How long can a person live without transcribing DNA?

 

The Roman emperor Claudius Caesar unwittingly provided an answer in A.D.54. Caesar’s wife Agrippina mixed into her husband’s favourite dish of edible Amanita caesarea a few of the poisonous species A. phalloides. These poisonous mushrooms contain a substance that inhibits transcription of DNA to RNA. For the first 10 hours after Caesar ate this delicacy, all seemed well. But as the poison was absorbed by his liver and kidneys, it began to block transcription. About 15 hours after his repast, with no new messenger RNA to make new proteins, Caesar’s liver stopped functioning, and nausea, diarrhea, and delirium began to hit him. Two days later, he died of liver failure. It is highly doubtful that Caesar learned to appreciate the valuable role of transcription; but perhaps, in a general way, Agrippina did.

(“Biology: Bringing Science to Life” –New York,1991)

 

Text 2

First Artificial Enzyme

With the goal of making synthetic biological components, researchers have crafted the first artificial enzyme – specifically, an enzyme that removes a proton from a carbon atom. The team, from the University of Washington, the University of California, Los Angeles, and the Weizmann Institute of Science in Rehovot, Israel, used a computational model to devise potential enzymes constructed from 200 amino acids. After finding the enzyme that showed the most activity, the group further improved it by making it undergo evolution in a test tube. Seven rounds of evolution – the introduction of mutations – improved the enzyme’s efficiency 200-fold. “Nature” published the study online March 19.

(Scientific American, June 2008)

 

Text 3

Year in Review

Prize for Physiology or Medicine

Two Britons – Sydney Brenner and John E. Sulston – and an American – H. Robert Horvitz – shared the 2002 Nobel Prize for Physiology and Medicine for discoveries about how genes regulate tissue and organ development via a key mechanism called programmed cell death, or apoptosis. Their research elucidated the exquisitely tuned process in which certain cells, at the right time and place, get a signal to commit suicide.

Programmed cell death is essential for normal development in all humans. During the fetal development of humans, huge numbers of cells must be eliminated as body structures form. Programmed cell death sculpts the fingers and toes, for instance, by removing tissue that was originally present between the digits. Likewise, it removes surplus nerve cells produced during early development of the brain. In a typical adult human, about a trillion new cells develop each day; a similar number must be eliminated to maintain health and keep the body from becoming overgrown with surplus cells.

To study programmed cell death in humans, Brenner, Sulston< and Horvitz relied on a n animal model, the nematode Caenorhabditis elegans, a near- microscopic soil worm. In the early 1960s Brenner had realized the difficulties of studying organ development and related processes in higher animal, which have enormous number of cells. His research for a simple organism with many of the basic biological characteristics of humans led to C. elegans, which begins life with just 1,090 cells. Moreover, the animal is transparent, which allows scientists to follow cell divisions under a microscope; it reproduces quickly; and it is inexpensive to maintain. As researchers later learned, programmed cell death eliminates 131 cells in C. elegans, so that adults wind up with 959 body cells. Brenner’s investigations showed that a chemical compound could induce genetic mutations in the worm and that the mutations had specific effects on organ development.

Sulston in the 1970s mapped a complete lineage for C. elegans, tracing the descent of every cell, through division and differentiation, from the fertilized egg. From this he showed that, in worm after worm, exactly the same 131 cells are eliminated by programmed cell death as the animals develop into adults. Sulston also identified the first known mutations in genes invokved in the process.

Beginning in the 1970s Horvitz used C.elegans to try to determine if a specific genetic program controlled cell death. In 1986 he reported the first two “death genes,” ced-3 and ced-4, which participate in the cell-killing process. Later he showed that another gene, ced-9, protects against cell death by interacting with ced-3 and ced-4. Horvitz also established that humans have a counterpart to the ced-3 gene. Scientists later found that most of the genes involved in the controlling programmed cell death in C. elegans have counterparts in humans.

Knowledge about programmed cell death led to important advances not only in the developmental biology but also in medicine. It helped, for example, to explain how some viruses and bacteria invade human cells and cause infections. In cancer and some other diseases, programmed cell death was seen to slow down, which allows survival of cells that normally are destined to die. In cancer the result is an excessive growth of cells that invade and destroy normal tissue. Some cancer treatments are based on the strategy of shifting the cell suicide program into higher gear.

(Encyclopaedia Britanica 2006)

Text 4

Year in Review 2004

Stem Cells

In February 2004 two researchers from Seoul National University announced that they had successfully cloned human embryos. Hwang Woo Suk, a specialist in veterinary medicine, and Moon Shin Yong, an obstetrician, harvested eggs from donors and developed cloned embryos. One of the embryos yielded stem cells – undifferentiated cells capable of developing into specific cell types. Scientists believed that stem cells might one day be used to treat illnesses resulting from damaged cells, including juvenile diabetes, Parkinson disease, and Alzheimer disease.

The announcement set off a new round of debates regarding the ethics of human cloning. Hwang and Moon voiced strong opposition to reproductive cloning and insisted that their research was continued solely for the purpose of therapeutic cloning – that is, for fighting disease. Opponents were not appeased. Some believed that the development opened the door to reproductive cloning. Many others continued to oppose stem-cell research of any kind on religious grounds.

Human cells had been cloned before, but the resulting fragile embryos died quickly. Hwang and Moon credited the success of their research to several factors. One was the large number of eggs they had available: 242. They were obtained from 16 female volunteer donors who underwent a rigorous screening process to ensure that they understood the implications of their participation. Another factor was the way in which material was extracted from eggs. Whereas past researchers had used suction, Hwang and Moon used a squeezing technique, which helped reduce damage to the eggs.

(Encyclopaedia Britannica 2006)

 

 

Text 5

 

Like Darwin, Alfred Russel Wallace devised a theory of evolution by natural selection to explain what he saw in his travels (even choosing the term natural selection independently!). By 1858, Wallace had published four papers containing parts of a theory of evolution that included the mechanism of natural selection, the notion of descent with modification, and the idea of survival of the fittest. Wallace sent Darwin his fourth paper in 1858, and Darwin – realizing that his life’s work was being scooped – rushed to prepare an abstract. The following year, Darwin released his monumental and well-documented book “The Origin of Species”. The intellectual stimulation each scientist gave the other provided generations of biologists with the broadest conceptual framework for understanding the living world.

 

 

Text 6

 

Birds: Airborne Vertebrates

 

One might expect that the first flying vertebrates – the giant, leathery-winged pterosaurs – gave rise to the birds, but they didn’t; they died out when the dinosaurs did. Biologists believe instead that small, two-legged, lizard-like reptiles (thecodonts) were the real ancestors of birds, and they have important fossil evidence to prove it. Five skeletons of the oldest bird, the crow-sized Archaeopteryx, have been found at different sites in rocks 150 million years old. The fossil imprintsuggest that this animal was a true intermediate: It had scaly skin, curving claws, a long, jointed tail, and sharp teeth like a reptile, but it had feathered forelimbs and tail like a bird.

 

Text 7

Making Memories

This much is known, however: neuron No.28, say, fires an electrical signal, and in the synapse where one of 28’s connectors touches a receiver of neuron No 29, a chemical change triggers an electrical signal in 29. That signal gets passed on to neuron No 30, and on and on. if the connection between 28 and 29 is made often enough, the bond between the two neurons grows stronger. This crucial marriage seems to be the stuff that memory is made of.

Many scientists believe new information is absorbed and then processed into memory in the hippocampus, a seahorse-shaped organ in the center of the brain. The memories are then stored in sometimes bizarre patterns in various parts of the brain. The names of natural things, such as plants and animals, are apparently lodged in one part of the brain; the names of chairs, machines and other man-made stuff are in another. Nouns seem to be separated from verbs.

While age affects our ability to remember, other factors also make a difference. Marilyn Albert, a researcher at Massachusetts General Hospital, notes that among elderly people she ahs been studying, those who are less educated, less active physically and less able to control their day-to day lives tend to experience greater memory loss than the better educated, who regard themselves as more in control.

(from “What we know about Memory” by Lee Smith)

 

 

Text 8

Chloroplast Reactions

 

Photosynthetic oxygen evolution outside the living cell was first observed clearly in 1937. Since then the preparative techniques have continuously improved and the number of photo-conversions studied in isolated chloroplasts has expanded greatly. The light-driven formation of ATP from ADP was first reported in chloroplasts in 1954. The reduction of CO2 has been achieved only with the rates that are vanishingly small compared to those observed in whole cells. Numerous other substances, however, are reduced at a rate comparable to that of complete photosynthesis. One of these benzoquinones, when simply added to a suspension of whole green algae stops most cellular activities including respiration, but in the light the quinine in reduced oxygen is evolved about as fast as photosynthesis. To observe Hill reaction activity with green algae and oxidant other than benzoquinone, the cells have to be disrupted. Active cell-free preparations have been obtained also from blue-green algae, the efficiency of their photo-conversions, however, has been rather poor.

Spinach has become a standard material from which to prepare chloroplasts. The initial preparation, grinding and washing is best carried out in a slightly alkaline, high osmotic sucrose or chloride containing medium in which activity is retained for many hours. Most Hill reactions then will proceed faster if in the actual measurement the material is suspended in osmotically dilute medium so that the particles are broken and substrate may diffuse more readily to the active sites. The effect of PH can be considered in some systems, especially photo-phosphorlyration, most phenomena discussed here are observed at PH values between 7 and 8. Chloride ion and intensely CO2 are required in small concentration for O2 evolution. Photo-phosphorlyration requires in addition magnesium ion. Aging of chloroplast preparation, even at 0-4 C results in a gradual loss of activity. The oxygen evolution step and noncyclic photo-phospholyration are first to disappear, in a few hours a day. PMS-mediated phospholyration and especially the ability to photo-oxidize electron donors other than water are relatively more stable and can survive several days of storage. Heat treatment, detergent, and mechanical disruption act in many respects like aging, annihilating first those processes that put the highest demand upon structural integrity.

 

 

Text 9

Drinking may be deadly

Based on new data showing that submersible pumps made with lead-based bronze can contaminate water, the US Environmental Protection Agency (EPA) has advised people who get their water from wells with fairly new pumps to drink only bottled water until they have their wells tested for lead contamination. Even though the data show that the pumps are most likely to leach lead during the first year of operation, EPA has recommended that people with older pumps test their water too and drink only bottled water.

Ground water may also become contaminated when rainfall and surface run off pass through contaminated soil. Water dissolves many substances and carries particles and microorganisms with it into the ground water. Landfills, mining, improperly applied pesticides, leaking underground storage tanks, improperly installed or failing septic tanks and other surface activities can significantly alter ground water quality. Contamination often goes undefeated for many years.

 

 

Text 10