7.1 DNA Structure and Replication Flashcards
What was concluded from the X-ray diffraction by Franklin and Wilkins?
the DNA forms a helix, the DNA twists every so and so often, DNA is double stranded, phosphate is outside
What are the enzymes in DNA replication?
Helicase, Gyrase, Primase, DNA polymerase III, DNA polymerase I, Ligase
What does Helicase do?
Unwinds the DNA and breaks the hydrogen bonds between the bases, separating the 2 strands
What does Gyrase do?
Relieves strains during uncoiling
What does primase do?
It adds RNA primers to the 3’ end of the DNA, because DNA polymerase III cannot add nucleotides without a primer. (the 3’ DNA end, is the 5’ end of the new strand)
What does DNA polymerase III do? In which direction?
Adds nucleotides in a 5’ to 3’ direction
What does DNA polymerase I do? And what does ligase do?
It replaces the RNA primers with nucleotides. Ligase ensures solid bonding between the nucleotides.
In which direction does DNA replication occur?
Primers bind to the 3’ end of the DNA, making the 5’ end of the new strand. The new nucleotides thus bind to the 3’ end end of the primer, and still go from 5’ to 3’.
What is the difference between the 2 strands of the replication fork?
There is a leading strand, on which the synthesis is continuous, and there is a lagging strand on which the synthesis is not continuous. On the lagging strand, the individual small strands of new DNA are called Okazaki fragments.
What is DNA sequencing?
the base sequence of the DNA is elucidated
What is special about Dideoxynucleotides (ddNTPs)?
They are like the nitrogenous bases, except they cannot form the bond between the phosphate and the OH. There are specific ddNTPs that can replace each base. So when they are used as a nucleotide, they hinder the strand form getting more nucleotides.
What is the Sanger method?
Four PCR mixes are set up, each containing normal nucleotides + one ddNTP (ddA,ddG,ddC or ddT). The PCR will make all possible fragments, and by separating the strands with gel electrophoresis, the sequence is revealed.
How can short tandem repeats in satellite dna be used for dna profiling?
The satellite dna is extracted with restriction enzymes and then put in a gel electrophorasis. As the number of short tandem repeats varies greatly between people, it creates a DNA profile.
