FOURTH EDITION
`
`Harvey Lodish
`
`Arnold Berk
`
`S. Lawrence Zipursky
`
`Paul Matsudaira
`
`David Baltimore ·
`
`James Darnell
`
`Media Con
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`W. H. FREEMAN AND COMPA
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`1
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`EXHIBIT 1013
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`

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`Library of Congress Cataloging-in-Publication Data
`
`Molecular cell biology/ Harvey Lodish p
`p.
`cm.
`Includes bibliographical references.
`ISBN 0-7167-3136-3
`2. Molecular biology.
`1. Cytology.
`QH581.2.M655
`571.6-dc21
`
`1999
`
`[et al.] - 4th ed.
`
`I. Lodish, Harvey F.
`
`99-30831
`CIP
`
`© 1986, 1990, 1995, 2000 by W. 1--I. Freeman and Company. All rights reserved.
`
`No part of this book may be reproduced by any mechanical, photographic, or
`electronic process, or in the form of a phonographic recording, nor may it be
`stored in a retrieval system, transmitted, or otherwise copied for public or private
`use, without written permission from the publisher.
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`Printed in the United States of America
`
`W. 1--I. Freeman and Company
`41 Madison Avenue, New York, New York 10010
`1--Ioundsmills, Basingstoke RG21 6XS, England
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`Third Printing. 2001
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`2
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`

`

`Thus the overall reaction of stages 1 and 2 can be sum-
`2z.1rized as
`i
`~ I I Many photosynthetic bacteria do not use water as the
`1; C<Jnor of electrons. Rather, they use molecules such as hy(cid:173)
`if Z'."."ogen gas (H2 ) or hydrogen sulfide (H2S) as the ultimate
`Ii ec•urce of electrons to reduce the ultimate electron acceptor
`I '~_.\D+ rather than NADP+).
`!;. f;eneration of ATP Protons move down their concentra -
`f ::an gradient from the thylakoid lumen to the stroma
`~ ,~:rough the F0F1 complex which couples proton movement
`( ::• the synt~esis of ATP from ~DP and_ P!. Th~s use _of the
`I, ::::-oton-mot1ve force to synthesize ATP 1s identical with the
`f :e::alogous process occurring during oxidative phosphoryla(cid:173)
`f ::on in the mitochondrion (see Figures 16-28 and 16-30).
`,, Carbon Fixation The ATP4
`- and NADPH generated by
`J ::~e second and third stages of photosynthesis provide the
`i t"::lergy and the electrons to drive the synthesis of polymers
`I f .. Ji six-carbon sugars from CO2 and H 2 0. The overall bal(cid:173)
`fi'. " 2-""lced equation is written as
`f,
`( :-, CO2 + 18 ATP4
`1
`
`- + 12 NADPH + 12 H 20 -
`
`The reactions that generate the ATP and NADPH used
`•:o carbon fixation are directly dependent on light energy;
`:l'.lus stages 1-3 are called the light reactions of photosyn(cid:173)
`:::esis. The reactions in stage 4 are indirectly dependent on
`• 'ght energy; they are sometimes called the dark reactions of
`;'hotosynthesis because they can occur in the dark, utilizing
`6e supplies of ATP and NADPH generated by light energy.
`However, the reactions in stage 4 are not confined to the
`.:!.ark; in fact, they primarily occur during illumination.
`
`Each Photon of Light Has a
`Defined Amount of Energy
`Quantum mechanics established that light, a form of electro(cid:173)
`:nagnetic radiation, has properties of both waves and parti(cid:173)
`cles. When light interacts with matter, it behaves as discrete
`packets of energy ( quanta) called photons. The energy of a
`photon, E, is proportional to the frequency of the light wave:
`
`Photosynthetic Stages and Light-Absorbing Pigments
`
`651
`
`E = h,', where his Planck's constant (1.58 X 10- 34 cal-s, or
`6.63 X 10- 34 Js), and ')' is the frequency of the light wave.
`It is customary in biology to refer to the wavelength of the
`light wave, A, rather than to its frequency, ')'. The two are
`related by the simple equation ')' = c + A, where c is the
`velocity of light (3 X 1010 cm/s in a vacuum). Note that
`photons of shorter wavelength have higher energies.
`Also, the energy in 1 mol of photons can be denoted by
`E = NE, where N is Avogadro's number (6.02 X 1023 mole(cid:173)
`cules or photons/mo!). Thus
`
`Nhc
`E = Nh1 = -
`A
`
`The energy of light is considerable, as we can calculate for
`light with a wavelength of 550 nm (550 X 10- 7 cm), typi(cid:173)
`cal of sunlight:
`
`(6.02 X 1023 photons/mol)(l.58 X 10-34 cal·s)(3 X 10 10 cm/s)
`E=-'-------=----'-.:.....:. _____ _:_.:_ ___ .:.....:.
`(550 X 10- 7 cm)
`
`= 51,881 cal/mo!
`
`or about 52 kcal/mo!, enough energy to synthesize several
`moles of ATP from ADP and P; if all the energy were used
`for this purpose.
`
`Chlorophyll a Is Present in Both
`Components of a Photosystem
`The absorption of light energy and its conversion into chem(cid:173)
`ical energy occurs in multiprotein complexes, called photo(cid:173)
`systems, located in the thylakoid membrane. A photosystem
`has two closely linked components, an antenna containing
`light-absorbing pigments and a reaction center comprising
`a complex of proteins and two chlorophyll a molecules. Each
`antenna (named by analogy with radio antennas) contains
`one or more light-harvesting complexes (LHCs). The energy
`of the light captured by LHCs is funneled to the two chloro(cid:173)
`phylls in the reaction center, where the primary events of
`photosynthesis occur.
`Found in all photosynthetic organisms, both eukaryotic
`and prokaryotic, chlorophyll a is the principal pigment in(cid:173)
`volved in photosynthesis, being present in both antennas and
`reaction centers. In addition to chlorophyll a, antennas con(cid:173)
`tain other light-absorbing pigments: chlorophyll b in vascu(cid:173)
`lar plants, and carotenoids in both plants and photosynthetic
`bacteria (Figure 16-36). The presence of various antenna
`
`lo. FIGURE 16-36 The structure of f:l-carotene, a pigment that
`assists in light absorption by chloroplasts. ,8-Carotene, which
`is related to the visual pigment retinal (see Figure 21-47), is one
`
`of a family of carotenoids containing long hydrocarbon chains
`with alternating single and double bonds.
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`3
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`