Cells Sense and Send Information

A living cell continuously monitors its surroundings and adjusts its own activities and composition accordingly. Cells also communicate by deliberately sending signals that can be received and interpreted by other cells. Such signals are common not only within an individual organism, but also between organisms. For instance, the odor of a pear detected by us and other animals signals a food source consumption of the pear by an animal aids in distributing the pear's seeds. Everyone benefits The...

Review The Concepts

When viewed by electron microscopy, the lipid bilayer is often described as looking like a railroad track. Explain how the structure of the bilayer creates this image. 2. Biomembranes contain many different types of lipid molecules. What are the three main types of lipid molecules found in biomembranes How are the three types similar, and how are they different 3. Lipid bilayers are considered to be two-dimensional fluids what does this mean What drives the movement of lipid molecules and...

Myelination Increases the Velocity of Impulse Conduction

As we have seen, action potentials can move down an axon without diminution at speeds up to 1 meter per second. But even such fast speeds are insufficient to permit the complex movements typical of animals. In humans, for instance, the cell bodies of motor neurons innervating leg muscles are located in the spinal cord, and the axons are about a meter in length. The coordinated muscle contractions required for walking, running, and similar movements would be impossible if it took one second for...

The Rate of Glucose Oxidation Is Adjusted to Meet the Cells Need for ATP

All enzyme-catalyzed reactions and metabolic pathways are regulated by cells so as to produce the needed amounts of metabolites but not an excess. The primary function of the oxidation of glucose to CO2 via the glycolytic pathway, the pyruvate dehydrogenase reaction, and the citric acid cycle is to produce NADH and FADH2, whose oxidation in mitochondria generates ATP. Operation of the glycolytic pathway and citric acid cycle is continuously regulated, primarily by allosteric mechanisms, to meet...

The Cell Biology of Atherosclerosis Heart Attacks and Strokes

In this concluding section we examine the relation between lipid metabolism and atherosclerosis, the most common cause of heart attacks and strokes. Atherosclerosis accounts for 75 percent of deaths due to cardiovascular disease in the United States. Advances in our understanding of the molecular mechanisms underlying lipid metabolism and its regulation are having an enormous effect on the treatment and prevention of this major health problem. Frequently called cholesterol-dependent clogging of...

Unicellular Organisms Help and Hurt Us

Bacteria and archaebacteria, the most abundant single-celled organisms, are commonly 1-2 m in size. Despite their small size and simple architecture, they are remarkable biochemical factories, converting simple chemicals into complex biological molecules. Bacteria are critical to the earth's ecology, but some cause major diseases bubonic plague (Black Death) from Yersinia pestis, strep throat from Streptomyces, tuberculosis from Mycobacterium tuberculosis, anthrax from Bacillus anthracis,...

Ctc

Where C is the concentration of Sout (initially, the concentration of Sin 0). Vmax, the rate of transport when all molecules of GLUT1 contain a bound S, occurs at an infinitely high Sout concentration. The lower the value of Km, the more tightly the substrate binds to the transporter, and the greater the transport rate at a fixed concentration of substrate. Equation 7-1 describes the curve for glucose uptake by erythrocytes shown in Figure 7-3 as well as similar curves for other uniporters. For...

Analyze The Data

In culture, normal human cells undergo a finite number of cell divisions until they no longer proliferate and enter a state known as replicative senescence. The inability to maintain normal telomere length is thought to play an important role in this process. Telomerase is a ribonucleoprotein complex that regenerates the ends of telomeres lost during each round of DNA replication. Human telomerase consists of a template containing RNA subunit and a catalytic protein subunit known as human...

Proteins Give Cells Structure and Perform Most Cellular Tasks

The varied, intricate structures of proteins enable them to carry out numerous functions. Cells string together 20 different amino acids in a linear chain to form a protein (see Figure 2-13). Proteins commonly range in length from 100 to 1000 amino acids, but some are much shorter and others longer. We obtain amino acids either by synthesizing them from other molecules or by breaking down proteins that we eat. The essential amino acids, from a dietary standpoint, are the eight that we cannot...

Proteins Can Be Removed from Membranes by Detergents or High Salt Solutions

Detergents are amphipathic molecules that disrupt membranes by intercalating into phospholipid bilayers and solubi-lizing lipids and proteins. The hydrophobic part of a detergent molecule is attracted to hydrocarbons and mingles with them readily the hydrophilic part is strongly attracted to water. Some detergents are natural products, but most are synthetic molecules developed for cleaning and for dispersing mixtures of oil and water (Figure 5-39). Ionic detergents, such as sodium deoxycholate...

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Cilia Microtubules

Filaments, or other microtubules, and its length controls how far apart microtubules are spaced (Figure 20-12). The microtubule-binding domain contains several repeats of a conserved, positively charged four-residue amino acid sequence that binds the negatively charged C-terminal part of tubulin. This binding is postulated to neu tralize the charge repulsion between tubulin subunits within a microtubule, thereby stabilizing the polymer. MAP1A and MAP1B are large, filamentous molecules found in...

Analysis of Familial Hypercholesterolemia Revealed the Pathway for Receptor Mediated Endocytosis of LDL Particles

There is no better example of the synergistic relation between basic molecular cell biology and medicine than the story of the discovery of the LDL receptor (LDLR) pathway for delivering cholesterol to cells. The series of elegant and Nobel Prize-winning studies leading to this discovery served as sources of insight into the mechanisms underlying LDL metabolism, the functions and properties of several key organelles, cellular systems for co-ordinately regulating complex metabolic pathways, and...

ABC Proteins Mediate Cellular Export of Phospholipids and Cholesterol

The export of phospholipids and cholesterol can be simultaneous owing to the activity of various members of the ABC superfamily (see Table 18-2). The best-understood example of this phenomenon is in the formation of bile, an aqueous fluid containing phospholipids, cholesterol, and bile acids, which are derived from cholesterol. After export from liver cells, phospholipids, cholesterol, and bile acids form water-soluble micelles in the bile, which is delivered through ducts to the gallbladder,...

Viruses Are the Ultimate Parasites

Virus-caused diseases are numerous and all too familiar chicken pox, influenza, some types of pneumonia, polio, measles, rabies, hepatitis, the common cold, and many others. Smallpox, once a worldwide scourge, was eradicated by a decade-long global immunization effort beginning in the mid-1960s. Viral infections in plants (e.g., dwarf mosaic virus in corn) have a major economic impact on crop production. Planting of virus-resistant varieties, developed by traditional breeding methods and more...

Two Treatments for Atherosclerosis Are Based on SREBPRegulated Cellular Cholesterol Metabolism

The complex pathogenesis of atherosclerosis, which we have only briefly sketched here, presents a daunting challenge to modern molecular medicine. However, as our understanding of the cell biology underlying this complexity has advanced, many opportunities for intervening in the disease process by modulating cellular pathways have arisen. We conclude this chapter by describing two examples of such interventions affecting cellular lipid metabolism. Because the risk for atherosclerotic disease is...

Overview Of Changes In Cells In Cancer

Overview Changes Cells Cancer

23.1 Tumor Cells and the Onset of Cancer 23.2 The Genetic Basis of Cancer 23.3 Oncogenic Mutations in Growth-Promoting Proteins 23.4 Mutations Causing Loss of Growth-Inhibiting and Cell-Cycle Controls 23.5 The Role of Carcinogens and DNA Repair in Cancer FIGURE 23-1 Overview of changes in cells that cause cancer. During carcinogenesis, six fundamental cellular properties are altered, as shown here, to give rise to the complete, most destructive cancer phenotype. Less dangerous tumors arise when...

LDLRIndependent Uptake of LDL Bad Cholesterol Leads to Formation of Foam Cells

As noted, the first unique step of atherosclerosis is the accumulation in the artery wall of macrophage foam cells filled with lipid droplets containing cholesteryl esters. The greater the plasma LDL concentration and the greater the concentration of LDL in the artery wall, the more rapidly foam cells develop and accumulate to form microscopically visible early fatty streaks. Given these facts, you might initially guess that LDLR-mediated endocytosis is responsible for foam cell formation, but...