Split (1)

train · 1.3k rows

text stringlengths 1.61k 10k
ry, in its modern form, includes the fol- lowing three principles: 1. All organisms are composed of one or more cells, and the life processes of metabolism and heredity occur within these cells. 2. Cells are the smallest living things, the basic units of organization of all organisms. 3. Cells arise only by division of...
d are characterized as gramnegative. The susceptibility of bacteria to antibiotics often depends on the structure of their cell walls. Penicillin and vancomycin, for example, interfere with the ability of bacteria to cross-link the peptide units that hold the carbohydrate chains of the wall together. Like removing all ...
o specific nucleotide sequences along the DNA. Without this access, DNA could not direct the day-to-day activities of the cell. The chromosomes are associated with packaging proteins called histones. When a cell prepares to divide, the DNA coils up around the histones into a highly condensed form. In the initial stages...
pinching off small, membranebounded secretory vesicles containing the glycoprotein and glycolipid molecules. These vesicles then move to other locations in the cell, distributing the newly synthesized molecules to their appropriate destinations. Liposomes are synthetically manufactured vesicles that contain any variet...
the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism, the oxygen-requiring process by which energy in macromolecules is stored in ATP. Mitochondria have their own DNA; this DNA contains several genes that produce proteins essential to the mitochondrion’s role in oxidative me...
te filament, is found in epithelial cells (cells that line organs and body cavities) and associated structures such as hair and fingernails. The intermediate filaments of nerve cells are called neurofilaments. As we will discuss in the next section, the cytoskeleton provides an interior framework that supports the shap...
n the walls of adjacent cells is a sticky substance called the middle lamella, which glues the cells together (figure 5.29). Some plant cells produce strong secondary walls, which are deposited inside the primary walls of fully expanded cells. Plant cells store substances in a large central vacuole, and encase themselv...
f these sheets piled on one another would just equal the thickness of this sheet of paper. The lipid layer that forms the foundation of a cell membrane is composed of molecules called phospholipids (figure 6.2). Phospholipids Like the fat molecules you studied in chapter 3, a phospholipid has a backbone derived from a ...
on of the receptor protein within the cell, inducing activity Form supporting scaffold beneath membrane, anchored to both membrane and cytoskeleton Proteins line coated pits and facilitate binding to specific molecules Specific receptors bind peptide hormones and neurotransmitters Red blood cell Localization of lowdens...
reas of protein FIGURE 6.8 How nonpolar regions lock proteins into membranes. A spiral helix of nonpolar amino acids (red) extends across the nonpolar lipid interior, while polar (purple) portions of the protein protrude out from the bilayer. The protein cannot move in or out because such a movement would drag nonpolar...
ill be in use and the capacity of the transport system will be saturated. In contrast, substances that move across the membrane by simple diffusion (diffusion through channels in the bilayer without the assistance of carriers) do not show saturation. Facilitated diffusion provides the cell with a ready way to prevent t...
takes in is particulate (made up of discrete particles), such as an organism or some other fragment of organic matter (figure 6.17a), the process is called phagocytosis (Greek phagein, “to eat” + cytos, “cell”). If the material the cell takes in is liquid (figure 6.17b), it is called pinocytosis (Greek pinein, “to dri...
m. This conformation has a low affinity for K+, so the two bound K+ dissociate from the protein and diffuse into the interior of the cell. The original conformation has a high affinity for Na+; when these ions bind, they initiate another cycle. Three Na+ leave the cell and two K+ enter in every cycle. The changes in pr...
sport • Exocystosis/ endocytosis • Exocystosis/ endocytosis • Exploration: Active Transport • Active Transport • Active Transport 7 Cell-Cell Interactions Concept Outline 7.1 Cells signal one another with chemicals. Receptor Proteins and Signaling between Cells. Receptor proteins embedded in the plasma membrane change ...
he nervous system provide rapid communication with distant cells. Their signal molecules, neurotransmitters, do not travel to the distant cells through the circulatory system like hormones do. Rather, the long, fiberlike extensions of nerve cells release neurotransmitters from their tips very close to the target cells ...
brane when a chemically gated ion channel opens depends on the specific threedimensional structure of the channel. Enzymic Receptors Many cell surface receptors either act as enzymes or are directly linked to enzymes (figure 7.6b). When a signal molecule binds to the receptor, it activates the enzyme. In almost all cas...
b) Ca++ pathway FIGURE 7.9 How second messengers work. (a) The cyclic AMP (cAMP) pathway. An extracellular receptor binds to a signal molecule and, through a G protein, activates the membrane-bound enzyme, adenylyl cyclase. This enzyme catalyzes the synthesis of cAMP, which binds to the target protein to initiate the c...
ered around them form long-lasting or permanent connections with each other called cell junctions (figure 7.15). The nature of the physical connections between the cells of a tissue in large measure determines what the tissue is like. Indeed, a tissue’s proper functioning often depends critically upon how the individua...
ons occur only at holes or gaps in the walls, where the plasma membranes of adjacent cells can come into contact with each other. Cytoplasmic connections that form across the touching plasma membranes are called plasmodesmata (figure 7.22). The majority of living cells within a higher plant are connected with their nei...
(6.023 × 1023) of carbon-hydrogen (C—H) bonds. During a chemical reaction, the energy stored in chemical bonds may transfer to new bonds. In some of these reactions, electrons actually pass from one atom or molecule to another. When an atom or molecule loses an electron, it is said to be oxidized, and the process by w...
nergies between reactants and products (∆H), minus any change in the degree of disorder of the system (T ∆S). Any reaction whose products contain less free energy than the reactants (∆G is negative) will tend to proceed spontaneouslya) Product Energy must be supplied. Reactant Reactant Endergonic (b) Exergonic Energy i...
ve site of the enzyme, which is shaped so that only a certain substrate molecule will fit into it. Active site Substrate (a) (b) FIGURE 8.8 How the enzyme lysozyme works. (a) A groove runs through lysozyme that fits the shape of the polysaccharide (a chain of sugars) that makes up bacterial cell walls. (b) When such a ...
of the enzyme and making it unable to bind to the substrate (figure 8.12). Most noncompetitive inhibitors bind to a specific portion of the enzyme called an allosteric site (Greek allos, “other” + steros, “form”). These sites serve as chemical on/off switches; the binding of a substance to the site can switch the enzy...
nergy, became more complex when the supply of F in the environment ran out. A new reaction was added in which the depleted molecule, F, is made from another molecule, E, which was also present in the environment: E → F + → H G Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Substrate Product FIGURE 8.15 A biochemical pathway. Th...
all eukaryotic cells are thought to be their descendants. Six major innovations highlight the evolution of metabolism as we know it today. Chapter 8 Energy and Metabolism 157 Chapter 8 Summary http://www.mhhe.com/raven6e http://www.biocourse.com Questions Media Resources 8.1 The laws of thermodynamics describe how ener...
gy in the cell. How is ATP able to transfer energy so readily? Recall from chapter 8 that ATP is composed of a sugar (ribose) bound to an organic base (adenine) and a chain of three phosphate groups. As shown in figure 9.3, each phosphate group is negatively charged. Because like charges repel each other, the linked ph...
t chain. Oxygen is the final electron acceptor. Anaerobic respiration donates the harvested electrons to other inorganic compounds. Glucose Glycolysis Pyruvate Lactate ATP NADH Plasma membrane Acetyl-CoA NADH Krebs cycle ATP NADH H2O ATP Mitochondrion Cytoplasm Extracellular fluid CO2 O2 FIGURE 9.6 An overview of aerob...
an important role in the metabolism of most organisms (figure 9.10), even those capable of aerobic respiration. The fate of the pyruvate that is produced by glycolysis depends upon which of these two processes takes place. The aerobic respiration path starts with the oxidation of pyruvate to a molecule called acetyl-Co...
ized, yielding a four-carbon molecule of oxaloacetate and two electrons that reduce a molecule of NAD+ to NADH. Oxaloacetate, the molecule that began the cycle, is now free to combine with another two-carbon acetyl group from acetyl-CoA and reinitiate the cycle. The Products of the Krebs Cycle In the process of aerobic...
cose involves a series of oxidation-reduction reactions that release energy by repositioning electrons closer to oxygen atoms. Energy is thus harvested from glucose molecules in gradual steps, using NAD+ as an electron carrier. Chapter 9 How Cells Harvest Energy 173 Stage Four: The Electron Transport Chain The NADH and...
reactions of glycolysis, the Krebs cycle, and fatty acid breakdown are inhibited, slowing ATP production. The regulation of these biochemical pathways by the level of ATP is an example of feedback inhibition. Conversely, when ATP levels in the cell are low, ADP levels are high; and ADP activates enzymes in the pathway...
ed in figure 9.A, involve only three or rarely four trophic levels. Too much energy is lost at each transfer to allow chains to be much longer than that. For example, it would be impossible for a large human population to subsist by eating lions captured from the Serengeti Plain of Africa; the amount of grass available...
ion. Photorespiration. The enzyme that catalyzes carbon fixation also affects CO2 release. FIGURE 10.1 Capturing energy. These sunflower plants, growing vigorously in the August sun, are capturing light energy for conversion into chemical energy through photosynthesis. Life on earth would be impossible without photosyn...
hat photosynthesis consists of an initial set of what he called “light” reactions, that are largely independent of temperature, and a second set of “dark” reactions, that seemed to be independent of light but limited by CO 2. Do not be confused by Blackman’s labels—the so-called “dark” reactions occur in the light (in ...
let (UV) light, which, because of its shorter wavelength, possesses considerably more energy than visible light. UV light is thought to have been an important source of energy on the primitive earth when life originated. Today’s atmosphere contains ozone (derived from oxygen gas), which absorbs most of the UV photons i...
e boosted in the pigment. Chapter 10 Photosynthesis 191 Organizing Pigments into Photosystems The light reactions of photosynthesis occur in membranes. In bacteria like those studied by van Niel, the plasma membrane itself is the photosynthetic membrane. In plants and algae, by contrast, photosynthesis is carried out b...
hat returns has only as much energy as it had before the photon was absorbed. The difference in the energy of that electron is the photosynthetic payoff, the energy that drives the proton pump. For more than a billion years, cyclic photophosphorylation was the only form of photosynthetic light reaction that organisms u...
es electrons to an iron-sulfur protein called ferredoxin (Fd). Making NADPH Photon Stroma H2O Thylakoid space 1 O2 2 2 H+ Q H+ ADP ATP H+ H+ H+ H+ H+ H+ Photosystem II b6-f complex ATP synthase Plant cell Chloroplast FIGURE 10.16 Chemiosmosis in a chloroplast. The b6-f complex embedded in the thylakoid membrane pumps p...
molecules of Glyceraldehyde 3-phosphate (3C) (G3P) 1 molecule of Glyceraldehyde 3-phosphate (3C) (G3P) Glucose and other sugars FIGURE 10.20 The Calvin cycle. For every three molecules of CO2 that enter the cycle, one molecule of the three-carbon compound, glyceraldehyde 3phosphate (G3P), is produced. Notice that the ...
I, driving a proton pump and bringing about the chemiosmotic synthesis of ATP. • When the electron arrives at photosystem I, another photon of light is absorbed, and energized electrons are channeled to a primary electron acceptor, which reduces NADP+ to NADPH. Use of NADPH rather than NADH allows plants and algae to ...
orsetail Adder’s tongue fern Total Number of Chromosomes Group Total Number of Chromosomes 2 14 20 42 80 216 1262 VERTEBRATES Opossum Frog Mouse Human Chimpanzee Horse Chicken Dog 22 26 40 46 48 64 78 78 Chapter 11 How Cells Divide 209 The Structure of Eukaryotic Chromosomes In the century since discovery of chromosome...
M phase takes only about an hour, a small fraction of the entire cycle. Most of the variation in the length of the cell cycle from one organism or tissue to the next occurs in the G1 phase. Cells often pause in G1 before DNA replication and enter a resting state called G0 phase; they may remain in this phase for days ...
, separating chromosomes to opposite poles • polar microtubules elongate, preparing cell for cytokinesis Mitotic spindle Centromere and kinetochore Mitotic spindle microtubules Kinetochore microtubules Chromatids Polar microtubules Spindle microtubules (pink) Chromosomes aligned on metaphase plate FIGURE 11.11 Mitosis ...
ins to copy its DNA, 218 Part IV Reproduction and Heredity G2 checkpoint M checkpoint M C G2 S G1 G1 checkpoint FIGURE 11.15 Control of the cell cycle. Cells use a centralized control system to check whether proper conditions have been achieved before passing three key “checkpoints” in the cell cycle. proceed to S? pau...
hropoietin triggers cell division in red blood cell precursors. Most animal cells need a combination of several different growth factors to overcome the various controls that inhibit cell division. The G0 Phase. If cells are deprived of appropriate growth factors, they stop at the G1 checkpoint of the cell cycle. With ...
ed to opposite poles of the cell by the microtubules attached to their centromeres. • In the fourth and final stage of mitosis, telophase, the mitotic apparatus is disassembled, the nuclear envelope re-forms, and the chromosomes uncoil. • When mitosis is complete, the cell divides in two, so that the two sets of chromo...
sion. Following chromosome replication, homologous chromosomes, or homologues (see chapter 11), pair all along their length. The process of forming these complexes of homologous chromosomes is called synapsis Homologous Recombination The second unique feature of meiosis is that genetic exchange occurs between the homol...
just as in mitosis. During diakinesis of prophase I, the chiasmata move down the paired chromosomes from their original points of crossing over, eventually reaching the ends of the chromosomes. At this point, they are called terminal chiasmata. Terminal chiasmata hold the homologous chromosomes together in metaphase I...
rganisms became larger and longer-lived, it must have become increasingly important for them to be able to repair such damage. The synaptonemal complex, which in early stages of meiosis precisely aligns pairs of homologous chromosomes, may well have evolved originally as a mechanism for repairing double-strand damage t...
to a recessive allele. Multiple Alleles: The ABO Blood Groups. The human ABO blood groups are determined by three I gene alleles. Patterns of Inheritance Can Be Deduced from Pedigrees. Hemophilia is sex-linked. Gene Disorders Can Be Due to Simple Alterations of Proteins. Sickle cell anemia is caused by a single amino ...
ndel was educated in a monastery and went on to study science and mathematics at the University of Vienna, where he failed his examinations for a teaching certificate. He returned to the monastery and spent the rest of his life there, eventually becoming abbot. In the garden of the monastery (figure 13.6), Mendel initi...
lways true-breeding. In the cross of white-flowered with purple-flowered plants, for example, the white-flowered F2 individuals reliably produced white-flowered offspring when they were allowed to selffertilize. By contrast, only 1⁄3 of the dominant purple-flowered F2 individuals ( 1⁄ 4 of all F2 offspring) proved true...
rozygous F1 individuals are crossed, three kinds of F2 offspring are possible: PP homozygotes (purple flowers); Pp heterozygotes (also purple flowers); and pp homozygotes (white flowers). Therefore, in the F2 generation, the ratio of dominant to recessive phenotypes is 3:1. However, the ratio of genotypes is 1:2:1 (1 P...
contrasting pairs of the pure-breeding lines to create heterozygotes. In a cross involving different seed shape alleles (round, R, and wrinkled, r) and different seed color alleles (yellow, Y, and green, y), all the F1 individuals were identical, each one heterozygous for both seed shape (Rr) and seed color (Yy). The ...
The heterozygous progeny have pink flowers and the genotype CRCW. If two of these heterozygotes are crossed, the phenotypes of their progeny occur in a ratio of 1:2:1 (red:pink:white). The degree to which an allele is expressed may depend on the environment. Some alleles are heat-sensitive, for example. Traits influen...
er (heterozygous) Normal (homozygous dominant) FIGURE 13.22 Tay-Sachs disease. Homozygous individuals (left bar) typically have less than 10% of the normal level of hexosaminidase A (right bar), while heterozygous individuals (middle bar) have about 50% of the normal level—enough to prevent deterioration of the central...
they tend to accumulate in those vessels and form clots. People who have large proportions of sickle-shaped red blood cells tend to have intermittent illness and a shortened life span. The hemoglobin in the defective red blood cells differs from that in normal red blood cells in only one of hemoglobin’s 574 amino acid...
. A single small fly provided the proof. In 1910 Thomas Hunt Morgan, studying the fruit fly Drosophila melanogaster, detected a mutant male fly, one that differed strikingly from normal flies of the same species: its eyes were white instead of red (figure 13.29). Morgan immediately set out to determine if this new trai...
al locations of the seven genes studied by Mendel in the garden pea. The genes for plant height and pod shape are very close to each other and rarely recombine. Plant height and pod shape were not among the characters Mendel examined in dihybrid crosses. One wonders what he would have made of the linkage he surely woul...
ted A through G), each characterized by a different size, shape, and appearance. The differences among the chromosomes are most clearly visible when the chromosomes are arranged in order in a karyotype (figure 13.35). Techniques that stain individual segments of chromosomes with different-colored dyes make the identifi...
roduced possess both X chromosomes and so are XX gametes; the other gametes that result from such an event have no sex chromosome and are designated “O” (figure 13.40). If an XX gamete combines with an X gamete, the resulting XXX zygote develops into a female with one functional X chromosome and two Barr bodies. She is...
. 13.2 Human genetics follows Mendelian principles. • Some genetic disorders are relatively common in human populations; others are rare. Many of the most important genetic disorders are associated with recessive alleles, which are not eliminated from the human population, even though their effects in homozygotes may b...
pregnant with her first child. If you were a genetic counselor, what would you tell her about the probability that her child will have cystic fibrosis? 16. How many chromosomes would you expect to find in the karyotype of a person with Turner syndrome? 17. A woman is married for the second time. Her first husband has ...
he protein VEGF rise in wild-type cells under conditions of hypoxia, increasing the immediate availability of oxygen to the tumor by promoting capillary formation. The researchers found levels of VEGF protein were lower in null cell tumors, and responded to hypoxia at a lower rate. Both the decrease in tumor size and t...
trains of frogs were used that differed from each other in the number of nucleoli their cells possessed. The nucleus was removed from an egg of one strain, either by sucking the egg nucleus into a micropipette or, more simply, by destroying it with ultraviolet light. A nucleus obtained from a differentiated cell of the...
is: DNA Is a Polymer Because Miescher’s nuclein was slightly acidic, it came to be called nucleic acid. For 50 years biologists did little research on the substance, because nothing was known of its function in cells. In the 1920s, the basic structure of nucleic acids was determined by the biochemist P. A. Levene, who ...
explained why Chargaff had obtained the results he had: in a double helix, adenine forms two hydrogen bonds with thymine, but it will not form hydrogen bonds properly with cytosine. Similarly, guanine forms three hydrogen bonds with cytosine, but it will not form hydrogen bonds properly with thymine. Consequently, ade...
eads 3′ to 5′ for mistakes, and a ring-shaped β2 dimer subunit that clamps the polymerase III complex around the DNA double helix. Polymerase III progressively threads the DNA through the enzyme complex, moving it at a rapid rate, some 1000 nucleotides per second (100 full turns of the helix, 0.34 micrometers). Table 1...
art V Molecular Genetics 14.4 What is a gene? The One-Gene/One-Polypeptide Hypothesis As the structure of DNA was being solved, other biologists continued to puzzle over how the genes of Mendel were related to DNA. oxidized rapidly when exposed to air, turning the urine black. In normal individuals, homogentisic acid i...
, some genes are devoted to the production of special forms of RNA, many of which play important roles in protein synthesis themselves. A half-century of experimentation has made clear that DNA is the molecule responsible for the inheritance of traits, and that this molecule is divided into functional units called gene...
ence, this stage is called transcription. Transcription is initiated when the enzyme RNA polymerase binds to a particular binding site called a promoter located at the beginning of a gene. Starting there, the RNA polymerase moves along the strand into the gene. As it encounters each DNA nucleotide, it adds the correspo...
ria was not quite the same as the “universal code” that has become so familiar to biologists. In the mitochondrial genomes, what should have been a “stop” codon, UGA, was instead read as the amino acid tryptophan; AUA was read as methionine rather than isoleucine; and AGA and AGG were read as “stop” rather than arginin...
tRNA molecules? The key translation step, which pairs the three-nucleotide sequences with appropriate amino acids, is carried out by a remarkable set of enzymes called activating enzymes. Activating Enzymes Particular tRNA molecules become attached to specific amino acids through the action of activating enzymes called...
of the gene that produced the mRNA. 3. With genetic engineering techniques (chapter 19), the portion of the nuclear DNA containing the gene that produced the mRNA was isolated. This procedure is referred to as cloning the gene in question. 4. Single-stranded forms of the cDNA and the nuclear DNA were mixed and allowed...
e promoter in a flexible and reversible way; eukaryotes by contrast regulate many of their genes by turning them on and off in a more permanent fashion. In bacteria 16.2 Regulatory proteins read DNA without unwinding it. How to Read a Helix without Unwinding It. Regulatory proteins slide special segments called DNAbind...
cal segments of the protein linked by a short nonhelical segment, the “turn” (figure 16.3). The first DNA-binding motif recognized, the helix-turn-helix motif has since been identified in hundreds of DNA-binding proteins. A close look at the structure of a helix-turn-helix motif reveals how proteins containing such mot...
d OFF switches, bacteria can create sophisticated transcriptional control systems. A particularly wellstudied example is the lac operon of E. coli (figure 16.9). This operon is responsible for producing three proteins that import the disaccharide lactose into the cell and break it down into two monosaccharides: glucose...
uence located adjacent to or overlapping an enhancer sequence, the corresponding activator that would normally have bound that enhancer is no longer able to do so. The activator is thus unavailable to interact with the transcription complex and initiate transcription. Eukaryotic Transcription Factors For RNA polymerase...
cases, gene expression is regulated by changing which splicing event occurs during different stages of development or in different tissues. An excellent example of alternative splicing in action is found in two different human organs, the thyroid and the hypothalamus. The thyroid gland (see chapter 56) is responsible f...
rp operon • Gene Regulation 16.1 Gene expression is controlled by regulating transcription. • Regulatory sequences are short stretches of DNA that function in transcriptional control but are not transcribed themselves. • Regulatory proteins recognize and bind to specific regulatory sequences on the DNA. 1. How do regul...
side of the embryo facing you, producing (b) a cluster of cells on this side of the embryo, which soon expands to become a (c) compact mass of cells. (d) This mass eventually invaginates into the interior of the embryo, forming a gastrula, then a neurula. (a) (c) FIGURE 17.3 The miracle of development. This nine-week-o...
can differentiate into the tissues of the plant. Another major difference between animals and plants is that most animals are mobile and can move away from unfavorable circumstances, while plants are anchored in position and must simply endure whatever environment they experience. Plants compensate for this restriction...
egetal pole cells are placed next to each other, some of the animal pole cells will develop as mesoderm. The interaction between the two cell types triggers a switch in the developmental path of the cells! When a cell switches from one path to another as a result of interaction with an adjacent cell, induction has take...
—a neat trick. The shock also kick-started the cell cycle, causing the cell to begin to divide. After six days, in 30 of 277 tries, the dividing embryo reached the hollow-ball “blastula” stage, and 29 of these were transplanted into surrogate mother sheep. A little over five months later, on July 5, 1996, one sheep gav...
tant regulatory role when it binds to DNA and regulates expression of specific genes. The variable region of the protein determines the specific activity of the protein. Also included in this protein is a small hinge region and the homeodomain, a 60-amino-acid sequence common to all proteins of this type. The homeodoma...
ng Rudimentary wing Genital Mouthparts Lip Adult fly Nervous system Pharynx The Nematode One of the most powerful models of animal development is the tiny nematode Caenorhabditis elegans. Only about 1 mm long, it consists of 959 somatic cells and has about the same amount of DNA as Drosophila. The entire genome has bee...
ay be as old as the individual. Glycation of collagen, elastin, and a diverse collection of other proteins within the cell produces a complex mixture of glucose-linked proteins called advanced glycosylation end products (AGEs). AGEs can cross-link to one another, reducing the flexibility of connective tissues in the jo...
se mechanisms “proofread” the replicated DNA strands for accuracy and correct any mistakes. The proofreading is not perfect, however. If it were, no variation in the nucleotide sequences of genes would be generated. Mistakes Happen In fact, cells do make mistakes during replication, and damage to the genetic message al...
sure to bright sunlight, UV-induced DNA damage, and skin cancer. A deep tan is not healthy! A rare hereditary disorder among humans called xeroderma pigmentosum causes these problems after a lesser exposure to UV. Individuals with this disorder develop extensive skin tumors after exposure to sunlight because they lack ...
by a sophisticated group of proteins described in chapter 11. Cancer results from the mutation of the genes encoding these proteins. Cancer can be caused by chemicals that mutate DNA or in some instances by viruses that circumvent the cell’s normal proliferation controls. Whatever the immediate cause, however, all can...
aulic fluids and lubricants, inks, adhesives, insecticides Chimney sweeps; bricklayers; firefighters; heating-unit service workers Insecticide/herbicide sprayers; tanners; oil refiners Wood product, paper, textiles, and metal product workers of causing cancer in laboratory animals. Among them are trichloroethylene, asb...
idely studied are myc and ras. Expression of myc stimulates the production of cyclins and cyclin-dependent protein kinases (Cdks), key elements in regulating the checkpoints of cell division. Gene ONCOGENES Table 18.4 Some Genes Implicated in Human Cancers Product Cancer Genes Encoding Growth Factors or Their Receptors...
of cancer in the United States in 1999; about 28% of them died of lung cancer. About 140,000 persons were diagnosed with lung cancer each year in the 1980s. Around 90% of them died within three years after diagnosis; 96% of them were cigarette smokers. Smoking is a popular pastime. In the United States, 24% of the pop...
completely, leading to ceaseless cell division. Forty percent of all cancers have a defective form of Rb. Therapies directed at this stage of the decision process are only now being attempted. They focus on drugs able to inhibit E2F, which should halt the growth of tumors arising from inactive Rb. Experiments in mice i...
genes as fixed entities, like beads on a string, did not readily accept the idea of transposons. Therefore, while Lederberg and Tatum were awarded a Nobel Prize for their discovery in 1958, McClintock did not receive the same recognition for hers until 1983 (figure 18.23). Excision Bacterial chromosome Integration Homo...
to some individuals that are homozygous for a variant “long-neck” allele. Similarly, a recessive mutation at the leg length locus leads to homozygous “long-leg” individuals. It is very unlikely that these two mutations would arise at the same time in the same individual because the probability of two independent events...
ing breaks in double-stranded DNA) has led to a radically different situation. Unequal crossing over between homologous chromosomes tends to promote the duplication of material rather than its reduction (figure 18.33b). Consequently, eukaryotic genomes have been in a constant state of flux during the course of their ev...
grouped together at one or a few sites on a chromosome. These genes encode products that are required by the cell in large amounts. • Multigene families consist of copies of genes clustered at one site on a chromosome that diverge in sequence more than the genes in a tandem cluster. 388 Part V Molecular Genetics • Stu...
estriction endonucleases so valuable for genetic engineering is the fact that any two fragments produced by the same restriction endonuclease can be joined together. Fragments of elephant and ostrich DNA cleaved by the same endonuclease can be joined to one another as readily as two bacterial DNA fragments. FIGURE 19.2...
ecombinant DNA is inserted into a bacterial cell, which reproduces and forms clones. In stage 4, the bacterial clones will be screened for the gene of interest. Chapter 19 Gene Technology 395 Stage 4: Screening The clones containing a specific DNA fragment of interest, often a fragment that includes a particular gene, ...

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.