Zusammenfassung der Ressource
DNA Separation Techniques
- Extraction
- Lysis
Anmerkungen:
- Cell lyses with Sodium dodecyl sulfate (detergent that disrupt membrane and denature proteins)
- Purification
Anmerkungen:
- 2 possible ways to do it.
Protein precipitation:
A high salt content solution is added to precipitate the protein due to the hydrophobic effect. Protein will be grouped together and after centrifuging, the supernatant will be the purified DNA.
Phenol/Chloroform:
3 layers will be form with DNA in the top layer.
- Test of Purity
Anmerkungen:
- A measure of how pure the supernatant is.
DNA/RNA absorb UV light best at 260nm while protein does best at 280nm.
A ratio (A260/A280) greater than 1.8 indicates that DNA/RNA sample is pure.
- Precipitation
Anmerkungen:
- Add organic solvent as DNA is a ionic compound (phosphate backbone is negatively charged)
DNA will precipitate after centrifuge.
Alternatively, just cool it down to extreme cold temperatures.
- Electrophoresis
Anmerkungen:
- Used to separate DNA or other molecules.
The bromophenolblue is used as a dye to "smear" plus glycerol makes it denser.
The process takes about 45 minutes.
Used ethidium or gel red and irradiated with UV light to see glow. In alternative, use a camera.
- Factors
Anmerkungen:
- Affected by size shape and charge.
Smaller molecules travel further
Compact molecules travel further
Negative charge travel further.
- Polymerase Chain Reaction
Anmerkungen:
- Exponential amplification of a defined sequence of DNA.
Visualized on the agarose gel.
Oligonucleotides provide the specificity for the reaction.
- Properties
Anmerkungen:
- a) Low pH: At low pH the purine (2 ringed, A,G) bases are released. Used in chemical sequencing of DNA
b)High pH: DNA is resistant and RNA will hydrolyse due to the extra OH side.
c) DNA is also very long and weak, quite susceptible to shearing.
d) DNA with higher G/C content is stronger than the one with A/T due to the extra hydrogen bonds
- Enzymatic Nucleases
Anmerkungen:
- Enzymes degrade nucleic acids with chemical specificity.
1. DNase or Rnase
2.DNase: Single stranded, Double stranded or both.
3. Either act on the end or in the strand itself.
- Exonucleases
Anmerkungen:
- Depending on the nuclease, it will chew off from one end and it will cleave one nucleoside at a time.
- Endonucleases
Anmerkungen:
- Cleave from within. Depends on the enzyme how to cut it will determine how it cleave
- Restriction Enzymes
Anmerkungen:
- Type II enzymes that act on unique genetic sequence, remember, read from 5' to 3'.
Some recognise 4 base pairs other recognise 6. Arrows indicate cleavage sites.
Needs to be palindromic.
- Applications
Anmerkungen:
- With usage of DNA ligase. We cans splice DNA into plasmids and put it into bacteria as recombinant bacteria.
- Organisation of DNA
Anmerkungen:
- Arranged in chromatin bacteria as a nucleosome core and it did it in a spiral.
In a eukaryotic cell it arranges in chromatids while bacteria it arranged in loops.