Bacterial Transformation - Online Tutor, Practice Problems & Exam Prep

Transformation is a process where bacteria uptake DNA from their environment, which can occur naturally when bacteria die and release their DNA or through experimental methods. Competent bacteria can take up this DNA, which may exist as plasmids or as fragments that integrate into their chromosome, forming heteroduplexes. This technique is crucial for gene mapping, as closely located genes are more likely to be taken up together during transformation, allowing scientists to determine gene loci effectively.

Transformation

Transformation is when a bacterium takes up DNA from the environment. So why or how does DNA get into the environment? Well, it can get there in two main ways. One is that it's experimentally placed there. It means that scientists were doing an experiment, and they had a bunch of bacteria, and they just threw in some DNA in that, you know, bacterial liquid. And so now it's just sort of in the culture that the bacterial is growing in. This method is through the experimental process. The second way is more natural, and this happens when a bacterium dies. Right? And it lyses, for instance, and it can lyse for a number of reasons: it swells and bursts, it is just a normal death, it has been infected by a virus, and now the virus has lysed it, but essentially, in any of these cases when that happens, the DNA that the bacterium had is now released into the environment. And so when it's released, it's just floating around in there, and other bacteria can take it up. Not all bacteria are capable of taking it up. The bacteria that are we call competent, and these are the ones that are capable of transformation. So competent bacteria are what we call competent cells. They have some kind of physiological state. It's natural, it can be experimentally induced, and this allows the bacteria to be, you know, looking for that DNA and able to take it in. Right? Because it can be easy. This bacterium does have a membrane around it. And so that DNA has to be able to get through that membrane, and that's not a normal process. So there has to be some kind of physiological state, either high salt or high temperature or something that loosens up that membrane to allow that DNA to get in, and so these are called competent cells.

Now, what's inside, the transferred DNA can stay in two forms. The first type is a plasmid, and this is the most common, is that the DNA that's found in the environment is a plasmid, and so once it gets into the bacterium, it stays a plasmid. Right? And this is the most common experimental approach. So, say, a scientist wants to grow a gene into a protein, wants to grow lots of protein, what they can do is put it on a plasmid, sort of, sit it with some bacteria, some competent bacteria, induce that bacterium to transform, take it up, and then grow that. The bacteria will now grow that plasmid and produce that protein. So this is a really common experimental approach. Now, the other way that it can happen is that if it's not a plasmid, it is instead this, like, double helix. It's just some kind of, like, chopped-up piece of a double helix DNA. Usually, what happens is the bacteria will digest it, so it's a single strand, and then align it at some point of the bacterial chromosome. Then what's formed is a structure called a heteroduplex, and there's a single strand and whatever portion it's aligned with, usually, it's similarly complementary. It's not perfect, but it's close enough that it aligns, and it will form this heteroduplex process. So what this looks like is if it's a plasmid, you can see it's just transformed and it's taken up by the cell. If it's double-stranded, you can see that it enters the cell, it's digested to a single strand, and then aligned to the complementary region in the bacterial DNA. This forms that heteroduplex.

Now, transformation can also be used to map genes. So here we are back to mapping. Determine where gene loci are. So what happens is you can induce some kind of fragmentation of the DNA. You can do this through DNA extraction, certain enzymes, or temperatures, or salt concentration. There are lots of ways to introduce fragments into DNA. Right, so if you have DNA and you want to know where the genes are located on it, chop it into a lot of pieces, incubate it with some bacteria and some competent bacteria, and then allow for transformation to take place. Now, the closer the two genes are together, the more likely they'll be taken up together, because it'll be less likely that they've been chopped up in between the genes, whereas the farther they are apart, the less likely it is they'll be taken up together. This phenomenon is called double transformation when two genes are taken up together. So, in this scenario, we have some genes, a red and a blue gene, that we're interested in mapping. We want to know how close they are together. So, in this case, they're close together. In this case, they're farther apart. Now, we do something to this DNA to chop it into a lot of pieces. Like I mentioned before, there are lots of different ways to do this. It doesn't matter which way you choose, but you chop the DNA into a lot of pieces. So now, we have our fragmented DNA. You can see that the genes that are close together remain close together. Right? There was nothing that chopped them up in between there. Where the genes that are farther apart actually ended up being chopped separately. And so they are two completely different fragments. And so when transformation happens, the genes that are close together will be picked up together, because they were never cut apart from each other. Whereas, the genes that are farther apart have been chopped up in between them, and so now you get only one of the genes incorporating. This process here is what allows us to map genes via transformation. So transformation is awesome. It's a huge experimental technique. If you ever plan on working in a lab, you'll do it at least once, so it's important to know. With that, let's now move on.

Transformation is the process of what occurring with DNA?

• A. Two DNA physically exchange DNA
• B. Bacteria take up DNA from the environment
• C. DNA is degraded
• D. DNA jumps from one bacteria cell to another

Scientists must use what type of cells to transform DNA in the laboratory?

• A. Viable cells
• B. Animal cells
• C. Competent cells
• D. Heat sensitive cells

The DNA from a bacterium with the genotype a+ b+ c+ is used to transform a bacteria with the genotype a b c. Gene pairs were checked for cotransformation with the following results. Using these results determine which genes are linked. 

• A. A and B
• B. B and C
• C. A and C

Here’s what students ask on this topic:

What is bacterial transformation and how does it occur?

Bacterial transformation is a process where bacteria take up DNA from their environment. This can happen naturally when bacteria die and release their DNA, or it can be induced experimentally. In natural transformation, DNA from lysed bacteria is released into the environment and can be taken up by competent bacteria, which are in a physiological state that allows DNA uptake. Experimentally, scientists can introduce DNA into a bacterial culture, and through methods like high salt or high temperature, make the bacteria competent to take up the DNA. The DNA can exist as plasmids or fragments that integrate into the bacterial chromosome, forming structures like heteroduplexes.

What are competent cells in bacterial transformation?

Competent cells are bacteria that have the ability to take up extracellular DNA from their environment. This competence can be a natural physiological state or induced experimentally. Naturally competent bacteria have specific mechanisms to uptake DNA, while in the lab, competence is often induced by treating bacteria with high salt concentrations or heat shock, which makes their cell membranes more permeable to DNA. Competent cells are crucial for transformation experiments, as they allow the uptake and incorporation of foreign DNA, which can be used for gene cloning, protein expression, and genetic mapping.

How is bacterial transformation used in gene mapping?

Bacterial transformation is used in gene mapping by determining the proximity of genes on a DNA molecule. Scientists fragment the DNA and incubate it with competent bacteria. During transformation, closely located genes are more likely to be taken up together, a process known as double transformation. By analyzing which genes are co-transformed, researchers can infer their relative positions on the chromosome. The closer two genes are, the higher the likelihood they will be taken up together, allowing for the mapping of gene loci based on transformation frequencies.

What is the difference between plasmid and chromosomal DNA uptake in bacterial transformation?

In bacterial transformation, plasmid DNA and chromosomal DNA are taken up differently. Plasmid DNA, which is circular and extrachromosomal, can enter the bacterial cell and replicate independently. This is commonly used in laboratory settings for cloning and protein expression. Chromosomal DNA, on the other hand, is usually linear and fragmented. Once inside the bacterial cell, it is often digested into single strands and integrated into the bacterial chromosome through homologous recombination, forming structures called heteroduplexes. This integration allows for the stable incorporation of new genetic material into the bacterial genome.

What are the main experimental methods to induce competence in bacteria?

The main experimental methods to induce competence in bacteria include chemical and physical treatments. Chemical methods often involve treating bacteria with calcium chloride (CaCl₂), which increases the permeability of the cell membrane to DNA. Physical methods include heat shock, where bacteria are exposed to a sudden increase in temperature, and electroporation, where an electric field is applied to create temporary pores in the cell membrane. These methods make the bacterial cell membrane more permeable, allowing the uptake of extracellular DNA during transformation.