HHMI's Holiday Lectures on Science
Summary: HHMI's Holiday Lectures on Science The Howard Hughes Medical Institute is a philanthropy that supports biomedical research and science education. As part of its mission to strengthen science education, the Institute presents the Holiday Lectures on Science, an annual series that brings the latest developments in a rapidly moving field of research into the classroom. These lectures are videotaped and technical, but even the lay person can learn from them. Audio files are available, but you do lose the visual aids. However, they are still useable. Previous subjects have included, dengue, RNA, and the idea of quorum sensing which is how bacteria decide when to attack, or fireflies coordinate their flashing sequence.
A 90-minute discussion session with the lecturers, Washington, D.C.-area high school students, and three HIV-positive individuals—Adam Barrett, Zinhle Thabethe, and Phill Wilson—who share their personal experiences about living with HIV.
After describing the fundamental properties of circadian rhythms, Dr. Takahashi takes us on an exciting journey into a very special region of the brain—the suprachiasmatic nucleus (SCN). The SCN functions as a "master" biological clock that governs our physiology and certain behaviors. The clock regulates rhythms of sleep and wakefulness that make us morning larks, evening owls, or something in between. When the master clock is out of synchrony with other biological clocks in the body, symptoms of jet lag ensue.
Dr. Rosbash reveals that the fruit fly (Drosophila melanogaster) has a biological clock in its nervous system. Although tiny in size, the fruit fly has had a major impact on our understanding of circadian rhythms. The fruit fly served as the instrument with which scientists proved that certain behaviors such as rest and activity are under direct genetic control. Although much remains to be learned, the outlines of how the biological clock functions have emerged from research on this singular insect.
Dr. Rosbash discloses how scientists have persuaded Mother Nature to reveal the inner workings of the fruit fly's biological clock. From the almost 14,000 genes in this organism, scientists have painstakingly identified a handful that regulate the "ticktock" of the biological clock. In doing so, scientists have also brilliantly shown how the environment resets our biological clocks so that they are in synchrony with the cycles of nature.
Dr. Takahashi describes the powerful strategies that he and others have harnessed for understanding biological clocks in mammals. To tease out the secrets of how the clocks in higher organisms function, scientists had to overcome uncommonly high hurdles posed by the complexity of mice, hamsters, and humans. Many of these studies used the increasingly important research tools of genomics and computer-based informatics. One payoff already is a better understanding of human sleep disorders that are linked to specific genes.
Is it a boy or a girl? Dr. Page looks at how we define male and female and summarizes the development of human sex characteristics. He then explains the role of the sex chromosomes, X and Y, and, in particular, the SRY gene. Dr. Page demonstrates the differences between species that reproduce sexually and those that reproduce clonally without sex. A likely major advantage of sexual reproduction is that meiotic recombination and subsequent natural selection can weed out deleterious mutations.
Dr. Meyer explains the value of studying model organisms and introduces the nematode C. elegans Affectionally known as "the worm," it has two sexes: male, which possesses a single X chromosome, and hermaphrodite, which possesses two X chromosomes. Dr. Meyer explains that sex determination is controlled by the xol-1 gene. Xol-1 gene expression is regulated by sex-determining factors produced by the X chromosome.
Having too many chromosomes can lead to too much gene expression. If a male and a female have a different number of X chromosomes, a dosage-compensation mechanism is necessary to equalize the level of gene expression. In human females who have two X chromosomes, one X chromosome in each cell is inactive, while in C. elegans hermaphrodites, the activity of both X chromosomes is reduced by half. Dr. Meyer explains how the gene that controls dosage compensation in C. elegans works. Some genes involved in dosage compensation also have a role in cell division.
Dr. Page interprets the results of an audience-participation experiment comparing testosterone levels in males and females of varying ages. He then explains how the Y chromosome is inherited from father to son in a near clonal fashion. He demonstrates that successive inversions and deletions during mammalian evolution have reduced the Y chromosome to its present form--small and sparsely populated with genes. In some men, a deletion in the Y chromosome can lead to infertility. Dr. Page describes how intracytoplasmic sperm injection can help these men father children.
Life processes are fundamentally chemical reactions. Left to themselves, however, the reactions would occur too slowly and nonspecifically to sustain life. Cellular enzymes are catalysts that tame reactions by accelerating them, lending specificity, and regulating their time and place. Some principles of biological catalysis are demonstrated.
Discovery of RNA's catalytic activity led to unexpected spin-offs, including a new scenario for the origin of life. In a different area, the ability of RNA catalysts (ribozymes) to cut and splice RNA molecules has sparked efforts to develop them as pharmaceuticals against viruses, cancer, and genetic diseases.
RNA and protein are built from different chemical units and assembled in distinct ways. Thus, the ability of RNA to exhibit catalytic activity rivaling that of traditional protein enzymes was unexpected. Studies of RNA catalytic centers have revealed much about their structure and mode of action.
Chromosomes of humans and other eukaryotes contain linear DNA molecules. The chromosome ends, or telomeres, are necessary for DNA stability and replication. Telomere replication is carried out by telomerase, whose RNA subunit acts as a template for telomeric DNA synthesis.
How are diseases recognized as infectious and how are their causes identified? In this lecture, Dr. Ganem describes how epidemiologists, physicians, and microbiologists work together to identify and study pathogens. He first explains what viruses are and how they reproduce and infect cells. Dr. Ganem then elucidates the increasingly important role of DNA-based techniques in identifying infectious agents by telling how he and other scientists uncovered a virus strongly implicated in causing Kaposi's sarcoma--the leading cancer that affects AIDS patients.
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. After describing how bacteria grow, reproduce, and spread, Dr. Finlay explains how antibiotics work--and why they are not always successful in stopping infection. He describes the "genetic Internet" that enables certain pathogenic bacteria or "superbugs" to "download" genes that are resistant to all available antibiotics. He also explains how vaccines--an important tool in fighting infectious diseases--are developed. Dr. Finlay concludes his talk with a look at the potential uses of pathogenomics (the genomics of bateria) in fighting infection.