3. section 6 stability of DNA Flashcards
what causes the stability of the DNA? (think about the bonding -4)
hydrogen bonding between base pairs (end to end)
hydrophobic and van der wells between bases (stacking)
what are the four ways DNA can be disrupted?
- reduced salt concentrations
- extremes of pH
- elevated temperature
- association of DNA with proteins
what are the effects of reduced salt concentrations to DNA double helix?
salt - Na+ which means a reductions causes the negative charge on phosphate backbone to no longer be neutralised.
falls apart with electrostatic repulsion
what are the effects of high or low pH to DNA?
changes the ionisation state of hydrogen bonding groups on bases (H+ added or removed)
(bonds to side chains of DNA)
what are the effects of elevated temperature to DNA?
high temperature = increased kinetic energy
therefore increase thermal motion which disrupts H bonds
how do proteins affect DNA?
transcription factors, ie DNA polymerase tear DNA apart (to transcribe)
why is there a hyperchromic shift for single stranded DNA at 260nm higher than double stranded DNA?
increased energy to melt single strands because the functional groups are exposed, whereas double strands have the double helix
why is the DNA melting curve higher for GC bases than AT?
GC bases have 3 hydrogen bonds
AT bases have 2
therefore GC requires more energy to break H bonds
what is the effects of dilute alkaline solution, eg NaOH added to a DNA double helix
dilute alkaline solution alters the H bond capacity of bases, resulting in strand seperation
similar to below image, meant to show strand seperation
how do proteins disrupt the double helix?
proteins bind to double stranded DNA by sequence specific interactions
H bonds are recognised on the groups in DNA
