DNA polymerase

Tiny workers help make copies of your life.

These workers build new parts for your body. They read old parts to know how to build. This helps your body grow.

First, a helper opens up the old parts. This makes space for the workers to move. The workers then add new pieces one by one. They match the new pieces to the old ones.

Sometimes the workers make a small mistake. They can go back to fix it. This keeps the new parts correct. This is how your body stays healthy.

These workers pass information down to new cells. This helps life keep going. It is amazing how much they do!

DNA polymerase is a special tool in your cells. It helps make new DNA. This is how cells pass on information to new cells.

Before the work starts, a helper called helicase opens the DNA. It unzips the two strands. This gives the DNA polymerase a place to work.

The enzyme acts like a builder. It reads the old DNA strands. Then it adds new building blocks, called nucleotides, one by one. These blocks must match the old ones. For example, guanine always pairs with cytosine. Adenine always pairs with thymine.

Sometimes the builder makes a mistake. It might add the wrong block. Some DNA polymerases can fix this. This is called proofreading. The enzyme moves backward to take out the wrong part. Then it puts in the right one. This keeps the DNA correct.

The shape of this enzyme looks like a right hand. It has a thumb, a finger, and a palm. These parts help it hold and move along the DNA. This way, it can build very fast.

DNA polymerase is a special kind of enzyme that builds DNA molecules. These enzymes are essential for a process called DNA replication. This is how a single original DNA strand becomes two identical copies. Every time a cell divides, these enzymes must work to duplicate the DNA. This ensures that a copy of the genetic information is passed to each new daughter cell. Without this work, life could not pass its instructions from one generation to the next.

To start the work, a helper enzyme called helicase must first unwind the DNA. It breaks the bonds between the parts to unzip the double strand. This creates two single strands that act as templates for the new ones. The DNA polymerase then reads these old strands to build new ones. It adds building blocks called nucleotides one at a time. These blocks must match the original strand in specific pairs. For example, cytosine always pairs with guanine, and adenine always pairs with thymine.

Scientists have been studying these enzymes for a long time. In 1956, Arthur Kornberg and his team discovered DNA polymerase I in E. coli. He later won the Nobel Prize in 1959 for this important work. Later, in 1970, Thomas Kornberg and Malcolm E. Gefter discovered DNA polymerase II. Other types like DNA polymerase III were found in the 1970s. Even more types, such as IV and V, were found in 1999. Since 1983, these enzymes have also been used in a tool called PCR.

DNA polymerase is a very careful builder, but it is not perfect. It makes about one mistake for every billion base pairs it copies. Some versions of the enzyme have a special skill called proofreading. This uses an exonuclease activity, which is a way to remove parts. If the enzyme finds a wrong match, it moves backward to take it out. Then, it puts the correct nucleotide back in its place. This helps prevent mistakes that could lead to problems like cancer.

The shape of this enzyme is very interesting to look at. It looks much like a human right hand with a thumb, finger, and palm. The palm helps the chemical reaction happen while the DNA is bound. The finger part helps grab the new building blocks. The thumb helps the enzyme stay in place as it slides along. To move even faster, it often works with a ring-shaped protein called a sliding clamp. This clamp keeps the enzyme from drifting away from the DNA strand.

DNA polymerase is a vital family of enzymes that catalyze the synthesis of DNA molecules. These enzymes are responsible for building DNA from molecular precursors known as nucleoside triphosphates. This process is essential for DNA replication, which occurs every time a cell divides. During replication, DNA polymerase works to create two identical DNA duplexes from a single original duplex. This ensures that genetic information is passed accurately from one generation of cells to the next.

Before the enzyme can begin its work, the DNA molecule must be prepared. An enzyme called helicase unwinds the tightly woven DNA molecule. Helicase functions by breaking the hydrogen bonds between the nucleotide bases. This action "unzips" the double-stranded DNA into two separate single strands. These single strands then serve as templates for the replication process. DNA polymerase reads these existing strands to guide the creation of matching new strands.

To build the new strand, DNA polymerase adds nucleotides to the 3' end of the growing chain. This process results in the elongation of the new strand in a 5' to 3' direction. Because of this, the enzyme must move along the original template strand in a 3' to 5' direction. This specific movement creates two strands that are antiparallel, meaning they run in opposite directions. The enzyme ensures accuracy by pairing nucleotides with specific bases. For example, cytosine always pairs with guanine, and thymine always pairs with adenine.

The discovery of these enzymes changed our understanding of biology. In 1956, Arthur Kornberg and his colleagues discovered DNA polymerase I in the bacterium Escherichia coli. They were able to describe how the enzyme copies the base sequence of a template strand. For this groundbreaking work, Kornberg was awarded the Nobel Prize in 1959. Later, in 1970, Thomas Kornberg and Malcolm E. Gefter discovered DNA polymerase II. Other types, including DNA polymerase III, were found in the 1970s, while polymerases IV and V were identified in 1999.

DNA polymerase is highly efficient due to a characteristic called processivity. Processivity refers to the average number of nucleotides an enzyme adds each time it binds to a template. While a nonprocessive enzyme might add only one nucleotide per second, processive enzymes add many more. In some cases, such as phage T4 DNA elongation in E. coli, the rate can reach 749 nucleotides per second. To maintain this speed, the enzyme often associates with a ring-shaped protein called a sliding DNA clamp. This clamp prevents the polymerase from diffusing away from the DNA template.

Although these enzymes are fast, they are not perfect. DNA polymerase makes approximately one mistake for every billion base pairs copied. To maintain high fidelity, many polymerases possess an exonuclease domain for proofreading. If the enzyme detects an incorrect base pair, it uses 3'-5' exonuclease activity to excise the wrong nucleotide. The enzyme then moves backward, removes the error, and re-inserts the correct base. This correction is vital because mismatches can lead to dysfunctional proteins or even cancer.

The physical structure of DNA polymerase is remarkably consistent across different species. This is known as a conserved structure, which suggests the enzyme performs an irreplaceable function. The shape of the enzyme is often compared to a human right hand, consisting of palm, finger, and thumb domains. The palm domain is where the chemical reaction is catalyzed. The finger domain binds the nucleoside triphosphates to the template base. Finally, the thumb domain helps with the positioning and translocation of the DNA.

Scientists categorize DNA polymerases into several distinct families based on their sequence homology. These include families A, B, C, D, X, Y, and RT. For instance, Family A includes repair polymerases like Pol I, which is found in prokaryotes. Family RT includes reverse transcriptase, an unusual enzyme used by retroviruses to polymerize DNA from an RNA template. These enzymes are also essential in biotechnology. Since 1983, they have been used in the polymerase chain reaction, or PCR. Since 1988, thermostable versions have been used to make the PCR process more efficient.