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milligrams per day of Fe, Cu, and Zn, even less of the others. The elemental requirements for plants and microorganisms are similar to those shown here; the ways in which they acquire these elements vary. 8885d_c01_013 1/15/04 3:28 PM Page 13 mac76 mac76:385_reb: form the strongest bonds. The trace elements (Fig. 1–12)... |
or out of cells. Proteins are perhaps the most versatile of all biomolecules. The nucleic acids, DNA and RNA, are polymers of nucleotides. They store and transmit genetic information, and some RNA molecules have structural and catalytic roles in supramolecular complexes. The polysaccharides, polymers of simple sugars ... |
all the chemical properties of tartaric acid, but in solution one type rotated polarized light to the left (levorotatory), the other to the right (dextrorotatory). Pasteur later described the experiment and its interpretation: Louis Pasteur 1822–1895 In isomeric bodies, the elements and the proportions in which they ar... |
in quantitative and chemical terms, the means by which energy is extracted, channeled, and consumed in living cells. We can consider cellular energy conversions—like all other energy conversions—in the context of the laws of thermodynamics. Living Organisms Exist in a Dynamic Steady State, Never at Equilibrium with The... |
g systems) is the means by which energy from fuel metabolism or light capture is coupled to a cell’s energy-requiring reactions. In thinking about energy coupling, it is useful to consider a simple mechanical example, as shown in Figure 1–26a. An object at the top of an inclined plane has a certain amount of potential ... |
ose 6-phosphate can therefore occur by reaction 3. The coupling of exergonic and endergonic reactions through a shared intermediate is absolutely central to the energy exchanges in living systems. As we shall see, the breakdown of ATP (reaction 2 in Fig. 1–26b) is the exergonic reaction that drives many endergonic proc... |
cussed in Chapter 15, have begun to offer important insights into the overall regulation of metabolism. Cells also regulate the synthesis of their own catalysts, the enzymes, in response to increased or diminished need for a metabolic product; this is the substance of Chapter 28. The expression of genes (the translatio... |
sequence complementary to one of the original strands. The result is two double-helical molecules, each identical to the original DNA. a three-dimensional cell. This change from one to three dimensions occurs in two phases. A linear sequence of deoxyribonucleotides in DNA codes (through an intermediary, RNA) for the pr... |
as catalysts in their own forma- 8885d_c01_033 12/20/03 7:09 AM Page 33 mac76 mac76:385_reb: Spark gap Condenser Electrodes Mixture of NH3, CH4, H2, and H2O at 80 °C FIGURE 1–33 Abiotic production of biomolecules. Spark-discharge apparatus of the type used by Miller and Urey in experiments demonstrating abiotic format... |
y acquiring greater motility, efficiency, or reproductive success than their free-living single-celled competitors. Further evolution of such clustered organisms led to permanent associations among individual cells and eventually to specialization within the colony—to cellular differentiation. The advantages of cellula... |
B Gene 1* Function 1 1 Gene duplication leads to a superfluous copy of gene 1 Homologous genes 1 and 1* are orthologs, encoding proteins of the same function in different species. Gene 1 Gene 1 copy Function 1 Function 1 2 Mutations in gene 1 copy give rise to gene 2. Gene 2 encodes a protein with a new, different func... |
nd Function, W. H. Freeman and Company, New York. Up-to-date discussions of stereochemistry, functional groups, reactivity, and the chemistry of the principal classes of biomolecules. Physical Foundations Atkins, P. W. & de Paula, J. (2001) Physical Chemistry, 7th edn, W. H. Freeman and Company, New York. Atkins, P.W. ... |
s long as 2 m—for example, the axons that originate in your spinal cord and terminate in the muscles of your toes. Small membrane-enclosed vesicles carrying materials essential to axonal function move along microtubules of the cytoskeleton, from the cell body to the tips of the axons. (a) If the average velocity of a v... |
try. We begin with water because its properties affect the structure and function of all other cellular constituents. For each class of organic molecules, we first consider the covalent chemistry of the monomeric units (amino acids, monosaccharides, nucleotides, and fatty acids) and then describe the structure of the m... |
stick and (b) space-filling models. The dashed lines in (a) represent the nonbonding orbitals. There is a nearly tetrahedral arrangement of the outer-shell electron pairs around the oxygen atom; the two hydrogen atoms have localized partial positive charges ( ) and the oxygen atom has a partial negative charge (2 ). (c... |
ater dissolves many crystalline salts by hydrating their component ions. The NaCl crystal lattice is disrupted ions. The ionic as water molecules cluster about the Cl and Na charges are partially neutralized, and the electrostatic attractions necessary for lattice formation are weakened. 8885d_c02_47-74 7/25/03 10:05 A... |
an der Waals radii. J. Phys. Chem. 96, 9194–9197. For covalent radii, Pauling, L. (1960) Nature of the Chemical Bond, 3rd edn, Cornell University Press, Ithaca, NY. Note: van der Waals radii describe the space-filling dimensions of atoms. When two atoms are joined covalently, the atomic radii at the point of bonding ar... |
ueous solutions. (a) At 101 kPa (1 atm) pressure, pure water boils at 100 C and freezes at 0 C. (b) The presence of solute molecules reduces the probability of a water molecule leaving the solution and entering the gas phase, thereby reducing the vapor pressure of the solution and increasing the boiling point. Similarl... |
pressed as the pH of the solution. To predict the state of ionization of solutes in water, we must take into account the relevant equilibrium constants for each ionization reaction. We therefore turn now to a brief discussion of the ionization of water and of weak acids and bases dissolved in water. Pure Water Is Sligh... |
ase states the pH of the blood is higher than normal, the condition of alkalosis. Weak Acids and Bases Have Characteristic Dissociation Constants Hydrochloric, sulfuric, and nitric acids, commonly called strong acids, are completely ionized in dilute aqueous solutions; the strong bases NaOH and KOH are also completely ... |
nated amino and carboxyl groups of amino acids and the phosphate groups of nucleotides, for example, function as weak acids; their ionic state depends on the pH of the surrounding medium. As we noted above, ionic interactions are among the forces that stabilize a protein molecule and allow an enzyme to recognize and bi... |
H of a bicarbonate buffer system depends on the , the proton donor concentration of H2CO3 and HCO3 and acceptor components. The concentration of H2CO3 in turn depends on the concentration of dissolved CO2, which in turn depends on the concentration of CO2 in the gas phase, called the partial pressure of CO2. Thus the p... |
n-Hasselbalch 64 66 equation condensation hydrolysis 69 66 69 Further Reading General Belton, P.S. (2000) Nuclear magnetic resonance studies of the hydration of proteins and DNA. Cell. Mol. Life Sci. 57, 993–998. Denny, M.W. (1993) Air and Water: The Biology and Physics of Life’s Media, Princeton University Press, Prin... |
to its amino group? (b) In a 0.1 M solution of glycine at pH 9.0, what frac- tion of glycine has its amino group in the ONH3 form? (c) How much 5 M KOH must be added to 1.0 L of 0.1 M glycine at pH 9.0 to bring its pH to exactly 10.0? (d) When 99% of the glycine is in its ONH3 form, what is the numerical relation betw... |
ino acids are -amino acids. They have a carboxyl group and an amino group bonded to the same carbon atom (the carbon) (Fig. 3–2). They differ from each other in their side chains, or R groups, which vary in structure, size, and electric charge, and which influence the solubility of the amino acids in water. In addition... |
izing protein structure by means of hydrophobic interactions. Glycine has the simplest structure. Although it is formally nonpolar, its very small side chain makes no real contribution to hydrophobic interactions. Methionine, one of the two sulfur-containing amino acids, has a nonpolar thioether group in its side chain... |
tion of the absorbing species (in moles per liter), and l is the path length of the lightabsorbing sample (in centimeters). The Lambert-Beer law assumes that the incident light is parallel and monochromatic (of a single wavelength) and that the solvent and solute molecules are randomly oriented. The expression log (I0/... |
ture of the ionizing R groups present. For example, glutamate H3N N H3 COOH C H C H2 C H2 pK1 COO C H C H2 C H2 pKR COOH COOH N H3 COO C H C H2 C H2 COO pK2 COO H2N C H C H2 C H2 COO Glutamate 10 pK2 9.67 pH 8 6 4 2 0 (a) pKR 4.25 pK1 2.19 1.0 OH (equivalents) 2.0 3.0 COOH COO COO COO H3N H3N CH pK1 C H C H2 C C H H N ... |
t the extreme is titin, a constituent of vertebrate muscle, which has nearly 27,000 amino acid residues and a molecular weight of about 3,000,000. The vast majority of naturally occurring proteins are much smaller than this, containing fewer than 2,000 amino acid residues. Some proteins consist of a single polypeptide ... |
mmonly, the extract is subjected to treatments that separate the proteins into different fractions based on a property such as size or charge, a process referred to as fractionation. Early fractionation steps in a purification utilize differences in protein solubility, which is a complex function of pH, temperature, sa... |
cedure on purification techniques developed for similar proteins. Published purification protocols are available for many thousands of proteins. Common sense dictates that inexpensive procedures such as salting out be used first, when the total volume and the number of contaminants are greatest. Chromatographic methods... |
reasing pI Isoelectric focusing gel is placed on SDS polyacrylamide gel. Second dimension SDS polyacrylamide gel electrophoresis Decreasing Mr (a) Decreasing pI After each purification step, the activity of the preparation (in units of enzyme activity) is assayed, the total amount of protein is determined independently... |
After the amino-terminal residue is labeled with one of these reagents, the polypeptide is hydrolyzed to its constituent amino acids and the labeled amino acid is identified. Because the hydrolysis stage destroys the polypeptide, this procedure cannot be used to sequence a polypeptide beyond its amino-terminal residue.... |
tablish which fragment is derived from the amino terminus. The two sets of fragments can be compared for possible errors in determining the amino acid sequence of each fragment. If the second cleavage procedure fails to establish continuity between all peptides from the first cleavage, a third or even a fourth cleavage... |
MS. (a) After proteolytic hydrolysis, a protein solution is injected into a mass spectrometer (MS-1). The different peptides are sorted so that only one type is selected for further analysis. The selected peptide is further fragmented in a chamber between the two mass spectrometers, and m/z for each fragment is measur... |
ld of each step is: 96.0% 99.8% 11 21 31 51 100 66 44 29 13 1.7 98 96 94 90 82 100-amino-acid protein would be synthesized with exquisite fidelity in about 5 seconds in a bacterial cell. A variety of new methods for the efficient ligation (joining together) of peptides has made possible the assembly of synthetic peptid... |
tion of a gap in the B. subtilis sequence allows a better alignment of amino acid residues on either side of the gap. Identical amino acid residues are shaded. 8885d_c03_108 12/23/03 10:27 AM Page 108 mac111 mac111:reb: 108 Chapter 3 Amino Acids, Peptides, and Proteins Of course, if a sufficient number of gaps are intr... |
ecies from another. If we trace two extant species to a common internal node (representing the common ancestor of the two species), the length of the branch connecting each external node to the internal node represents the number of amino acid substitutions separating one extant species from this ancestor. The sum of t... |
he worst pH regions for buffering power. 12 10 11.30 9.60 (V) (IV) pH 8 6 4 2 0 5.97 (III) 2.34 (II) (I) 0.5 1.0 1.5 2.0 OH (equivalents) 3. How Much Alanine Is Present as the Completely Uncharged Species? At a pH equal to the isoelectric point of alanine, the net charge on alanine is zero. Two structures can be drawn ... |
uence of the peptide antibiotic. Show your reasoning. When you have arrived at a structure, demonstrate that it is consistent with each experimental observation. 17. Efficiency in Peptide Sequencing A peptide with the primary structure Lys–Arg–Pro–Leu–Ile–Asp–Gly–Ala is sequenced by the Edman procedure. If each Edman c... |
difference in free energies of the folded and unfolded states, may be close to zero. We must therefore look elsewhere to explain why the native conformation of a protein is favored. We find that the contribution of weak interactions to protein stability can be understood in terms of the properties of water (Chapter 2).... |
ate. (b) Three bonds separate sequential carbons in a polypeptide chain. The NOC and COC bonds can rotate, with bond angles designated and , respectively. The peptide CON bond is not free to rotate. Other single bonds in the backbone may also be rotationally hindered, depending on the size and charge of the R groups. I... |
in which the other four fingers are curled as shown (counterclockwise). The resulting helix is right-handed. Your left hand will demonstrate a lefthanded helix, which rotates in the clockwise direction as it spirals up your thumb. A constraint on the formation of the helix is the presence of Pro or Gly residues. In pr... |
wisted b sheets 180 120 60 0 60 120 ) s e e r g e d ( w Left-handed a helix Right-handed a helix 180 180 (a) 0 f (degrees) 180 180 120 60 0 60 120 180 180 ) b) 0 f (degrees) 180 FIGURE 4–9 Ramachandran plots for a variety of structures. (a) The values of and for various allowed secondary structures are overlaid on the ... |
, usually a compound containing a thiol or sulfhydryl group (OSH), is then applied with heat. The reducing agent cleaves the cross-linkages by reducing each disulfide bond to form two Cys residues. The moist heat breaks hydrogen bonds and causes the -helical structure of the polypeptide chains to uncoil. After a time t... |
tooth loss, poor wound healing and the reopening of old wounds, bone pain and degeneration, and eventually heart failure. Despondency and oversensitivity to stimuli of many kinds are also observed. Milder cases of vitamin FIGURE 1 Iroquois showing Jacques Cartier how to make cedar tea as a remedy for scurvy. C deficie... |
ommended daily allowance of vitamin C. Eat your fresh fruit and vegetables. to function, and even the evolutionary paths by which proteins arrived at their present state, which can be glimpsed in the family resemblances that are revealed as protein databases are sifted and sorted. The sheer variety of structures can se... |
also present (Fig. 4–18). Four disulfide bonds contribute stability to this structure. The helices line a long crevice in the side of the molecule, called the active site, which is the site of substrate binding and catalysis. The bacterial polysaccharide that is the substrate for lysozyme fits into this crevice. Prote... |
ure of Proteins BOX 4–4 WORKING IN BIOCHEMISTRY (continued from previous page) carried out on macromolecules in solution, whereas xray crystallography is limited to molecules that can be crystallized. NMR can also illuminate the dynamic side of protein structure, including conformational changes, protein folding, and i... |
Thick lines represent connections at the ends nearest the viewer; thin lines are connections at the far ends of the strands. The connections on a given end (e.g., near the viewer) do not cross each other. (c) Because of the twist in strands, connections between strands are generally right-handed. Lefthanded connection... |
hese structural comparisons can help illuminate every aspect of biochemistry, from the evolution of individual proteins to the evolutionary history of complete metabolic pathways. Protein Quaternary Structures Range from Simple Dimers to Large Complexes Protein Architecture—Quaternary Structure Many proteins have multi... |
47 12/23/03 7:52 AM Page 147 mac111 mac111:reb: motifs, or folds. The thousands of known protein structures are generally assembled from a repertoire of only a few hundred motifs. Regions of a polypeptide chain that can fold stably and independently are called domains. ■ Quaternary structure results from interactions b... |
rgy funnel. At the top, the number of conformations, and hence the conformational entropy, is large. Only a small fraction of the intramolecular interactions that will exist in the native conformation are present. As folding progresses, the thermodynamic path down the funnel reduces the number of states present (decrea... |
4_152 12/23/03 7:53 AM Page 152 mac111 mac111:reb: 152 Chapter 4 The Three-Dimensional Structure of Proteins The second class of chaperones is called chaperonins. These are elaborate protein complexes required for the folding of a number of cellular proteins that do not fold spontaneously. In E. coli an estimated 10% t... |
Astbury’s observations. (b) When wool sweaters or socks are washed in hot water or heated in a dryer, they shrink. Silk, on the other hand, does not shrink under the same conditions. Explain. 3. Rate of Synthesis of Hair -Keratin Hair grows at a rate of 15 to 20 cm/yr. All this growth is concentrated at the base of the... |
transformations. —Emil Fischer, article in Berichte der deutschen chemischen Gesellschaft zu Berlin, 1906 Knowing the three-dimensional structure of a protein is an important part of understanding how the protein functions. However, the structure shown in two dimensions on a page is deceptively static. Proteins are dy... |
5–3, the helical segments are named A through H. An individual amino acid residue is designated either by its position in the amino acid sequence or by its location within the sequence of a particular -helical segment. For example, the His residue coordinated to the heme in myoglobin, His93 (the 93rd amino acid residu... |
able rate. However, rapid molecular flexing of the amino acid side chains produces transient cavities in the protein structure, and O2 evidently makes its way in and out by moving through these cavities. Computer simulations of rapid structural fluctuations in myoglobin suggest that there are many such pathways. One ma... |
lved in ion pairs are shown in blue, their negatively charged partners in red. The Lys C5 of each subunit and Asp FG1 of each subunit are visible but not labeled (compare Fig. 5–9a). Note that the molecule is oriented slightly differently than in Figure 5–9. The transition from the T state to the R state shifts the sub... |
the subunits of a cooperatively binding protein are functionally identical, that each subunit can exist in (at ) Hemoglobin nH 3 Hemoglobin high-affinity state nH 1 Myoglobin nH 1 Hemoglobin low-affinity state nH 1 1 0 1 2 3 log pO2 FIGURE 5–14 Hill plots for the binding of oxygen to myoglobin and 1, there is no eviden... |
y or active). Depending on the or all equilibrium, K1, between and binding of one or more ligand molecules (L) will pull the equilibrium toward the form. Subunits with bound L are shaded. In the sequential model (b), each individual subunit can be in either the forms, the or form. A very large number of conformations i... |
rmal adult hemoglobin, and a correspondingly higher affinity for O2. Oxygen-Binding Proteins—Hemoglobin Is Susceptible to Allosteric Regulation Sickle-Cell Anemia Is a Molecular Disease of Hemoglobin The great importance of the amino acid sequence in determining the secondary, tertiary, and quaternary structures of glo... |
pable of recognizing and binding to molecules that might signal an infection. The immune response consists of two complementary systems, the humoral and cellular immune systems. The humoral immune system (Latin humor, “fluid”) is directed at bacterial infections and extracellular viruses (those found in the body fluids... |
s of different binding specificities in the Tcell receptors. Within the highly varied T-cell population there is almost always a contingent of cells that can specifically bind any antigen that might appear. The vast majority of these cells never encounter a foreign antigen to which they can bind, and they typically die... |
a mixture of proteins is added to (a) Conformation with no antigen bound (b) Antigen bound (hidden) (c) Antigen bound (shown) FIGURE 5–27 Induced fit in the binding of an antigen to IgG. The molecule, shown in surface contour, is the Fab fragment of an IgG. The antigen bound by this IgG is a small peptide derived from ... |
s Amino terminus Light chains 17 nm Heads 20 nm 2 nm Carboxyl terminus 150 nm Tail Myosin trypsin Light meromyosin (b) (c) Heavy meromyosin + papain S1 S1 S2 36 nm (b) F-actin G-actin subunits Myosin head Actin filament (c) FIGURE 5–30 The major components of muscle. (a) Myosin aggregates to form a bipolar structure ca... |
of immunoglobulins with antigens, is reversible and leaves the participants unchanged. When ATP binds myosin, however, it is hydrolyzed to ADP and Pi. Myosin is not only an actinbinding protein, it is also an ATPase—an enzyme. The function of enzymes in catalyzing chemical transformations is the topic of the next chap... |
ere are almost 500 naturally occurring variants of hemoglobin. Most are the result of a single amino acid substitution in a globin polypeptide chain. Some variants produce clinical illness, though not all variants have deleterious effects. A brief sample is presented below. HbS (sickle-cell Hb): substitutes a Val for a... |
cause. Measurements of the activities of enzymes in blood plasma, erythrocytes, or tissue samples are important in diagnosing certain illnesses. Many drugs exert their biological effects through interactions with enzymes. And enzymes are important practical tools, 8885d_c06_190-237 1/27/04 7:13 AM Page 191 mac76 mac76... |
cells. Furthermore, many common reactions in biochemistry entail chemical events that are unfavorable or unlikely in the cellular environment, such as the transient formation of unstable charged intermediates or the collision of two or more molecules in the precise orientation required for reaction. Reactions required ... |
ed for cell survival. Reaction Rates and Equilibria Have Precise Thermodynamic Definitions Reaction equilibria are inextricably linked to the standard free-energy change for the reaction, G, and re- *In this chapter, step and intermediate refer to chemical species in the reaction pathway of a single enzyme-catalyzed re... |
n state. This means that optimal interactions between substrate and enzyme occur only in the transition state. Figure 6–5c demonstrates how such an enzyme can work. The metal stick binds to the stickase, but only a subset of the possible magnetic interactions are used in forming the ES complex. The bound substrate must... |
a change in conformation when the substrate binds, induced by multiple weak interactions with the substrate. 8885d_c06_190-237 1/27/04 7:13 AM Page 200 mac76 mac76:385_reb: 200 Chapter 6 Enzymes Reaction O C O C (a) CH3 CH3 (b) O C OR O C O (c) O OR OR k (M 1s1) O CH3 CH3 OR k (s1) O C C O O O C O OR C O OR k (s1) O C ... |
yme active site is structured so that some of these weak interactions occur preferentially in the reaction transition state, thus stabilizing the transition state. The need for multiple interactions is one reason for the large size of enzymes. The binding energy, GB, can be used to lower substrate entropy or to cause a... |
both sides of the equation and simplifying gives k1[Et][S] (k1[S] k1 k2)[ES] (6–16) We then solve this equation for [ES]: k t] [E 1 (6–17) [ES] k k1[S ] ] [S k2 1 This can now be simplified further, combining the rate constants into one expression: [ES] [Et][S] [S] (k2 k1)/k1 (6–18) The term (k2 k1)/k1 is defined as t... |
t and Km that reflect the cellular environment, the concentration of substrate normally encountered in vivo by the enzyme, and the chemistry of the reaction being catalyzed. The parameters kcat and Km also allow us to evaluate the kinetic efficiency of enzymes, but either parameter alone is insufficient for this task. ... |
inhibitor binding to ES. (c) Mixed inhibitors bind at a separate site, but may bind to either E or ES. V m V0 K ] [S ax ] [S m (6–28) where ] I 1 [ K I and ] ][ I KI [E ] I [E Equation 6–28 describes the important features of competitive inhibition. The experimentally determined variable Km, the Km observed in the pres... |
rprising. Amino acid side chains in the active site may act as weak acids and bases with critical functions that depend on their maintaining a certain state of ionization, and elsewhere in the protein ionized side chains may play an essential role in the interactions that maintain protein structure. Removing a proton f... |
that this reflected a rapid acylation of all the enzyme molecules (with release of p-nitrophenol), with the rate for subsequent turnover of the enzyme limited by a slow deacylation step. Similar results have since been obtained with many other enzymes. The observation of a burst phase provides yet another example of t... |
ntermediate, with oxygen in the oxyanion hole again taking on a negative charge. *The tetrahedral intermediate in the chymotrypsin reaction pathway, and the second tetrahedral intermediate that forms later, are sometimes referred to as transition states, which can lead to confusion. An intermediate is any chemical spec... |
tional chemical groups added in each substrate (A to B to C) are shaded. As the table shows, the interaction between the enzyme and these added functional groups has a minimal effect on Km (taken here as a reflection of Kd) but a large, positive effect on kcat and kcat/Km. This is what we would expect if the interactio... |
nomeric configurations of carbohydrates are examined in Chapter 7), and all of which are known to have reactive covalent intermediates like that envisioned in the alternative (SN2) pathway. Hence, the Phillips mechanism ran counter to experimental findings for closely related enzymes. A compelling experiment tipped the... |
Some of the differences are structural. In addition to active sites, allosteric enzymes generally have one or more regulatory, or allosteric, sites for binding the modulator (Fig. 6–26). Just as an enzyme’s active site is specific for its substrate, each regulatory site is specific for its modulator. Enzymes with sever... |
by protein phosphatases. The addition of a phosphoryl group to a Ser, Thr, or Tyr residue introduces a bulky, charged group into a region that was only moderately polar. The oxygen atoms of a phosphoryl group can hydrogen-bond with one or several groups in a protein, commonly the 8885d_c06_190-237 1/27/04 7:13 AM Page... |
n protein kinases. Some Enzymes and Other Proteins Are Regulated by Proteolytic Cleavage of an Enzyme Precursor For some enzymes, an inactive precursor called a zymogen is cleaved to form the active enzyme. Many proteolytic enzymes (proteases) of the stomach and pancreas are regulated in this way. Chymotrypsin and tryp... |
, A.J.(2001) The lysozyme mechanism sorted—after 50 years. Nat. Struct. Biol. 8, 737–739. Many good illustrations of the principles introduced in this chapter. A nice discussion of the catalytic power of enzymes and the principles underlying it. Kinetics Cleland, W.W. (1977) Determining the chemical mechanisms of enzym... |
ial sulfhydryl groups to form mercaptides: Enz–SH Ag On Enz–S–Ag H Calculate the minimum molecular weight of the enzyme. Why does the value obtained in this way give only the minimum molecular weight? 15. Clinical Application of Differential Enzyme Inhibition Human blood serum contains a class of enzymes known as acid ... |
ldotriose H Dihydroxyacetone, a ketotriose (a) H O C C C OH H H HO H C OH CH OH CH2OH D-Glucose, an aldohexose H O C CH OH H C OH CH OH (b) H C C C C OH O H OH H HO H CH OH CH2OH D-Fructose, a ketohexose H O C CH 2 H C OH CH OH CH2OH CH2OH D-Ribose, an aldopentose 2-Deoxy-D-ribose, an aldopentose (c) FIGURE 7–1 Represe... |
s of monosaccharides. However, the six-membered pyranose ring is not planar, as Haworth perspectives suggest, but tends to assume either of two “chair” conformations (Fig. 7–8). Recall from Chapter 1 (p. 19) that two conformations of a molecule are interconvertible without the breakage of covalent bonds, H O C1 HO H H ... |
of a sugar to a nitrogen atom in glycoproteins (see Fig. 7–31) and nucleotides (see Fig. 8–1). The oxidation of a sugar’s anomeric carbon by cupric or ferric ion (the reaction that defines a reducing sugar) occurs only with the linear form, which exists in equilibrium with the cyclic form(s). When the anomeric carbon i... |
rch in plant cells and glycogen in animal cells. Both polysaccharides occur intracellularly as large clusters or granules (Fig. 7–14). Starch and glycogen molecules are heavily hydrated, because they have many exposed hydroxyl groups available to hydrogen-bond with water. Most plant cells have the ability to form starc... |
on about each bond is limited by steric hindrance by substituents. The three-dimensional structures of these molecules can be described in terms of the dihedral angles, and , made with the glycosidic bond (Fig. 7–19), analogous to angles and made by the peptide bond (see Fig. 4–2). Because of the bulkiness of the pyran... |
CH2OH O H H O (1n4) H H NH A C A CH3 OP GlcNAc CH2OH O H H O (1n4) H H NH A C A CH3 OP O3SO H O H (1n3) GalNAc4S OSO3 O CH2 H H OH H O (1n4) H O H (1n3) NH A C A CH3 OP Gal GlcNAc6S COO H or H H O COO OH H O H Heparin 15–90 CH2 H H OSO3 O H OSO3 H (1n4) O H NH SO3 H OSO3 GlcA2S or IdoA2S (1n4) GlcNS3S6S 8885d_c07_238-2... |
ins. Proteoglycans Are Glycosaminoglycan-Containing Macromolecules of the Cell Surface and Extracellular Matrix Mammalian cells can produce at least 30 types of molecules that are members of the proteoglycan superfamily. These molecules act as tissue organizers, influence the development of specialized tissues, mediate... |
ellular and extracellular molecules. These interactions serve not merely to anchor cells to the extracellular matrix but also to provide paths that direct the migration of cells in developing tissue and, through integrins, to convey information in both directions across the plasma membrane. Glycoproteins Have Covalentl... |
targeting of newly synthesized proteins, and allow for specific recognition by other proteins. ■ Glycolipids and lipopolysaccharides are components of the plasma membrane with covalently attached oligosaccharide chains exposed on the cell’s outer surface. 7.4 Carbohydrates as Informational Molecules: The Sugar Code Gly... |
complex for transfer to the lysosome (see Fig. 27–36). A common structural feature on the surface of these glycoproteins, the signal patch, causes them to be recognized by an enzyme that phosphorylates a mannose residue at the terminus of an oligosaccharide chain. This mannose phosphate residue is recognized by the ca... |
ns. ■ Lectins, proteins with highly specific carbohydrate-binding domains, are commonly found on the outer surface of cells, where they initiate interaction with other cells. In vertebrates, oligosaccharide tags “read” by lectins govern the rate of degradation of certain peptide hormones, circulating proteins, and bloo... |
ructure-function relationships of some paradigmatic proteoglycans are discussed in depth, and novel aspects of their biology are examined. Jackson, R.L., Busch, S.J., & Cardin, A.D. (1991) Glycosaminoglycans: molecular properties, protein interactions, and role in physiological processes. Physiol. Rev. 71, 481–539. An ... |
her stereoisomer rotates plane-polarized light to the same extent but to the right (clockwise) and is called the dextrorotatory isomer, designated (). An equimolar mixture of the () and () forms does not rotate plane-polarized light. The optical activity of a stereoisomer is expressed quantitatively by its optical rota... |
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