Recombinant DNA

Scientists can mix tiny bits of life.

They take parts from one thing and add them to another. This makes something new.

All living things have the same building blocks. This lets scientists join them together. They can join plant parts with tiny germs. They can even join human parts with fungus.

This helps make many things. It helps make medicine for sick people. It even helps make cheese!

This is a very cool way to work.

Scientists can mix tiny bits of life. They do this using a method called recombinant DNA technology. This is a way to join DNA from different sources. DNA is the material that tells living things how to grow.

All living things share the same chemical structure. This means scientists can join parts from many different species. They can join plant DNA with bacteria. They can even join human DNA with fungus. Sometimes, they use DNA that is made in a lab.

One way to do this is through molecular cloning. This is a process that happens inside a living cell. Scientists use a vector to help. A vector is a small piece of DNA that carries the new parts.

This work helps make many important things. It can make human insulin for people with diabetes. It can also make chymosin to help make cheese. In fact, about 60% of hard cheese in the U.S. uses this enzyme. This technology also helps make vaccines and growth hormones. It is a very useful tool for medicine and science.

Recombinant DNA is a special kind of DNA created in a lab. It is made by joining DNA fragments from different sources together. This creates new sequences that would not normally be found in a genome. Scientists can call these molecules chimeric DNA. This name comes from a mythical creature made of different animals.

This work is possible because all living things share the same chemical structure. Only the sequence of nucleotides is different between species. Scientists can join plant DNA to bacterial DNA. They can even join human DNA with fungal DNA. They can also use DNA made through chemical synthesis.

One way to make this DNA is through molecular cloning. This is a laboratory process used to produce recombinant DNA. It is different from a method called PCR. PCR copies DNA in a test tube without living cells. Molecular cloning happens inside a living cell instead.

To do this, scientists use a cloning vector. A vector is a small DNA molecule that replicates in a cell. These are often made from viruses or plasmids. The process involves seven main steps. First, scientists choose a host organism and a vector. Then they prepare the vector and the DNA to be cloned. After that, they create the recombinant DNA and put it into the host. Finally, they select and screen the organisms for the right properties.

Once the DNA is inside a host, it might be expressed. Expression means the cell uses the DNA to make a recombinant protein. This requires a process called transfection. Scientists use host cells like bacteria, yeast, or even mammalian cells. Some common cells used are human embryonic kidney cells. To make a protein, the gene often needs restructuring. It needs specific parts like a promoter or a transcriptional terminator. These parts help the host cell read the new instructions correctly. Without these, the host might just replicate the DNA without making anything.

Most organisms with recombinant DNA look and act normally. Their appearance and behavior usually do not change. Scientists often use a PCR test to find the new DNA. Sometimes, the new DNA can cause changes. It might cause toxicity to the host cell. It can also cause insertional inactivation. This happens when the new DNA lands inside a host gene. Scientists sometimes use this to "knock out" a gene to see what it does. It can also accidentally turn on a gene that was silent.

This technology is used in many places today. You can find its products in pharmacies and supermarkets. For example, it helps make chymosin for cheese. This enzyme is used in about 60% of hard cheese in the U.S. In 1990, the FDA named it safe for use. Recombinant DNA also makes human insulin for people with type 1 diabetes. Before this, insulin came from pigs or cattle. It also helps make growth hormone and the hepatitis B vaccine. Even some pet shops sell animals like GloFish made with this technology.

Recombinant DNA, often called rDNA, consists of DNA molecules created through laboratory methods of genetic recombination. These methods bring together genetic material from multiple different sources. This process creates new sequences that would not naturally exist within a single genome. Because these molecules can be made from two different species, they are sometimes called chimeric DNA. This name refers to the mythical chimera, a creature composed of parts from different animals. Recombinant DNA is possible because all organisms share the same basic chemical structure. The only difference between species is the specific sequence of their nucleotides.

Scientists use a process called molecular cloning to produce these molecules. Molecular cloning is one of two main methods used to direct the replication of specific DNA sequences. The other common method is called polymerase chain reaction, or PCR. There are two fundamental differences between these techniques. PCR replicates DNA inside a test tube without the use of living cells. In contrast, molecular cloning involves replicating DNA within a living host cell. While PCR amplifies an existing sequence, cloning requires cutting and pasting different DNA sequences together.

To perform molecular cloning, researchers must use a cloning vector. A vector is a small DNA molecule that can replicate inside a living cell. These vectors are generally derived from viruses or plasmids. They contain the necessary genetic signals for replication. Vectors also include extra elements to help insert foreign DNA or identify cells that contain the recombinant DNA. The choice of vector depends on the host organism and the size of the DNA being cloned. The standard cloning protocol involves seven specific steps. First, a host organism and vector are chosen. Then, the vector DNA and the target DNA are prepared. Next, the recombinant DNA is created and introduced into the host. Finally, scientists select and screen the organisms to find the desired clones.

Once the recombinant DNA is inside a host, it may undergo DNA expression. This is the process where the cell uses the DNA to produce a recombinant protein. To achieve this, scientists must perform transfection, which is the introduction of DNA into host cells. Common host cells include bacteria, yeast, insect, or mammalian cells. Scientists often use human embryonic kidney cells or Chinese hamster ovary cells. Simply putting DNA into a cell does not guarantee expression. The DNA might be replicated without ever being used to make a protein. To ensure expression, the gene often requires restructuring. It must include parts like a promoter, a translational initiation signal, and a transcriptional terminator. These parts allow the host's machinery to read the foreign instructions.

Most organisms containing recombinant DNA maintain a normal phenotype. This means their appearance, behavior, and metabolism usually stay the same. Scientists often use a polymerase chain reaction (PCR) test to detect the presence of the new sequences. However, some changes can occur. The recombinant gene might cause toxicity to the host organism. It can also cause insertional inactivation. This happens when the recombinant DNA inserts itself directly into a host cell's gene. Researchers sometimes use this to "knock out" a gene to study its function. In other cases, the insertion might inappropriately activate a previously silent host gene.

Recombinant DNA technology has massive applications in medicine and industry. It is used in basic research to identify, map, and sequence genes. It is also used to create recombinant proteins, which serve as reagents in many laboratory experiments. One famous example is recombinant chymosin. Chymosin is an enzyme used to make cheese. Traditionally, it was taken from the stomachs of calves. Now, scientists use engineered E. coli bacteria to produce it. This microbiologically produced enzyme is identical to the calf version. Today, about 60% of hard cheese in the United States is made using this genetically engineered chymosin. The FDA granted it "generally recognized as safe" status in 1990.

Medicine has also been transformed by this technology. Recombinant human insulin has almost entirely replaced insulin taken from pigs or cattle. This is vital for patients with type 1 diabetes. Using recombinant insulin prevents the immune system from attacking the medicine. Similarly, recombinant human growth hormone (HGH) is used for patients with growth deficiencies. Before this, HGH was taken from human cadavers, which was an unsafe practice. Recombinant factor VIII is also used to treat hemophilia. This protein helps blood clot in patients who cannot do so naturally. Finally, the hepatitis B vaccine is created using a recombinant subunit method. This involves producing a virus surface antigen within yeast cells.