Có 40+ tài liệu thuộc chủ đề "RNA trao đổi chất"
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core of the protein. The extensively H-bonded nature of -helices and -sheets is ideal for this purpose, and these structures effectively stabilize the polar groups of the peptide backbone in the protein core.. The framework of sheets and helices in the interior of a globular protein is typi- cally constant and conserved in both sequence and structure. Typically, much of...
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6.5 How Do Protein Subunits Interact at the Quaternary Level of Protein Structure?. Liver al- cohol dehydrogenase, shown in Figure 6.41, is such a protein. Alcohol consumed in a beer or mixed drink is oxidized in the liver by alcohol dehydrogenase. Oxygen is carried in the blood by hemoglobin, which contains two each of two different subunits (het- erotetramer). Muscle...
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For monosaccharides with two or more asymmetric carbons, the prefix D or L refers to the configuration of the highest numbered asymmetric carbon (the asymmetric car- bon farthest from the carbonyl carbon). O C CH 2 OH 1. CH 2 OH. CH 2 OH 3. CH 2 OH 4. O C CH 2 OH. CH 2 OH 5. FIGURE 7.3...
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D -Lactose (O-- D -galactopyranosyl-(1⎯ →4)- D -glucopyranose) (Figure 7.18) is the principal carbohydrate in milk and is of critical nutritional importance to mammals in the early stages of their lives. It must first be broken down into galactose and glucose by lactase, an intestinal enzyme that exists in young, nursing mammals but is not produced in significant quantities in...
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Cell Walls of Gram-Negative Bacteria In Gram-negative bacteria, the peptidogly- can wall is the rigid framework around which is built an elaborate membrane struc- ture (Figure 7.30). The peptidoglycan layer encloses the periplasmic space and is at- tached to the outer membrane via a group of hydrophobic proteins.. As shown in Figure 7.31, the outer membrane of Gram-negative bacteria is...
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Cartilage matrix proteoglycan is responsible for the flexibility and resilience of car- tilage tissue in the body. In cartilage, long filaments of hyaluronic acid are studded or coated with proteoglycan molecules, as shown in Figure 7.39. Cartilage proteoglycan possesses a hyaluronic acid–binding domain on the NH 2 - terminal portion of the polypeptide, which binds to hyaluronate with the assistance...
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Triacylglycerols are rich in highly reduced carbons and thus yield large amounts of energy in the oxidative reactions of metabolism. A 1,2-diacylglycerol that has a phosphate group esterified at carbon atom 3 of the glycerol backbone is a glycerophospholipid, also known as a phosphoglyceride or a glycerol phosphatide (Figure 8.4). These lipids form one of the largest and most im-...
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8.7 What Are Steroids, and What Are Their Cellular Functions?. Cholesterol (Figure 8.16) is the most common steroid in animals and the precursor for all other animal steroids. The polyprenyl nature of this compound is particularly evident in the side chain. Significantly, the carbons at positions 10 and 13 and the alkyl group at position 17 are nearly always oriented...
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or in the membrane and the transport of ions, sugars, and amino acids across mem- branes. Thus, for ex- ample, the lipid makeup of red blood cell membranes is consistent across species, whereas the lipid complement of different (specialized) membranes within a par- ticular cell type (rat liver, Figure 9.2) reflects differences of function. FIGURE 9.1 Electron micrographs of several...
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This behavior, with the side chain pointing up out of the membrane core, has been termed snorkeling (Figure 9.16). If a Phe residue occurs near the lipid–water interface, it is typically arranged with the aromatic ring oriented toward the membrane core. Membrane Protein Structures Show Many Variations on the Classical Themes Although it revealed many insights of membrane protein structure,...
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At higher temperatures, the acyl chains undergo much more motion, with rotations around the acyl chain C–C bonds and significant large- scale bending of the acyl chains. The membrane is then said to be in a liquid crys- talline phase or liquid-disordered state (L d state) (Figure 9.27). The sharpness of the transition in pure lipid preparations shows that the...
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FIGURE 9.40 The structures of channel proteins that transport (a) glycerol (pdb id 1FX8),(b) glutamate (pdb id 1XFH), (c) ammonia (pdb id 1U7G),(d) chloride (pdb id 1OTS),(e) potassium (pdb id 2A79), (f) water (pdb id 1J4N), and (g) proteins (pdb id 1RHZ). In all cases, the view is in the plane of the membrane. Note the transmembrane -helices in the...
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which are in fact V-type ATPases—on the portion of the plasma membrane that at- taches to the bone. This region of the osteoclast membrane is called the ruffled border. The osteoclast attaches to the bone in the manner of a cup turned upside down on a saucer (Figure 9.53), leaving an extracellular space between the bone surface and the cell....
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The aromaticity of the pyrimidine and purine ring systems and the electron-rich nature of their carbonyl and ring nitrogen substituents endow them with the ca- pacity to undergo keto–enol tautomeric shifts. That is, pyrimidines and purines ex- ist as tautomeric pairs, as shown in Figure 10.6 for uracil and Figure 10.7 for gua- nine. In other words, pK a values...
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The amount of DNA in a diploid mammalian cell is typically more than 1000 times that found in an E. (Compare Figures 10.3 and 10.17 to con- vince yourself that U would pair with A in the same manner T does.) Such base pair- ing creates secondary structure.. Messenger RNA Carries the Sequence Information for Synthesis of a Protein Messenger...
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For the isolation of even larger nu- cleotide sequences, such as those of genes encoding large polypeptides (or those of eukaryotic genes that are disrupted by large introns), partial or limited digestion of DNA by restriction enzymes can be employed. Restriction Endonucleases Can Be Used to Map the Structure of a DNA Fragment. Restriction digestion of a DNA molecule is...
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The edges of the base pairs have a specific relationship to these grooves. edges of the base pairs (“top” as defined by placing the glycosidic bond at the bottom, as in Figure 11.7) are exposed along the interior surface or “floor” of the major groove. the base-pair edges nearest to the glycosidic bond form the interior surface of the minor...
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of hybridization is a measure of the sequence similarity or relatedness between the two species. Depending on the conditions of the experiment, about 25% of the DNA from a human forms hybrids with mouse DNA, implying that some of the nu- cleotide sequences (genes) in humans are very similar to those in mice (Figure 11.20). The probe specifically base pairs...
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FIGURE 11.30 Bulges and loops formed in RNA when aligned sequences are not fully complementary. F., eds.The RNA World, 2nd ed. FIGURE 11.31 Junctions and coaxial stacking in RNA.. strongly tilted from the plane perpendicular to the helix axis (see Figure 11.9).. Stems of stem-loop structures may also have bulges (or internal loops) where the RNA strand is forced into...
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Crystal structure of the nucleosome core particle at 2.8 Å resolution. A structural analysis of the role of the nuclear matrix and DNA loops in the organization of the nucleus and chromosomes. A., eds., Higher order structure in the nucleus. Proceedings of the National Academy of Sciences U.S.A. The complete atomic structure of the large riboso- mal subunit at 2.4...