Biological Pathways Fact Sheet

National Human Genome Research Institute

National Institutes of Health
U.S. Department of Health and Human Services

Biological Pathways

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What is a biological pathway?

A biological pathway is a series of actions among molecules in a cell that leads to a certain product or a change in a cell. Such a pathway can trigger the assembly of new molecules, such as a fat or protein. Pathways can also turn genes on and off, or spur a cell to move.

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How do biological pathways work?

For your body to develop properly and stay healthy, many things must work together at many different levels - from organs to cells to genes.

Cells are constantly receiving cues from both inside and outside the body, which are prompted by such things as injury, infection, stress or even food. To react and adjust to these cues, cells send and receive signals through biological pathways. The molecules that make up biological pathways interact with signals, as well as with each other, to carry out their designated tasks.

Biological pathways can act over short or long distances. For example, some cells send out signals to nearby cells to repair localized damage, such as a scratch on your knee. Other cells produce substances, such as hormones, that travel through your blood to distant target cells.

Biological pathways can also produce small or large outcomes. For example, some pathways subtly affect how the body processes drugs, while others play a major role in how a fertilized egg develops into a baby.

There are many other examples of how biological pathways help our bodies work. The pupil in your eye opens or closes in response to light. If your skin senses that the temperature is rising, your body sweats to cool you down. In fact, without biological pathways, we-and all other living creatures-could not exist.

Still, it's important to keep in mind that biological pathways do not always work properly. When something goes wrong in a pathway, the result can be a disease such as cancer or diabetes.

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What are some types of biological pathways?

There are many types of biological pathways. Some of the most common are involved in metabolism, the regulation of genes and the transmission of signals.

Metabolic pathways make possible the chemical reactions that occur in our bodies. An example of a metabolic pathway is the process by which your cells break down food into energy molecules that can be stored for later use. Other metabolic pathways actually help to build molecules.

Gene regulation pathways turn genes on and off. Such action is vital because genes produce proteins, which are the key components needed to carry out nearly every task in our bodies. Proteins make up our muscles and organs, help our bodies move and defend us against germs.

Signal transduction pathways move a signal from a cell's exterior to its interior. Different cells are able to receive specific signals through structures on their surface, called receptors. After interacting with a receptor, the signal travels through the cell where its message is transmitted by specialized proteins that trigger a specific action in the cell. For example, a chemical signal from outside the cell might be turned into a protein signal inside the cell. In turn, that protein signal may be converted into a signal that prompts the cell to move.

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What is a biological network?

Researchers are learning that biological pathways are far more complicated than once thought. Most pathways do not start at point A and end at point B. In fact, many pathways have no real boundaries, and they often work together to accomplish tasks. When multiple biological pathways interact with each other, it is called a biological network.

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How do researchers find biological pathways?

Researchers have discovered many important biological pathways through laboratory studies of cultured cells, bacteria, fruit flies, mice and other organisms. Many of the pathways identified in these model systems are the same or have similar counterparts in humans.

Still, many biological pathways remain to be found. It will take years of research to identify and understand the complex connections among all of the molecules in all biological pathways, as well as to understand how these pathways work together.

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What can biological pathways tell us about disease?

Researchers are able to learn a lot about human disease from studying biological pathways. Identifying what genes, proteins and other molecules are involved in a biological pathway can provide clues about what goes wrong when a disease strikes.

For example, researchers may compare certain biological pathways in a healthy person to the same pathways in a person with a disease to discover the roots of the disorder. Keep in mind that problems in any number of steps along a biological pathway can often lead to the same disease.

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How can biological pathway information improve health?

Finding out what pathway is involved in a disease-and identifying which step of the pathway is affected in each patient-may lead to more personalized strategies for diagnosing, treating and preventing disease.

Researchers currently are using information about biological pathways to develop new and better drugs. It likely will take some time before we routinely see drugs that are specifically designed using the pathway approach. However, doctors are already beginning to use pathway information to more effectively choose and combine existing drugs.

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Why are cancer researchers excited about biological pathways?

Take the case of cancer. Until recently, many had hoped that most types of cancers were driven by a single genetic error and could be treated by designing drugs to target those specific errors. Much of that hope was based on the success of imatinib (Gleevec), a drug that was specifically designed to treat a blood cancer called chronic myeloid leukemia (CML). CML occurs because of a single genetic glitch that leads to the production of a defective protein that spurs uncontrolled cell growth. Gleevec binds to that protein, stopping its activity and producing dramatic results in many CML patients.

Unfortunately, the one-target, one-drug approach has not held up for most other types of cancer. Recent projects that deciphered the genomes of cancer cells have found an array of different genetic mutations that can lead to the same cancer in different patients. Then, based on the genetic profile of their particular tumor, patients could receive the drug or drug combination that is most likely to work for them.

The complexity of the findings appears daunting. Instead of attempting to discover ways to attack one well-defined genetic enemy, researchers now faced the prospect of fighting lots of little enemies. Fortunately, this complex view can be simplified by looking at which biological pathways are disrupted by the genetic mutations. Rather than designing dozens of drugs to target dozens of mutations, drug developers could focus their attentions on just two or three biological pathways. Patients could then receive the one or two drugs most likely to work for them based on the pathways affected in their particular tumors.

You might think of it like this: Imagine a thousand people from all across the United States travelling towards the front door of a single building in Chicago. How would you keep all of these people from entering the building?

If you had limitless resources, you could hire workers to go out and stop each person as he or she drove down the highway, arrived at the train station or waited at the airport. That would be the one-target, one-drug approach.

But if you wanted to save a lot of time and money, you could just block the door to the building. That is the pathway-based strategy that many researchers are now pursuing to design drugs for cancer and other common diseases.

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Last Reviewed: June 12, 2012