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Prokaryotic
- E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon and energy. E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA.
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E. coli is a chemoheterotroph whose chemically defined medium must include a source of carbon and energy. E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA. Under ...
- Overview
- Key points:
- Introduction
- How do prokaryotes reproduce?
- Prokaryotes reproduce fast!
- Bacteria in molecular biology
- E. coli as DNA and protein factories
- Steps of transformation
How prokaryotes reproduce by binary fission. Use of E. coli bacteria in molecular biology.
•Prokaryotes (bacteria and archaea) reproduce asexually through binary fission. Most prokaryotes reproduce rapidly.
•Due to their fast growth and simple genetics, E. coli bacteria are widely used in molecular biology.
•In the laboratory, a gene can be transferred into E. coli bacteria on a small, circular DNA molecule called a plasmid. The plasmid is taken up by the bacteria in a process called transformation.
•Prokaryotes (bacteria and archaea) reproduce asexually through binary fission. Most prokaryotes reproduce rapidly.
•Due to their fast growth and simple genetics, E. coli bacteria are widely used in molecular biology.
•In the laboratory, a gene can be transferred into E. coli bacteria on a small, circular DNA molecule called a plasmid. The plasmid is taken up by the bacteria in a process called transformation.
•The transformed E. coli bacteria can be used to make many copies of the plasmid. In some cases, they will also express the gene on the plasmid and make protein.
Let's say you have one bacterium. How can you get more identical bacteria? How quickly can you get them? And, most importantly, why on Earth would you want a whole bunch of identical bacteria?
Let's fast-forward to that last question: some bacteria, most notably Escherichia coli (E.coli), are widely used in molecular biology labs. There, they serve as little "factories" that churn out many copies of a desired DNA molecule, or many molecules of a needed protein (such as the insulin used by diabetics to regulate their blood sugar). The more bacteria, the more of the DNA or protein product that can be made.
Prokaryotes reproduce through a cell division process called binary fission. Like mitosis in eukaryotes, this process involves copying the chromosome and separating one cell into two.
Binary fission is an asexual form of reproduction, meaning that it does not involve production of eggs and sperm or mixing of genetic material from two individuals. Except in the case of rare mutations, or changes in DNA sequence, binary fission produces daughter cells that are genetically identical to the mother cell.
Prokaryotes in general reproduce much faster than multicellular eukaryotes. This can be measured in terms of generation time, or the length of time from the birth of one generation to the birth of the next.
For humans, a typical generation time might be in the neighborhood of 20 years. For a typical bacterium, that might be closer to 20 minutes! As a matter of fact, the E. coli bacteria that live inside your gut, and that are widely used in laboratory research, can produce a new generation every 17 minutes or so1 .
Bacteria that reproduce quickly and are easy to grow in the lab make good model organisms for many scientific studies. E. coli, for instance, is one of the most widely used organisms in biological research.
Although you may have heard of E. coli as a food contaminant, harmless strains of E. coli are used in biology labs worldwide. In fact, many basic biological processes, like the mechanism of DNA replication, were first discovered in E. coli.
Today, E. coli are sometimes used as tiny “factories” to synthesize DNA or proteins. Researchers can insert a gene of interest into E. coli cells through a process called transformation (uptake of DNA from the environment), which is described further in the article on prokaryote genetic variation. In such experiments, the gene of interest is typically borne on a piece of circular DNA called a plasmid, which can be copied by the bacterium and passed on to its offspring.
Once they contain the plasmid with the gene of interest, the E. coli cells will replicate it and pass it along each time they divide, making many copies of the plasmid DNA. If the plasmid contains the right control sequences, the E. coli can also be instructed to transcribe and translate the gene of interest, producing protein. For example, most of the insulin used by diabetics is produced in E. coli cells using this strategy.
In a typical transformation experiment, the target gene (blue DNA above) is first inserted into a plasmid. In addition to the target gene, the plasmid also contains a gene that provides resistance to a particular antibiotic (red DNA above). If the goal is to use the bacteria to synthesize protein from the gene, the plasmid will also contain a promoter, or control sequence, that allows the target gene to be expressed in bacteria (green DNA above).
When copies of the plasmid are mixed with E. coli cells and the cells are heat-shocked (exposed briefly to high temperature), a small fraction of them will take up the plasmid. All of the E. coli are then spread on a nutrient plate containing the antibiotic. The purpose of the antibiotic is to only let bacteria with the plasmid survive and grow.
Steps of bacterial transformation.
E. coli lacking the plasmid will be killed by the antibiotic. E. coli that contain the plasmid, however, can survive and reproduce (thanks to the antibiotic resistance gene in the plasmid). Each resistant cell will form a colony of genetically identical bacteria, which appears on the agar plate as small dot. An antibiotic-resistant colony can be analyzed (checked by other methods to confirm it contains the correct plasmid), then grown up to make a large culture of identical, plasmid-bearing bacteria.
What use is a large culture of plasmid-bearing bacteria? Sometimes, researchers need many copies of the plasmid DNA for use in another experiment, and they can extract this DNA from the culture. Alternatively, if the plasmid contains the right promoter, the bacteria can be induced (instructed) to express the gene and synthesize protein. This technique is used to produce some medically important proteins, such as insulin and human growth hormone.
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While prokaryotes are always unicellular organisms, eukaryotes can be either unicellular or multicellular. For example, most protists are single-celled eukaryotes! Even though prokaryotes do not have a nucleus, they DO contain genetic information. Prokaryotes generally have single circular chromosomes where they store their genetic information.
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- A eukaryote is an organism with complex cells, or a single cell with a complex structures. In these cells the genetic material is organized into ch...
- No worries! We were all new to this at one time or another! To answer your question, yes, it doesn't need to be inside a membrane-bound nucleus in...
- I believe that the debate is continued, so we should still agree to the previous answer that prokaryotes CANNOT be multicellular. Bacteria might be...
- Biofilm Structure A microbial biofilm is made up of many prokaryotic organisms that combine to form a colony. The colony is adhered to a surface an...
- The answer really lies in whether or not the cells combine to form a multicellular mass or if they prefer living by themselves. Ones that form toge...
- It is not saying that a cell is multicellular. When it says eukaryotes can be multicellular it is referring to an organism made of eukaryotic cells.
- The cell wall is a sturdy structure that forms a protective envelope around the cell, and prevents physical damage.
For instance, the E. coli genome is less than half the size of the genome of yeast (a simple, single-celled eukaryote), and almost 700 times smaller than the human genome 13 ! By definition, prokaryotes lack a membrane-bound nucleus to hold their chromosomes.
A prokaryotic cell is a simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle. We will shortly come to see that this is significantly different in eukaryotes. Prokaryotic DNA is found in the central part of the cell: a darkened region called the nucleoid (Figure \(\PageIndex{1}\)).
Jan 26, 2021 · The main difference between prokaryotes and eukaryotes is that eukaryotes contain membrane-bound organelles, and prokaryotes do not. This means that prokaryotes do not have a nucleus; instead, they keep their DNA in a cell region called the nucleoid.
Dec 18, 2016 · A prokaryotic cell is a type of cell that does not have a true nucleus or membrane-bound organelles. Organisms within the domains Bacteria and Archaea are based on the prokaryotic cell, while all other forms of life are eukaryotic. However, organisms with prokaryotic cells are very abundant and make up much of Earth’s biomass. Overview.
