DNA replication Flashcards
what is nuclear division?
the process by which the nucleus of a cell divides during cell division - mitosis and meiosis
what is cytokinesis?
the process by which the whole cell divides (after nuclear division).
before a nucleus divides, why must DNA be replicated?
to ensure that all daughter cells have the genetic information to produce the enzymes and the other proteins they need.
what is semi-conservative replication?
DNA replication whereby each new DNA molecule contains one of the original DNA strands.
what are the requirements for semi-conservative replication?
the four types of nucleotides with their different bases must be present (free nucleotides).
DNA molecule as template for attachment of free nucleotides.
the enzymes DNA helicase and polymerase
a source of chemical energy to drive the process.
what is the function of DNA Polymerase?
an enzyme that joins the free daughter nucleotides bound to the parent template strands by creating phosphodiester bonds between nucleotides.
what is the function of free DNA nucleotides in DNA replication?
to bind to a separated strand of parent DNA to form a new complementary strand of daughter DNA.
what is the function of DNA Helicase?
an enzyme that breaks the hydrogen bonds between the base pairs of a DNA double helix.
describe semi-conservative DNA replication
- enzyme DNA helicase - breaks hydrogen bonds of complimentary base pairs of parent DNA.
- double helix of parent DNA unwinds and separates into two strands.
- each exposed polynucleotide strand acts as a template to which complimentary free nucleotides bind by specific base pairing.
- nucleotides are joined in a condensation reaction by the enzyme DNA polymerase (phosphodiester bonds) to form the ‘missing’ strand, on each of the parent strands of DNA.
- half the parent DNA has been saved and built into each of the daughter DNA molecules.
describe the experiment that Meselson and Stahl carried out to confirm the semi-conservative method of DNA replication
Grow E. coli bacteria in 15N (heavy isotope), which is assimilated into its base pairs, causing it to have heavy DNA. Take a sample of this and ‘normal’ 14N grown E.coli
Allow ‘heavy DNA’ E. Coli to divide once in 14N growth medium and take a sample.
Allow E. Coli to divide once more in 14N growth medium and take another sample.
Remove DNA from each sample and perform gradient density centrifugation.
Check the mass of DNA present in each sample.
give 3 features of DNA and explain how each is important for semi conservative replication
- weak H bonds to allow unzipping of 2 strands
- CBP to allow for accurate replication
- Two strands so both can act as template
name the Scientists who confirmed that the Semi-conservative model of DNA replication was the valid model
Matthew Meselson
Franklin Stahl
