Control of Gene Expression

Cell-specific gene expression helps explain how different cells make different proteins, even when they contain the same DNA. This process is central to development and to the way specialized tissues form.

Gene expression is controlled by regulatory signals that turn particular genes on or off in specific cells. As a result, one cell can follow a different molecular program from another cell in the same organism. These differences help create the variety of cell types needed for normal...

Gene expression control happens at several stages. Cells can change when a gene is active and how much product it makes. This regulation helps the cell respond to changing needs.

One major control point is transcription. In eukaryotes, transcription can be regulated before it starts. It can also be regulated while it is already underway. These steps help determine whether a gene is copied into RNA.

Cells can also regulate expression after transcription. The RNA may be processed, moved, or...

Cis-regulatory sequences are DNA switches that help control gene expression. They do not code for proteins. Instead, they can turn nearby genes on or off and help determine when a gene is active.

These sequences include promoters and enhancers. They are often found near the genes they regulate, and their effect depends on where they are in the genome. Because they work through DNA itself, they help cells control which genes are used in different situations.

Cis-regulatory sequences are an...

Transcription regulators can bind cooperatively to control gene expression. In cooperative binding, the binding of one regulator can make it easier for another regulator to bind nearby DNA. This shared effect helps cells fine-tune when genes are turned on or off.

The topic also connects to how regulators interact with each other and with DNA. These interactions can strengthen binding at a target site. They can also change how strongly a gene is controlled in a specific cell or condition.

Prokaryotic gene regulators control transcription by helping or blocking RNA polymerase. Activators and repressors are two main types of regulatory proteins that influence whether a gene is expressed. These proteins let bacteria adjust gene activity in response to changing conditions.

Activators help transcription start. They bind to specific DNA sequences near a promoter, which is the region where RNA polymerase begins transcription. By making RNA polymerase bind more easily, activators...

Eukaryotic promoter sequences control where transcription begins. A promoter is a DNA region that helps start gene expression. In eukaryotes, this region is usually found upstream of the gene it regulates.

The promoter contains specific DNA sequences that can bind proteins needed for transcription. These sequences help position RNA polymerase at the correct start site. They also help determine whether a gene is turned on at the right time and in the right cell type.

Eukaryotic promoters can...

Co-activators and co-repressors help control gene expression. They do not usually bind DNA themselves. Instead, they work with transcription factors to change how strongly a gene is turned on or off.

Co-activators support transcription. They help transcription factors and RNA polymerase work together, which can increase gene expression. Co-repressors do the opposite. They help reduce transcription and lower gene expression.

These proteins are important because cells need precise control over...

Master transcription regulators help control when genes turn on and off. These proteins sit at the top of gene regulation networks and shape how cells respond to signals. In many cases, they act early in development and influence which cell types form.

These regulators bind DNA and affect transcription, which is the first step in making RNA from a gene. By turning transcription on or off, they can change the levels of many downstream genes at once. That broad effect makes them important for...

mRNA localization helps cells move messenger RNA to specific places before proteins are made. This process is regulated, so the cell can control when and where a protein is produced.

Messenger RNA, or mRNA, carries genetic instructions from DNA to the protein-making machinery. By transporting mRNA to a defined location, a cell can keep protein production focused where it is needed most.

Regulated mRNA transport is an important part of this control. It links the movement of RNA with later...

mRNA degradation helps control how much protein a cell makes. Messenger RNA, or mRNA, carries the genetic message from DNA to the ribosome, where proteins are built. When mRNA stays intact longer, it can be used more often. When it breaks down faster, protein production drops.

Cells regulate mRNA stability with cis-acting elements. These are sequences within the mRNA itself that influence how long the message lasts. They can affect whether the mRNA is protected or targeted for decay. This...

MicroRNA (miRNA) is a short regulatory RNA that helps control gene expression. It is transcribed from introns, which are non-coding parts of a gene, or from intergenic regions, which are stretches of DNA between genes. miRNA begins as a longer primary transcript and must go through several processing steps before it becomes active.

The first transcript, called primary miRNA or pri-mRNA, folds back on itself to form a stem-loop structure. In the nucleus, the endonuclease Drosha shortens this...

Small interfering RNA, or siRNA, is a short RNA molecule that helps silence genes. It works after a gene has been copied into RNA, making it part of post-transcriptional gene silencing. Scientists study siRNA because it shows how cells can control which genetic messages are used.

siRNA acts by guiding the cell to destroy a matching RNA message. This lowers the amount of protein that can be made from that message. The process is specific, because the siRNA must match the target RNA sequence...

Long non-coding RNAs, or lncRNAs, are RNA molecules that do not code for proteins. Instead, they can help control how genes are used in cells. This makes them important regulators of cell behavior.

lncRNAs can work in several ways. Some influence chromatin modification, which changes how tightly DNA is packed and how easy it is for genes to be turned on or off. Others help guide the process of cell differentiation, when unspecialized cells develop into more specific cell types.

Because of...

DNA methylation and X-chromosome inactivation help control which genes are turned on or off. These epigenetic changes alter the physical structure of DNA without changing the DNA sequence. They help each cell make only the proteins it needs. For example, bone growth proteins are not made in muscle cells.

Epigenetic control is important for normal development. It also helps cells keep the right patterns of gene activity. When these controls fail, diseases can develop. Cancer is one example, but...