Polymerase is a type of enzyme found within cells that is involved in the polymerization of a polynucleotide, or the creation of DNA or RNA molecules. Enzymes are complex proteins that take part in chemical reactions within the cells, while remaining unchanged after the reaction. Most enzymes reduce the amount of energy needed for the reaction to go ahead, called the activation energy. These types of enzymes are called catalysts.
DNA and RNA are made up of long strands of nucleotides. Specifically, DNA is made up of adenine, guanine, cytosine and thymine. RNA is formed from strands of adenine, guanine, cytosine and uracil, instead of thymine. The polymerase enzymes reduce the energy needed to form the bonds between the nucleotides, thus allowing the larger molecules to be produced. There are different types of polymerases, but all are involved in reactions dealing with either DNA or RNA.
There are a variety of DNA polymerases, each with a separate role. DNA polymerase I, II, III and IV all play a part in the synthesis of a DNA molecule. DNA Pol III is the main enzyme involved in DNA replication. DNA Pol II is the enzyme involved in DNA repair, while DNA Pol I plays a role in the synthesis of the DNA molecule and proofreading for errors after DNA Pol III has created the new molecule.
The polymerases have a high accuracy, but errors can occur within the genetic code, which can cause mutations in the cells and organism. Proofreading is done as the DNA molecule is replicated and if an error is found, DNA Pol 1 can make the correction. When replication is not taking place, DNA Pol II scans the molecules to look for any errors or gaps that may have occurred over time. DNA Pol IV, or the SOS repair polymerase, is found within bacterial systems only and is one possible theory behind bacterial evolution.
As with DNA polymerase, there are also several RNA polymerases. RNA polymerase I, II and III, or Pol I, II and III, exist in higher-level, multi-cellular organisms. Each polymerase is responsible for transcribing a particular section of the DNA during transcription.
Pol I transcribes those genes that encode part of the ribosome. Ribosomes are the organelles where transcription takes place within the cells and each one is made up of a large and small subunit. The genes transcribed by Pol I produce the large subunit and part of the small subunit. Pol II transcribes the genes for messenger RNA, mRNA, and Pol III transcribes the genes for transfer RNA, tRNA. mRNA is the template for translation, or creating new proteins, and tRNA carries single amino acids to the ribosome and mRNA for linking into a larger chain to form the protein.