2.7 DNA -> Protein Flashcards
Why do we say DNA replication is semi-conservative?
One strand is from the original molecule and one is newly synthesised
Which enzymes are involved in the replication of DNA?
Helicase
DNA Polymerase
Who confirmed DNA replication was semi conservative and when?
Meselson-Stahl in 1958
Describe what a dispersive model of DNA would have meant?
New molecules were thought to be made of segments of old and new DNA
Describe what a conservative model of DNA would have meant?
An entirely new molecules is synthesised from an (unaltered) DNA template
How did Meselson and Stahl prove that DNA replication was semi-conservative?
DNA was prepared in heavy 15 N (nitrogen) and then allowed to replicate once in 14 N
After 1 replication they were found to contain a mix of 14 and 15 N and after 2 replications some showed only 14N or only 15 N
What disproved the conservative model?
That after 1 replication in N14, the DNA molecules contained a mix of N14 and N15
What disproved the dispersive model?
That after 2 replications in N14, some DNA molecules were only N14
What is the function of helicase?
Unwinds the double helix by breaking hydrogen bonds
What is the function of DNA polymerase?
Synthesises new strands by aligning complementary base partners
Where does the energy come from for DNA polymerase to add the bases?
The nucleotides are in triphosphate groups, the 2 extra phosphates are released, releasing energy to make link the nucleotide to the new strand
What does PCR stand for?
Polymerase Chain Reaction
What is the purpose of the PCR technique?
To amplify quantities of a specific sequence of DNA from an initial minute sample
By what scale factor does the amount of DNA in a PCR replicate in every cycle?
It doubles
Describe the steps of PCR
Denaturation
Annealing
Elongation
Describe the step of denaturation in PCR
DNA sample is heated to 90* to separate 2 strands
Describe the step of annealing in PCR
Sample is cooled (55*) to allow primers to anneal
Describe the step of elongation in PCR
Sample is heated to the optimal temperate for a heat-tolerant polymerase (Taq) to function (75*)
What is Taq polymerase
An enzyme used in PCR to extend the nucleotide chain from the primers so that they can be copied
What is the optimum temperature of taq polymerase?
75* C
Describe transcription
The process by which an RNA sequence is produced from a DNA template
Function of RNA polymerase
Separates the DNA strands and synthesises a complementary RNA copy from on of the strand
Why do the nucleotides involved in transcription have additional phosphate groups (ribonucleotide triphosphates)?
So that RNA polymerase can remove these phosphates to release the energy needed to covalently bond the nucleotides to the growing sequence
What is the direction of transcription?
5’ - 3’
