Manipulating genomes 6.3 Flashcards
Define DNA sequencing
DNA sequencing = a technique that allows genes to be isolated and read
What did Fred Sanger do?
Fred Sanger developed a method that allowed scientists to sequence whole genomes through chain termination
What was the proc and cons of fred sangers method?
DNA sequencing by chain termination
- safe
- efficient
- time consuming
- expensive
What was the first step of chain termination?
DNA sequencing by chain termination
1.Single strand of DNA used.
4 dishes which contained a solution of A, T, C, G, DNA polymerase and a primer
What was the second step of chain termination?
DNA sequencing by chain termination
2. modified DNA base labelled with radioactive isotope was added to the dishes. The base was modified so that once incorporated into the synthesis complementary strand of DNA, no more bases can be added. Chain stops
What was the third step of chain termination?
DNA sequencing by chain termination
3.DNA fragments of varying lengths produced and passed through a gel by electrophoresis. Smaller fragments travel further so fragments get sorted by length
What was the fourth step of chain termination?
DNA sequencing by chain termination
4. nucleotide base at the end of each fragment was read and you can then work out the base on the complimentary strand
How do you separate DNA into single strands?
DNA is separated into single strands through constant heating
Why is a primer needed in chain termination?
Primer is needed so that the DNA polymerase has something to bind to so that it can work
How is DNA cloned?
Cloning DNA:
- gene isolated using restriction enzymes from bacterium
- DNA inserted into a bacterial plasmid (vector)
- plasmid inserted into E.coli bacterium host
- E.coli cultured + divides
- lengths of dna isolated using plasmid prePRTION
- DNA sequenced
describe the first DNA sewurncing machine
First DNA sequencing machine:
- 1986
- used fluroscent dyes instead of radioactive isotopes
- scanned by laser beam
- light signature identified by a computer
- meant technicians didn’t need to waste time reading autoradiograms
What is pyrosequencing?
Pyrosequencing reads the chain of DNA as you go along using one nucleotide at a time (instead of all at once in chain termination) I involves synthesising a ingle strand of DNA one base at a time and detecting light emission
What are the basic stages of pyrosequencing?
Pyrosequencing:
- nubuliser cuts long DNA into fragments
- degraded to single strand DNA, act as template DNA which are immoiblised
- sequencing primer added and DNA incubated with 4 enzymes and 2 substrates
- one of the 4 activated nucleotide added at a time
- any light is detected by a camera
Discuss light emissions from pyrosequencing
Pyrosequencing: amount of light detected is proportional to the amount of ATP available and therefore how many of the nucleotides incorporated successfully
- light = complimentary activated nucleotide has joined
- no light = no activated nucleotides have joined
In the third stage of pyrosequencing what enzymes and substrates are added?
Pyrosequencing:
3. DNA incubated with enzymes DNA polymerase, ATP sulfurylase, luciferase and apyrase and the substartes; adenosine 5’ phosphosulfate (aps) and luciferin
What does activated nucleotide mean?
Activated nucleotides have been phosphorylated, they have 2 phosphates joined on to them (e.g. TTP). When they join they release the 2 phophoryls pyrophosphate which gets converted to ATP
What happens to unincorporated activated nucleotides?
Unincorporated activated nucleotides are degraded by apyrase
Describe in detail the fourth step of pyrosequencing
Pyrosequencing:
- (a) Activated nucleotide is incorporated into a complimentary strand of DNA, using the strand to be sequenced as a template.
(b) The 2 phosphoryls are released as pyrophosphate
(c) In the presence of APS ATP sulfurylase converts the pyrophosphate to ATP
(d) In the presence of ATP luciferase converts luciferin to oxyluciferin which generates visible light which is detected by a camera
What is the amount of light generated proportional to in pyrosequencing?
In pyrosequencing the amount of light generated is proportional to the amount of ATP available and therefore indicates how many of the same type of activated nucleotide were incorporated adjacently into the complimentary DNA strand
What are all of the activated nucleotides?
Activated nucleotides:
GTP, CTP. ATP, TTP
What is the shorthand for single stranded DNA?
Single stranded DNA = ssDNA
What is a pro of pyrosequencing?
Pyrosequencing is cheap and fast
What is bioinformarics?
Bioinformatics is a bracnh of biology and its how the massive amounts of data generated from DNA sequencing is stored. It would have been impossible to store and analyse this data prior to the computers and microchips.
What is electrophoresis?
Electrophoresis is the process used to spearate proteins or DNA fragaments of differwent sizes for identification and analysis
How is DNA digested before electrophoresis? Conditions?
DNA gets digested with restriction enzymes at special recognition sites into fragments. This is done at 35-40 degrees celcius and takes up to an hour
How is the tank for electrophoresis set up?
The tank has agarose gel poured into the centre and combs are placed at one end t create wells
What covers the agarose gel in electrophoresis?
Buffer solution is added to cover the agarose gel and end sections
What is added to the digested DNA in electrophoresis? Then whats done with it?
Loading dye is added to the digested DNA and this solution is hen pipetted into the buffer solution above the wells, then dense dye will carry the DNA into the wells
What voltage is the electrodes using and for how long? variation?
The electrodes are put into place and connected to a 18V battery for 6-8 hours. OR you use a higher voltage and leave for less that two hours
What is the overall charge of DNA and how does this affect electrophoresis?
The overall charge of DNA is negative due to the phosphate groups. So the DNA will move toward the anode (positive) and away from the cathode (negative)
What are the final two stages of electrophoresis? (how its actually separated)
DNA fragments move through gel at different speeds, smaller fragments go faster.
The buffer solution gets poured away and dye is added to the gel. The dye adheres to DNA and stains the fragments
Whats the difference between anodes and cathodes?
Anodes are positively charged
Cathodes are negatively charged
Very briefly outline electrophoresis
Electrophoresis
- digested with restriction enzymes
- tank set up
- loading dye added to DNA and pipette into buffer
- Electrodes put into place 18V
- DNA is negative and fragments different speeds
- remove buffer solution
- dye added to gel to adhere to fragments
In general what is the charge on proteins?
Proteins do not have the same charge all over but different areas of charge
Why is Sodium Dodecyl sulfate used for electrophoresis of proteins?
sodium dodecyl sulfate is used to equalise the surface charge of proteins as they do not have the same charge all over and denature them
What does sodium dodecyl sulfate allow the proteins to do?
Adding sodium dodecyl sulfate (equalizes surface charge) allows the proteins to separate by molecular mass as they move through the gel. Then they can move to the anode
How can proteins be separated without using sodium dodecyl sulfate?
Proteins can also be separated according to mass and then surface charge
How does electrophoresis of proteins and DNA differ?
DNA uses restriction enzymes to cut it up
Proteins use sodium dodecyl sulfate to equalize and denature them so they can move and separate
What is electrophroesis of proteins used for?
Electrophoresis of proteins is used for analysing different types of haemoglobin proteins for diagnosing:
-sickle cell anaemia (have Hb S not Hb A)
- aplastic anaemia
- thalassaemia (more fetal Hb, less normal)
- leukaemia
What is a DNA probe?
A DNA probe is a short single stranded DNA length that is complimentary to a section of DNA being investigated
What are DNA useful fro/
DNA probes are useful for locating specific gene sequences
Why do DNA probes need to locate specific gene sequences?
Locating DNA sequences for :
- locating gene needed for genetic engineering
- identify the same gene in a variety of genomes from different species when doing genome comparison studies
- Identify presence or absence of a specific allele for a particular genetic disease/susceptibility for condition
What can the DNA probe be labelled with? How can these labels be seen?
The DNA probe labeling:
- Fluorescent marker that emits a colour on exposure to UV light
- Radioactive marker. P32 in one of the phosphate groups in the probe strand. Once annealed by complimentary base pairing to the DNA this can be exposed by photographic film
What is a micro array?
Micro array is a number of probes that are specific to sequences found in mutated alles that cause genetic disease on a fixed surface