H. Lodish - Molecular Cell Biology (5ed, Freeman, 2003) (796244), страница 25
Текст из файла (страница 25)
The G for the reaction X Y n XY is 1000cal/mol. What is the G at 25C (298 Kelvin) starting with0.01 M each X, Y, and XY? Suggest two ways one couldmake this reaction energetically favorable.REFERENCESAlberty, R. A., and R. J. Silbey. 2000. Physical Chemistry, 3d ed.Wiley.Atkins, P. W. 2000. The Elements of Physical Chemistry, 3d ed.W. H. Freeman and Company.Berg, J. M., J. L. Tymoczko, and L. Stryer. 2002. Biochemistry,5th ed. W. H. Freeman and Company.Cantor, P. R., and C.
R. Schimmel. 1980. Biophysical Chemistry.W. H. Freeman and Company.Davenport, H. W. 1974. ABC of Acid-Base Chemistry, 6th ed.University of Chicago Press.Edsall, J. T., and J. Wyman. 1958. Biophysical Chemistry, vol.1. Academic Press.Eisenberg, D., and D. Crothers. 1979. Physical Chemistry withApplications to the Life Sciences. Benjamin-Cummings.Gennis, R. B. 1989. Biomembranes: Molecular Structure andFunction.
Springer-Verlag, New York.Guyton, A. C., and J. E. Hall. 2000. Textbook of Medical Physiology, 10th ed. Saunders.Hill, T. J. 1977. Free Energy Transduction in Biology. AcademicPress.Klotz, I. M. 1978. Energy Changes in Biochemical Reactions.Academic Press.ReferencesLehninger, A. L., D. L. Nelson, and M. M. Cox.
2000. Principles of Biochemistry, 3d ed. Worth.Murray, R. K., et al. 1999. Harper’s Biochemistry, 25th ed.Lange.Nicholls, D. G., and S. J. Ferguson. 1992. Bioenergetics 2. Academic Press.Oxtoby, D., H. Gillis, and N. Nachtrieb. 2003. Principles ofModern Chemistry, 5th ed. Saunders.Sharon, N. 1980. Carbohydrates. Sci. Am. 243(5):90–116.Tanford, C. 1980.
The Hydrophobic Effect: Formation of Micelles and Biological Membranes, 2d ed. Wiley.57Tinoco, I., K. Sauer, and J. Wang. 2001. Physical Chemistry—Principles and Applications in Biological Sciences, 4th ed. PrenticeHall.Van Holde, K., W. Johnson, and P. Ho. 1998. Principles of Physical Biochemistry. Prentice Hall.Voet, D., and J.
Voet. 1995. Biochemistry, 2d ed. Wiley.Watson, J. D., et al. 2003. Molecular Biology of the Gene, 5thed. Benjamin-Cummings.Wood, W. B., et al. 1981. Biochemistry: A Problems Approach,2d ed. Benjamin-Cummings.3PROTEIN STRUCTUREAND FUNCTIONElectron density map of the F1-ATPase associated witha ring of 10 c-subunits from the F0 domain of ATPsynthase, a molecular machine that carries out thesynthesis of ATP in eubacteria, chloroplasts, andmitochondria. [Courtesy of Andrew Leslie, MRC Laboratory ofMolecular Biology, Cambridge, UK.]Proteins, the working molecules of a cell, carry out theprogram of activities encoded by genes.
This programrequires the coordinated effort of many different typesof proteins, which first evolved as rudimentary moleculesthat facilitated a limited number of chemical reactions. Gradually, many of these primitive proteins evolved into a widearray of enzymes capable of catalyzing an incredible range ofintracellular and extracellular chemical reactions, with aspeed and specificity that is nearly impossible to attain in atest tube.
With the passage of time, other proteins acquiredspecialized abilities and can be grouped into several broadfunctional classes: structural proteins, which provide structural rigidity to the cell; transport proteins, which control theflow of materials across cellular membranes; regulatory proteins, which act as sensors and switches to control proteinactivity and gene function; signaling proteins, including cellsurface receptors and other proteins that transmit externalsignals to the cell interior; and motor proteins, which causemotion.A key to understanding the functional design of proteinsis the realization that many have “moving” parts and are capable of transmitting various forces and energy in an orderlyfashion.
However, several critical and complex cellprocesses—synthesis of nucleic acids and proteins, signaltransduction, and photosynthesis—are carried out by hugemacromolecular assemblies sometimes referred to as molecular machines.A fundamental goal of molecular cell biologists is to understand how cells carry out various processes essential forlife. A major contribution toward achieving this goal is theidentification of all of an organism’s proteins—that is, a listof the parts that compose the cellular machinery. The compilation of such lists has become feasible in recent years withthe sequencing of entire genomes—complete sets of genes—of more and more organisms.
From a computer analysis ofOUTLINE3.1 Hierarchical Structure of Proteins3.2 Folding, Modification, and Degradationof Proteins3.3 Enzymes and the Chemical Work of Cells3.4 Molecular Motors and the Mechanical Workof Cells3.5 Common Mechanisms for Regulating ProteinFunction3.6 Purifying, Detecting, and Characterizing Proteins5960CHAPTER 3 • Protein Structure and Functiongenome sequences, researchers can deduce the number andprimary structure of the encoded proteins (Chapter 9). Theterm proteome was coined to refer to the entire protein complement of an organism.
For example, the proteome of theyeast Saccharomyces cerevisiae consists of about 6000 different proteins; the human proteome is only about five timesas large, comprising about 32,000 different proteins. Bycomparing protein sequences and structures, scientists canclassify many proteins in an organism’s proteome and deducetheir functions by homology with proteins of known function. Although the three-dimensional structures of relativelyfew proteins are known, the function of a protein whosestructure has not been determined can often be inferred fromits interactions with other proteins, from the effects result(a)MOLECULAR STRUCTUREPrimary (sequence)Secondary (local folding)Tertiary (long-range folding)3.1 Hierarchical Structure of ProteinsQuaternary (multimeric organization)Supramolecular (large-scale assemblies)(b)"off"RegulationSignaling"on"StructureFUNCTIONMovementing from genetically mutating it, from the biochemistry of thecomplex to which it belongs, or from all three.In this chapter, we begin our study of how the structureof a protein gives rise to its function, a theme that recursthroughout this book (Figure 3-1).
The first section examineshow chains of amino acid building blocks are arranged andthe various higher-order folded forms that the chains assume.The next section deals with special proteins that aid in thefolding of proteins, modifications that take place after theprotein chain has been synthesized, and mechanisms that degrade proteins. The third section focuses on proteins as catalysts and reviews the basic properties exhibited by allenzymes.
We then introduce molecular motors, which convert chemical energy into motion. The structure and functionof these functional classes of proteins and others are detailedin numerous later chapters. Various mechanisms that cellsuse to control the activity of proteins are covered next. Thechapter concludes with a section on commonly used techniques in the biologist’s tool kit for isolating proteins andcharacterizing their properties.TransportCatalysisAB▲ FIGURE 3-1 Overview of protein structure and function.(a) The linear sequence of amino acids (primary structure) foldsinto helices or sheets (secondary structure) which pack into aglobular or fibrous domain (tertiary structure).
Some individualproteins self-associate into complexes (quaternary structure) thatcan consist of tens to hundreds of subunits (supramolecularassemblies). (b) Proteins display functions that include catalysis ofchemical reactions (enzymes), flow of small molecules and ions(transport), sensing and reaction to the environment (signaling),control of protein activity (regulation), organization of the genome,lipid bilayer membrane, and cytoplasm (structure), and generationof force for movement (motor proteins).
These functions andothers arise from specific binding interactions and conformationalchanges in the structure of a properly folded protein.Although constructed by the polymerization of only 20 different amino acids into linear chains, proteins carry out anincredible array of diverse tasks. A protein chain folds intoa unique shape that is stabilized by noncovalent interactionsbetween regions in the linear sequence of amino acids. Thisspatial organization of a protein—its shape in three dimensions—is a key to understanding its function.
Only when aprotein is in its correct three-dimensional structure, or conformation, is it able to function efficiently. A key concept inunderstanding how proteins work is that function is derivedfrom three-dimensional structure, and three-dimensionalstructure is specified by amino acid sequence. Here, we consider the structure of proteins at four levels of organization,starting with their monomeric building blocks, the aminoacids.The Primary Structure of a Protein Is Its LinearArrangement of Amino AcidsWe reviewed the properties of the amino acids used in synthesizing proteins and their linkage by peptide bonds into linear chains in Chapter 2. The repeated amide N, carbon(C), and carbonyl C atoms of each amino acid residue formthe backbone of a protein molecule from which the variousside-chain groups project (Figure 3-2).
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
