Dr. Zoghbi shows how a mouse that has been given the gene responsible for Rett syndrome exhibits some of the same neurological symptoms as human Rett patients.
How did the human Y chromosome become so small relative to its X counterpart? This animation depicts the 300-million-year odyssey of the sex chromosomes that began when the proto X and Y were an identical pair.
The Y chromosome has been likened to a hall of mirrors because its sequence contains many sections that appear to be palindromes. These palindromes provide a clue to some interesting events that may have occurred during the course of the chromosome's evolution.
This animation shows how the random deactivation of one of the X chromosomes in a pair can lead to a mozaicism in the expression genes.
The zebrafish heart is similar to the human heart in many respects. But unlike the human heart, the fish heart closes wounds rapidly and then regenerates to nearly full function. Fibroblast growth factor (FGF) is an important molecule in the regeneration process.
This "morph" animation demonstrates how the expression of a particular toolkit gene in a butterfly larva corresponds to the location of the wing eyespots in an adult butterfly.
A sample is put on a Virochip microarray, and results are compared to databases of all known viral sequences.
Delivering a single virus to a cell allows the virus to infect the cell, replicate, and give rise to many progeny viruses. These viruses can then infect many neighboring cells.
The geometric structures of viruses are beautiful and can be used, along with genomic information, to identify them.
This animation shows how a growing tumor can recruit nearby blood vessels in order to gain a supply of blood.
This animation illustrates how a small molecule binds to a protein. As a result of the binding, the protein alters its shape and becomes inactivated.
This animation demonstrates how cancerous cells could be destroyed using a modified virus.
A visual representation of the U.S. AIDS epidemic from 1981 to 1997. Each dot represents 30 cases.
Slippage during DNA replication can lead to expanding sections of repeating nucleotides. Watch this animation to see how this problem occurs.
View the animation to see how one type of immune cell—the helper T cell—interprets a message presented at the surface of the cell membrane. The message is an antigen, a protein fragment taken from an invading microbe. A series of events unfolds that results in the production of many clones of...
A quarry site in Nevada carries the evolutionary history of a population of stickleback fish that resided there when it was a freshwater lake.
This animation shows a rotating 3-D image of a stickleback skeleton. The pelvic region, including the pelvic spines, is highlighted in red. Armored plating covers the flanks of the fish. The three prominent dorsal spines give the fish its name.
A molecular menagerie of small molecules is displayed, with two particular molecules singled out for attention: rapamycin and furrowstatin, which are discussed in the remainder of Dr. Schreiber's lectures on chemical genetics.
Microarray technology is useful for screening many small molecules at once. Automated devices have made it possible for thousands of different small molecules to be printed as an array of spots on a glass slide. A single type of protein which has been tagged with a fluorescent marker can then...
Varying concentrations of a signaling molecule activate different transcription factors and determine cell fate.
Somatic cell nuclear transfer (SCNT) is a technique for cloning. The nucleus is removed from a healthy egg. This egg becomes the host for a nucleus that is transplanted from another cell, such as a skin cell. The resulting embryo can be used to generate embryonic stem cells with a genetic match...
In mammals, the controlling clock component that generates a 24-hour rhythm is the suprachiasmatic nucleus (SCN), located in a part of the brain called the hypothalamus. The SCN produces a signal that can keep the rest of the body on an approximately 24-hour schedule. This animation illustrates...
Illustrates how studying one family's pedigree can reveal an entire history of passing on a genetic disorder such as SCA1.
In this animation, you can see how one S. typhimurium invades an epithelial cell of the intestinal tract, survives the intracellular defense mechanisms of the host cell, and multiplies.
Since RNA is single-stranded, it can fold upon itself and form structures that are protein-like in both appearance and functionality.
HIV's reverse transcriptase mistakes AZT for thymidine. Once incorporated, AZT stops reverse transcription.
The growth cone of a neuron avoids repellant molecules and navigates to innervate the appropriate muscle.
When two different strains of influenza infect a single cell, their genetic material can mix freely, resulting in a new third strain of influenza.
Rapamycin is a small molecule originally isolated from nature. It has antibiotic and immunosuppressive properties. It also allows two proteins which do not normally interact to bind together in the cell, which causes problems in the nutrient-sensing pathway.
Meiosis, the form of cell division unique to egg and sperm production, sets the stage for sex determination by creating sperm that carry either an X or a Y sex chromosome. But what is it about the X or Y that determines sex?
This animation illustrates how mistakes made during DNA replication are repaired.
Quorum sensing regulates gene expression by a protein phosphorylation cascade that controls transcription.
A 3D animation showing how proteins in the cell are tagged for disposal and degraded by the proteasome.
Protease inhibitors prevent maturation of viral proteins inside HIV particles.
Prialt does not block the mammalian motor synapse, but blocks the pain pathway in the spinal cord.
Prialt, a drug derived from cone snail venom, paralyzes fish by blocking calcium channels at a motor synapse.
The PPAR-gamma receptor activates certain genes in a fat cell, resulting in the storage of fat and changes in hormone levels.
The PPAR-delta receptor activates certain genes in a muscle cell, resulting in the burning of fat.
The rock pocket mouse is found in two color variants, or morphs: light and dark. In different environments, their visibility to predators such as owls varies. The dark morph is more vulnerable on light sandy desert, and the light morph on dark lava rock.
This simulation shows the spread of a favorable mutation through a population of pocket mice. Even a small selective advantage can lead to a rapid evolution of the population.
In the stickleback fish, pelvic-fin reduction resulted from changes in the regulatory switch elements of the Pitx1 gene. In the marine ancestor, the Pitx1 gene is activated in the pelvic-fin region during development to generate the fin. In the pelvic-reduced stickleback, the...
PCR is a standard laboratory technique that allows amplification of specific segments of DNA based on complementarity.
In two related Drosophila species, a so-called paintbrush gene is activated to "paint" the pigment on the body. In one species, an extra switch activates the gene, resulting in spotted wings.
A 3D animation showing the molecule p53 binds to DNA and initiates the transcription of mRNA.
Urodele amphibians—newts and salamanders—are able to regenerate fully functional limbs in response to amputation. Cells in and near the limb stump dedifferentiate to form a mass of stemlike cells that can produce all the specialized tissues of the limb, such as muscle, nerves, and blood vessels...
Neurons in the cortical area 5 are active when a cat is straddling an obstacle.
Myosin II is one of the molecules involved in furrow formation in dividing cells. This animation shows how the molecule operates, and how furrowstatin blocks the mechanism and halts division of a cell.
Multiple cone snail toxins attack different molecules of the nervous system and cause paralysis.
After a chemical biologist has made many novel small molecules by diversity-oriented synthesis, the next step is to find those that are useful. Molecules need to be "screened." Conceptually, screening is like using proteins as a custom filter to catch potentially useful small molecules.
Electrical and chemical signals are used by neurons to communicate with one another at contact points called synapses.
This animation shows how MIX-1 facilitates both chromosome condensation and dosage compensation.
This animation shows how the protein MECP2, in conjuction with another protein complex, can act as an "on-off' switch for gene expression.
This animation shows the molecular interactions involved in the negative feedback loop responsible for circadian rhythms in mammals.
This animation series shows four experiments that compare the activity patterns of a wild-type fly keeping a normal schedule with those of a mutant fly apparently following a 19-hour internal clock.
A cancer tumor forms in a bed of healthy cells. The animation goes on to show how the tumor recruits blood vessels and how metastasis occurs.
How a cell infected by a virus signals cytotoxic T lymphocytes to kill the cell before the virus replicates and spreads.
Long-term memory requires the activation of CREB, turning on specific genes that support new synaptic growth.
Short-term memory relies on serotonin activating a protein kinase to modify existing synaptic strength.
Comparison of the change in BMI for a given height and varying weights.
One technique for discovering small molecules of biological relevance is to expose cultured cells to a variety of small molecules and look for changes in the cells' appearance, behavior or other measurable qualities.
DNA's chemical properties can be harnessed for a variety of biotechnology applications.
The hypothetical relationship of chemical space and biological space is plotted on a three-dimensional graph, giving a glimpse of the future direction of research at the intersections of various disciplines.
A dramatic illustration of how hearing happens in the ear.
Bacteria can transfer genetic material, and thus drug resistance, to other bacteria via conjugation.
The inner cell mass (ICM) cells of blastocyst-stage early human embryos can be removed and cultured. These cells can be grown in the lab indefinitely. Various growth factors cause these cells to develop into a variety of differentiated cells, such as muscle or nerve cells.
Cytoplasmic factors play a significant part in determining how a cell develops. This segment discusses their importance in turning the appropriate genes on and off for proper development.
Dengue virus has sophisticated mechanisms for entering a cell, for replicating its RNA genome, and for translating proteins.
Since the 1960s dengue fever has spread to many countries and total case numbers have exploded.
The dengue virus's outer envelope proteins form symmetrical units and overlay the lipid envelope, capsid, and the RNA genome.
Infection begins when the dengue virus uses receptors on an immune cell's surface to gain entry and release its genome.
The fetal brain grows enormously during pregnancy, both in terms of its size and the number of neurons it has.
As a human embryo develops, its cells become progressively restricted in the types of specialized cells that they can produce. Inner cell mass (ICM) cells of the blastocyst can make any type of body cell. Gastrula-stage cells can give rise to the cells of a given germ layer. Later, cells become...
This animation describes two different ways by which chemicals migrate through membranes: passive diffusion and active transport.
General transcription factors, activators, and repressors interact to regulate the transcription of eukaryotic DNA into RNA.
Adenine (A), cytosine (C), guanine (G), and thymine (T) are the components of nucleic acid that make up DNA.
In 1950, Erwin Chargaff published a paper stating that in the DNA of any given species, the ratio of adenine to thymine is equal, as is the ratio of cytosine to guanine. This became known as Chargaff's ratio, and it was an important clue for solving the structure of DNA.
Chronic myeloid leukemia (CML) is caused by a mutation that leads to an abnormal protein that is always active. The drug Gleevec has a shape that fits into the active site of the abnormal protein and stops its harmful effects.
Of the 3 billion letters in the human genome, only 1% directly code for proteins. Of the rest, about 25% make up genes and their regulatory elements. The functions of the remaining letters are still unclear.
Reactive molecules, such as free radicals, and solar ultraviolet radiation can lead to mutations in DNA. Most mutations are corrected, but in rare cases mutations can accumulate and cause diseases such as cancer.
A new gene can be inserted into a loop of bacterial DNA called a plasmid. This is done by cutting the plasmid DNA with a restriction enzyme, which allows a new piece of DNA to be inserted. The ends of the new piece of DNA are stitched together by an enzyme called DNA ligase. The genetically...
The human genome is organized into structures called chromosomes, consisting of 22 matching pairs and one pair of sex chromosomes.
The public Human Genome Project started by identifying unique marker sequences distributed throughout the genome. Then, many copies of a small section of DNA were randomly cleaved into smaller fragments, and each small fragment was sequenced. Because there were originally many copies of the DNA...
Once a gene has been transcribed into messenger RNA (mRNA), it is edited in a process called splicing. Noncoding regions called introns are removed, leaving protein-coding regions called exons.
DNA is tightly packed in the nucleus of every cell. DNA wraps around special proteins called histones, which form loops of DNA called nucleosomes. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin in turn forms larger loops and coils to form chromosomes.
DNA has a double helix structure. If untwisted, DNA looks like two parallel strands. Each strand has a linear sequence of A, C, G, and T. The precise order of the letters carries the coded instructions. One strand is a complementary image of the other: A always pairs with T, and C always pairs...
One of the failed hypothetical models of DNA is Linus Pauling's triple helix model. This structure would be unstable under normal cellular conditions.
Polymerase chain reaction, or PCR, is a technique for making many copies of a specific DNA sequence. DNA is repeatedly heated and cooled in the presence of primers that bracket the desired sequence and of the enzyme Tac polymerase. In as few as 30 cycles, a billion copies of the target sequence...
The structure of DNA, discovered by James Watson and Francis Crick, suggests a mechanism of replication. The double helix unwinds, and each strand acts as a template for the construction of the new DNA molecule.
Using information from molecular research, this 3-D animation shows how DNA is replicated at the molecular level. It involves an enzyme that unwinds the DNA, and other enzymes that copy the two resulting strands.
Both strands of the DNA double helix act as templates for the new DNA strands. Incoming DNA is unraveled by the enzyme helicase, resulting in the 3' strand and the 5' strand. The 3' strands and the 5' strands are replicated by a DNA polymerase enzyme but in different ways.
Fred Sanger developed the first technique for sequencing DNA. DNA is replicated in the presence of chemically altered versions of the A, C, G, and T bases. These bases stop the replication process when they are incorporated into the growing strand of DNA, resulting in varying lengths of short...
In shotgun sequencing many copies of the entire genome are "blown up" into millions of small fragments. Each small fragment is sequenced. Powerful computers then assemble the individual fragments into the original configuration. Repeat sequences pose a problem for this approach because their...
Sickle cell anemia is a genetic disease that affects hemoglobin.
The first phase of the process of reading DNA information to make proteins starts with a molecule unzipping the DNA. The molecule then copies one of the strands of DNA into a strand of RNA, a close cousin of DNA. This process is called transcription.
The process of copying DNA into messenger RNA (mRNA) is called transcription. Transcription factors assemble at the promoter region of a gene, bringing an RNA polymerase enzyme to form the transcription initiation complex. Activator proteins at the enhancer region of DNA then activate the...
The ribosome is a molecular factory that translates the genetic information in RNA into a string of amino acids that becomes a protein. Inside the ribosome, the genetic code of the RNA is read three letters at a time and compared with the corresponding code on a transfer molecule. When a match...
Messenger RNA (mRNA) carries DNA's genetic information to the ribosome, where it is translated into a sequence of amino acids. mRNA is fed into the ribosome, and it is positioned so that it can be read in groups of three letters, known as codons. Each mRNA codon is matched against the transfer...
Once the structure of DNA was discovered, the next challenge was determining how the sequence of letters coded for the 20 amino acids. In theory, one or two letters can only code for 4 or 16 amino acids, respectively. A scheme using three letters, a triplet code, is the minimum necessary to...
During the process of trying to elucidate the structure of DNA, Jim Watson made some cardboard models to try to understand how DNA nucleotides are paired. It helped him visualize how hydrogen atoms of paired nucleotides interact with each other to form a symmetrical structure that fits the...
In diversity-oriented synthesis, many combinations of chemical building blocks undergo relatively few reaction steps to form a vast variety of different molecules. In this example, 45 x 45 x 45 combinations yield more than 88,000 novel molecules.