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Mutations in the genes encoding collagens often have detrimental consequences, resulting in severely crippling diseases. Particularly devastating are mutations that change glycines, which are required at every third position in the collagen polypeptide chain so that it can assemble into the characteristic triple-helica... | {
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"Header 3": "Question 20–2",
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To do their job, collagen fibrils must be correctly aligned. In skin, for example, they are woven in a wickerwork pattern, or in alternating layers with different orientations so as to resist tensile stress in multiple directions (Figure 20–13). In tendons, which attach muscles to bone, they are aligned in parallel bun... | {
"Header 1": "1 µm (A) (B) 200 nm 0.1 µm cellulose microfibril being added to preexisting wall plasma membrane connector protein microtubule attached to plasma membrane cellulose synthase complex CYTOSOL",
"Header 3": "Cells Organize the Collagen That They Secrete",
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If cells are to pull on the matrix and crawl over it, they must be able to attach to it. Cells do not attach well to bare collagen. Another extracellular matrix protein, fibronectin, provides a linkage: part of the fibronectin molecule binds to collagen, while another part forms an attachment site for a cell (Figure 20... | {
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"Header 3": "Integrins Couple the Matrix Outside a Cell to the Cytoskeleton Inside It",
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While collagen provides tensile strength to resist stretching, a completely different group of macromolecules in the extracellular matrix of
Figure 20–17 Glycosaminoglycans (GAGs) are built from repeating disaccharide units.... | {
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"Header 3": "Gels of Polysaccharides and Proteins Fill Spaces and Resist Compression",
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... |
Proteoglycans are characterized by the abundance of negative charges on their sugar chains. How would the properties of these molecules differ if the negative charges were not as abundant?
with only a small amount of collagen. In general, GAGs are strongly hydrophilic and tend to adopt highly extended conformations, ... | {
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"Header 3": "Question 20–3",
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There are more than 200 visibly different cell types in the body of a vertebrate. The majority of these are organized into epithelia (singular epithelium)—multicellular sheets in which the cells are joined together, side to side. In some cases, the sheet is many cells thick, or *stratified*, as in the epidermis (the ou... | {
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"Header 3": "Epithelial Sheets and Cell Junctions",
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An epithelial sheet has two faces: the apical surface is free and exposed to the air or to a watery fluid; the basal surface is attached to a sheet of connective tissue called the basal lamina (Figure 20–20). The basal lamina consists of a thin, tough sheet of extracellular matrix, composed mainly of a specialized type... | {
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"Header 3": "Epithelial Sheets Are Polarized and Rest on a Basal Lamina",
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Epithelial cell junctions can be classified according to their function. Some provide a tight seal to prevent the leakage of molecules across the epithelium through the gaps between its cells; some provide strong mechanical attachments; and some provide for a special type of intimate chemical communication. In most epi... | {
"Header 1": "1 µm (A) (B) 200 nm 0.1 µm cellulose microfibril being added to preexisting wall plasma membrane connector protein microtubule attached to plasma membrane cellulose synthase complex CYTOSOL",
"Header 3": "Tight Junctions Make an Epithelium Leak-proof and Separate Its Apical and Basal Surfaces",
"to... |
The cell junctions that hold an epithelium together by forming mechanical attachments are of three main types. *Adherens junctions* and *desmosomes* bind one epithelial cell to another, while *hemidesmosomes* bind epithelial cells to the basal lamina. All of these junctions provide mechanical strength by the same strat... | {
"Header 1": "1 µm (A) (B) 200 nm 0.1 µm cellulose microfibril being added to preexisting wall plasma membrane connector protein microtubule attached to plasma membrane cellulose synthase complex CYTOSOL",
"Header 3": "Cytoskeleton-linked Junctions Bind Epithelial Cells Robustly to One Another and to the Basal Lam... |
The final type of epithelial cell junction, found in virtually all epithelia and in many other types of animal tissues, serves a totally different purpose. In the electron microscope, this gap junction appears as a region where the membranes of two cells lie close together and exactly parallel, with a very narrow gap o... | {
"Header 1": "1 µm (A) (B) 200 nm 0.1 µm cellulose microfibril being added to preexisting wall plasma membrane connector protein microtubule attached to plasma membrane cellulose synthase complex CYTOSOL",
"Header 3": "Gap Junctions Allow Cytosolic Inorganic Ions and Small Molecules to Pass from Cell to Cell",
"... |
Gap junctions are dynamic structures that, like conventional ion channels, are gated: they can close by a reversible conformational change in response to changes in the cell. The permeability of gap junctions decreases within seconds, for example, when the intracellular Ca2+ concentration is raised. Speculate why this ... | {
"Header 1": "(A) (B) before dopamine after dopamine injected neuron neurons labeled through gap junctions <sup>20</sup>µ<sup>m</sup>",
"Header 3": "Question 20–5",
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One cannot contemplate the organization of tissues without wondering how these astonishingly patterned structures come into being. This question raises an even more challenging one—a puzzle that is one of the most ancient and fundamental in all of biology: how is a complex multicellular organism generated from a single... | {
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"Header 3": "Tissue Maintenance and Renewal",
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Schematic diagrams showing the cellular architecture of the main lavers of thick skin. Skin can be viewed as a large organ composed of two main tissues: epithelial tissue (the epidermis) on the outside, and connective tissue on the inside. The outermost layer of the epidermis consists of flat dead cells. whose intracel... | {
"Header 1": "(A) (B) before dopamine after dopamine injected neuron neurons labeled through gap junctions <sup>20</sup>µ<sup>m</sup>",
"Header 3": "Figure 20–34 Mammalian skin is made of a mixture of cell types.",
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Tissues vary enormously in their rate and pattern of *cell turnover*. At one extreme is nervous tissue, in which most of the nerve cells last a lifetime without replacement. At the other extreme is the intestinal epithelium, in which cells are replaced every three to six days. Between these extremes there is a spectrum... | {
"Header 1": "(A) (B) before dopamine after dopamine injected neuron neurons labeled through gap junctions <sup>20</sup>µ<sup>m</sup>",
"Header 3": "Different Tissues Are Renewed at Different Rates",
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... |
Most of the specialized, or differentiated, cells that need continual replacement are themselves unable to divide. Red blood cells, the epidermal cells on the skin surface, and the absorptive and goblet cells of the gut epithelium are all examples of this type. Such cells are referred to as *terminally differentiated*:... | {
"Header 1": "(A) (B) before dopamine after dopamine injected neuron neurons labeled through gap junctions <sup>20</sup>µ<sup>m</sup>",
"Header 3": "Stem Cells Generate a Continuous Supply of Terminally Differentiated Cells",
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Every stem-cell system requires control mechanisms to ensure that new cells are generated in the appropriate places and in the right numbers. The controls depend on extracellular signals exchanged between the stem cells, their progeny, and other cell types in the area. These signals, and the intracellular signaling pat... | {
"Header 1": "(A) (B) before dopamine after dopamine injected neuron neurons labeled through gap junctions <sup>20</sup>µ<sup>m</sup>",
"Header 3": "Specific Signals Maintain Stem-Cell Populations",
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Why do you suppose epithelial cells lining the gut are renewed frequently, whereas most neurons last for the lifetime of the organism?
20 µm
Figure 20–38 Blood contains many circulating cell types, all derived from a single type of stem cell. A sample of blood is smeared onto a glas... | {
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"Header 3": "Question 20–7",
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The term "cloning" has been used in confusing ways as a shorthand term for several quite distinct types of procedure, particularly in public debates about the ethics of stem-cell research. It is important to understand the distinctions
As biologists define the term, a clone is simply a set of cells or individuals tha... | {
"Header 1": "Therapeutic Cloning and Reproductive Cloning Are Very Different Enterprises",
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The problems associated with making personalized ES cells by nuclear transplantation can now be bypassed by an alternative approach, in which cells are taken from an adult tissue, grown in culture, and reprogrammed into an ES-like state by artificially driving the expression of a set of three transcription regulators c... | {
"Header 1": "Induced Pluripotent Stem Cells Provide a Convenient Source of Human ES-like Cells",
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In reproductive cloning, a whole new multicellular individual is generated; in therapeutic cloning, only cells (personalized ES cells) are produced. Both procedures begin with nuclear transplantation, in which a nucleus taken from an adult cell is transferred into the cytoplasm of an enucleated egg cell, so as to creat... | {
"Header 1": "Figure 20–43 Nuclear transplantation can be used for \"cloning\" in two quite different senses of the word.",
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Humans pay a price for having tissues that can renew and repair themselves. The delicately adjusted mechanisms that control these processes can go wrong, leading to catastrophic disruption of tissue structure. Foremost among the diseases of tissue renewal is cancer, which stands alongside infectious illness, malnutriti... | {
"Header 1": "Figure 20–43 Nuclear transplantation can be used for \"cloning\" in two quite different senses of the word.",
"Header 3": "Cancer",
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As tissues grow and renew themselves, each individual cell must adjust its behavior according to the needs of the organism as a whole. The cell must divide only when new cells of that type are needed, and refrain from dividing when they are not; it must live as long as it is needed, and kill itself when it is not; it m... | {
"Header 1": "Figure 20–43 Nuclear transplantation can be used for \"cloning\" in two quite different senses of the word.",
"Header 3": "Cancer Cells Proliferate, Invade, and Metastasize",
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Prevention is always better than cure, but to prevent cancer we need to know what causes it. Do factors in our environment or features of our way of life trigger the disease and help it to progress? If so, what are they? Answers to these questions come mainly from *epidemiology*—the statistical analysis of human popula... | {
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Cancer is fundamentally a genetic disease: it arises as a consequence of pathological changes in the information carried by DNA. It differs from other genetic diseases in that the mutations underlying cancer are mainly somatic mutations—those that occur in individual somatic cells of the body—as opposed to germ-line mu... | {
"Header 1": "Epidemiological Studies Identify Preventable Causes of Cancer",
"Header 3": "Cancers Develop by an Accumulation of Mutations",
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The mutations that lead to cancer do not cripple the mutant cells. On the contrary, they give these cells a competitive advantage over their neighbors. It is this advantage enjoyed by the mutant cells that leads to disaster for the organism as a whole. As an initial population of mutant cells grows, it slowly evolves: ... | {
"Header 1": "Epidemiological Studies Identify Preventable Causes of Cancer",
"Header 3": "Cancer Cells Evolve, Giving Them an Increasingly Competitive Advantage",
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Investigators have made use of a variety of approaches to track down the genes and mutations that are critical for cancer—from studying viruses that cause cancer in chickens to following families in which a particular cancer occurs unusually often. Though many of the most important of these genes have been identified, ... | {
"Header 1": "Epidemiological Studies Identify Preventable Causes of Cancer",
"Header 3": "Two Main Classes of Genes Are Critical for Cancer: Oncogenes and Tumor Suppressor Genes",
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From the point of view of a cancer cell, oncogenes and tumor suppressor genes—and the mutations that affect them—are flip sides of the same coin. Activation of an oncogene and inactivation of a tumor suppressor gene can both promote the development of cancer. And both types of mutations are called into play in most can... | {
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"Header 3": "Cancer-causing Mutations Cluster in a Few Fundamental Pathways",
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Colorectal cancer provides one well-studied example of how a tumor suppressor can be identified and its role in tumor growth determined. Colorectal cancer arises from the epithelium lining the colon and rectum; most cases are seen in old people and do not have any discernible hereditary cause. A small proportion of cas... | {
"Header 1": "Epidemiological Studies Identify Preventable Causes of Cancer",
"Header 3": "Colorectal Cancer Illustrates How Loss of a Tumor Suppressor Gene Can Lead to Cancer",
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The better we understand the tricks that cancer cells use to survive, proliferate, and spread, the better are our chances of finding ways to defeat them. The task is made more challenging because cancer cells are highly mutable and, like weeds or parasites, rapidly evolve resistance to treatments used to exterminate th... | {
"Header 1": "Epidemiological Studies Identify Preventable Causes of Cancer",
"Header 3": "An Understanding of Cancer Cell Biology Opens the Way to New Treatments",
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Determining what a gene—or its encoded product does inside a cell is not a simple task. Imagine isolating an uncharacterized protein and being told that it acts as a protein kinase. That information does not reveal how the protein functions in the context of a living cell. What proteins does the kinase phosphorylate? I... | {
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"Header 3": "Guilt by association",
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Not long before the discovery that APC binds to β-catenin, developmental biologists working on the fruit fly *Drosophila* had noticed that the human β-catenin protein is very similar in amino acid sequence to a *Drosophila* protein called Armadillo. Armadillo was known to be a key protein in a signaling pathway that ha... | {
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"Header 3": "Wingless flies",
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Although it may seem counterintuitive, one of the most direct ways of finding out what a gene normally does is to see what happens to the organism when that gene is missing. If one can pinpoint the processes that are disrupted or compromised, one can begin to decipher the gene's function.
With this in mind, researche... | {
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"Header 3": "Tales from the crypt",
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- • Tissues are composed of cells and extracellular matrix.
- • In plants, each cell surrounds itself with extracellular matrix in the form of a cell wall, which is made chiefly of cellulose and other polysaccharides.
- • An osmotic swelling pressure on plant cell walls keeps plant tissue turgid.
- • Cellulose microfib... | {
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"Header 3": "Essential Concepts",
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genetic instability
#### QUESTIONS
#### QUESTION 20-9
Which of the following statements are correct? Explain your answers.
- A. Gap junctions connect the cytoskeleton of one cell to that of a neighboring cell or to the extracellular matrix.
- B. A wilted plant leaf can be likened to a deflated bicycle tire
- C.... | {
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"Header 3": "adherens junction glycosaminoglycan (GAG) apical hemidesmosome basal induced pluripotent stem (iPS) cell basal lamina integrin cadherin metastasis cancer oncogene cell junction plasmodesma cell wall (plural plasmodesmata) ce... |
ANSWER 1–1 Trying to define life in terms of properties is an elusive business, as suggested by this scoring exercise (Table A1–1). Vacuum cleaners are highly organized objects, and take matter and energy from the environment and transform the energy into motion, responding to stimuli from the operator as they do so. O... | {
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"Header 3": "Chapter 1",
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Thus, 1012 cells would occupy 1750 pages (= 1012/[57 × 107]).
Answer 1–11 In this plant cell, A is the nucleus, B is a vacuole, C is the cell wall, and D is a chloroplast. The scale bar is about 10 μm, the width of the nucleus.
Answer 1–12 The three major filaments are actin filaments, intermediate filaments, and m... | {
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- A. The atomic number is 6; the atomic weight is 12 (= 6 protons + 6 neutrons).
- B. The number of electrons is six (= the number of protons).
- C. The first shell can accommodate two and the second shell eight electrons. Carbon therefore needs four additional electrons (or would have to give up four electrons) to obt... | {
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"Header 3": "Answer 2–2",
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There are two reasons for the 1.7-fold difference in the two calculations: (1) carbon is not the only atom in cellulose; and (2) paper is not an atomic lattice of precisely arranged cellulose molecules (as a diamond would be for precisely arranged carbon atoms), but a random meshwork of fibers.
#### ANSWER 2-12
A. ... | {
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"Header 3": "Answer 2–2",
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- A,B. (A) and (B) are both correct formulas of the amino acid phenylalanine. In formula (B), phenylalanine is shown in the ionized form that exists in an aqueous solution, where the basic amino group is protonated and the acidic carboxylic group is deprotonated. ess2 EA2.20/2.20
- C. Incorrect. This structure of a pep... | {
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"Header 3": "Answer 2–21",
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ANSWER 3–1 The equation represents the "bottom line" of photosynthesis, which occurs as a large set of individual reactions that are catalyzed by many individual enzymes. Because sugars are more complicated molecules than $CO_2$ and $H_2O$ , the reaction generates a more ordered state inside the cell. As demanded by... | {
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"Header 3": "Chapter 3",
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- A. The rocks in Figure 3–30B provide the energy to lift the bucket of water. In the reaction X + ATP → Y + ADP + Pi, ATP hydrolysis is driving the reaction; thus ATP corresponds to the rocks on top of the cliff. The broken debris in Figure 3–30B corresponds to ADP and Pi, the products of ATP hydrolysis. In the reacti... | {
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"Header 3": "Answer 3–7",
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98) we know that a free-energy difference of 4.3 kcal/mole corresponds to an equilibrium constant of 10–3, i.e., [A\*]/[A] = 10–3. The concentration of A\* is therefore 1000-fold lower than that of A at equilibrium.
- B. The ratio of A to A\* would be unchanged. Lowering the activation energy barrier with an enzyme wou... | {
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"Header 3": "Answer 3–7",
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ANSWER 4–1 Urea is a very small organic molecule that functions both as an efficient hydrogen-bond donor (through its $-NH_2$ groups) and as an efficient hydrogen-bond acceptor (through its -C=0 group). As such, it can squeeze between hydrogen bonds that stabilize protein molecules and thus destabilize protein struct... | {
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"Header 3": "Chapter 4",
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ES represents the enzyme–substrate complex.
- B. Enzyme and substrate are in equilibrium between their free and bound states; once bound to the enzyme, a substrate molecule may either dissociate again (hence the bidirectional arrows) or be converted to product. As the substrate is converted to product (with the concomi... | {
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#### Answer 5–1
- A. False. The polarity of a DNA strand commonly refers to the orientation of its sugar–phosphate backbone, one end of which contains a phosphate group and the other a hydroxyl group.
- B. True. G-C base pairs are held together by three hydrogen bonds, whereas A-T base pairs are held together by only... | {
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"Header 3": "Chapter 5",
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This is approximately the distance from London to Istanbul, San Francisco to Kansas City, Tokyo to the southern tip of Taiwan, and Melbourne to Cairns. Adjacent nucleotides would be about 0.85 mm apart (which is only about the thickness of a stack of 12 pages of this book). A gene that is 1000 nucleotide pairs long wou... | {
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#### Answer 6–1
- A. The distance between replication forks 4 and 5 is about 280 nm, corresponding to 824 nucleotides (= 280/0.34). These two replication forks would collide in about 8 seconds. Forks 7 and 8 move away from each other and would therefore never collide.
- B. The total length of DNA shown in the electro... | {
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This requires $4 \times 10^5$ (= $1.2 \times 10^7/30$ ) glucose molecules, which weigh $1.2 \times 10^{-16}$ g (= $4 \times 10^5$ molecules $\times 180$ g/mole/ $6 \times 10^{23}$ molecules/mole), which is 0.01% of the total weight of the cell.
ANSWER 6–12 The statement is correct. If the DNA in somatic cel... | {
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ANSWER 7-1 Perhaps the best answer was given by Francis Crick himself, who coined the term in the mid-1950s: "I called this idea the central dogma for two reasons, I suspect. I had already used the obvious word hypothesis in the sequence hypothesis, which proposes that genetic information is encoded in the sequence of ... | {
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(Note that "translation" is also used in a quite different sense, both in ordinary language and in scientific contexts, to mean a movement from one place to another.)
Answer 7–12 With four different nucleotides to choose from, a code of two nucleotides could specify 16 different amino acids (= 42), and a triplet code... | {
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#### Answer 8–1
- A. Transcription of the tryptophan operon would no longer be regulated by the absence or presence of tryptophan; the enzymes would be permanently turned on in scenarios (1) and (2) and permanently shut off in scenario (3).
- B. In scenarios (1) and (2), the normal tryptophan repressor molecules woul... | {
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Answer 9–1 When it comes to genetic information, a balance must be struck between stability and change. If the mutation rate were too high, a species would eventually die out because all its individuals would accumulate mutations in genes essential for survival. And for a species to be successful—in evolutionary terms—... | {
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The initiation codon for protein synthesis (nearly always an ATG) has a statistical association with adjacent nucleotides that seem to enhance its recognition by translation factors.
- 7. The terminal exon will have a signal (most commonly AATAAA) for cleavage and polyadenylation close to its 3ʹ end.
The statistical ... | {
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Answer 10–1 The presence of a mutation in a gene does not necessarily mean that the protein expressed from it is defective. For example, the mutation could change one codon into another that still specifies the same amino acid, and so does not change the amino acid sequence of the protein. Or, the mutation may cause a ... | {
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Cleavage of human genomic DNA with HaeIII would generate about 11 × 106 different fragments [= 3 × 109/44] and with EcoRI about 730,000 different fragments [= 3 × 109/46]. There will also be some additional fragments generated because the maternal and paternal chromosomes are very similar but not identical in DNA seque... | {
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ANSWER 11-1 Water is a liquid, and thus hydrogen bonds between water molecules are not static; they are continually formed and broken again by thermal motion. When a water molecule happens to be next to a hydrophobic molecule, it is more restricted in motion and has fewer neighbors with which it can interact because it... | {
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Using the equation above, we calculate the constant D in this case to be 8 × 107 cm2/sec and the time required to travel 6 m about 2 msec (= 6002/(1.6 × 108)).
Answer 11–13 Transmembrane proteins anchor the plasma membrane to the underlying cell cortex, strengthening the membrane so that it can withstand the forces o... | {
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#### Answer 12–1
- A. The movement of a solute mediated by a transporter can be described by a strictly analogous equation: equation 1: T + S ↔ TS → T + S\* where S is the solute, S\* is the solute on the other side of the membrane (i.e., although it is still the same molecule, it is now located in a different enviro... | {
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They have enzymelike properties, i.e., they bind solutes and need to undergo
Figure A12–9
- conformational changes during their functional cycle. This limits the maximal rate of transport to about 1000 solute molecules per second, whereas channels can pass up to 1,000,000 solute mol... | {
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Both of these components add to the energy that is stored in the gradient and that must be supplied to generate it. The electrochemical gradient will limit the transfer of more H+. If, however, the membrane also contains Cl– channels, the negatively charged Cl– in the cytosol will flow into the endosomes and diminish t... | {
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ANSWER 13–1 To keep glycolysis going, cells need to regenerate NAD+ from NADH. There is no efficient way to do this without fermentation. In the absence of regenerated NAD+, step 6 of glycolysis (the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate (Panel 13–1, pp. 428–429) could not occur and the pro... | {
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"Header 3": "Chapter 13",
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Answer 13–13 If one glucose produces 30 ATPs, then to generate 109 ATP molecules will require 1 × 109/30 = 3.3 × 107 glucose molecules and 6 × 3.3 × 107 = 2 × 108 molecules of oxygen. Thus in one minute the cell will consume 2 × 108/(6 × 1023) or 3.3 × 10–16 moles of oxygen, which would occupy 3.3 × 10–16 × 22.4 = 7.... | {
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"Header 3": "Chapter 13",
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Answer 14–1 By making membranes permeable to protons, DNP collapses—or at very small concentrations ess A4.15
diminishes—the proton gradient across the inner mitochondrial membrane. Cells continue to oxidize food molecules to feed high-energy electrons into the electrontransport chain, but H+ ions pumped across the m... | {
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"Header 3": "Chapter 14",
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Both components add to the driving force that makes it energetically favorable for H+ to flow back into the matrix.
- D. True. Both move rapidly in the plane of the membrane.
- E. False. Not only do plants need mitochondria to make ATP in cells that do not have chloroplasts, such as root cells, but mitochondria make mo... | {
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Answer 15–1 Although the nuclear envelope forms one continuous membrane, it has specialized regions that contain special proteins and have a characteristic appearance. One such specialized region is the inner nuclear membrane. Membrane proteins can indeed diffuse between the inner and outer nuclear membranes, at the co... | {
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When the pH of the endosome is raised, viruses are still endocytosed, but
Figure A15–11
because the viral fusion protein cannot be activated, the virus cannot enter the cytosol. Remember this the next time you have the flu and have access to a stable.
#### Answer 15–12
- A. The p... | {
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Answer 16–1 Most paracrine signaling molecules are very short-lived after they are released from a signaling
cell: they are either degraded by extracellular enzymes or are rapidly taken up by neighboring target cells. In addition, some become attached to the extracellular matrix and are thus prevented from diffusing ... | {
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"Header 3": "Chapter 16",
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- 1. You would expect a high background level of Ras activity, because Ras cannot be turned off efficiently.
- 2. Because some Ras molecules are already GTP-bound, Ras activity in response to an extracellular signal would be greater than normal, but this activity would be liable to saturate when all Ras molecules are c... | {
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Answer 17–1 Cells that migrate rapidly from one place to another, such as amoebae (A) and sperm cells (F), do not in general need intermediate filaments in their cytoplasm, since they do not develop or sustain large tensile forces. Plant cells (G) are pushed and pulled by the forces of wind and water, but they resist t... | {
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- A. Successive actin molecules in an actin filament are identical in position and conformation. After a first protein (such as troponin) had bound to the actin filament, there would be no way in which a second protein could recognize every seventh monomer in a naked actin filament. Tropomyosin, however, binds along th... | {
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In the absence of microtubules, cells still go through the motions normally associated with cell movement, such as the extension of lamellipodia, but in the absence of cell polarity these are futile exercises because they happen indiscriminately in all directions.
Antibodies bind tightly to the antigen (in this case ... | {
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"Header 3": "Answer 17–10",
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Answer 18–1 Because all cells arise by division of another cell, this statement is correct, assuming that "first cell division" refers to the division of the successful founder cell from which all life as we know it has derived. There were probably many other unsuccessful attempts to start the chain of life.
Answer 1... | {
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As a result, the M-Cdk target proteins become dephosphorylated by phosphatases, and the cells exit from mitosis: they disassemble the mitotic spindle, reassemble the nuclear envelope, decondense their chromosomes, and so on. The M cyclin is degraded by ubiquitin-dependent destruction in proteasomes, and the activation ... | {
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Association of a Cdk protein with a cyclin is required for its activity (hence its name cyclin-dependent kinase). Furthermore, phosphorylation at a specific site and dephosphorylation at other sites on the Cdk protein are required for the cyclin–Cdk complex to be active.
Answer 18–27 Cells in an animal must behave fo... | {
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ANSWER 19-1 Although each daughter cell ends up with a diploid amount of DNA after the first meiotic division, each cell has effectively only a haploid set of chromosomes (albeit in two copies), representing only one or other homolog of each type of chromosome (although some mixing will have occurred during crossing-ov... | {
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In practice, for organisms studied in a laboratory, the genotype is usually specified as a list of the known differences between the individual and the wild type, which is the standard, naturally occurring type. The phenotype is a description of the visible characteristics of the individual. In practice, the
- phenot... | {
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Answer 20–1 The horizontal orientation of the microtubules will be associated with a horizontal orientation of cellulose microfibrils deposited in the cell walls. The growth of the cells will therefore be in a vertical direction, expanding the distance between the cellulose microfibrils without stretching them. In this... | {
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Successive mutations can alter cell numbers and cell behavior, and thereby change both the probability of subsequent mutations and the selection pressures that drive the evolution of cancer.
Answer 20–17 During exposure to the carcinogen, mutations are induced, but the number of relevant mutations in any one cell is ... | {
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"Header 3": "Chapter 20",
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#### **acetyl CoA** (**acetyl coenzyme A**)
Activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions, including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A (CoA) by a thioester bond that releases a large amount... | {
"Header 1": "Glossary",
"token_count": 794,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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An alternative form of a gene; for a given gene, many alleles may exist in the gene pool of the species.
#### **allosteric**
Describes a protein that can exist in multiple conformations depending on the binding of a molecule (ligand) at a site other than the catalytic site; changes from one conformation to another ... | {
"Header 1": "Glossary",
"Header 3": "**allele**",
"token_count": 431,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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#### **aminoacyl-tRNA synthetase**
During protein synthesis, an enzyme that attaches the correct amino acid to a tRNA molecule to form a "charged" aminoacyl-tRNA.
#### **AMP** (**adenosine 5ʹ monophosphate**)
Nucleotide produced by the energetically favorable hydrolysis of the final two phosphate groups from ATP,... | {
"Header 1": "Glossary",
"Header 3": "**amino terminus—***see* **N-terminus**",
"token_count": 1349,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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#### (**β sheet**)
Folding pattern found in many proteins in which neighboring regions of the polypeptide chain associate side by side with each other through
hydrogen bonds to give a rigid, flattened structure.
#### **bi-orientation**
The symmetrical attachment of a sister chro... | {
"Header 1": "Glossary",
"Header 3": "**beta sheet**",
"token_count": 876,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with release of energy; intermediates in these reactions are sometimes called catabolites.
#### **catalysis**
The acceleration of a chemical reaction brought about by the action of a catalyst; virtually all reactions in a cell... | {
"Header 1": "Glossary",
"Header 3": "**catabolism**",
"token_count": 316,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Mechanically strong fibrous layer deposited by a cell outside its plasma membrane. Prominent in most plants, bacteria, algae, and fungi, but not present in most animal cells.
#### **cell-cycle control system**
Network of regulatory proteins that govern the orderly progression of a eukaryotic cell through the stages... | {
"Header 1": "Glossary",
"Header 3": "**cell wall**",
"token_count": 646,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Complex of DNA and proteins that makes up the chromosomes in a eukaryotic cell.
#### **chromatin-remodeling complex**
Enzyme (typically multisubunit) that uses the energy of ATP hydrolysis to alter the arrangement of nucleosomes in eukaryotic chromosomes, changing the accessibility of the underlying DNA to other pr... | {
"Header 1": "Glossary",
"Header 3": "**chromatin**",
"token_count": 398,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Protein that makes up the coat of a type of transport
vesicle that buds from either the Golgi apparatus (on the outward secretory pathway) or from the plasma membrane (on the inward endocytic pathway).
#### **coated vesicle**
Small membrane-enclosed sac that wears a distinctive layer of proteins on its cytosolic ... | {
"Header 1": "Glossary",
"Header 3": "**clathrin**",
"token_count": 1676,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Soapy substance used to solubilize membrane proteins.
#### **diacylglycerol** (**DAG**)
Small messenger molecule produced by the cleavage of membrane inositol phospholipids in response to extracellular signals. Helps activate protein kinase C.
#### **dideoxy sequencing or Sanger sequencing**
The standard method... | {
"Header 1": "Glossary",
"Header 3": "**detergent**",
"token_count": 217,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Covalent cross-link formed between the sulfhydryl groups on two cysteine side chains; often used to reinforce a secreted protein's structure or to join two different proteins together.
#### **divergence**
Differences in sequence that accumulate over time in DNA segments derived from a common ancestral sequence.
#... | {
"Header 1": "Glossary",
"Header 3": "**disulfide bond**",
"token_count": 433,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Chemical linkage formed when two atoms share four electrons.
#### **double helix**
The typical structure of a DNA molecule in which the two complementary polynucleotide strands are wound around each other with base-pairing between the strands.
#### **dynamic instability**
The ra... | {
"Header 1": "Glossary",
"Header 3": "**double bond**",
"token_count": 1378,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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A high-energy electron carrier produced by reduction of FAD during the breakdown of molecules derived from food, including fatty acids and acetyl CoA.
#### **fat**
Type of lipid used by living cells to store metabolic energy. Mainly composed of triacylglycerols. (*See* Panel 2–4, pp. 72–73.)
#### **fatty acid** ... | {
"Header 1": "Glossary",
"Header 3": "**FADH2** (**reduced flavin adenine dinucleotide**)",
"token_count": 526,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Energy that can be harnessed to do work, such as driving a chemical reaction.
#### **free-energy change** (**Δ***G*)
"Delta *G*": in a chemical reaction, the difference in free energy between reactant and product molecules. A large negative value of Δ*G* indicates that the reaction has a strong tendency to occur. T... | {
"Header 1": "Glossary",
"Header 3": "**free energy** (*G*)",
"token_count": 436,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Gap 2 phase of the eukaryotic cell cycle; falls between the end of DNA synthesis and the beginning of mitosis.
#### **gain-of-function mutation**
Genetic change that increases the activity of a gene
or makes it active in inappropriate circumstances; such mutations are usually dominant.
#### **gamete**
Cell ty... | {
"Header 1": "Glossary",
"Header 3": "**G2 phase**",
"token_count": 2040,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
#### **horizontal gene transfer**
Process by which DNA is passed from the genome of one organism to that of another, even to an individual from another species. This contrasts with "vertical" gene transfer, which refers to the transfer of genetic information from parent to progeny.
#### **hormone**
Extracellula... | {
"Header 1": "Glossary",
"Header 3": "**G2 phase**",
"token_count": 1319,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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Transmembrane receptor protein or protein complex that opens in response to the binding of a ligand to its external face, allowing the passage of a specific inorganic ion.
#### **ionic bond**
Interaction formed when one atom donates electrons to another; this transfer of electrons c... | {
"Header 1": "Glossary",
"Header 3": "**ion-channel-coupled receptor**",
"token_count": 1147,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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A genetic alteration that reduces or eliminates the activity of a gene. Such mutations are usually recessive: the organism can function normally as long as it retains at least one normal copy of the affected gene.
#### **lumen**
The space inside a hollow or tubular structure; can refer to the cavity in a tissue or ... | {
"Header 1": "Glossary",
"Header 3": "**loss-of-function mutation**",
"token_count": 283,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
Protein complex that triggers the M phase of the cell cycle; consists of an M cyclin plus a mitotic cyclindependent protein kinase (Cdk).
#### **macromolecule**
Polymer built from covalently linked subunits; includes proteins, nucleic acids, and polysaccharides with a molecular mass greater than a few thousand dalt... | {
"Header 1": "Glossary",
"Header 3": "**M-Cdk**",
"token_count": 2010,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
#### **Na+ pump** (**sodium pump**)
Transporter found in the plasma membrane of most animal cells that actively pumps Na+ out of the cell and K+ in using the energy derived from ATP hydrolysis.
#### **NAD<sup>+</sup>** (**nicotine adenine dinucleotide**)
Activated carrier that accepts a hydride ion (H–) from a ... | {
"Header 1": "Glossary",
"Header 3": "**M-Cdk**",
"token_count": 2010,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
#### **photosynthesis**
The process by which plants, algae, and some bacteria use the energy of sunlight to drive the synthesis of organic molecules from carbon dioxide and water.
#### **photosystem**
Large multiprotein complex containing chlorophyll that captures light energy and converts it into chemical energy... | {
"Header 1": "Glossary",
"Header 3": "**phosphorylation—***see* **protein phosphorylation**",
"token_count": 2004,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
76–77.)
#### **pyruvate**
Three-carbon metabolite that is the end product of the glycolytic breakdown of glucose; provides a crucial link to the citric acid cycle and many biosynthetic pathways.
#### **quaternary structure**
Complete structure formed by multiple, interacting pol... | {
"Header 1": "Glossary",
"Header 3": "**phosphorylation—***see* **protein phosphorylation**",
"token_count": 1653,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
} |
Hypothetical period in Earth's early history in which life-forms were thought to use RNA both to store genetic information and to catalyze chemical reactions.
#### **RNA-Seq**
Sequencing technique used to determine directly the nucleotide sequence of a collection of RNAs.
#### **rough endoplasmic reticulum**
Re... | {
"Header 1": "Glossary",
"Header 3": "**RNA world**",
"token_count": 2036,
"source_pdf": "datasets/websources/biochem/Alberts_-_Essential_Cell_Biology__4th_ed._.pdf"
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