2.2 DNA replication Flashcards
When does DNA replication start and what is it?
In interphase more specifically S phase
It is the DNA replicating to provide a copy for the new cells
What is semi conservative replication
In the daughter DNA one strand is from the parental DNA and one strand is newly synthesised
(daughter DNA is the dna created and parental DNA is the original DNA )
Why is it important for the nitrogenous bases to be complimentary?
Enables identical copes of DNA to be created and reduce copying errors which could lead to mutations
Name the two enzymes affiliated in DNA replication
DNA helicase and DNA polymerase
What does DNA helicase do
Breaks the hydrogen bonds between the nitrogenou bases to unwind the double helix
What is the role of DNA polymerase
To join adjacent nucleotides together to make the new strand via condensation reactions
Describe the process of semi-conseravtive DNA replication. (7)
- DNA helicase breaks the hydrogen bonds between the two DNA strands and the DNA helix unwinds
- Each strand acts as a template for a new strand
- Individual free DNA nucleotides join up along the template strand by complementary base pairings
- DNA polymerase joins the individual nucleotides together, so that the sugar-phosphate backbone forms
- Hydrogen bonds them form between the bases on each strand and the strand twist to form a double-helix
- Two identical DNA molecules are produced
- Each of the new molecules contains a single strand from the original DNA molecule and a single new strand
Who discovered the structure of DNA
Watson and Crick
They hypothesied that DNA must replicate either conservatively or semi conservatively
Along with the help of Rosalind Franklin
What was their first hypothesis
That DNA was replicated semi conservatively-Each replicated DNA molecule contains one of the original DNA strands strand and one newly synthesied DNA strand
What was the second hypothesis
That DNA was replicated conservatively-The original DNA remains intact following DNA replication and the two newly synthesised strands of DNA join together
What are the three experimental background information
- DNA bases are nitrogenous
- Nitrogen has two isotopes N14 and N15
- Bacteria take in the nitrogen isotopes to make new DNA nucelotides
How would you determine which DNA sample has Isotope N15 or N14
Spin the sample in a centrifuge to determine thier density
N15 will settle lower down as it is more dense
N14 will settle high as it is more less dense
C-ATOM ARRANGEMENT IN PENTOSE SUGAR MOLECULES
C-atoms numbered after oxygen clockwise. Carbon-5 is outside pentose molecule.
Carbon 3 has hydroxyl (OH) group attached.
Carbon 5 has phosphate group attached.
As the strands are antiparallel, One strand runs 3’to 5’
(ends with phosphate group) and one goes
5’ to 3’ (ends with hydroxyl group)
DNA REPLICATION ENZYMES
DNA HELICASE - unzipping, breaks hydrogen bonds to separate the polynucleotide strands.
DNA POLYMERASE - join together adjacent nucleotide.
DNA PRIMASE - catalyze the synthesis of short RNA molecules used as primers for DNA polymerases.
DNA LIGASE - joins DNA fragments together.
STAGES OF SEMI-CONSERVATIVE DNA REPLICATION
DNA helicase attaches to molecule, breaks hydrogen bonds between bases on parental DNA . 2 strands unwind from each other and separate. Each strand is a template for new strand.
Free activated DNA nucleotides (3 phosphate groups) attach to complementary exposed base pairs from original strand. Only held by hydrogen bonds between nucleotides.
DNA polymerase catalyses condensation reactions (loss of water) so that a phosphodiester bond can form between the activated adjacent nucleotides to form a new polynucleotide chain/sugar-phosphate backbone. Activated nucleotides lose 2 of their phosphate groups which leave and provide energy for the reaction.
Now have 2 sets of daughter DNA each with one strand of original DNA and one newly synthesised strand.
