molecule and one new strand that is formed containing N14 so it creates a mixture with equal amounts.
