Transcription (genetics)
Transcription in genetics is a crucial biological process where the genetic information encoded in DNA is copied into messenger RNA (mRNA). This process is essential for the synthesis of proteins, which are vital molecules that perform various functions within cells. During transcription, the double-helix structure of DNA unwinds, allowing RNA polymerase, the key enzyme, to read one of the DNA strands as a template. This results in the formation of a complementary mRNA strand, following nucleic acid pairing rules, where uracil replaces thymine found in DNA.
Transcription involves several supporting enzymes, including helicase, which separates the DNA strands, and DNA ligase, which reseals them after transcription. Although errors can occur during transcription, the cell has mechanisms to minimize potential negative effects, such as mutations that could lead to diseases like cancer. Following transcription, the mRNA molecule moves to the cytoplasm, where it participates in the next step, translation, to synthesize proteins. Understanding transcription is fundamental to genetics and molecular biology, as it underpins how genetic information is expressed and utilized in living organisms.
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Transcription (genetics)
DNA molecules contain the blueprints for life. More specifically, they contain genetic information responsible for telling cells in organisms what to do. However, in order for these blueprints to be used, they first need to undergo a process called transcription. In biology, deoxyribonucleic acid, or DNA, contains genetic information, while ribonucleic acid, or RNA, copies it. Only after a gene sequence has been transcribed can it undergo the final step, translation.
Together, transcription and translation help cells produce the molecules they need to function. The molecules produced from the copying of DNA are proteins. Proteins are the primary working molecules within all cells. They allow cells to communicate with one another, help digest food into usable energy, and provide structural support within cells. But none of this could be achieved if a cell did not have the ability to transcribe and translate its own genetic code in the first place.
Brief History
Little was known about DNA prior to the 1950s. In 1953, four scientists, Francis Crick (1916–2004), James D. Watson (1928–), Maurice Wilkins (1916–2004), and Rosalind Franklin (1920–58) made a remarkable breakthrough in this field. They determined the structure of DNA, for which Crick, Watson, and Wilkins received the Noble Prize in 1962. Though Franklin died before the prize was awarded, she is widely credited with producing a photograph of the helical structure of DNA in 1952 and other contributions leading to the discovery of DNA’s structure. In 1961, Jacques Monod (1910–76), André Lwoff (1902–94), and François Jacob (1920–2013) proposed the idea that genetic material directed the creation of proteins. The three scientists shared the 1965 Nobel Prize for their work. In addition, there were many other scientists along the way who contributed to the discovery of DNA transcription.
In 1959 the Spanish biochemist Severo Ochoa (1905–93) received a Nobel Prize for replicating the RNA synthesis process in a laboratory. By 1965, several laboratories began pursuing the transcription process as well. Finally, in 2006, another scientist by the name of Roger D. Kornberg (1947–) received the Nobel Prize in Chemistry for his contributions to the field of eukaryotic transcription, or plant and animal transcription.
Overview
For a gene to be copied and used, it first needs to be transcribed. During transcription, DNA’s double-helix structure opens up, exposing two separate nucleic acid strands. From here, a variety of different RNA molecules will locate the needed genetic information and begin transcribing. The enzyme responsible for the reading and copying of genes is RNA polymerase. RNA polymerase opens up the double helix, and uses one strand of DNA as a template for constructing a messenger RNA molecule.
RNA polymerase follows the traditional nucleic acid base pairing rules—that is, uracil will replace thymine and pair with adenine as a result. The pieces of genetic information being read are called the template strands, while the pieces of genetic information that are not being read are called the nontemplate strands. RNA polymerase cannot promote transcription on its own, however. It requires cooperation from several other enzymes within the cell, including helicase, DNA ligase, and topoisomerase.
Helicase is the enzyme in transcription that is responsible for melting or breaking away the hydrogen bonds that hold the two halves of the DNA double helix together. DNA ligase is the enzyme that helps reseal the DNA strands once all necessary transcriptions have taken place. Topoisomerase is the enzyme that is in charge of breaking and resealing DNA’s sugar phosphate backbone in order to lessen the amount of tension being caused by twisting.
Transcription errors sometimes arise during cell division, but this is rare, and organisms have several ways to minimize the negative effects, which may include cancer-causing mutations. Research has suggested that high numbers of transcription errors in certain neurons may cause neurodegenerative diseases such as Alzheimer's. To ensure that the only nucleic acid molecules left behind after transcription are that of DNA, the enzyme DNA polymerase 1 slides along the DNA strand that is being transcribed and removes RNA nucleotides. It then replaces them with their DNA counterpart.
After transcription is complete, the newly created messenger RNA molecule will move to the second phase of the process, translation. The messenger RNA travels to the cytoplasm of the cell, actively searching for a ribosome, a protein-producing organelle, to bind with. Ribosomes are unable to produce proteins on their own and need to read the genetic code carried by the messenger RNA molecules.
The translation of a particular gene follows three steps. First, it must bind to a ribosome’s binding site, where it starts translating the genetic code into amino acids, which are the building blocks of proteins. The next step of the translation process involves elongating the amino acid chain. In this context, the term protein is reserved for amino acid chains that are more than twenty peptides long.
Once all the necessary amino acids have been constructed, the ribosome will stop translating the genetic information. For the production of the protein to be complete, it is released from the ribosome, where it further becomes modified into its final protein structure.
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