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...
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...
When a malaria-carrying mosquito bites a human host, the malaria parasite enters the bloodstream, multiplies in the liver cells, and is then released back into the bloodstream, where it infects and destroys red blood cells.
A mosquito becomes infected with malaria when it sucks the blood from an infected human. Once inside the mosquito, the parasites reproduce in the gut and accumulate in the salivary glands, ready to infect another human host with the next bite.
Adam Barrett describes his seven-drug antiretroviral regimen and the importance of adherence.
A touch to the Aplysia's siphon causes a gill withdrawal, a simple reflex for studying memory.
An interview with Dr. Zoghbi.
An interview with Kwame Atsina, an undergraduate who discusses what it's like to be in a lab doing scientific research.
Dr. Brett Finlay shows how bacteria can grow rapidly to incredible numbers, and also explains what limits this explosive growth.
An interview with Grant Barish, a scientist in Dr. Evans's lab.
Adam Barrett, a nurse who is HIV positive, discusses his first symptoms and the challenges of adhering to a drug regimen.
The fight against dengue fever, and the mosquitoes that carry the virus, is being carried out by "brigadistas" in Managua's neighborhoods. Spanish with English subtitles.
An interview with Dr. Bassler.
An interview with Silvia Caballero, an undergraduate who discusses what it's like to be in a lab doing scientific research.
Mr. Carlson outlines the path that he took to becoming a graduate student in the White lab, including his experience as a chef.
An interview with Dr. Carroll.
Video closeup of the C. elegans sperm that moves like an amoeba.
A patient can both comprehend and articulate language, but cannot verbalize what is a clear idea in her mind.
Dr. Rosenthal describes how antlers are one of the few examples of complete mammalian regeneration.
An interview with Dr. DeRisi.
An interview with Dr. Evans.
Ms. Everhart recounts her fieldwork experiences as a member of the Shea lab and the results of her first flintknapping attempt.
An interview with Dr. Finlay.
An interview with Dr. Friedman.
An interview with Dr. Ganem.
An interview with Jennifer Gatchel, a scientist in Dr. Zoghbi's lab.
Ms. Gomez explains her research in the Tishkoff lab and how it may help in understanding malaria resistance.
An interview with Amy Greenwood and Alice Chen, two scientists in Dr. Melton's lab.
An interview with Dr. Adam Hantman, a post-doctoral student in Thomas Jessell's lab.
An interview with Dr. Harris.
An interview with Tessa Hirschfeld-Stoler, a lab technician in Eric Kandel's lab.
An interview with Chris Hittinger, a scientist in Dr. Carroll's lab.
An interview with Dr. Jessell.
An interview with Dr. Jose Gonzales, Manager of the Laboratory Animal Resources and Knockout Mouse Facility at EMBL in Monterotondo Italy.
An interview with Manolis Kamvysselis, a scientist in Dr. Lander's lab.
An interview with Dr. Kandel.
An interview with Dr. Kingsley.
An interview with Angela Koehler, a scientist in Dr. Schreiber's lab.
An interview with Dr. Lander.
An interview with Dr. Michael McIntosh, who discovered the drug Prialt while working as an undergraduate in Dr. Olivera's lab.
An interview with Dr. Melton.
A brief interview with Dr. Meyer.
An interview with Olivier Mirabeau, a scientist in Dr. Rosenthal's lab.
An interview with Dr Mumna Al Banchaabouchi, researcher in the Mouse Phenotyping Core at EMBL in Monterotondo Italy.
An interview with Stephanie Nuñez, a student in Dr. Kingsley's lab.
An interview with Tobi Ogbechie, an undergraduate who discusses what it's like to be in a lab doing scientific research.
An interview with Dr. Ojikutu.
An interview with Dr. Olivera.
A brief interview with Dr. Page.
Ms. Pepe talks about her experiences doing field work with the Shea lab as an undergraduate at Stony Brook University.
An interview with Shirly Pinto, a scientist in Dr. Friedman's lab.
An interview with Dr. Audra Pompeani, a graduate student in Bonnie Bassler's lab.
An interview with Harith Rajagopalan, a scientist in Dr. Vogelstein's lab.
An interview with Priya Rajasethupathy, an MD/PhD student in Eric Kandel's lab.
A brief interview with Dr. Rosbash.
An interview with Dr. Rosenthal.
An interview with Dr. Schreiber.
Dr. Shea discusses his early interest in anthropology, how field work has changed over the years, and his outside interests.
Katherine Sorber, a graduate student in the DeRisi lab, describes her research on malaria.
An interview with Dr. Lee Swem, a post-doctoral fellow in Bonnie Bassler's lab.
A brief interview with Dr. Takahashi.
A Taser hyperexcites the nervous system to cause a rigid immobilization of its target.
Dr. Tishkoff explains how studying genetic diversity can shed light on modern-day diseases, such as diabetes and obesity.
Ben Vincent describes his summer work collecting mosquitoes for Dr. Marm Kilpatrick's research on the ecology and epidemiology of the West Nile virus.
An interview with Dr. Vogelstein.
An interview with Dr. Walker.
Clive Wearing has lost his ability to remember and lives in a perpetual state of having just awoken.
Dr. White talks about his passion both for his fieldwork and for educating the scientists of tomorrow.
Kate Williams, a graduate student in the Harris lab, describes her epidemiological research linking antibodies and severe dengue in Nicaragua.
Nathan Yozwiak, a graduate student in the Harris/DeRisi labs, discusses working in Nicaragua to discover a new virus infecting children.
An interview with Dr. Laskaro Zagoraiou, a post-doctoral student in Thomas Jessell's lab.
An interview with Katie Walter, an undergraduate who discusses what it's like to be in a lab doing scientific research.
Where and when did humans arise? What distinguishes us from other species? Did our distant ancestors look and behave like us?
How reasoning and evidence are used to understand human evolution.
Genetic evidence shows that humans evolved in Africa and continue to evolve.
Stone tools are well-preserved evidence of past human activity.