Using a technique called immunofluorescence, researchers can stain specific parts of a cell with fluorescent dyes. Here, a biologist has caught a cell dividing. Cell division underlies embryonic growth and the maintenance and healing of our bodies. Errors in cell division cause many disorders, including cancer, Down syndrome, and, perhaps, Alzheimer's disease. Duplicated chromosomes (blue) are separated by strong spindle fibers (green) to help form two new daughter cells. Part of the cellular skeleton (intermediate filaments) is shown in red. Photo source: Conly Rieder, Wadsworth Center, Albany, NY

A person wearing safety goggles examines a beaker. Photo source: Photodisc

Fluorescent dyes allow scientists to study how cells move. Cell migration is crucial to normal development, wound healing, and immune response. Abnormal migration allows the spread of cancer. Here, colors represent the shapes and positions of two large cells at three time points during a study: the beginning (red), middle (green), and end (blue). Areas the cells occupied during the entire study are shown in white. Photo source: K. Donais and Donna Webb, University of Virginia School of Medicine, Charlottesville

The chemical structures show the building blocks of DNA. The results of a DNA sequencing experiment stand in the background, revealing the order of these building blocks, known as bases, in a given DNA molecule. The precise sequence of bases in DNA directs each cell’s activities and distinguishes one organism from another. Photo source: Photodisc

A light microscope image shows the chromosomes, stained dark blue, in a dividing cell of an African globe lily (Scadoxus katherinae). This is one frame of a time-lapse sequence that shows cell division in action. The lily is considered a good organism for studying cell division because its chromosomes are much thicker and easier to see than human ones. Photo source: Andrew S. Bajer, University of Oregon, Eugene

A computer-generated model shows the structure of a protein. The one shown here, a G protein, is involved in cell signaling, a process essential to life. For example, cell signaling allows embryonic development, immune response, and perception. When signaling goes awry, cancer and other diseases can arise. Photo source: Protein Data Bank (http://www.pdb.org)

Many researchers use the mouse (Mus musculus) as a model organism to study mammalian biology. Mice carry out practically all the same life processes as humans and, because of their small size and short generation times, are easily raised in labs. Scientists studying a certain cellular activity or disease can choose from tens of thousands of specially bred strains of mice to select those prone to developing certain tumors, neurological diseases, metabolic disorders, premature aging, or other conditions. Photo source: Bill Branson, NIH, Bethesda, MD.

A tool called a gene chip lets scientists track the activity of hundreds or thousands of genes simultaneously. For example, researchers can compare the activities of genes in healthy and diseased cells, allowing the scientists to pinpoint which genes and cell processes might be involved in the development of a disease. Photo source: Juanita Martinez and Angelina Rodriguez, University of New Mexico, Albuquerque

Dyes called quantum dots, made using nanotechnology, can simultaneously reveal the fine details of many cell structures. Here, a human epithelial cell has been stained to show its nucleus (blue), a specific nuclear protein (magenta), mitochondria (orange), microtubules (green), and actin filaments (red). The technology may one day be used for speedy disease diagnosis, DNA testing, or analysis of biological samples. Photo source: Quantum Dot Corp., Hayward, CA

Structural biologists create crystals of proteins, shown here, as a first step in a process called X-ray crystallography, which can reveal detailed, three-dimensional protein structures. Photo source: Alex McPherson, University of California, Irvine

A person examines a flask of liquid. Photo source: Photodisc

Researchers can use a technique called FISH (fluorescence in situ hybridization) to paint the chromosomes of a cell different colors. Normally, a cell contains two copies of each type of chromosome, but in many cancer cells and in certain genetic diseases, like Down syndrome, the numbers are skewed. Photo source: Octavian Henegariu, Yale University, New Haven, CT

Bacillus anthracis, the bacterium that causes anthrax, has been used as a bioterrorist weapon. A 1993 anthrax attack by the Aum Shinrikyo cult in Japan had no casualties, but in 2001, anthrax spores sent in the U.S. mail killed 5 people and infected 22. By tracing the lineage of specific strains of anthrax, evolutionary biologists were able to identify the spores mailed in 2001 and to explain why the 1993 attack was not deadly. The lab plate shown here is filled with a jellylike substance containing blood, which sustains bacterial spores isolated from the 1993 attack. Photo source: Paul Keim, Northern Arizona University, Flagstaff

A pipette fills liquid into tubes arranged on a laboratory plate. Photo source: Photodisc