A cell in prometaphase during mitosis: The nuclear membrane breaks apart, and the spindle starts to interact with the chromosomes. Mitosis is responsible for growth and development, as well as for replacing injured or worn out cells throughout the body. For simplicity, mitosis is illustrated here with only six chromosomes.

Enzymes convert substrates into products very quickly. See image 2522 for a labeled version of this illustration. Featured in The Chemistry of Health.

The largest human cell (by volume) is the egg. Human eggs are 150 micrometers in diameter and you can just barely see one with a naked eye. In comparison, consider the eggs of chickens...or ostriches!

Many disease-causing microbes manipulate their host’s metabolism and cells for their own ends. Microsporidia—which are parasites closely related to fungi—infect and multiply inside animal cells, and take the rearranging of cells’ interiors to a new level. They reprogram animal cells such that the cells start to fuse, causing them to form long, continuous tubes. As shown in this image of the roundworm Caenorhabditis elegans, microsporidia (shown in red) have invaded the worm’s gut cells (the large blue dots are the cells' nuclei) and have instructed the cells to merge. The cell fusion enables the microsporidia to thrive and propagate in the expanded space. Scientists study microsporidia in worms to gain more insight into how these parasites manipulate their host cells. This knowledge might help researchers devise strategies to prevent or treat infections with microsporidia.

For more on the research into microsporidia, see this news release from the University of California San Diego. Related to images 5777 and 5778.

A zebrafish embryo. The blue areas are cell bodies, the green lines are blood vessels, and the red glow is blood. This image was created by stitching together five individual images captured with a hyperspectral multipoint confocal fluorescence microscope that was developed at the Eliceiri Lab.

T cells engulf and digest cells displaying markers (or antigens) for retroviruses, such as HIV.

Relapsing fever is caused by a bacterium and transmitted by certain soft-bodied ticks or body lice. The disease is seldom fatal in humans, but it can be very serious and prolonged. This scanning electron micrograph shows Borrelia hermsii (green), one of the bacterial species that causes the disease, interacting with red blood cells. Micrograph by Robert Fischer, NIAID. Related to image 3586.
For more information about relapsing fever, see https://www.cdc.gov/relapsing-fever/index.html.
This image is part of the Life: Magnified collection, which was displayed in the Gateway Gallery at Washington Dulles International Airport June 3, 2014, to January 21, 2015.

Like a paint-by-numbers picture, painted probes tint individual human chromosomes by targeting specific DNA sequences. Chromosome 13 is colored green, chromosome 14 is in red and chromosome 15 is painted yellow. The image shows two examples of fused chromosomes—a pair of chromosomes 15 connected head-to-head (yellow dumbbell-shaped structure) and linked chromosomes 13 and 14 (green and red dumbbell). These fused chromosomes—called dicentric chromosomes—may cause fertility problems or other difficulties in people.

This ribbon drawing of a protein hand drawn and colored by researcher Jane Richardson in 1981 helped originate the ribbon representation of proteins that is now ubiquitous in molecular graphics. The drawing shows the 3-dimensional structure of the protein triose phosphate isomerase. The green arrows represent the barrel of eight beta strands in this structure and the brown spirals show the protein's eight alpha helices. A black and white version of this drawing originally illustrated a review article in Advances in Protein Chemistry, volume 34, titled "Anatomy and Taxonomy of Protein Structures." The illustration was selected as Picture of The Day on the English Wikipedia for November 19, 2009. Other important and beautiful images of protein structures by Jane Richardson are available in her Wikimedia gallery.

Mitochondria are the powerhouses of the cells, generating the energy the cells need to do their tasks and to stay alive. Researchers have studied mitochondria for some time because when these cell organelles don't work as well as they should, several diseases develop. In this photograph of cow cells taken with a microscope, the mitochondria were stained in bright yellow to visualize them in the cell. The large blue dots are the cell nuclei and the gray web is the cytoskeleton of the cells.

The three neurons (red) visible in this image were derived from human embryonic stem cells. Undifferentiated stem cells are green here. Image and caption information courtesy of the California Institute for Regenerative Medicine.

Embryonic stem cells store pre-activated Bax (red) in the Golgi, near the nucleus (blue). Featured in the June 21, 2012, issue of Biomedical Beat.

Yeast cells with nuclear envelopes shown in magenta and tubulin shown in light blue. The nuclear envelope defines the borders of the nucleus, which houses DNA. Tubulin is a protein that makes up microtubules—strong, hollow fibers that provide structure to cells and help direct chromosomes during cell division. This image was captured using wide-field microscopy with deconvolution.

Related to images 6791, 6792, 6793, 6794, 6797, and videos 6795 and 6796.

A mouse liver glows after being tagged with specially designed infrared-fluorescent protein (IFP). Since its discovery in 1962, green fluorescent protein (GFP) has become an invaluable resource in biomedical imaging. But because of its short wavelength, the light that makes GFP glow doesn't penetrate far in whole animals. So University of California, San Diego cell biologist Roger Tsien--who shared the 2008 Nobel Prize in chemistry for groundbreaking work with GFP--made infrared-fluorescent proteins (IFPs) that shine under longer-wavelength light, allowing whole-body imaging in small animals.

Yeast cells with nuclei shown in green and contractile rings shown in magenta. Nuclei store DNA, and contractile rings help cells divide. This image was captured using wide-field microscopy with deconvolution.

Related to images 6791, 6793, 6794, 6797, 6798, and videos 6795 and 6796.

A light microscope image of a cell from the endosperm 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. Staining shows microtubules in red and chromosomes in blue. Here, condensed chromosomes are clearly visible and lined up.

Related to images 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1018, and 1019.

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.

Model of the mandelate racemase enzyme from Bacillus subtilis, a bacterium commonly found in soil.

Closeup of C. elegans, tiny roundworms, with a ribosomal protein glowing red and muscle fibers glowing green. Researchers used these worms to study a molecular pathway that affects aging. The ribosomal protein is involved in protein translation and may play a role in dietary restriction-induced longevity. Image created using confocal microscopy.
View single roundworm here 6581.
View group of roundworms here 6582.

This montage of tiny, transparent C. elegans--or roundworms--may offer insight into understanding human infertility. Researchers used fluorescent dyes to label the worm cells and watch the process of sex cell division, called meiosis, unfold as nuclei (blue) move through the tube-like gonads. Such visualization helps the scientists identify mechanisms that enable these roundworms to reproduce successfully. Because meiosis is similar in all sexually reproducing organisms, what the scientists learn could apply to humans.

X-ray co-crystal structure of Src kinase bound to a DNA-templated macrocycle inhibitor. Related to images 3413, 3414, 3415, 3416, 3417, and 3419.

Ecteinascidin 743 (ET-743, brand name Yondelis), was discovered and isolated from a sea squirt, Ecteinascidia turbinata, by NIGMS grantee Kenneth Rinehart at the University of Illinois. It was synthesized by NIGMS grantees E.J. Corey and later by Samuel Danishefsky. Multiple versions of this structure are available as entries 2790-2797.

This image shows the uncontrolled growth of cells in squamous cell carcinoma, the second most common form of skin cancer. If caught early, squamous cell carcinoma is usually not life-threatening.

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

The enzyme Dicer generates microRNAs by chopping larger RNA molecules into tiny Velcro^®-like pieces. MicroRNAs stick to mRNA molecules and prevent the mRNAs from being made into proteins. See image 2556 for an unlabeled version of this illustration. Featured in The New Genetics.

This illustration shows pathogenic bacteria behave like a Trojan horse: switching from antibiotic susceptibility to resistance during infection. Salmonella are vulnerable to antibiotics while circulating in the blood (depicted by fire on red blood cell) but are highly resistant when residing within host macrophages. This leads to treatment failure with the emergence of drug-resistant bacteria.

This image was chosen as a winner of the 2016 NIH-funded research image call, and the research was funded in part by NIGMS.

Cells in an early-stage fruit fly embryo, showing the DIAP1 protein (pink), an inhibitor of apoptosis.

This short video shows a model of the DNA helicase in yeast. This DNA helicase has 11 proteins that work together to unwind DNA during the process of copying it, called DNA replication. Scientists used a technique called cryo-electron microscopy (cryo-EM), which allowed them to study the helicase structure in solution rather than in static crystals. Cryo-EM in combination with computer modeling therefore allows researchers to see movements and other dynamic changes in the protein. The cryo-EM approach revealed the helicase structure at much greater resolution than could be obtained before. The researchers think that a repeated motion within the protein as shown in the video helps it move along the DNA strand. To read more about DNA helicase and this proposed mechanism, see this news release by Brookhaven National Laboratory.

In this image, viewed with a ZEISS ORION NanoFab microscope, the community of cells lining a mouse airway is magnified more than 10,000 times. This collection of cells, known as the mucociliary escalator, is also found in humans. It is our first line of defense against inhaled bacteria, allergens, pollutants, and debris. Malfunctions in the system can cause or aggravate lung infections and conditions such as asthma and chronic obstructive pulmonary disease. The cells shown in gray secrete mucus, which traps inhaled particles. The colored cells sweep the mucus layer out of the lungs.

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

Watch a cell ripple toward a beam of light that turns on a movement-related protein.

These cells are induced stem cells made from human adult skin cells that were genetically reprogrammed to mimic embryonic stem cells. The induced stem cells were made potentially safer by removing the introduced genes and the viral vector used to ferry genes into the cells, a loop of DNA called a plasmid. The work was accomplished by geneticist Junying Yu in the laboratory of James Thomson, a University of Wisconsin-Madison School of Medicine and Public Health professor and the director of regenerative biology for the Morgridge Institute for Research.

Mycobacterium tuberculosis, the bacterium that causes tuberculosis, has infected one-quarter of the world's population and causes more than one million deaths each year, according to the World Health Organization.

CCD-1 is an enzyme produced by the bacterium Clostridioides difficile that helps it resist antibiotics. Using X-ray crystallography, researchers determined the structure of a complex between CCD-1 and the antibiotic cefotaxime (purple, yellow, and blue molecule). The structure revealed that CCD-1 provides extensive hydrogen bonding (shown as dotted lines) and stabilization of the antibiotic in the active site, leading to efficient degradation of the antibiotic.

Related to images 6764, 6765, and 6766.

These time series show the heart rates of four different individuals. Automakers use steel scraps to build cars, construction companies repurpose tires to lay running tracks, and now scientists are reusing previously discarded medical data to better understand our complex physiology. Through a website called PhysioNet developed in part by Beth Israel Deaconess Medical Center cardiologist Ary Goldberger, scientists can access complete physiologic recordings, such as heart rate, respiration, brain activity and gait. They then can use free software to analyze the data and find patterns in it. The patterns could ultimately help health care professionals diagnose and treat health conditions like congestive heart failure, sleeping disorders, epilepsy and walking problems. PhysioNet is supported by NIH's National Institute of Biomedical Imaging and Bioengineering as well as by NIGMS.

The parasitic worm that causes schistosomiasis hatches in water and grows up in a freshwater snail, as shown here. Once mature, the worm swims back into the water, where it can infect people through skin contact. Initially, an infected person might have a rash, itchy skin, or flu-like symptoms, but the real damage is done over time to internal organs.

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

This illustration shows, in simplified terms, how the CRISPR-Cas9 system can be used as a gene-editing tool.

Frame 1 shows the two components of the CRISPR system: a strong cutting device (an enzyme called Cas9 that can cut through a double strand of DNA), and a finely tuned targeting device (a small strand of RNA programmed to look for a specific DNA sequence).

In frame 2, the CRISPR machine locates the target DNA sequence once inserted into a cell.

In frame 3, the Cas9 enzyme cuts both strands of the DNA.

Frame 4 shows a repaired DNA strand with new genetic material that researchers can introduce, which the cell automatically incorporates into the gap when it repairs the broken DNA.

For an explanation and overview of the CRISPR-Cas9 system, see the iBiology video.

Download the individual frames: Frame 1, Frame 2, Frame 3, and Frame 4.

Ecteinascidin 743 (ET-743, brand name Yondelis), was discovered and isolated from a sea squirt, Ecteinascidia turbinata, by NIGMS grantee Kenneth Rinehart at the University of Illinois. It was synthesized by NIGMS grantees E.J. Corey and later by Samuel Danishefsky. Multiple versions of this structure are available as entries 2790-2797.

This image represents the structure of TrpRS, a novel member of the tryptophanyl tRNA-synthetase family of enzymes. By helping to link the amino acid tryptophan to a tRNA molecule, TrpRS primes the amino acid for use in protein synthesis. A cluster of iron and sulfur atoms (orange and red spheres) was unexpectedly found in the anti-codon domain, a key part of the molecule, and appears to be critical for the function of the enzyme. TrpRS was discovered in Thermotoga maritima, a rod-shaped bacterium that flourishes in high temperatures.

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

Proteins in the neural tissues of this zebrafish embryo direct cells to line up and form the neural tube, which will become the spinal cord and brain. Studies of zebrafish embryonic development may help pinpoint the underlying cause of common neural tube defects--such as spina bifida--which occur in about 1 in 1,000 newborn children.

The light organ (~0.5 mm across) of a juvenile Hawaiian bobtail squid, Euprymna scolopes, stained blue. The two pairs of ciliated appendages, or “arms,” on the sides of the organ move Vibrio fischeri bacterial cells closer to the two sets of three pores at the base of the arms that each lead to an interior crypt. This image was taken using a confocal fluorescence microscope.

Related to images 7017, 7018, 7019, and 7020.

Scientists revealed a detailed image of the genetic defect that causes myotonic dystrophy type 2 and used that information to design drug candidates to counteract the disease.

Ovarioles in female insects are tubes in which egg cells (called oocytes) form at one end and complete their development as they reach the other end of the tube. This image, taken with a confocal microscope, shows ovarioles in a very popular lab animal, the fruit fly Drosophila. The basic structure of ovarioles supports very rapid egg production, with some insects (like termites) producing several thousand eggs per day. Each insect ovary typically contains four to eight ovarioles, but this number varies widely depending on the insect species.

Scientists use insect ovarioles, for example, to study the basic processes that help various insects, including those that cause disease (like some mosquitos and biting flies), reproduce very quickly.

A nanometer-sized biosensor can detect a single deadly bacterium in tainted ground beef. How? Researchers attached nanoparticles, each packed with thousands of dye molecules, to an antibody that recognizes the microbe E. coli O157:H7. When the nanoball-antibody combo comes into contact with the E. coli bacterium, it glows. Here is the transition, a single bacterial cell glows brightly when it encounters nanoparticle-antibody biosensors, each packed with thousands of dye molecules.

About half of all human proteins include chains of sugar molecules that are critical for the proteins to function properly. Appears in the NIGMS booklet Inside the Cell.

X-ray structure of a DNA repair enzyme superfamily representative from the human gastrointestinal bacterium Enterococcus faecalis. European scientists used this structure to generate homologous structures. Featured as the May 2007 Protein Structure Initiative Structure of the Month.

Enzymes speed up chemical reactions by reducing the amount of energy needed for the reactions. The substrate (lactose) binds to the active site of the enzyme (lactase) and is converted into products (sugars).

Image of the colon of a mouse mono-colonized with Bacteroides fragilis (red) residing within the crypt channel. The red staining is due to an antibody to B. fragilis, the green staining is a general dye for the mouse cells (phalloidin, which stains F-actin) and the light blue glow is from a dye for visualizing the mouse cell nuclei (DAPI, which stains DNA). Bacteria from the human microbiome have evolved specific molecules to physically associate with host tissue, conferring resilience and stability during life-long colonization of the gut. Image is featured in October 2015 Biomedical Beat blog post Cool Images: A Halloween-Inspired Cell Collection.

Researchers have created artificial cilia that wave like the real thing. Zvonimir Dogic and his Brandeis University colleagues combined just a few cilia proteins to create cilia that are able to wave and sweep material around--although more slowly and simply than real ones. The researchers are using the lab-made cilia to study how the structures coordinate their movements and what happens when they don't move properly. Featured in the August 18, 2011, issue of Biomedical Beat.

Elastin is a fibrous protein in the extracellular matrix (ECM). It is abundant in artery walls like the one shown here. As its name indicates, elastin confers elasticity. Elastin fibers are at least five times stretchier than rubber bands of the same size. Tissues that expand, such as blood vessels and lungs, need to be both strong and elastic, so they contain both collagen (another ECM protein) and elastin. In this photo, the elastin-rich ECM is colored grayish brown and is most visible at the bottom of the photo. The curved red structures near the top of the image are red blood cells.