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Resuspension

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Purpose We started our wet lab steps by resuspending Fragment-1, Fragment-2, and Fragment-3 to amplify them using a PCR reaction. The Fragments carry different genetic parts that will be used in our project according to the following figures:
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Materials
  • DNA fragments.

  • Distilled water.

  • Pipette tips.

  • PCR tubes.

  • 96-well plate.

  • Eppendorf tube.

Methods
  • The DNA fragment locations were detected from the 96-well plate provided by Twist Bioscience.

    • Fragment-1 → A2

    • Fragment-2 → H1

    • Fragment-3 → D2

  • The tip of the pipette penetrated the cover of the multiwell plate to avoid cross-contamination.

  • The lyophilized fragments were diluted with 100 µL of distilled water.

  • We ensured that each lyophilized tube was well sealed.

  • Then, the lyophilized tube was mixed properly with the distilled water by shaking the tube forcefully until the pellet at the bottom was no longer visible.

  • The tube was spun down to collect the residuals on the wall of the tube.

  • 100 µL of the medium was transferred to a sterile 1.5 mL Eppendorf tube. Then, the original tube was stored at -20°C until use (short-term storage).

  • Finally, each Eppendorf tube was labeled.

  • Figure: Pulsatile vs. continuous release
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PCR

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PCR amplification of the resuspended fragments was performed to obtain sufficient copies for subsequent laboratory procedures.
Materials
  • DNA templates (Fragment-1, Fragment-2, Fragment-3).

  • Primers compatible with each fragment.

  • Mastermix.

  • Distilled water.

  • PCR tubes.

Methods
  • The lyophilized primers were resuspended by adding the following amount of distilled water to the lyophilized primers:

  • Primer concentrations Stock solution
    Fragment-1 Forward 24 nmol 240 µL
    Fragment-1 Reverse 24.9 nmol 250 µL
    Fragment-2 Forward 27.1nmol 270 µL
    Fragment-2 Reverse 23.1 nmol 230 µL
    Fragment-3 Forward 22.4 nmol 224 µL
    Fragment-3 Reverse 20.1 nmol 200 µL
    Figure: Pulsatile vs. continuous release
  • Then, we prepared the working solution of each fragment by adding 10 µL of its stock solution to 90 µL of distilled water for a total of 100 µL for each primer. Then we mixed it properly.

  • Aiming for a final pure volume of 50 µL, we added 25 µL of Master mix (2x concentration) for 3 PCR tubes.

  • Figure: Pulsatile vs. continuous release
  • Then, we added 2 µL of the working solution of the forward and reverse primers for each fragment to the master mix. Subsequently, we mixed them properly.

  • Finally, we added 0.5 µL of the template fragment.

  • PCR tube (50 µL) Forward primer (working solution) Reverse primer (working solution) Master mix DNA Template Distilled water
    Fragment-1 2 µL 2 µL 25 µL
    0.5 µL
    20.5 µL
    Fragment-2 2 µL 2 µL 25 µL
    0.5 µL
    20.5 µL
    Fragment-3 2 µL 2 µL 25 µL
    0.5 µL
    20.5 µL
    Figure: Pulsatile vs. continuous release
  • We put the final tubes into the PCR, and we set our program as follows:

    • Annealing temperature: 55 °C.

    • Elongation time: 1 min.

    Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
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Gel electrophoresis

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Purpose Gel electrophoresis was performed to verify the size of the synthesized fragments, ensuring their suitability for downstream applications.
Materials
  • Agarose powder.

  • TAE buffer.

  • Ethidium bromide.

  • Loading dye.

  • Microwavable flask.

  • Electrophoresis box.

  • UV light device.

Methods

Gel preparation

    Purpose of gel preparation: To create a solid, porous matrix through which DNA fragments can travel.

  • Ideally, the gel concentration should be 1.5 g of agarose powder in 100 ml of TAE buffer in a microwavable flask. To prepare our 50 ml tray volume. We had added 0.75 agarose powder to the 50 ml TAE buffer.

  • Subsequently, it was mixed properly and heated in the microwave for 1 min until the agarose was completely dissolved.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
  • 1.5 µL of Ethidium bromide was added to the agarose. Ethidium bromide allows us to visualize the DNA bands under ultraviolet (UV) light.

  • The gel was poured into a tray with a well comb (agarose was poured slowly to avoid bubble formation), which created wells for loading the samples.

  • The gel was allowed to solidify completely at room temperature for 20-30 minutes before use.

  • Sample loading and electrophoresis

    Purpose of sample loading and electrophoresis: To introduce the DNA samples into the gel and use an electric current to separate the fragments.

  • Once solidified, the agarose gel was placed in an electrophoresis box filled with TAE buffer. This buffer conducts electricity and maintains a stable pH, allowing the negatively charged DNA to migrate through the gel.

  • Then, the gel box was filled with ethidium bromide until the gel was covered.

  • Then, a molecular weight ladder, containing DNA fragments of known sizes, was loaded into the first lane of the gel. It serves as a reference to estimate the sizes of the PCR products.

  • 2 µL of the loading dye was mixed with 5 µL of each of the PCR products before loading.

  • Figure: Pulsatile vs. continuous release
  • Then,5 µL of the samples were loaded carefully into the remaining wells.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
  • The electric current at 80 -150 V was applied to the gel electrophoresis, with the negative electrode near the wells. This causes the negatively charged DNA fragments to move toward the positive electrode. Smaller fragments travel faster and farther than larger ones.

  • The run was stopped when the loading dye had moved approximately 75-80% of the way down the gel, which indicates sufficient separation of the DNA fragment (the run time was about 1-1.5h).

  • After the run time, the electrodes were disconnected from the power source, and then the gel was carefully removed from the gel box.

  • Visualization and interpretation of results

    Purpose of visualization: To observe the separated DNA fragments and analyze the results.

  • Finally, we transferred the gel into a UV light device to visualize our fragments and interpret the results by comparing the position of the PCR product bands to the bands of the molecular weight ladder.

  • Figure: Pulsatile vs. continuous release

    Figure: electrophoresis showing the size of fragments 1,2 and 3.

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Gel purification

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Purpose Gel purification is a molecular biology technique employed for the isolation and purification of a specific DNA fragment after agarose gel electrophoresis. This protocol is critical for various downstream applications, including cloning, PCR, and sequencing, as it effectively removes confounding contaminants such as unwanted DNA fragments, salts, and residual enzymes that could impede the fidelity and efficiency of subsequent experimental procedures.
Materials
  • Agarose gel.

  • gel extraction kit.

  • Microcentrifuge tubes.

  • Clean razor blade.

  • UV light source.

  • Microcentrifuge.

  • Heating block or water bath.

Methods

Excise the DNA Band

  • During the interpretation of gel electrophoresis results, a protective glass plate was utilized to shield the UV transilluminator, and exposure time to UV light was minimized to mitigate potential DNA damage.

  • The desired DNA band was precisely excised from the gel using a sterile razor blade, ensuring cuts were made as close as possible to the band to minimize the volume of co-excised agarose.

  • The excised gel slice was then transferred into a pre-weighed microcentrifuge tube. Subsequently, the tube containing the gel slice was weighed to determine the exact mass of the agarose, which is crucial for calculating the appropriate volume of solubilization buffer required in the following step.

  • Dissolve the Gel Slice

  • A 3:1 volume ratio of solubilization buffer to excised gel slice (e.g., 300 µL of buffer for a 100 mg gel slice) was added to the microcentrifuge tube.

  • The mixture was then inverted for fragments smaller than 5 kb or gently vortexed for larger fragments, with periodic mixing every few minutes to facilitate complete dissolution of the agarose.

  • The tube was subsequently incubated at 50-60°C for approximately 5 minutes, or until the gel slice was entirely dissolved.

  • A pH indicator was employed to confirm that the solution maintained a yellow color, signifying the optimal pH for efficient DNA binding. If necessary, a pH-adjusting solution was added to achieve the desired pH.

  • Bind the DNA to the Spin Column

  • A spin column was inserted into a collection tube, and the entire dissolved gel mixture was carefully transferred to the spin column.

  • The column was then centrifuged at 13,000-17,000 x g for 1 minute to facilitate DNA binding to the silica membrane.

  • Following centrifugation, the flow-through was discarded, and the spin column was re-inserted into the collection tube.

  • Wash the DNA:

  • Approximately 500-750 µL of wash buffer was added to the spin column, and the column was centrifuged again at 13,000-17,000 x g for 1 minute.

  • The flow-through was discarded. Depending on the sensitivity of subsequent applications to residual salts, an additional wash step with wash buffer was performed.

  • A final centrifugation step was executed at maximum speed (≥17,000 x g) for 1 minute to ensure complete drying of the silica membrane and to remove any residual ethanol, which is known to inhibit downstream enzymatic reactions.

  • The spin column was then carefully removed from the collection tube, which was subsequently discarded along with any residual flow-through.

  • Elute the DNA

  • The spin column was meticulously transferred to a new, sterile microcentrifuge tube.

  • 30-50 µL of Elution Buffer (pre-warmed to 50°C for enhanced yield) was dispensed directly onto the center of the column membrane, taking care to avoid contact with the pipette tip.

  • The column was then allowed to sit at room temperature for 1-2 minutes, providing sufficient time for the DNA to rehydrate and dissociate from the membrane.

  • Finally, the column was centrifuged at 13,000-17,000 x g for 1 minute to collect the purified DNA into the clean microcentrifuge tube.

  • Quantify and Store the Purified DNA

  • The concentration and purity of the eluted DNA were assessed using a spectrophotometer.

  • The purified DNA was stored at 4°C for short-term experimental use or at -20°C for long-term preservation.

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Transformation

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Purpose Following PCR, transformation of the recombinant plasmids into JM109 competent cells was performed to assess M13 functionality and to amplify the fragments for subsequent experiments.
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Materials
  • DNA vector.

  • Competent cells.

  • Culture media.

  • Ampicillin.

  • Ice.

  • Distilled water.

  • Falcon tube.

  • Transformation tubes.

  • LB media.

  • Shaker.

Methods
  • The JM109 competent cells were taken out of -80°C and thawed on ice (approximately 20-30 mins).

  • The agar plates that contain the antibiotic were removed from storage at 4°C and allowed to warm up at room temperature.

  • The lyophilized DNA had been resuspended by adding 20 µL of distilled water to the DNA. Then, we mixed them properly.

  • 5 µL of the resuspended DNA was added to 20-50 μL Jm109 competent cells in a Falcon tube. Then, it was gently mixed by flicking the bottom of the tube with your finger a few times.

  • The competent cells/DNA mixture was incubated on ice for 10 min.

  • Each of the transformation tubes was transferred to a hot path for 45 seconds, as the bottom 1/2 to 2/3 of the tube was placed in the path.

  • Then, the tubes were turned back on ice for 2 minutes.

  • 250-1,000 μl LB media was added to the transformed bacteria, and it was left to grow on the shaker for 30 minutes.

  • Then, all the transformed bacteria were plated onto a 10 cm LB agar plate containing 5 µL of Ampicillin and were added to a liquid medium.

  • Finally, we put our mixture on the media, and it was left on the shaker at 37°C overnight.

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PCR

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Purpose PCR amplification was repeated for fragments 1 and 2 to achieve sufficient yield. Fragment 3 required gradient PCR to optimize annealing temperature. Additionally, the functionality of M13 primer variants was confirmed by their use in PCR amplification of the 1-D5 plasmid.
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Figure: Pulsatile vs. continuous release
Materials
  • DNA fragments.

  • Distilled water.

  • Pipette tips.

  • PCR tubes.

  • 96-well plate.

  • Eppendorf tube.

Methods
    Figure: Pulsatile vs. continuous release
  • We made another PCR reaction for fragment 1, 2 with the same protocol.

  • Moreover, we ran a gradual PCR reaction for fragment 3 on 6 different annealing temperatures due to gradient bands shown yesterday.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
  • Also, we ran a PCR reaction for plasmid (1-5d) with an elongation time of 1 min and an annealing temperature of 48°C to test the functionality of M13 primer variants (3 forward and 2 reverse) with a total of 6 probabilities.

  • Primer Code
    M-13 Forward-1 1
    M-13 Reverse-1 2
    M-13 Reverse-2 3
    M-13 Forward-2 4
    M-13 Forward-3 5
  • Each of the forward primers we had was tested with the two reverse primers.

  • Forward primer Reverse primer
    M-13 Forward-1 (1) M-13 Reverse-1 (2)
    M-13 Forward-1 (1) M-13 Reverse-2 (3)
    M-13 Forward-2 (4) M-13 Reverse-1 (2)
    M-13 Forward-2 (4) M-13 Reverse-2 (3)
    M-13 Forward-3 (5) M-13 Reverse-1 (2)
    M-13 Forward-3 (5) M-13 Reverse-2 (3)
    Figure: Pulsatile vs. continuous release
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Glycerol Stock

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Purpose Glycerol stock preparation was performed to ensure the short and long-term cryopreservation of the transformed bacterial cultures.
Materials
  • Bacterial culture.

  • LB media.

  • Glycerol stocks.

  • Sterile water.

  • Ampicillin.

  • Eppendorf tube.

Methods
  • After the steps of Overnight Liquid Culture Inoculation

  • We took two portions of the actively growing overnight culture. This ensured a backup in case one stock is contaminated or lost.

  • We took 2 glycerol stocks for our 1-5d transformed bacterial growth, each stock contained 500 μL of each overnight culture mixed with 500 μL of 50% glycerol in a 2 mL screw top tube.

  • The solution was mixed gently by inverting the tube several times, ensuring the glycerol was evenly distributed among the bacteria.

  • TThe prepared glycerol stock was snap frozen by placing the tubes into a liquid nitrogen bath. This rapid freezing technique helps prevent the formation of large, destructive ice crystals.

  • After snap-freezing, the stock was transferred to a -80°C freezer for long-term storage. Where it can remain viable for many years.

  • Figure: Pulsatile vs. continuous release
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Activation protocol

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Purpose To cultivate a high-density, pure culture of bacteria harboring the recombinant plasmid.
Materials
  • LB media.

  • Ampicilin.

  • Plates of the transformed bacteria

  • Shaker.

Methods
  • 5 μL of ampicillin was added to 5 mL of LB media, ensuring that only the bacteria that successfully took up the ampicillin-resistant plasmid would survive and grow, while any untransformed bacteria would be killed.

  • A colony from the plate was taken and seeded in the LB media, which guarantees that the entire liquid culture will be genetically uniform and contain the correct plasmid.

  • The colony was left in the LB media in the shaker overnight. The overnight provides sufficient time for the bacteria to grow and reach a high cell density, while the agitation of the shaker provides aeration by continuously mixing oxygen into the media.

  • Figure: Pulsatile vs. continuous release
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Plasmid Extraction

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Purpose Plasmid extraction was performed from amplified transformed cells via a three-step process involving cell lysis, DNA binding, and elution. The extracted plasmid was subsequently used for cloning.
Materials
  • Tris-HCl buffer.

  • EDTA.

  • RNase A.

  • Glucose.

  • Wash buffers.

  • Isopropanol.

  • Alkaline lysis buffer.

  • Resuspension buffer.

  • N3 buffer.

  • Silica membrane.

Methods

    Step (1): Lysis

  • We started by lysing the bacterial cells.

  • 200 µL of P1 buffer (resuspension buffer) was added to rehydrate the bacterial pellet, which often contains RNase A to degrade cellular RNA. Then the P1 buffer was mixed by pipetting.

  • 50 µL of P2 buffer (alkaline lysis buffer) was added to disrupt the cell membrane and denature proteins and DNA, including the bacterial chromosome and the plasmid. Then the P2 was mixed by inverting.

  • The P2 buffer was left for 5 minutes to allow complete lysis of the cell membrane.

  • 350 µL of N3 buffer was added to neutralize the pH, leading to precipitation of the large chromosomal DNA and denatured protein, while the small, supercoiled plasmid DNA remains in solution. Then the N3 buffer was mixed by inverting.

  • Step (2): Binding and washing

  • The culture medium was centrifuged for 4 minutes to pellet the precipitated chromosomal DNA and cellular debris, leaving the plasmid DNA in the supernatant.

  • The upper layer was transferred to a spin column to allow the plasmid DNA to bind to the column's silica membrane in the presence of the high salt concentration from the N3 buffer.

  • Subsequently, the spin column was centrifuged, which forced the liquid (flow-through) containing cellular waste and other impurities through the column, leaving the plasmid DNA bound to the membrane.

  • 500 µL of AW1 and 500 µL of AW2 (wash buffers) were added to remove any residual salts from the first wash.

  • We let the mixture dry for 2 minutes, which allows for the removal of all traces of the wash buffers, especially the alcohol, which can interfere with subsequent steps.

  • Step (3): elution

  • The mixture was eluted with 50 µL water and placed in a new Eppendorf, which facilitated the release of the DNA from the silica membrane

  • Then, a new Eppendorf tube was used to collect the clean DNA.

  • Then, we waited for 3 minutes, which allowed the water to fully rehydrate the DNA and dissociate it from the membrane, increasing the final yield.

  • Finally, the eluted DNA was centrifuged for 3 minutes.

  • Figure: Pulsatile vs. continuous release
◆ ◆ ◆

DNA purification

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Purpose Following the initial plasmid extraction, a dedicated purification step was deemed essential to enhance the efficiency of subsequent cloning and assembly processes.
Materials
  • Tris-HCl buffer.

  • EDTA.

  • RNase A.

  • Wash buffers.

  • Isopropanol.

  • RNA lysis buffer.

  • Resuspension buffer.

  • Eppendorf tubes.

Methods

    Step 1: Binding

  • 200 µL of RLT (RNA lysis buffer) was added to allow binding of DNA to the silica membrane in the spin column. Then it was mixed by pipetting.

  • 40 µL of isopropanol was added, which promotes the binding of nucleic acids to the silica membrane by helping to dehydrate the DNA. Then it was mixed by inverting.

  • The mixture was poured into a spin column.

  • Then, the mixture was left for 5 minutes to allow the binding of the DNA to the column's membrane.

  • Step (2): washing

  • The mixture was centrifuged for 30 seconds, which allowed the removal of the unbound primers, enzymes, and salts.

  • Then, the mixture was washed with 500 µL of AW2 (wash buffer), which removed any remaining salts and impurities.

  • Then, the mixture was centrifuged to spin the buffer through the column and discard the flow-through.p>

  • Subsequently, we left it dry for 2 minutes. This ensured that all residual ethanol from the wash buffer was removed from the column

  • Step (3): elution

  • The mixture was eluted with 50 µL water and placed in a new Eppendorf, which facilitated the release of the DNA from the silica membrane.

  • Figure: Pulsatile vs. continuous release
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Digestion

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Purpose To digest fragments 1, 2, and 3 by specific restriction enzymes, thereby isolating specific genetic parts for subsequent use in the project. These genetic parts are:

Fragment 1

Part name Restriction 1 Restriction 2 Buffer
1- P11 promotor Ecor1 Sac1 R2-1
2- Antitoxin promotor Sac1 Kpn1 R2-1
3- SV40 Poly A signal Kpn1 BamH R1-1
4- Trrn B terminator BamH Xbal R2-1
5- RBS Xbal Sel1 R3-1/span>
6- T7 promotor Sel1 Pst1 R3-1
7- P-kat A promoter Pst1 Hind 3 R2-1

Fragment 2

Part name Restriction 1 Restriction 2 Buffer
1- P32 promoter + lac R operon Sac1 Kpn1 R2-1
2- Pkat A + Rep repressor Kpn1 Pst1 R1-1

Fragment 3

Part name Restriction 1 Restriction 2 Buffer
1- Pkat + operator Hind3 Xbal R2-1
2- T7 + SVTR kozakr Xbal Ecor1 R2-1
3- P170-Cp promotor Ecor1 Sac1 R2-1
4- P32 promoter with lac operon Sac1 Kpn1 R2-1
Materials
  • Restriction enzymes.

  • DNA aliquot.

  • Nuclease-free water.

  • Digestion vessels.

Methods
  • Our genetic parts were digested using different pairs of restriction enzymes. The restriction enzymes were used in specific amounts with various elements, ensuring that each part has different "sticky ends" on each side for directional cloning.

  • The vector was cut with the same pair of restriction enzymes used for a specific genetic part to make it compatible with each Part.

  • We ran the digested vectors and PCR products on PCR, specifically the digestion protocol, which consists of 2 stages

  • The vector was cut with the same pair of restriction enzymes used for a specific genetic part to make it compatible with each Part.

    Parts reaction Volume Vector reaction Volume
    1- PCR product (part) 5 μL Vector 2 μL
    2- Restriction 1 1 μL Restriction 1 1 μL
    3- Restriction 2 1 μL Restriction 2 1 μL
    4- Buffer 2 μL Buffer 2 μL
    5- H2O 11 μL H2O 11 μL
    Figure: Pulsatile vs. continuous release

    Incubation and inactivation

    • Stage (1) Heat activation step to provide the optimal temperature (37 °C for 1 hr) for most restriction enzymes to cleave DNA efficiently.
    • Stage (2) Heat-inactivation step to denature and kill the restriction enzymes at 85 °C, preventing them from cutting the DNA during the next ligation step.
    Figure: Pulsatile vs. continuous release
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Gel Electrophoresis

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Purpose Gel electrophoresis was performed to verify the size of the fragments amplified during the repeated PCR reaction.
Materials
  • Agarose powder.

  • TAE buffer.

  • Ethidium bromide.

  • Loading dye.

  • microwavable flask.

  • electrophoresis box.

  • UV light device.

Methods

We performed gel electrophoresis for all today's PCR products, as follows:

  • Gel electrophoresis for the gradual PCR amplification of Fragment-3, and the amplified Fragments-1,2:

  • Figure: Pulsatile vs. continuous release
  • Gel electrophoresis for the 1-d5 plasmid PCR product, which was performed using different M-13 primer variants to find the viable pair, and for the purified Fragments 1, 2, and 3 from yesterday’s and today’s reactions:

  • Figure: Pulsatile vs. continuous release
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Ligation

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Purpose To ligate the excised genetic insert into its corresponding vector, forming a novel recombinant plasmid in a final reaction volume of 20 μL
Materials
  • T4 DNA Ligase.

  • Ligation Buffer (10X).

  • Nuclease-free water.

  • Vector DNA.

  • Insert DNA.

Methods
  • We added 5 μL of the digested PCR product to 10 μL of the digested corresponding vector with 2 μL of the buffer ligase, 1 μL ligase enzyme, and 1 μL ATP.

  • The final component ratio was 2:1 of vector to insert volume (10 µL vector, 5 µL insert).

  • Finally, this mixture was incubated at room temperature for 1 hour, which is the optimal temperature to form phosphodiester bonds, sealing the nicks in the DNA backbone.

Figure: Pulsatile vs. continuous release
◆ ◆ ◆

Transformation

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Purpose To introduce the ligated plasmids into JM109 competent cells to assess the viability of the recombinant constructs, following the established protocol.
Materials
  • DNA vector.

  • Competent cells.

  • Culture media.

  • Ampicillin.

  • Ice.

  • Distilled water.

  • Falcon tube.

  • Transformation tubes.

  • LB media.

  • Shaker.

Methods
  • 5 μL of the ligated plasmids was added to Jm109 competent cells.

  • Then, the heat shock protocol was performed to increase the efficiency of DNA uptake by bacterial cells as follows:

    • The mixture was left on the ice for 10 min, as the cold temperature stabilizes the cell membranes, making them more receptive to the plasmid DNA.

    • Then, the mixture was exposed to heat shock by being transferred to a hot bath for 45 seconds. This creates a thermal imbalance across the cell membrane, allowing the DNA to enter.

    • Then, they were turned back to the ice for 2 minutes, allowing for the recovery and stabilization of the bacterial membranes.

  • 250 μL of LB media was added to each of the 13 tubes, as it provides nutrients for the cells to recover and begin expressing the genes on the newly acquired plasmid.

  • Then, they were left on the shaker for 1 hour, ensuring proper aeration for the cells as they recover and begin expressing the antibiotic resistance gene on the plasmid.

  • Figure: Pulsatile vs. continuous release
  • We melted the solid media.

  • Then, 100 μL of Ampicillin and 50 μLof X-gal were added to the media, as the Ampicillin selects the bacteria that successfully took the plasmid, while the X-gal is used to differentiate between recombinant and non-recombinant plasmids.

  • The media was poured on the plates.

  • Then, 100 μLof Jm109 competent cells were added to the plates containing the selection media.

  • We spread the cells using glass beads.

  • Finally, the plates were incubated at 37 °C overnight, allowing the transformed bacteria to grow into colonies.

  • Figure: Pulsatile vs. continuous release
◆ ◆ ◆

Plasmid Extraction

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Purpose Plasmid extraction was performed from amplified transformed cells via a three-step process involving cell lysis, DNA binding, and elution. The extracted plasmid was subsequently used for cloning.
Materials
  • Tris-HCl buffer.

  • EDTA.

  • RNase A.

  • Proteinase K.

  • Wash buffers.

  • Isopropanol.

  • RNA lysis buffer.

  • Resuspension buffer.

  • Eppendorf tubes.

Methods

      Step (1): Lysis

    • We started by lysing the bacterial cells.

    • 200 µL of P1 buffer (resuspension buffer) was added to rehydrate the bacterial pellet, which often contains RNase A to degrade cellular RNA. Then the P1 buffer was mixed by pipetting.

    • 50 µL of P2 buffer (alkaline lysis buffer) was added to disrupt the cell membrane and denature proteins and DNA, including the bacterial chromosome and the plasmid. Then the P2 was mixed by inverting.

    • The P2 buffer was left for 5 minutes to allow complete lysis of the cell membrane.

    • 350 µL of N3 buffer was added to neutralize the pH, leading to precipitation of the large chromosomal DNA and denatured protein, while the small, supercoiled plasmid DNA remains in solution. Then the N3 buffer was mixed by inverting.

    • Step (2): Binding and washing

    • The culture medium was centrifuged for 4 minutes to pellet the precipitated chromosomal DNA and cellular debris, leaving the plasmid DNA in the supernatant.

    • The upper layer was transferred to a spin column to allow the plasmid DNA to bind to the column's silica membrane in the presence of the high salt concentration from the N3 buffer.

    • Subsequently, the spin column was centrifuged, which forced the liquid (flow-through) containing cellular waste and other impurities through the column, leaving the plasmid DNA bound to the membrane.

    • 500 µL of AW1 and 500 µL of AW2 (wash buffers) were added to remove any residual salts from the first wash.

    • We let the mixture dry for 2 minutes, which allows for the removal of all traces of the wash buffers, especially the alcohol, which can interfere with subsequent steps.

    • Step (3): elution

    • The mixture was eluted with 50 µL water and placed in a new Eppendorf, which facilitated the release of the DNA from the silica membrane

    • Then, a new Eppendorf tube was used to collect the clean DNA.

    • Then, we waited for 3 minutes, which allowed the water to fully rehydrate the DNA and dissociate it from the membrane, increasing the final yield.

    • Finally, the eluted DNA was centrifuged for 3 minutes.

◆ ◆ ◆

Gel electrophoresis

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Purpose Gel electrophoresis was performed to verify the size of the extracted fragments, ensuring their suitability for downstream applications.
Materials
  • Agarose powder.

  • TAE buffer.

  • Ethidium bromide.

  • Loading dye.

  • microwavable flask.

  • electrophoresis box.

  • UV light device.

Methods

Gel preparation

    Purpose of gel preparation: To create a solid, porous matrix through which DNA fragments can travel.

  • Ideally, the gel concentration should be 1.5 g of agarose powder in 100 ml of TAE buffer in a microwavable flask. To prepare our 50 ml tray volume. We had added 0.75 agarose powder to the 50 ml TAE buffer.

  • Subsequently, it was mixed properly and heated in the microwave for 1 min until the agarose was completely dissolved.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
  • 1.5 µL of Ethidium bromide was added to the agarose. Ethidium bromide allows us to visualize the DNA bands under ultraviolet (UV) light.

  • The gel was poured into a tray with a well comb (agarose was poured slowly to avoid bubble formation), which created wells for loading the samples.

  • The gel was allowed to solidify completely at room temperature for 20-30 minutes before use.

  • Sample loading and electrophoresis

    Purpose of sample loading and electrophoresis: To introduce the DNA samples into the gel and use an electric current to separate the fragments.

  • Once solidified, the agarose gel was placed in an electrophoresis box filled with TAE buffer. This buffer conducts electricity and maintains a stable pH, allowing the negatively charged DNA to migrate through the gel.

  • Then, the gel box was filled with ethidium bromide until the gel was covered.

  • Then, a molecular weight ladder, containing DNA fragments of known sizes, was loaded into the first lane of the gel. It serves as a reference to estimate the sizes of the PCR products.

  • 2 µL of the loading dye was mixed with 5 µL of each of the PCR products before loading.

  • Then,5 µL of the samples were loaded carefully into the remaining wells.

  • Figure: Pulsatile vs. continuous release
  • The electric current at 80 -150 V was applied to the gel electrophoresis, with the negative electrode near the wells. This causes the negatively charged DNA fragments to move toward the positive electrode. Smaller fragments travel faster and farther than larger ones.

  • The run was stopped when the loading dye had moved approximately 75-80% of the way down the gel, which indicates sufficient separation of the DNA fragment (the run time was about 1-1.5h).

  • After the run time, the electrodes were disconnected from the power source, and then the gel was carefully removed from the gel box.

  • Visualization and interpretation of results

    Purpose of visualization: To observe the separated DNA fragments and analyze the results.

  • Finally, we transferred the gel into a UV light device to visualize our fragments and interpret the results by comparing the position of the PCR product bands to the bands of the molecular weight ladder.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release

    Figure: electrophoresis showing the size of the isolated parts

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Gel purification

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Purpose Gel purification is a molecular biology technique employed for the isolation and purification of a specific DNA fragment after agarose gel electrophoresis. This protocol is critical for various downstream applications, including cloning, PCR, and sequencing, as it effectively removes confounding contaminants such as unwanted DNA fragments, salts, and residual enzymes that could impede the fidelity and efficiency of subsequent experimental procedures.
Materials
  • Agarose gel.

  • gel extraction kit.

  • Microcentrifuge tubes.

  • Clean razor blade.

  • UV light source.

  • Microcentrifuge.

  • Heating block or water bath.

Methods

Excise the DNA Band

  • During the interpretation of gel electrophoresis results, a protective glass plate was utilized to shield the UV transilluminator, and exposure time to UV light was minimized to mitigate potential DNA damage.

  • The desired DNA band was precisely excised from the gel using a sterile razor blade, ensuring cuts were made as close as possible to the band to minimize the volume of co-excised agarose.

  • The excised gel slice was then transferred into a pre-weighed microcentrifuge tube. Subsequently, the tube containing the gel slice was weighed to determine the exact mass of the agarose, which is crucial for calculating the appropriate volume of solubilization buffer required in the following step.

  • Dissolve the Gel Slice

  • A 3:1 volume ratio of solubilization buffer to excised gel slice (e.g., 300 µL of buffer for a 100 mg gel slice) was added to the microcentrifuge tube.

  • The mixture was then inverted for fragments smaller than 5 kb or gently vortexed for larger fragments, with periodic mixing every few minutes to facilitate complete dissolution of the agarose.

  • The tube was subsequently incubated at 50-60°C for approximately 5 minutes, or until the gel slice was entirely dissolved.

  • A pH indicator was employed to confirm that the solution maintained a yellow color, signifying the optimal pH for efficient DNA binding. If necessary, a pH-adjusting solution was added to achieve the desired pH.

  • Bind the DNA to the Spin Column

  • A spin column was inserted into a collection tube, and the entire dissolved gel mixture was carefully transferred to the spin column.

  • The column was then centrifuged at 13,000-17,000 x g for 1 minute to facilitate DNA binding to the silica membrane.

  • Following centrifugation, the flow-through was discarded, and the spin column was re-inserted into the collection tube.

  • Wash the DNA:

  • Approximately 500-750 µL of wash buffer was added to the spin column, and the column was centrifuged again at 13,000-17,000 x g for 1 minute.

  • The flow-through was discarded. Depending on the sensitivity of subsequent applications to residual salts, an additional wash step with wash buffer was performed.

  • A final centrifugation step was executed at maximum speed (≥17,000 x g) for 1 minute to ensure complete drying of the silica membrane and to remove any residual ethanol, which is known to inhibit downstream enzymatic reactions.

  • The spin column was then carefully removed from the collection tube, which was subsequently discarded along with any residual flow-through.

  • Elute the DNA

  • The spin column was meticulously transferred to a new, sterile microcentrifuge tube.

  • 30-50 µL of Elution Buffer (pre-warmed to 50°C for enhanced yield) was dispensed directly onto the center of the column membrane, taking care to avoid contact with the pipette tip.

  • The column was then allowed to sit at room temperature for 1-2 minutes, providing sufficient time for the DNA to rehydrate and dissociate from the membrane.

  • Finally, the column was centrifuged at 13,000-17,000 x g for 1 minute to collect the purified DNA into the clean microcentrifuge tube.

  • Quantify and Store the Purified DNA

  • The concentration and purity of the eluted DNA were assessed using a spectrophotometer.

  • The purified DNA was stored at 4°C for short-term experimental use or at -20°C for long-term preservation.

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Digestion

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Purpose To digest the transformed parts by specific restriction enzymes, thereby isolating specific genetic parts for the level one assembly.
Materials
  • Restriction enzymes.

  • DNA aliquot.

  • Nuclease-free water.

  • Digestion vessels.

Methods
  • Our genetic parts were digested using different pairs of restriction enzymes. The restriction enzymes were used in specific amounts with various elements, ensuring that each part has different "sticky ends" on each side for directional cloning.

  • The vector was cut with the same pair of restriction enzymes used for a specific genetic part to make it compatible with each Part.

  • We ran the digested vectors and PCR products on PCR, specifically the digestion protocol, which consists of 2 stages

  • The vector was cut with the same pair of restriction enzymes used for a specific genetic part to make it compatible with each Part.

    Incubation and inactivation

    • Stage (1) Heat activation step to provide the optimal temperature (37 °C for 1 hr) for most restriction enzymes to cleave DNA efficiently.
    • Stage (2) Heat-inactivation step to denature and kill the restriction enzymes at 85 °C, preventing them from cutting the DNA during the next ligation step.
    Figure: Pulsatile vs. continuous release
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Ligation

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Purpose To ligate the excised genetic insert into its corresponding vector, forming a novel recombinant plasmid in a final reaction volume of 20 μL
Materials
  • T4 DNA Ligase.

  • Ligation Buffer (10X).

  • Nuclease-free water.

  • Vector DNA.

  • Insert DNA.

Methods
  • We added 5 μL of the digested PCR product to 10 μL of the digested corresponding vector with 2 μL of the buffer ligase, 1 μL ligase enzyme, and 1 μL ATP.

  • The final component ratio was 2:1 of vector to insert volume (10 µL vector, 5 µL insert).

  • Finally, this mixture was incubated at room temperature for 1 hour, which is the optimal temperature to form phosphodiester bonds, sealing the nicks in the DNA backbone.

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Transformation

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Purpose To introduce the ligated plasmids into JM109 competent cells to assess the viability of the recombinant constructs, following the established protocol.
Materials
  • DNA vector.

  • Competent cells.

  • Culture media.

  • Ampicillin.

  • Ice.

  • Distilled water.

  • Falcon tube.

  • Transformation tubes.

  • LB media.

  • Shaker.

Methods
  • 5 μL of the ligated plasmids was added to Jm109 competent cells.

  • Then, the heat shock protocol was performed to increase the efficiency of DNA uptake by bacterial cells as follows:

    • The mixture was left on the ice for 10 min, as the cold temperature stabilizes the cell membranes, making them more receptive to the plasmid DNA.

    • Then, the mixture was exposed to heat shock by being transferred to a hot bath for 45 seconds. This creates a thermal imbalance across the cell membrane, allowing the DNA to enter.

    • Then, they were turned back to the ice for 2 minutes, allowing for the recovery and stabilization of the bacterial membranes.

  • 250 μL of LB media was added to each of the 13 tubes, as it provides nutrients for the cells to recover and begin expressing the genes on the newly acquired plasmid.

  • Then, they were left on the shaker for 1 hour, ensuring proper aeration for the cells as they recover and begin expressing the antibiotic resistance gene on the plasmid.

  • We melted the solid media.

  • Then, 100 μL of Ampicillin and 50 μLof X-gal were added to the media, as the Ampicillin selects the bacteria that successfully took the plasmid, while the X-gal is used to differentiate between recombinant and non-recombinant plasmids.

  • The media was poured on the plates.

  • Then, 100 μLof Jm109 competent cells were added to the plates containing the selection media.

  • We spread the cells using glass beads.

  • Finally, the plates were incubated at 37 °C overnight, allowing the transformed bacteria to grow into colonies.

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PCR

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Purpose To isolated the level 1 ligated plasmids from JM109 competent cells to assess the viability of the recombinant constructs, following its transformation.
Materials
  • DNA fragments.

  • Distilled water.

  • Pipette tips.

  • PCR tubes.

  • 96-well plate.

  • Eppendorf tube.

Methods
  • The lyophilized primers were resuspended by adding the following amount of distilled water to the lyophilized primers:

  • Then, we prepared the working solution of each of the level 1 ligated parts by adding 10 µL of its stock solution to 90 µL of distilled water for a total of 100 µL for each primer. Then we mixed it properly.

  • Aiming for a final pure volume of 50 µL, we added 25 µL of Master mix (2x concentration) for 3 PCR tubes.

  • Then, we added 2 µL of the working solution of the forward and reverse primers for each fragment to the master mix. Subsequently, we mixed them properly.

  • Finally, we added 0.5 µL of the template fragment.

  • Figure: Pulsatile vs. continuous release
    Figure: Pulsatile vs. continuous release
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