BIO282 Lecture Notes - Lecture 9: Dna Sequencing, Dideoxynucleotide, Chain Termination

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20 Jun 2018

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DNA SEQUENCING

Key points

• What are Primers, template DNA, deoxy and dideoxy- nucleotides?

• What is Sanger/chain termination method and how does it work?

• How does the automated dideoxy sequencing work?

• What are the Next Generation Sequencing Methods, how do they work?

• What are the Third Generation Sequencing Methods

DNA Sequencing

• DNA sequencing is a process that determines the precise order of bases in a piece of DNA.

• Major breakthrough came in 1977

• 1980 Nobel Prize: Sanger and Gilbert for DNA sequencing

• The Sanger method also known as a chain termination method

revolutionized DNA sequencing.

It was based on-

• Primer: a small oligonucleotide of a known sequence

• DNA polymerase: an enzyme that synthesizes DNA

• Dideoxynucleotides: to terminate DNA synthesis

DNA polymerase

In a presence of a template DNA, a primer and deoxynucleotides, DNA polymerase synthesizes

DNA by adding complementary bases at the end of the primer/growing chain.

Will add the next one but it can’t differentiate. The different colour show the different

things are added. Remember there are thousands of molecules available. At each

place there is an equal opportunity for them to be added. Either it can incorporate a

terminator or not.

DNA template

5`-ATGCGTGCGTACATACGCAATTCGAACTGCGCTAACGGCCTTGCG-3`

Primer

5`-CGCAAGGCCGTTAGCGCAG-3`

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• No OH group on the sugar

• If a ddNTP incorporates into a growing chain, it causes termination of DNA synthesis. Why?

o There is no OH group to form a phosphodiester bond between the 3' and 5' hydroxyl

Reactions are performed in 4 tubes each containing a template, a primer, all four dNTPs and a single

ddNTP

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• This method allows you to have different sized fragments

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Related Questions

Evaluation of PCR product electrophoresed on a 0.8% agarose gel shows non-specific bands. The appropriate modification for the next PCR reaction is toa )increase the concentration of Taq polymerase.b) increase the number of PCR cycles.c) decrease the template denaturation temperature.d) reduce the concentration of primers.In the Sanger sequencing method, chain termination is the result ofa)misincorporation of dUTP instead of dTTP.b)incorporation of ddGTP.c)secondary structures in the template strand.d)sequencing through repeats.The purpose of EDTA in a DNA storage buffer is toa)maintain single strands.b)bind magnesiumc)activate DNases.d)dissolve DNA into solution.The thermal cycler ramp refers to thea)degree of incline of the machine on the laboratory bench.b)gradient between denaturation and annealing temperature.c)programming key to set number of PCR cycles.d)amount of time required to reach the desired temperature.Evaluation of a blood sample indicates the presence of a clot. Corrective action to salvage this specimen for analysis would most likely requirea)digestion with proteinase K.b)homogenizing the sample under UV irradiation.c)removal of the clot with urea.d)requesting a new sample immediately.Incorporation of biotin into template DNA by nick-translation requiresa)DNase.b)ligase.c)random hexanucleotides.d)3 temperatures.An isolated DNA sample is viscous, difficult to pipet, and will not resuspend in TE buffer after rehydration at 37C for 24 hours. The most appropriate step is toa)digest the DNA with a frequent cutting restriction enzyme.b)re-extract the original sample with higher volumes of reagents.c)increase the rehydration temperature to 95C.d)add more TE buffer.Excess glycerol in a restriction digestion reaction results ina)enzyme degradation.b)diminished enzyme activity.c)increased temperature required for digestion.d)decreased enzyme buffer pH.Primer dimers will most likely be a result of PCR whena)3' and 5' primers are designed as 50% GC.b)DNA template concentration is very low.c)enhancing agents are added to the master mix.d)template DNA is initially denatured completely.Correct operation of a pH meter requiresa)calculation of the electrode millivolt equivalents.b)standardization of the meter with a range of buffers.c)documentation of absorbance and standard deviation.d)verification of pH readings with calf thymus DNA.The uracil DNA glycosylase pre-PCR decontamination procedure failed. The most likely cause of the failure is thea)enzyme solution was heated prior to PCR.b)enzyme buffer solution was alkaline pH.c)N-glycosidic DNA bonds cleaved after enzyme treatment.d)PCR was performed with dTTP instead of dUTP.The real-time PCR analysis does not show the characteristic melting curve for the patient or control samples. The fluorimetry readings of the PCR products indicate the appropriate concentration of template was added to the real-time PCR reaction mix. Which of the following reagents was likely missing from the PCR master mix to account for this finding?a)SYBR Green Ib)template DNAc)DMSOd)5X Cresol RedWhich of the following conditions favor enhanced specificity of PCR?a)decrease in the concentration of dNTPsb)increase in the sodium chloride concentrationc)increase in the concentration of Taq polymerased)decrease in the ramp speed and temperatureWhich of the following compounds is an inhibitor of Taq polymerase?a)magnesiumb)hemoglobinc)DMSOd)betaineWhich of the following compositions of gels would allow for the efficient separation of linear DNA molecules in the range of 100 to 300 base pairs in length?a)0.3% agaroseb)1.0% agarosec)1.0% polyacrylamided)8.0% polyacrylamide4.92*10^4 cpm of a random primed 32P dCTP (3000 Ci/mmol) labeled oligonucleotide probe were precipitated from a 50 uL standard reaction by TCA and 5.28*10^4 cpm is the total cpm in the sample. What is the percent incorporation of radioactivity for this labeling reaction?a)1.86%b)46.50%c)93.00%d)98.40%The stock solution of HCl is 1M. How much stock solution is required to prepare 250 mL of 50 mM HCl?a)0.2 mLb)5 mLc)12.5 mLd)125 mLSpectroscopy measurement of a DNA sample isolated by salt extraction technique gave the following absorbance readings: A260 0.4032 A280 0.3765This sample is:a)acceptable for molecular testing.b)contaminated with salt.c)contaminated with protein.d)contaminated with high amounts of RNA.What is the dilution factor if 50 uL of blood is diluted with 950 uL of saline?a)19b)20c)40d)50Which of the following are used to prepare a 0.9% agarose gel?a)0.9 g agarose + 100 mL distilled waterb)0.9 g agarose + 100mL TAEc)9 g agarose + 100mL TBEd)90 g agarose + 100 mL bufferThe concentration of double-stranded DNA with an optical density reading of 1.0 isa)0.5 ug/ulb)1.0 ug/ulc)10 ng/uld)50 ng/ulHow much Tris base (MW 121.1) would be required to make 4 liters of Tris-EDTA buffer that is 15 mM Tris?a)0.7266 gramsb)0.1211 gramsc)1.8165 gramsd)7.266 grams

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BIO282 Lecture Notes - Lecture 9: Dna Sequencing, Dideoxynucleotide, Chain Termination

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