BioBuilding: Synthetic Biology for Teachers: Lab 2: Difference between revisions
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With this assay you will determine the amount of beta-galactosidase activity associated with each sample of cells. As a class you should try to perform replicate assays of each sample (so each strain gets measured two or three times) and then pool your class data to gain some confidence in the values you measure. A data table is included to help you organize your assay, but you can make one of your own if you prefer. Note that the volumes here are given for spectrophotometers that use glass test tubes (13x100 mm). | With this assay you will determine the amount of beta-galactosidase activity associated with each sample of cells. As a class you should try to perform replicate assays of each sample (so each strain gets measured two or three times) and then pool your class data to gain some confidence in the values you measure. A data table is included to help you organize your assay, but you can make one of your own if you prefer. Note that the volumes here are given for spectrophotometers that use glass test tubes (13x100 mm). | ||
# Make 3.0 ml of a 1:10 dilution of each cell sample, | # Make 3.0 ml of a 1:10 dilution (300μL of cells in 2.7 mls of Z buffer) of each cell sample. | ||
# If you made the dilution in glass spectrophotometer tubes, you can proceed to the next step. If not, you will need to transfer some of this diluted cell mixture to a cuvette or glass spectrophotometer tube. The exact amount to transfer will depend on the size of the cuvette you use. Your teacher will provide further instructions. | |||
# Measure the Absorbance at 600 nm (OD 600) of this dilution. Record the value '''X 10''' in the data table. This is the density of the undiluted cells. | # Measure the Absorbance at 600 nm (OD 600) of this dilution. Record the value '''X 10''' in the data table. This is the density of the undiluted cells. | ||
# Add 1.0 ml of | #You can now dispose of these tubes as instructed by your teacher. | ||
# Add 1.0 ml of Z buffer to 11 test tubes labeled B (blank), R (reference), and 1 though 9 (the samples). These are the reaction tubes. | |||
# Add 30 μl of the cells (undiluted) to each tube. Add 30 μl of LB to tube B, to serve as your blank. | # Add 30 μl of the cells (undiluted) to each tube. Add 30 μl of LB to tube B, to serve as your blank. | ||
# Next you will lyse the cells by add 60 μl of 0.1% SDS and, in the hood, add 50 μl of CHCl3 to each tube. Wear gloves when you add the CHCl<sub>3</sub> and cap the tubes when you're done. | # Next you will lyse the cells by add 60 μl of 0.1% SDS and, in the hood, add 50 μl of CHCl3 to each tube. Wear gloves when you add the CHCl<sub>3</sub> and cap the tubes when you're done. | ||
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# Start the reactions by adding 300 μl of ONPG to each tube at 15 second intervals, including your blank. | # Start the reactions by adding 300 μl of ONPG to each tube at 15 second intervals, including your blank. | ||
# After 7 minutes, stop the reactions by adding 750 μl of Na<sub>2</sub>CO<sub>3</sub> to each tube at 15 second intervals. Seven minutes is sufficient time to provide results that are yellow enough to give a reliable reading in the spectrophotometer, best between 0.1 and 1.0. Usually this color is approximately the same as that of a yellow tip for your pipetman. Don't be surprised when the Na<sub>2</sub>CO<sub>3</sub> makes the reactions look more yellow. The reactions are now stable and can be set aside to read another day. Your teacher will inform you if that is the case. | # After 7 minutes, stop the reactions by adding 750 μl of Na<sub>2</sub>CO<sub>3</sub> to each tube at 15 second intervals. Seven minutes is sufficient time to provide results that are yellow enough to give a reliable reading in the spectrophotometer, best between 0.1 and 1.0. Usually this color is approximately the same as that of a yellow tip for your pipetman. Don't be surprised when the Na<sub>2</sub>CO<sub>3</sub> makes the reactions look more yellow. The reactions are now stable and can be set aside to read another day. Your teacher will inform you if that is the case. | ||
# If you conducted the reaction in glass spectrophotometer tubes (your teacher will tell you this), you can skip to the next step. If not, you will need to transfer some of the reaction mixture from the reaction tubes to a cuvette or glass spectrophotometer tube. The exact amount to transfer will depend on the size of the cuvette you use. Your teacher will provide further instructions. It is important that you carefully pipet this mixture during this transfer such that you do not transfer any of the chloroform in the bottom of the reaction tube. The chloroform will appear as a clear layer at the bottom of the tube. | |||
# Read the absorbance of each sample tube at 420nm (OD 420). These values reflect the amount of yellow color in each tube. | # Read the absorbance of each sample tube at 420nm (OD 420). These values reflect the amount of yellow color in each tube. | ||
# Calculate the beta-galactosidase activity in each sample according to the formula below. | # Calculate the beta-galactosidase activity in each sample according to the formula below. | ||
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====Procedure if a Spec 20 is not available==== | ====Procedure if a Spec 20 is not available==== | ||
[[Image:Note mini.png]]''<font color = red> TEACHERS: If a Spec 20 is not available, your students can conduct the protocol presented | [[Image:Note mini.png]]''<font color = red> TEACHERS: If a Spec 20 is not available, your students can conduct the protocol presented below. While these results will not be as precise, they do provide accurate data for analysis. </font color> <br> | ||
=====Estimate the OD 600===== | =====Estimate the OD 600===== | ||
====Procedure if a Spec 20 is not available==== | ====Procedure if a Spec 20 is not available==== |
Revision as of 11:50, 9 August 2011
Eau That Smell Lab notes |
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Lab 2: iTune DeviceTeacher ConsiderationsThis lab examines the role of parts, such as promoters and ribosome binding sites, in predicting the output of a genetic device. The students measure b-galactosidase enzymatic activity as the device's output, thereby looking through the lens of molecular genetics to predict and then evaluate a device's behavior. It provides an excellent way to study the transcription, translation, the lac operon and enzyme function within a synthetic biology context. Part 1 of the lab offers an opportunity for the students to develop microbiology skills, though this procedure may be done by the teacher if time is an issue. In Part 2, the students will lyse the cells to release the β-galactosidase enzyme and then carry out the reaction. It is important that the timing of each step be as precise as possible. You may want them to rehearse this procedure prior to the actual experiment. All of Part 2 can be done in one lab period. However, the reaction mixture is stable once the reaction has been stopped. If you prefer, you can store these tubes overnight and read the OD 420 the next day. Just allow the tubes to warm to room temperature so condensation isn't collecting on the tubes when they are being read in the spectrophotometer. If a spectrophotometer is not available, the cell density and β-gal activity can be easily measured using the McFarland Turbidity methodology, as explained below. If a microfuge is available for the students to use and cuvettes for the spectrophotometer, then we recommend transferring the stopped reactions to microfuge ("eppendorf") tubes, spinning the solutions for a minute to pellet the debris and then transferring the yellow supernatant to cuvettes to read the OD420. When the cleared liquid is measured in this way, then the OD420 measurement is no longer confounded by the cell debris that is present in the glass tubes. An introductory power point for the lab can be found here. Needed MaterialsTeacher Provides
Kit Provides10 strains (see table below)
ChemicalsRoom Temperature
4° (fridge)
Chemical Hood
WorkflowClassroom Content
Annotated Laboratory Procedure TEACHERS:Note that "Part 1: Culturing Bacteria" can be done by the students or by you (the teacher) depending on how much time and preparation you intend to take on/delegate. The only exception is the aliquot of CHCl3 (Day 3) that should be done in the fume hood by the teacher.
Part 1: Culturing BacteriaWe will be receiving our bacteria with the plasmid already inserted. This culture may come in the form of a "stab" or "slant," a test tube with a small amount of bacteria on a slanted media, in which case you will have to streak out the bacteria onto a petri dish to continue the experiment. If the bacteria have arrived on petri dishes, you can proceed to "Day 2." Day 1:
A video of this procedure is here.
A video of this procedure is here. Part 2: Beta-galactosidase assayProcedure using a Spec 20With this assay you will determine the amount of beta-galactosidase activity associated with each sample of cells. As a class you should try to perform replicate assays of each sample (so each strain gets measured two or three times) and then pool your class data to gain some confidence in the values you measure. A data table is included to help you organize your assay, but you can make one of your own if you prefer. Note that the volumes here are given for spectrophotometers that use glass test tubes (13x100 mm).
TEACHERS: If a microfuge is available, you can transfer some of the reaction mixture to a microfuge tube, spin the eppendorf tube for one minute, and then transfer that cleared solution to a cuvette to read the OD 420. However, the microfuge tube will not hold enough of the reaction mixture to read the absorbance using the larger glass tubes. If you must use the larger glass tubes or do not have a microfuge, you can skip this step, though allow time for the debris to settle. It is possible that the remaining cell debris will result in some negative values. These can be set to zero for calculation purposes. Procedure if a Spec 20 is not available TEACHERS: If a Spec 20 is not available, your students can conduct the protocol presented below. While these results will not be as precise, they do provide accurate data for analysis. Estimate the OD 600Procedure if a Spec 20 is not availableEstimate the OD 600
Estimate the OD 420 TEACHERS: For this procedure it is not necessary to use a centrifuge.
Data TableIn your lab notebook, you will need to construct a data table as shown below. If you are testing only a subset of the promoter and RBS collection, be sure to note which ones you are investigating:
CalculationsThe β-gal production is reported in Miller Units
Abs 420 is the Spec 20 absorbance at 420 nm. It is a measure of the yellow color produced by the β-gal activity. It is a unitless number. Abs 600 is the Spec 20 absorbance at 600 nm. It is a measure of the cell density. It is a unitless number. t is the reaction time in minutes. v is the volume of cells added to the reactionin mls. (Not μl!) Summary Data TableIn your lab notebook, you will need to construct a data table as shown below. Fill in as many values as possible. Lab ReportAs you write, be sure to define and properly use all highlighted terms throughout the introduction and other parts of the lab. I. Introduction
II. Methods
III. Results
IV. Discussion
Sample Data SetAssessmentLab Report RubricLab Report ScoreSheetSurvey Monkey LinkTo help us improve the labs, you can send the students here where they can offer anonymous feedback. Thanks! Variations to try
FeedbackWe're always looking to hear back from you if you've thought about this unit, tried it, or stumbled across it and want to know more. Please email us through BioBuilder, info AT biobuilder DOT org.
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