Molecular cloning

Scientists can make many copies of tiny DNA.

First, they take DNA from a living thing. They use special tools to cut it. Then, they join it to a small ring of DNA.

This ring is put into tiny bacteria. The bacteria act like a host. As the bacteria grow, they copy the DNA too. This makes a large group of identical parts.

This helps us study how life works.

Scientists use a set of steps called molecular cloning. This way lets them make many copies of DNA.

First, they pick a host. Most people use E. coli bacteria. These bacteria are easy to grow in a lab. Next, they pick a vector. A vector is a small ring of DNA called a plasmid.

This ring carries the new DNA into the bacteria.

To start, scientists prepare the DNA. They use enzymes to cut the DNA into small pieces. Enzymes are like tiny tools that can cut or join parts. They use one enzyme to cut the DNA. Then, they use another enzyme called DNA ligase. This enzyme acts like glue to join the pieces together. This creates recombinant DNA. This is DNA made from two different sources.

Next, they put the new DNA into the host bacteria. The bacteria then grow and make many copies of the DNA. This makes a large group of identical DNA. We call these copies clones.

This helps scientists study genes in medicine and biology.

Molecular cloning is a set of methods used in biology. It helps scientists make many copies of a specific DNA molecule. This process is very important for modern medicine and biology. Scientists use it to build recombinant DNA. This is DNA made from two different sources. The goal is to make a whole group of cells that all have the same DNA. This group is called a clone.

There are many steps in this way it works. First, scientists pick a host organism and a vector. A vector is a tool like a plasmid, which is a small ring of DNA.

Next, they prepare the vector DNA and the DNA they want to clone. They use special tools called restriction endonucleases to cut the DNA. These enzymes cut the DNA at specific spots. Then, they use an enzyme called DNA ligase. This enzyme acts like glue to join the pieces together. This creates the recombinant DNA. Finally, they put this DNA into the host, like E. coli bacteria.

This field changed a lot in the 1970s. Before then, it was hard to study single genes from complex living things. Microbiologists found ways to study how bacteria stop certain viruses. They discovered restriction endonucleases that could cut DNA at specific sequences. They also found DNA ligase to join fragments together. The first recombinant DNA molecules were made and studied in 1972. This discovery allowed scientists to produce large amounts of purified DNA in lab cultures.

Many facts make this process work. Most experiments start with E. coli bacteria because they grow very fast. A plasmid vector usually has four important parts. It needs an origin of replication to make copies. It also needs sites for cutting, a marker gene, and a tag gene. Some DNA is harder to clone than others. For example, pieces larger than 10 kbp are hard to insert. However, scientists can use something called bacteriophage lambda to carry larger pieces up to 40 kbp.

You can think of molecular cloning like a copying machine for life. It is similar to a tool called PCR. PCR also makes many copies of DNA. But PCR happens in a liquid solution without living cells. Molecular cloning uses a living microorganism to do the work. This lets the tiny host cells grow and expand the DNA for us. By using these methods, scientists can study the very building blocks of all living things.

Molecular cloning is a collection of experimental methods used in molecular biology. These methods allow scientists to assemble recombinant DNA molecules. Recombinant DNA is DNA created by combining sequences from two different organisms. Once assembled, these molecules are directed to replicate within a living host organism. The term "cloning" describes the result of this process. It produces a large population of cells that all contain identical DNA molecules. This technique is a foundation for many modern biological and medical fields.

The process relies on the fact that DNA structure is fundamentally the same in all living things. If a DNA segment is inserted into a sequence that contains replication instructions, the host will copy it. This works because the host's own cellular machinery recognizes the foreign DNA. This method is similar to Polymerase Chain Reaction, also known as PCR. However, PCR replicates DNA in a liquid solution without living cells. Molecular cloning uses a living microorganism to perform the replication. This allows the DNA to be copied as the host cells grow and divide.

A standard molecular cloning experiment follows a specific sequence of seven steps. First, scientists choose a host organism and a cloning vector. A vector is a DNA molecule used to carry foreign genetic material. Second, they prepare the vector DNA by cutting it. Third, they prepare the specific DNA sequence they wish to clone. Fourth, they use enzymes to create recombinant DNA by joining these pieces. Fifth, they introduce the recombinant DNA into the host organism. Sixth, they select only the organisms that successfully took up the DNA. Finally, they screen those organisms to ensure they have the correct genetic properties.

Most experiments begin with a laboratory strain of Escherichia coli, or E. coli. This bacterium is used because it is easy to grow and highly versatile. Scientists often use a plasmid as the cloning vector. A plasmid is a small, circular piece of DNA.

A functional plasmid vector must contain four essential components. It needs an origin of replication so the host can copy the DNA. It requires unique restriction endonuclease recognition sites where foreign DNA can be inserted. It also needs a selectable genetic marker gene to help identify successful cells. Finally, a tag gene allows scientists to screen for cells containing the desired inserts.

To prepare the DNA, scientists use specialized enzymes called restriction endonucleases. These enzymes act like molecular scissors that cut DNA at specific sequences. Scientists often use the same enzyme to cut both the vector and the target DNA. This ensures the ends of the fragments are compatible for joining. Sometimes, an enzyme called alkaline phosphatase is used to treat the vector. This prevents the vector from simply closing back up without the new DNA. Once the pieces are ready, an enzyme called DNA ligase acts as glue. It joins the fragments together to form the final recombinant molecule.

The history of this field changed significantly in the 1970s. Before this time, scientists struggled to isolate individual genes from complex organisms. This changed when microbiologists studied how bacteria restrict the growth of bacteriophages. They discovered restriction endonucleases that cleave DNA at specific locations. They also identified DNA ligase, which could join these fragments in new combinations. The first recombinant DNA molecules were successfully generated and studied in 1972. This allowed researchers to produce large quantities of purified DNA from bacterial cultures.

While most DNA can be cloned, some sequences are more difficult to work with. Inverted repeats, origins of replication, centromeres, and telomeres are harder to clone. Size is also a major factor in success. Inserting DNA sequences larger than 10 kbp is very difficult. However, scientists can use modified bacteriophages, such as bacteriophage lambda, to carry larger sequences. These can successfully insert up to 40 kbp of DNA.

Modern scientists often use computer software to plan these complex steps. Programs like SnapGene or ApE allow them to simulate the entire process before starting in the lab.