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.
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.
The hominid fossil record of the past six million years gives us surprising insights into the path of human evolution.
How humans perceive bitter taste, and the evolution of taste perception.
Second discussion in the 2011 Holiday Lectures on human evolution, on how to effectively report scientific results to the general public.
How has the amazing diversity of plants and animals evolved? What can fossils, butterflies, and stickleback fish tell us about the deep common ancestry of all living forms?
How Darwin came to publish The Origin of Species, and examples of how quickly evolution can change a population.
Comparing the artificial selection of dogs and corn with the natural selection of the stickleback fish.
The genetic mechanisms by which evolution occurs, and an overview of the evidence for evolutionary theory.
How and why butterflies and fruit flies got their spots, and the fossil record for human evolution.
A discussion on reconciling religion and science with students, the lecturers, and guest speakers.
Leading evolution educator Ken Miller discusses the controversy surrounding the teaching of evolution.
Leading evolution educator Ken Miller discusses the controversy surrounding the teaching of evolution.
Watch two leading virus researchers explain how they use both simple and sophisticated technologies to detect and fight infectious agents.
Learn about research aimed at thwarting dengue fever in the lab and in communities.
New technologies like the Virochip harness DNA's properties to identify and fight new viruses.
Understanding the immune response is essential to developing safe vaccines for dengue and other diseases.
The SARS epidemic was successfully halted by a global research effort to identify a new virus.
This discussion from the 2010 Holiday Lectures on Science explores the ethics of genetically-modified organisms and other topics.
Why has it been so hard to develop a vaccine against HIV? How are new medicines revolutionizing AIDS treatment? Can AIDS be cured?
The genesis of AIDS, identifying HIV as the virus that causes AIDS, and the modern global epidemic.
The HIV life cycle, and how the virus destroys the immune system's ability to respond to infection.
Treating HIV infection with antiretroviral therapy, and HIV's ability to develop drug resistance.
The search for an effective HIV vaccine, and advances in genomics that may lead to a breakthrough.
A discussion with three students who are helping in the global fight against HIV and AIDS.
Three HIV-positive individuals share their personal experiences about living with HIV.
Dr. Donald Ganem describes how epidemiologists, physicians, and microbiologists work together to identify and study pathogens.
Dr. Brett Finlay explains why bacterial diseases continue to be a major health problem worldwide, causing a third of the world's deaths every year.
Dr. Finlay showcases three types of bacteria to illustrate how molecular biology is allowing researchers to probe the molecular workings of bacterial infections.
Dr. Ganem analyses the complex causes of epidemics—how changes in the environment and in human social behavior can give rise to new infectious diseases.
What medical secrets do venomous snails hold? How can listening in on bacterial conversations help develop new antibiotics? In four presentations, Dr. Bonnie L. Bassler and Dr. Baldomero M. Olivera reveal how a deeper understanding of nature and biodiversity informs their research into new...
Venomous carniverous cone snails are a rich source of molecules for scientific research and potential drug development.
Bacteria are capable of communicating and coordinating their activities with a molecular signaling system called quorum sensing.
Cone snails have evolved many different toxins for different uses. Total molecular biodiversity may number in the millions.
The quorum sensing system is a target for a new class of drugs that interfere with virulence without killing bacteria.
A discussion on biodiversity, endangered habitats, and how best to preserve the Earth's ecosystems, presented by the lecturers along with Dr. E.O. Wilson and Dr. Eric Chivian.
In this 13-minute Q&A session, Dr. Bonnie Bassler answers questions on quorum sensing and other topics related to bacteria.
In this ten-minute Q&A session, Dr. Olivera answers questions on cone snail behavior, venoms, and biodiversity.
What is mind? Can molecular biology help us understand mental function?
The history of localization of function in the brain, and research that led to the understanding of localization of memory.
How a nerve cell gets its identity, sends axons, and makes connections with other cells.
Understanding the neural circuits in the spinal cord that control movement.
The cellular and molecular nature of learning and memory, investigated in simpler sea slugs and more-complex mice.
The lecturers, joined by Dr. Kay Jamison of the Johns Hopkins University School of Medicine and Dr. Gerald Fischbach of the Simons Foundation, answer questions concerning autism, manic depression, and other mental illnesses.
As part of the 2003 Holiday Lectures on Science, Dr. Bert Vogelstein and Dr. Huda Y. Zoghbi discuss how their patients have led to a deeper understanding of the genetic and molecular bases of neurological disorders and cancer. Thanks to these patients, researchers can now apply the knowledge...
Although there are numerous kinds of cancer, all stem from alterations that allow cell division to outstrip cell demise.
The identification of hundreds of genes involved in the formation and spread of cancer is leading to promising new methods for diagnosis, prevention, and treatment.
Mutations in key genes can lay waste to the nervous system. By studying large families predisposed to developing these genetic disorders, scientists can identify the responsible altered gene.
Girls with Rett syndrome develop normally for about 18 months and then begin to regress. With the help of affected girls and their families, Dr. Zoghbi and her collaborators searched for the gene responsible for this neurological disorder.
Genetic research benefits health, but also raises thorny ethical issues.
In four talks, A. James Hudspeth, MD, PhD, and Jeremy H. Nathans, MD, PhD, discuss how sensory information is encoded and transmitted to the brain. They describe the detailed workings of two senses of great importance to humans—vision and hearing.
Dr. Hudspeth will begin by discussing how simple organisms—such as bacteria—have the capacity to detect and react to a stimulus.
Dr. Nathans will discuss how the visual process involves the detection of light by photo-receptors in the retina.
Dr. Hudspeth will explain the basis for the ear’s remarkable ability to detect sound through the hair cell, the sensory receptor found in the inner ear.
Dr. Nathans will complete the lecture series by clarifying what is known about the brain’s ability to process and integrate various elements of the visual system, such as color, motion, and depth.
Doug Melton and Nadia Rosenthal are leaders in stem cell research, working primarily with mouse and human tissue. They will discuss where embryonic and adult stem cells come from and the biology of how they supply the cells the body needs.
An overview of embryonic development, the progressive differentiation of cells, and properties of embryonic stem cells.
The role of stem cells in regeneration, and ongoing research to improve mammalian regeneration potency.
In cloning, a cell's genetic machinery is reprogrammed. Can we similarly coax stem cells to become specific cell types?
Finding factors to reverse age-related loss of cell maintenance, and some examples of stem cell therapies.
A discussion on policies and ethical issues associated with stem cell research.
In the 2004 Holiday Lectures on Science, HHMI investigators Ronald M. Evans and Jeffrey M. Friedman discuss how the body regulates weight by carefully controlling the storage and burning of fat—and how a better understanding of these complex metabolic systems could lead researchers to treatments...
Dr. Friedman introduces the genes and circuits that control appetite, including the key role of leptin.
Dr. Evans describes how fat communicates with muscle and how diet and exercise influence that relationship.
Dr. Evans reviews how PPARs regulate body weight by controlling whether fat is burned or stored.
Dr. Friedman shows how leptin rewires neural circuits, and how population studies may identify obesity genes.
A Q&A session on obesity and related issues, with the lecturers and students attending the Holiday Lectures on Science.
In four presentations, Stuart L. Schreiber, PhD, and Eric S. Lander, PhD, open a window onto the fast-paced world of genomic science and chemical genetics.
Dr. Eric Lander takes us on a tour of this remarkable genetic century, describing the rapid advances in DNA sequencing technologies and information science.
To understand life's processes, perturb them. How a process responds to an insult can provide clues about normal function or mimic a specific disease state.