Có 60+ tài liệu thuộc chủ đề "nguyên tắc của hóa sinh"
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heterologous probes because they are not derived from the homologous (same) organism.. eukaryotic genes can be tens or even hundreds of kilobase pairs in size. Thus, the DNA identified by the probe may represent a clone that carries only part of the desired gene. However, most cloning strategies are based on a partial digestion of the genomic DNA, a technique...
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that transcription of a reporter gene driven by the GAL4 promoter can take place (Figure 12.17b). This method can be used to screen cells for protein “targets” that interact specifically with a particular “bait” protein. To do so, cDNAs encoding proteins from the cells of in- terest are inserted into the TA-containing plasmid to create fusions of the cDNA cod-...
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Situated at key junctions of metabolic pathways are specialized regulatory enzymes capa- ble of sensing the momentary metabolic needs of the cell and adjusting their cat- alytic rates accordingly. The responses of these enzymes ensure the harmonious integration of the diverse and often divergent metabolic activities of cells so that the living state is promoted and preserved.. 13.1 What Characteristic...
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can be derived from V max /2, so the two constants of the Michaelis–Menten equa- tion can be obtained from plots of v versus [S]. That is, according to Equation 13.23, to get v 0.99 V max , [S] must equal 99 K m , a con- centration that may be difficult to achieve in practice.. From Equation 13.23, when...
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For example, the antibiotic penicillin exerts its effects by covalently reacting with an essential serine residue in the active site of glycopeptide transpeptidase, an enzyme that acts to crosslink the peptidoglycan chains during synthesis of bacterial cell walls (Figure 13.18). A re- active peptide bond in the -lactam ring covalently attaches to a serine residue in the active site of...
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Catalytic antibodies are antibodies with catalytic activity (catalytic antibodies are also called abzymes, a word created by combining “Ab,” the abbreviation for antibody, with “enzyme. In this case, however, the antigen is purposefully engineered to be an analog of the transition state in a re- action. The rationale is that a protein specific for binding the transition state of a...
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When a substrate with charged groups moves from water into an enzyme active site (Figure 14.4), the charged groups are often desolvated to some extent, becoming less stable and therefore more reactive.. Similarly, when a substrate enters the active site, charged groups may be forced to interact (unfavorably) with charges of like sign, resulting in electrostatic destabilization (Figure 14.4). If...
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FIGURE 14.14 Thermolysin is an endoprotease (that is, it cleaves polypeptides in the middle of the chain) with a catalytic Zn 2 ion in the active site. 14.6 What Can Be Learned from Typical Enzyme Mechanisms?. Only about half of the common amino acid residues (that is, His, Cys, Asp, Glu, Arg, Lys, Tyr, Ser, Thr, Asn, and Gln) engage...
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These drugs are all specific inhibitors of the HIV protease. By inhibiting the protease, they prevent the de- velopment of new virus particles in the cells of infected patients. Four of the protease inhibitors approved for use in humans by the U.S. that is, the drug molecules were designed to bind tightly to the active site of the HIV-1 protease....
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Once synthesized, the enzyme may also be degraded, either through normal turnover of the protein or through specific decay mechanisms that target the enzyme for destruction. Enzyme Activity Can Be Regulated Allosterically. Enzymatic activity can also be activated or inhibited through noncovalent interaction of the enzyme with small molecules (metabolites) other than the substrate. This form of control is termed...
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subunit contact interface in glycogen phosphorylase. Glycogen Phosphorylase Activity Is Regulated Allosterically. Muscle Glycogen Phosphorylase Shows Cooperativity in Substrate Binding The binding of the substrate inorganic phosphate (P i ) to muscle glycogen phosphorylase is highly cooperative (Figure 15.14a), which allows the enzyme activity to increase markedly over a rather narrow range of substrate concentration.. FIGURE 15.13 Structure of the...
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The shift in helix F upon oxygenation leads to rupture of the Tyr 145:Val 98 hydrogen bond. In deoxyhemoglobin, with these interactions intact, the C-termini of the four subunits are restrained, and this con- formational state is termed T, the tense or taut form. Oxygen is accessible only to the heme groups of the -chains when hemoglobin is in the...
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Extensions of the sarcolemma, called transverse tubules, or t-tubules, reach deep into the muscle fiber, enabling the sarcolemmal membrane to be in contact with each myofibril.. Examination of myofibrils in the electron microscope reveals a banded or striated structure. The bands are traditionally identified by letters (Figure 16.2). Small, dark Z lines lie in the middle of the I bands,...
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FIGURE 16.14 (a) Domain structure of kinesins, myosin V, and cytoplasmic dynein. domain is located in different places in the sequence, depending on the function of the specific family.. Cytoplasmic dynein consists of a dimer of two heavy chains (500 kD) with several other tightly associated light chains (Figure 16.14). Each heavy chain contains a large motor domain (380 kD)...
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hairpin loops of the six protein subunits form a spiral staircase, following the ssDNA as it threads through the central pore of the hexamer (Figure 16.26).. Eric Enemark and Leemor Joshua-Tor have suggested that a central hairpin loop from one of the AAA subunits coordinates each DNA nucleotide as it enters the helicase pore. Then, as each AAA domain proceeds...
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the end product of heterotrophic carbon metabolism, and CO 2 is returned to the at- mosphere for reuse by the photoautotrophs. In effect, solar energy is converted to the chemical energy of organic molecules by photoautotrophs, and heterotrophs recover this energy by metabolizing the organic substances. The flow of energy in the biosphere is thus conveyed within the carbon cycle,...
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The biosynthesis of the complex constituents of the cell begins at the level of intermediates derived from the degradative pathways of catab- olism. or, less commonly, biosynthesis begins with oxidized substances available in the inanimate environment, such as carbon dioxide. NADPH is generated when NADP is reduced with electrons in the form of hydride ions. In these organisms, NADPH can...
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Then the biochemical consequences of the mutation can be investigated.. Rapid advances in chemical analysis have made it possible to carry out comprehensive studies of the many metabolites in a living organism. Name three principal inorganic sources of oxygen atoms that are commonly available in the inanimate environment and readily accessible to the biosphere.. which the slowest? For each of...
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ADP levels in cells are typically 10% of ATP levels, and AMP levels are often less than 1% of the ATP concentration. Under such conditions, a small net change in ATP concentration due to ATP hydrolysis results in a much larger rela- tive increase in the AMP levels because of adenylate kinase activity.. Clearly, the activity of phosphofructokinase depends on...
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The second step, the reduction of acetaldehyde to ethanol by NADH, is catalyzed by alcohol dehydrogenase (Figure 18.21). When skeletal muscles are exercised strenuously, the available tis- sue oxygen is consumed and the pyruvate generated by glycolysis can no longer be oxidized in the TCA cycle. Instead, excess pyruvate is reduced to lactate by lactate dehydrogenase (Figure 18.21). Anyone who...