Nucleic Acid Structure- Alternate Forms + Properties Flashcards
what form is the common double helix DNA
B form
what are the features of B form DNA
right handed helix, major and minor grooves are visible, bases project inwards from backbone and are perpendicular to it
10.5 bp per turn of helix
distance between each bp is fixed- approx 0.332nm
when might A form of DNA arise
reduced relative humidity and certain purine stretches around the helix
characteristics of A-DNA
right handed helix width 2.3nm (much wider than B-DNA)
wider and more compressed than B-DNA
BP are tilted from the axis
helix often formed from a DNA-RNA hybrid
when might Z-DNA form
when alternating pyrimidine-purine occurs
characteristics of Z-DNA
left handed helix, 1.8 nm. 12 bp per turn
is DNA more stable than RNA + why/why not
DNA more stable- double helix, hydrophobic nature
how does acid effect nucleotides
strong acid with an elevated temp 100 degrees nucleic acids are hydrolysed completely (broken to H, C, N etc)
dilute acid pH 3-4= glycosidic bond between purine and sugar breaks leaving an apurinic site
effect of alkali on nucleotides
DNA: tautomeric shift (change in environment = base pairs breaking down + DNA strands pull apart) affects hydrogen bonding so DNA breaks down and becomes denatured
RNA: denaturation of helical areas- RNA hydrolysis
what is the effect of temperature on DNA
when heated the two strands denature (come apart)
how is strand separation measured in a melting curve analysis
measured by the absorbance of the DNA solution at 260nm
what does hyperchromic shift mean
an increase in the absorbance, happens when the DNA strands pull apart
what other ways are there to denature DNA
organic solvents, high pH or a low salt conc
how might DNA be renatured
temperature 25 degrees lower than the melting temperature, DNA conc (higher conc = faster annealing) and time ( longer = more annealing)
what is hybridisation
putting two strands from diff nucleic acid together
