Transcription (biology)

Transcription is a key process in living things. It is how a small piece of DNA makes a copy of itself as a molecule called RNA. This helps cells make proteins, which act like tiny workers 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 helps make proteins, which are important for many functions in our bodies. The DNA has special areas 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.

Role of RNA polymerase in post-transcriptional changes in RNA

RNA polymerase helps change RNA after it is first made. It has a special part called the CTD, like a tail that changes shape. This tail helps with important jobs, like splicing, capping, and polyadenylation. These steps get the RNA ready to work in the cell.

Inhibitors

Transcription inhibitors are special 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.

Endogenous inhibitors

Main article: Regulation of transcription in cancer

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

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. There are about 10,000 of these factories in a typical cell. They contain enzymes that work together to create different pieces of RNA.

History

Scientists have always wanted to know how genes make proteins. In the 1950s, they learned how to make RNA in a lab. This helped us understand the genetic code. Later, they found out how special proteins called enzymes build RNA from DNA.

One scientist, Roger D. Kornberg, won a Nobel Prize in 2006 for his work on this process in complicated cells. His research showed the steps that let genes turn on and make proteins.

Measuring and detecting

Scientists use different ways to measure and detect transcription. Some methods, like the G-Less Cassette assay, show how strong a gene's "on switch" is. Others, such as Run-off transcription, help find where genes start to be read.

Newer tools, including RNA-Seq and Single cell RNA-Seq, let scientists study all the RNA in a cell or even a single cell. These tools help us learn 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.