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Structural View of Biology

Biomolecular structures allow us to understand the molecular nature of healthy cells and treat the underlying molecular causes of disease. Our cells contain thousands of molecules that must all work in concert to keep us healthy. When any of these molecules fails, or when a poison or pathogenic organism attacks these molecules, it may cause disease. Our bodies have many defenses against disease, and medical science has developed powerful drugs to assist these defenses.

Blood contains a complex collection of molecules to protect against injury. When we are injured, our blood forms a sturdy clot that seals the break. Blood clotting is a tricky process that must be carefully controlled, to ensure that the clot is formed in only the proper place and time.

Scroll to a Molecule of the Month Feature in this subcategory:

  • Fibrin


    When you cut yourself, you bleed, but the bleeding rapidly stops. Blood has a built-in emergency repair system that quickly blocks any damage to the circulatory system, creating a temporary patch that allows time for more permanent repairs. Three basic mechanisms are at work. First, platelets (small fragments of blood cells that circulate in the blood) clump at the site of the wound, forming a weak plug. Second, neighboring blood vessels constrict, reducing the amount of blood flowing into the area. Finally, the protein fibrin assembles into a tough network that clots the blood and forms an insoluble blockage. Together, these methods stop the loss of blood and create a sturdy scab to protect the area as you heal.

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  • Serpins


    Our cells are often forced to work with dangerous machinery. For instance, cells build many machines for demolition, such as nucleases that break down DNA and RNA, amylases and related enzymes that break down carbohydrates, lipases that chew up lipids, and proteases that disassemble proteins. These destructive enzymes are needed in many capacities. They are used in digestion, to break food molecules into workable pieces. They are used in defense, to attack invading viruses and bacteria. They are used to break down defective or obsolete molecules inside cells. They are also used in signaling cascades, to activate signaling molecules instantly when a message is received. These enzymes are essential when used at the proper place and time, but can spell disaster if they get loose.

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  • Thrombin


    Oxygen and nutrients are delivered throughout our bodies through the watery transport system of the blood. Using a liquid delivery method poses two challenges. First, it leaves the entire body open to infection, since bacteria and viruses will be quickly distributed everywhere that the blood goes. The immune system, with antibodies as the first line of defense, fights this danger. Second, there is the constant danger of damage to the blood circulatory system. Blood is pumped throughout the body under pressure, and any small leak could lead to a rapid emptying of the entire system. Fortunately, the blood carries an emergency repair system: the blood clotting system. When we are cut or wounded, our blood builds a temporary dam to block the damage, giving the surrounding tissues time to build a more permanent repair.

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  • Tissue Factor

    Tissue Factor

    Blood performs many essential jobs in your body: it transports oxygen and nutrients, it protects your cells from infection, and it carries hormones and other messages from place to place in your body. But since blood is a liquid that is pumped under pressure, we must protect ourselves from leaks. Fortunately, the blood has a built-in repair method that quickly stops up breaks in the blood circulatory system as soon as they happen. You see these repairs in action whenever you cut yourself: the blood thickens and forms a gooey clot, which then dries into a scab that seals and protects the cut until it can heal.

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Please see our usage polices for citation and reprint information. Copies of the illustrations used in these features are available for download as high resolution TIFF images. Please note that the structures used to illustrate each installment are chosen at the discretion of the authors; the features are not intended to represent a historical record. The process behind the creation of this feature is described by the author.