The worm Caenorhabditis elegans is a popular laboratory animal because its small size and fairly simple body make it easy to study. Scientists use this small worm to answer many research questions in developmental biology, neurobiology, and genetics. This image, which was taken with transmission electron microscopy (TEM), shows a cross-section through C. elegans, revealing various internal structures.

The image is from a figure in an article published in the journal eLife. There is an annotated version of this graphic at 5760.

Pigment cells are cells that give skin its color. In fishes and amphibians, like frogs and salamanders, pigment cells are responsible for the characteristic skin patterns that help these organisms to blend into their surroundings or attract mates. The pigment cells are derived from neural crest cells, which are cells originating from the neural tube in the early embryo. This image shows pigment cells in the fin of pearl danio, a close relative of the popular laboratory animal zebrafish. Investigating pigment cell formation and migration in animals helps answer important fundamental questions about the factors that control pigmentation in the skin of animals, including humans. Related to images 5754, 5755, 5756 and 5758.

CCD-1 is an enzyme produced by the bacterium Clostridioides difficile that helps it resist antibiotics. Researchers crystallized complexes where a CCD-1 molecule and a molecule of the antibiotic cefotaxime were bound together. Then, they shot X-rays at the complexes to determine their structure—a process known as X-ray crystallography. This image shows the X-ray diffraction pattern of a complex.

Related to images 6764, 6766, and 6767.

Two highly stressed osteosarcoma cells are shown with a set of green droplet-like structures followed by a second set of magenta droplets. These droplets are composed of fluorescently labeled stress-response proteins, either G3BP or UBQLN2 (Ubiquilin-2). Each protein is undergoing a fascinating process, called phase separation, in which a non-membrane bound compartment of the cytoplasm emerges with a distinct environment from the surrounding cytoplasm. Subsequently, the proteins fuse with like proteins to form larger droplets, in much the same way that raindrops merge on a car’s windshield.

A study using Caulobacter crescentus showed that some bacteria use just-in-time processing, much like that used in industrial delivery, to make the glue that allows them to attach to surfaces, an important step in the infection process for many disease-causing bacteria. In the image shown, this freshwater bacterium has a holdfast at the top and a propelling flagellum at the end. From an Indiana University news release.

Enzymes convert substrates into products very quickly. See image 2521 for an unlabeled version of this illustration. Featured in The Chemistry of Health.

A light organ (~0.5 mm across) of a Hawaiian bobtail squid, Euprymna scolopes, stained blue. At the time of this image, the crypts within the tissues of only one side of the organ had been colonized by green-fluorescent protein-labeled Vibrio fischeri cells, which can be seen here in green. This image was taken using confocal fluorescence microscopy.

Related to images 7016, 7017, 7018, and 7019.

This crystal structure shows a conserved hypothetical protein from Mycobacterium tuberculosis. Only 12 other proteins share its sequence homology, and none has a known function. This structure indicates the protein may play a role in metabolic pathways. Featured as one of the August 2007 Protein Structure Initiative Structures of the Month.

The fledgling field of X-ray microscopy lets researchers look inside whole cells rapidly frozen to capture their actions at that very moment. Here, a yeast cell buds before dividing into two. Colors show different parts of the cell. Seeing whole cells frozen in time will help scientists observe cells' complex structures and follow how molecules move inside them.

This skyline of New York City was created by “printing” nanodroplets containing yeast (Saccharomyces cerevisiae) onto a large plate. Each dot is a separate yeast colony. As the colonies grew, a picture emerged, creating art. To make the different colors shown here, yeast strains were genetically engineered to produce pigments naturally made by bacteria, fungi, and sea creatures such as coral and sea anemones. Using genes from other organisms to make biological compounds paves the way toward harnessing yeast in the production of other useful molecules, from food to fuels and drugs.

During development, a zebrafish embryo is transformed from a ball of cells into a recognizable body plan by sweeping convergence and extension cell movements. This process is called gastrulation. Each line in this video represents the movement of a single zebrafish embryo cell over the course of 3 hours. The video was created using time-lapse confocal microscopy. Related to image 6775.

This graphic that resembles a firework was created from a picture of a fruit fly spermatid. This fruit fly spermatid recycles various molecules, including malformed or damaged proteins. Actin filaments (red) in the cell draw unwanted proteins toward a barrel-shaped structure called the proteasome (green clusters), which degrades the molecules into their basic parts for re-use.

This is a fibroblast, a connective tissue cell that plays an important role in wound healing. Normal fibroblasts have smooth edges. In contrast, this spiky cell is missing a protein that is necessary for proper construction of the cell's skeleton. Its jagged shape makes it impossible for the cell to move normally. In addition to compromising wound healing, abnormal cell movement can lead to birth defects, faulty immune function, and other health problems.

This image was part of the Life: Magnified exhibit that ran from June 3, 2014, to January 21, 2015, at Dulles International Airport.

These mitochondria (brown) are from the heart muscle cell of a rat. Mitochondria have an inner membrane that folds in many places (and that appears here as striations). This folding vastly increases the surface area for energy production. Nearly all our cells have mitochondria. Related to image 3661.

Neutrophil-like cells (blue) in a microfluidic chip preferentially migrating toward LTB4 over fMLP. A neutrophil is a type of white blood cell that is part of the immune system and helps the body fight infection. Both LTB4 and fMLP are molecules involved in immune response. Microfluidic chips are small devices containing microscopic channels, and they are used in a range of applications, from basic research on cells to pathogen detection. The scale bar in this video is 500μm.

Cancer cells can change their migration phenotype, which includes their shape and the way that they move to invade different tissues. This movie shows breast cancer cells forming a tumor spheroid—a 3D ball of cancer cells—and invading the surrounding tissue. Images were taken using a laser scanning confocal microscope, and artificial intelligence (AI) models were used to segment and classify the images by migration phenotype. On the right side of the video, each phenotype is represented by a different color, as recognized by the AI program based on identifiable characteristics of those phenotypes. The movie demonstrates how cancer cells can use different migration modes during growth and metastasis—the spreading of cancer cells within the body.

Sensory organs have cells equipped for detecting signals from the environment, such as odors. Receptors in the membranes of nerve cells in the nose bind to odor molecules, triggering a cascade of chemical reactions tranferred by G proteins into the cytoplasm.

Cells move forward with lamellipodia and filopodia supported by networks and bundles of actin filaments. Proper, controlled cell movement is a complex process. Recent research has shown that an actin-polymerizing factor called the Arp2/3 complex is the key component of the actin polymerization engine that drives amoeboid cell motility. ARPC3, a component of the Arp2/3 complex, plays a critical role in actin nucleation. In this photo, the ARPC3+/+ fibroblast cells were fixed and stained with Alexa 546 phalloidin for F-actin (red) and DAPI to visualize the nucleus (blue). ARPC3+/+ fibroblast cells with lamellipodia leading edge. Related to images 3328, 3329, 3330, 3331, and 3333.

Body organs such as the liver and kidneys process chemicals and toxins. These "target" organs are susceptible to damage caused by these substances. See image 2497 for a labeled version of this illustration.

In this image of a stained fruit fly ovary, the ovary is packed with immature eggs (with DNA stained blue). The cytoskeleton (in pink) is a collection of fibers that gives a cell shape and support. The signal-transmitting molecules like STAT (in yellow) are common to reproductive processes in humans. Researchers used this image to show molecular staining and high-resolution imaging techniques to students.

X-ray co-crystal structure of Src kinase bound to a DNA-templated macrocycle inhibitor. Related to 3413, 3415, 3416, 3417, 3418, and 3419.

Jon Lorsch at his swearing in as NIGMS director in August 2013. Also shown are Francis Collins, NIH Director, and Judith Greenberg, former NIGMS Acting Director.

A special "messy" region of a potassium ion channel is important in its function.

To splice a human gene into a plasmid, scientists take the plasmid out of an E. coli bacterium, cut the plasmid with a restriction enzyme, and splice in human DNA. The resulting hybrid plasmid can be inserted into another E. coli bacterium, where it multiplies along with the bacterium. There, it can produce large quantities of human protein. See image 2565 for a labeled version of this illustration. Featured in The New Genetics.

Model of aspartoacylase, a human enzyme involved in brain metabolism.

The proteasome is a critical multiprotein complex in the cell that breaks down and recycles proteins that have become damaged or are no longer needed. This illustration shows a protein substrate (red) that is bound through its ubiquitin chain (blue) to one of the ubiquitin receptors of the proteasome (Rpn10, yellow). The substrate's flexible engagement region gets engaged by the AAA+ motor of the proteasome (cyan), which initiates mechanical pulling, unfolding and movement of the protein into the proteasome's interior for cleavage into small shorter protein pieces called peptides. During movement of the substrate, its ubiquitin modification gets cleaved off by the deubiquitinase Rpn11 (green), which sits directly above the entrance to the AAA+ motor pore and acts as a gatekeeper to ensure efficient ubiquitin removal, a prerequisite for fast protein breakdown by the 26S proteasome. Related to video 3764.

Ribosomes are complex machines made up of more than 50 proteins and three or four strands of genetic material called ribosomal RNA (rRNA). The busy cellular machines make proteins, which are critical to almost every structure and function in the cell. To do so, they read protein-building instructions, which come as strands of messenger RNA. Ribosomes are found in all forms of cellular life—people, plants, animals, even bacteria. This illustration of a bacterial ribosome was produced using detailed information about the position of every atom in the complex. Several antibiotic medicines work by disrupting bacterial ribosomes but leaving human ribosomes alone. Scientists are carefully comparing human and bacterial ribosomes to spot differences between the two. Structures that are present only in the bacterial version could serve as targets for new antibiotic medications.

This illustration shows, in simplified terms, how the CRISPR-Cas9 system can be used as a gene-editing tool. This is the first frame in a series of four. The CRISPR system has two components joined together: a finely tuned targeting device (a small strand of RNA programmed to look for a specific DNA sequence) and a strong cutting device (an enzyme called Cas9 that can cut through a double strand of DNA).

For an explanation and overview of the CRISPR-Cas9 system, see the iBiology video, and find the full CRIPSR illustration here.

Actin gliding powered by myosin 1D. Note the counterclockwise motion of the gliding actin filaments.

DNA consists of two long, twisted chains made up of nucleotides. Each nucleotide contains one base, one phosphate molecule, and the sugar molecule deoxyribose. The bases in DNA nucleotides are adenine, thymine, cytosine, and guanine. See image 2541 for an unlabeled version of this illustration. Featured in The New Genetics.

The G switch allows our bodies to respond rapidly to hormones. G proteins act like relay batons to pass messages from circulating hormones into cells. A hormone (red) encounters a receptor (blue) in the membrane of a cell. Next, a G protein (green) becomes activated and makes contact with the receptor to which the hormone is attached. Finally, the G protein passes the hormone's message to the cell by switching on a cell enzyme (purple) that triggers a response. See image 2536 and 2537 for other versions of this image. Featured in Medicines By Design.

If a picture is worth a thousand words, what's a movie worth? For researchers studying cell migration, a "documentary" of fruit fly cells (bright green) traversing an egg chamber could answer longstanding questions about cell movement. See 2315 for video.

This illustration shows, in simplified terms, how the CRISPR-Cas9 system can be used as a gene-editing tool. The CRISPR system has two components joined together: a finely tuned targeting device (a small strand of RNA programmed to look for a specific DNA sequence) and a strong cutting device (an enzyme called Cas9 that can cut through a double strand of DNA). In this frame (2 of 4), the CRISPR machine locates the target DNA sequence once inserted into a cell.

For an explanation and overview of the CRISPR-Cas9 system, see the iBiology video, and find the full CRIPSR illustration here.

This painting shows a cross section of a small respiratory droplet, like the ones that are thought to transmit SARS-CoV-2, the virus that causes COVID-19. The virus is shown in pink, and the droplet is also filled with molecules that are present in the respiratory tract, including mucins (green), pulmonary surfactant proteins and lipids (blue), and antibodies (tan).

Model of a protein, antigen 85B, that is the most abundant protein exported by Mycobacterium tuberculosis, which causes most cases of tuberculosis. Antigen 85B is involved in building the bacterial cell wall and is an attractive drug target. Based on its structure, scientists have suggested a new class of antituberculous drugs.

The cytoskeleton (green) and DNA (purple) are highlighed in these cells by immunofluorescence.

Cross section of human skeletal muscle. Image taken with a confocal fluorescent light microscope.

An atomic force microscopy image shows DNA folded into an intricate, computer-designed structure. Image is featured on Biomedical Beat blog post Cool Image: DNA Origami. See also related image 3689 .

Related to image 6355.

Dengue virus is a mosquito-borne illness that infects millions of people in the tropics and subtropics each year. Like many viruses, dengue is enclosed by a protective membrane. The proteins that span this membrane play an important role in the life cycle of the virus. Scientists used cryo-EM to determine the structure of a dengue virus at a 3.5-angstrom resolution to reveal how the membrane proteins undergo major structural changes as the virus matures and infects a host. For more on cryo-EM see the blog post Cryo-Electron Microscopy Reveals Molecules in Ever Greater Detail. Related to image 3756.

This 2-hour-old fly embryo already has a blueprint for its formation, and the process for following it is so precise that the difference of just a few key molecules can change the plans. Here, blue marks a high concentration of Bicoid, a key signaling protein that directs the formation of the fly's head. It also regulates another important protein, Hunchback (green), that further maps the head and thorax structures and partitions the embryo in half (red is DNA). The yellow dots overlaying the embryo plot the concentration of Bicoid versus Hunchback proteins within each nucleus. The image illustrates the precision with which an embryo interprets and locates its halfway boundary, approaching limits set by simple physical principles. This image was a finalist in the 2008 Drosophila Image Award.

This photo shows a Varian Unity Inova 900 MHz, 21.1 T standard bore magnet Nuclear Magnetic Resonnance (NMR) spectrometer. NMR spectroscopy provides data used to determine the structures of proteins in solution, rather than in crystal form, as in X-ray crystallography. The technique is limited to smaller proteins or protein fragments in a high throughput approach.

This is a tomographic reconstruction of a mitochondrion from an insect flight muscle. Mitochondria are cellular compartments that are best known as the powerhouses that convert energy from the food into energy that runs a range of biological processes. Nearly all our cells have mitochondria.

Hippocampal neuron from rodent brain with dendrites shown in blue. The hundreds of tiny magenta, green and white dots are the dendritic spines of excitatory synapses.

The intense X-rays produced by synchrotrons such as the Advanced Photon Source are ideally suited for protein structure determination. Using synchrotron X-rays and advanced computers scientists can determine protein structures at a pace unheard of decades ago.

Anaphase is the critical step during mitosis when sister chromosomes are disjoined and directed to opposite spindle poles, ensuring equal distribution of the genome during cell division. In this image, one pair of sister chromosomes at the top was lost and failed to divide after chemical inhibition of polo-like kinase 1. This image depicts chromosomes (blue) separating away from the spindle mid-zone (red). Kinetochores (green) highlight impaired movement of some chromosomes away from the mid-zone or the failure of sister chromatid separation (top). Scientists are interested in detailing the signaling events that are disrupted to produce this effect. The image is a volume projection of multiple deconvolved z-planes acquired with a Nikon widefield fluorescence microscope.

This image was chosen as a winner of the 2016 NIH-funded research image call. The research that led to this image was funded by NIGMS.

Related to image 5765.

The structure of the pore-forming protein VDAC-1 from humans. This molecule mediates the flow of products needed for metabolism--in particular the export of ATP--across the outer membrane of mitochondria, the power plants for eukaryotic cells. VDAC-1 is involved in metabolism and the self-destruction of cells--two biological processes central to health.

Related to images 2494, 2495, and 2488.

Composite image of beta-galactosidase showing how cryo-EM’s resolution has improved dramatically in recent years. Older images to the left, more recent to the right. Related to image 5882. NIH Director Francis Collins featured this on his blog on January 14, 2016.

This image shows the hierarchical ontology of genes, cellular components and processes derived from large genomic datasets. From Dutkowski et al. A gene ontology inferred from molecular networks Nat Biotechnol. 2013 Jan;31(1):38-45. Related to 3436.

Bioengineers were able to coax bacteria to blink in unison on microfluidic chips. They called each blinking bacterial colony a biopixel. Thousands of fluorescent E. coli bacteria, shown here, make up a biopixel. Related to images 3265 and 3266. From a UC San Diego news release, "Researchers create living 'neon signs' composed of millions of glowing bacteria."