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Lab 9: Bacterial Transformation & Spectrophotometry, Part 1
Activity 9a
Bacterial Transformation, Part 1
Purpose and Background In this lab, you will perform a procedure known as genetic transformation. Transformation is defined as the insertion of a gene into an organism in order to change the organism’s trait(s). Genetic transformation is used in many areas of biotechnology.
- In medicine, gene therapy involves transforming a sick person’s cells with healthy copies of the defective gene that causes the disease.
- In research, bacteria are transformed with genes encoding human proteins for biomanufacturing production or for further study of these proteins.
- In agriculture, genes coding for traits such as frost-, pest-, or spoilage-resistance can be genetically transformed into plants.
- In bioremediation, bacteria can be transformed with genes that enable them to digest oil spills. We will be transforming bacteria with a gene that codes for Green Fluorescent Protein (GFP). This gene originally came from the bioluminescent jellyfish Aequorea Victoria. GFP is the protein that causes this jellyfish to glow in the dark. If your transformation is successful, the transformed bacteria expressing the GFP protein will glow a brilliant green color under ultraviolet light. Before beginning the laboratory activities, we will first learn more background on transformation in general and our particular experiment in a Powerpoint lecture (see next 4 pages for notes).
Methods of Transformation
!! Electroporation "!Electrical shock makes cell membranes permeable to DNA !! Calcium Chloride/Heat-Shock "!Chemically-competent cells uptake DNA after heat shock
Transformation Procedure - summary
!! Suspend bacterial colonies in Transformation solution !! Add pGLO plasmid DNA !! Place tubes in ice !! Heat-shock at 42°C and place back on ice !! Incubate with nutrient broth !! Streak plates
Reasons for Performing Each
Transformation Step
1.! Transformation solution = CaCI 2 Positive charge of Ca++^ ions shields negative charge of DNA phosphates to help DNA get into cell Cl-^ ions enter cell with water, causing cell to swell and have tiny holes in membrane--allow DNA to get in Ca++ Ca++ CH 2 O O P O O O (^) **Base CH 2 O P O O O Base OH Sugar Sugar Ca++ O
- Incubate on ice** slows fluid cell membrane 3. Heat-shock Increases permeability of membranes 4. Nutrient broth incubation Allows beta-lactamase expression Beta-lactamase (ampicillin resistance) Cell wall GFP
Reasons for Performing Each
Transformation Step, continued
What is Nutrient Broth?
!! Luria-Bertani (LB) broth !! Medium that contains nutrients for bacterial growth and gene expression "!Carbohydrates "!Amino acids "!Nucleotides "!Salts "!Vitamins
Grow?
Glow?
!! Follow protocol !! On which plates will
colonies grow?
!! Which colonies will glow?
Procedure The step-by-step procedure for performing your transformation is outlined with illustrations in the quick guide on the next two pages. Before beginning the transformation procedure, go over the quick guide and make sure you understand every step. If you have any questions, be sure to ask your instructor in lab. To review a few key points from the Powerpoint notes:
- The plasmid that you will be transforming into the E. coli bacterial cells is the pGLO plasmid. Plasmids are made of DNA.
- The pGLO plasmid contains four regions that are important for the functioning of the plasmid inside bacterial cells. These four regions are:
. The gene encoding the protein GFP (Green
Fluorescent Protein)
. The gene encoding the beta-lactamase
enzyme, breaks down ampicillin and allows bacteria containing the pGLO plasmid to be resistant to the ampicillin antibiotic.
. The araC regulatory region that controls the
expression of GFP. Under the control of the araC regulatory region, the GFP protein will only be expressed when arabinose is added to the medium.
. The origin of replication ( ori ), which allows
the plasmid to be replicated inside bacterial cells.
- You will be transforming the pGLO plasmid into the bacterial cells using the calcium chloride/heat shock method. In your lab notebook, diagram your plates , recording:
- which plates received bacteria +pGLO and which received bacteria - pGLO
- whether plates contained ampicillin, arabinose, etc. Also, be sure to record any notes about how you carried out the transformation in your lab notebook (exactly how long your heat shock was, how long your incubations were on ice, in the 37 ° incubator, etc.) That way, if you find next week that your transformation results weren’t as good as you expected, you might be able to figure out what could be improved if you were to repeat the experiment. After you have finished setting up the transformation, label your plates, tape them together into one stack, and put them in the incubator upside down to grow. Finally, given what you have learned about bacterial transformation and the regulation of the GFP gene by arabinose, record some predictions in your lab notebook as to what results do you expect for each plate. Next week, we will examine our results and determine our transformation efficiency.
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Activity 9b
Learning to Use the Spectrophotometer
Purpose In this activity you will familiarize yourself with one type of spectrophotometer and determine the wavelength ranges for colors of visible light produced by the spectrophotometer. Background A spectrophotometer is a laboratory instrument that uses light to study molecules that are in solution. To understand how to use the spectrophotometer (aka spec ), we need to learn a little bit about light. All light energy travels in waves. The distance between each wave crest is called the wavelength. The wavelengths of different types of light energy determines their properties. The shorter the wavelength, the more energy that type of light carries. The range of wavelengths of visible colored light is called the visible light spectrum , and extends from 400 – 700 nm (see figure). We can’t actually see the light waves, but the cells in our eyes have photoreceptors that can detect light waves between 400 – 700 nm. White light contains all the wavelengths of visible light. Molecules can either absorb or transmit part or all of this light energy. Substances appear to be a certain color because of the light energy they do not absorb. For example, plants appear green because the pigment molecules in their leaves absorb all except green visible light waves.
Activity 9c
Using the Spectrophotometer to Study Molecules
Purpose In this activity you will learn how to measure the absorbance of molecules in solution at different wavelengths using a spectrophotometer. In this activity, three different colored solutions are studied to determine which wavelengths of light they absorb. The data you collect will then be graphed to create an absorbance spectrum for each solution tested. By graphing your data, you will learn about the relationship between the color of light and the ability of different molecules to absorb light energy. Background When molecules absorb wavelengths of light in the UV and visible range of the light spectrum, this absorbance can be detected by a spectrophotometer. In order to study molecules with a spec, a technician shines a light on a sample containing molecules in solution and measures the absorbance of light by the molecules. Absorbance is measured in absorbance units (au). The maximum amount of absorbed light that can be detected by a typical VIS (visible light) spec has a value of 2 au; therefore, all the absorbance values fall between 0 and 2 au. Procedure
- Measure the absorbance of each dye solutions at different wavelengths in the visible light spectrum (from 400 nm – 620 nm). Record your data in your lab notebook in data tables similar to Tables 9.2, 9.3, and 9.4 (see next page). - NOTE: We may be using the older VIS (visible light) spectrophotometers for this activity that were used earlier in Activity 9b). There is also a possibility that we will be able to use digital UV/VIS spectrophotometers, which will provide data much more quickly. Depending on which equipment is available, your instructor will give you more specific instructions about which cuvettes to use and how to operate the spectrophotometer in class. - Regardless of which spectrophotometer we use, you will always use water as your “blank” in this experiment; the blank is used to calibrate the spectrophotometer before taking measurements.
- When you have finished recording all of the data, graph the absorbance spectra for the three dyes. The X axis will have wavelength values from 400 – 620 nm, and the Y axis will have absorbance units (au). You can create one graph with three different lines (one for each color dye). Each line on the graph represents the absorbance spectrum for that color dye.
- What do you notice about the minimum absorbance values (lambdamin, or λmin) for each dye in terms of where they fall in the visible light spectrum (you can refer back to Activity 9b for the wavelength ranges of each color in the visible light spectrum)?
Table 9. Absorbance of Red dye at Different Wavelengths
Red dye
Wavelength Abs
Table 9. Absorbance of Green dye at Different Wavelengths
Green dye
Wavelength Abs
Table 9. Absorbance of Blue dye at Different Wavelengths
Blue dye
Wavelength Abs
Lab 9 Homework Name: ________________________
- On which plate(s) would you expect to find bacteria most like the original non-transformed E. coli colonies you initially observed on your starter plate? Explain your predictions.
- If there are any genetically transformed bacterial cells, on which plate(s) would they be located? Explain your prediction.
- For each of the four plates you set up (labeled below), predict: a) whether there will be bacterial growth or not b) if there are bacteria growing, will they glow green or not? Explain your predictions.
- Given your data from Activity 9b, what are the approximate wavelengths of the following colors? a) blue-green: b) greenish-yellow: c) red-orange:
- Looking at the absorbance spectrum for the red sample, does the red dye absorb red light or non-red light the most? What about the blue and green spectra?
- Given your data and what you have learned about light absorption, what color light would you expect purple grape juice to absorb?
