The Molecules Of Aids

The World Health Organization estimates that since its discovery in 1981 AIDS has caused more than 25 million deaths around the world, and about 33 million people are currently infected by HIV, the virus that causes AIDS. It is transmitted through blood or body fluids that pass from one individual to another during sex, when they share needles, or from mother to child during childbirth. Researchers have not yet been able to create an effective vaccine against HIV because of the way HIV infects...

The Innate Immune System

Innate immunity (also known as nonspecific immunity) is a very basic system for dealing with infections that evolved long ago in the ancestor of vertebrates and insects. The adaptive immune system evolved later and is much more sophisticated it can learn to recognize a threat, mount a response, and remember it later. Innate immunity, in contrast, offers either or protection It recognizes and destroys an invader, or it does not. Its main actors are specialized kinds of white blood cells...

Membrane Channels And Pumps

Ligands and receptor proteins are one of the main ways that cells sense each other and the environment. A subset of proteins in the membrane called membrane channels permits cells to communicate in another way, by changing their electrical charge. These molecules also help maintain a balance between the environment of the cell and the outer world, regulating how cells take up water, energy, and nutrients. Membranes undoubtedly played a central role in the evolution of life. Without them...

Nicotine And Addiction

Nicotine is a bitter-tasting substance found in the leaves of the tobacco plant. When smoked in a cigarette, it passes through the lungs, enters the bloodstream, and reaches the brain in seven or eight seconds. Because its structure is similar to a neu-rotransmitter called acetylcholine, it imitates this natural signal. When it binds to its receptors, it opens calcium channels and causes the body to release the hormone adrenaline. This raises the rate of the heartbeat and breathing and releases...

Neurotransmitters And Synapses

Membrane receptors and ion channels work together so that nerve cells can communicate with each other, permitting thought and conscious movement. The signals that pass between them involve both small molecules called neurotransmitters and electrical stimulation. Neurons make up only about 10 percent of the cells in the brain, but they have traditionally been considered the most important communicators. They have an unusual, treelike structure that sprouts from a small cell body, the soma, which...

Prions And Mad Cow Disease

In the late 19th century Louis Pasteur (1822-95) became firmly convinced that all infectious diseases were caused by bacteria. The idea became so widely accepted that when a Frenchman named Charles-Louis-Alphonse Laveran (1845-1922) claimed that malaria was caused by another type of one-celled parasite, it took several years for the medical community to believe him. (When they did, he was awarded the 1907 Nobel Prize in physiology or medicine.) Early virus researchers confronted a similar...

Electron Microscopes And Cryoelectron Tomography

Ideally scientists would like to develop a sort of GoogleEarth of the cell, where microscopes can zoom in on locations, pinpointing what molecules are active there and what they are doing. But even the most powerful electron microscopes lack the resolution to see single molecules. They can, however, catch a glimpse of very large proteins or protein machines. That might at least allow scientists to look at an image of a cell and point out the locations of particular machines. Doing so would...