Transcription (biology)

Transcription is a very important process in living things. It is how a tiny piece of DNA makes a copy of itself as a molecule called RNA. This helps cells make proteins, which are like tiny workers that do many jobs to keep us alive and healthy.

Some parts of DNA are copied into a special kind of RNA called messenger RNA, or mRNA. These mRNA molecules carry the instructions to make proteins. Other parts of DNA make a different kind of RNA called non-coding RNA, which also has important jobs in the cell.

Both DNA and RNA are made of building blocks called nucleotides. During transcription, a special enzyme called RNA polymerase reads the DNA and makes a matching RNA strand. This new RNA piece is called a primary transcript.

In viruses that use RNA instead of DNA, transcription also happens. These viruses need to make their own proteins to grow and spread, so they use a special enzyme to copy their RNA into messages that the host cell can understand. This helps the virus replicate and stay alive.

Background

During transcription, a part of DNA is copied into a molecule called RNA. This RNA can help make proteins, which are important for many functions in our bodies. The DNA has special areas called regulatory sequences that help control when and how much protein is made. There are areas before the main code called five prime untranslated regions (5'UTR) and areas after called three prime untranslated regions (3'UTR).

Unlike when DNA makes more DNA, transcription creates RNA that includes a nucleotide called uracil instead of thymine. Only one strand of DNA is used as a guide for making RNA. This process creates RNA in a specific direction, matching the DNA strand but with uracil replacing thymine. Transcription doesn’t need the extra steps that DNA replication uses, making it a bit less exact.

Major steps

Further information: Bacterial transcription and Eukaryotic transcription

Transcription is the process of making RNA from DNA. It has four main steps: starting, getting ready, making the RNA, and stopping.

When transcription starts, special proteins called transcription factors help RNA polymerase bind to the right spot on the DNA. This spot is called the promoter. In some cases, distant parts of the DNA called enhancers can also help by looping closer to the promoter.

During the making step, RNA polymerase reads one strand of the DNA and builds a matching RNA molecule. This RNA can be a message for making proteins (mRNA) or a special kind of RNA that does other jobs in the cell (non-coding RNA). The process stops when the RNA is finished, and the new RNA molecule is released.

Role of RNA polymerase in post-transcriptional changes in RNA

RNA polymerase is very important in all the steps that change RNA after it is first made. It has a special part called the CTD, which is like a tail that changes shape. This tail helps carry out important jobs, like splicing, capping, and polyadenylation. These steps help prepare the RNA to do its job in the cell.

Inhibitors

Transcription inhibitors are special kinds of medicines that can stop harmful bacteria and fungi from growing. For example, rifampicin works against bacteria by stopping them from making important instructions. Another example, 8-hydroxyquinoline, helps fight fungi in a similar way. These inhibitors can also affect how cells read their DNA, which plays a role in many biological processes.

Endogenous inhibitors

Main article: Regulation of transcription in cancer

In animals, many genes have special areas called promoters that contain CpG islands. When these CpG sites are methylated, it can turn off or silence the gene. In some cancers, like colorectal cancer, this silencing of genes by methylation may be more important than mutations in causing the disease. Other changes, like the production of microRNAs, can also silence genes in cancer. For example, in breast cancer, a microRNA called microRNA-182 can sometimes silence a important gene called BRCA1 more often than methylation does.

Transcription factories

Main article: Transcription factories

Inside cells, special areas called transcription factories help make RNA from DNA. These factories are found in the nucleus and can be seen using special tagging methods. There are about 10,000 of these factories in a typical cell, with most containing a group of enzymes that work together to create different pieces of RNA.

History

Scientists have long been fascinated by how genes lead to proteins. In the 1950s, researchers discovered ways to create RNA in a test tube, helping us understand the genetic code. Later, important studies showed how enzymes build RNA from DNA.

One scientist, Roger D. Kornberg, received a Nobel Prize in 2006 for his detailed work on how this process works in complex cells. His research helped us learn the molecular steps that allow genes to become active and produce proteins.

Measuring and detecting

Scientists have many ways to measure and detect transcription. Some methods, like the G-Less Cassette assay, help determine how strong a gene’s “on switch” is. Others, such as Run-off transcription, help find where genes start to be read.

Newer techniques, including RNA-Seq and Single cell RNA-Seq, let scientists look at all the RNA in a cell or even a single cell, revealing how much RNA is made and discovering new gene forms. These tools help us understand how genes work and how they change.

Reverse transcription

Main article: Reverse transcription

Some viruses, like HIV, can change RNA into DNA. This process is called reverse transcription and uses a special enzyme called reverse transcriptase. In HIV, this enzyme makes a DNA copy from the virus's RNA. Another enzyme, ribonuclease H, helps by breaking down the RNA, and integrase places the new DNA into the host cell's genes.

Our cells also have a similar enzyme called telomerase, which adds protective ends called telomeres to chromosomes. This helps keep important genes safe when cells divide. Telomerase can also help cancer cells grow continuously by protecting their chromosomes.