Noncyclic electron transport produces ATP and NADPH

In noncyclic electron transport, light energy is used to oxidize water, forming O2, H+, and electrons. Follow the steps in Figure 8.9 as you read this section.

tached to each ribose (see Figure 7.4). Whereas NAD+ partic-

8.9 Noncyclic Electron Transport Uses Two Photosystems

Photosystems I and II both make use of the excited chlorophyll molecules of their respective reaction centers.

Photosystem II

Electron transport chain

Photosystem I ip^N

Photosystem II

Electron transport chain

Photosystem I ip^N

Photosystem Produces

NADP+ (NADPH

NADP+ (NADPH

5| Photosystem I reduces an oxidizing agent, ferredoxin (Fd), which in turn reduces NADP+ to NADPH + H+.

Electrons from water replenish the electrons that chlorophyll molecules lose when they are excited by light. As the electrons are passed from water to chlorophyll, and ultimately to NADP+, they pass through a chain of electron carriers. These redox reactions are exergonic, and some of the free energy released is used ultimately to form ATP by a chemiosmotic mechanism.

two photosystems are required. Noncyclic electron transport requires the participation of two different photosystems. These photosystems are light-driven molecular units, each of which consists of many chlorophyll molecules and accessory pigments bound to proteins in separate energy-absorbing antenna systems.

► Photosystem I uses light energy to reduce NADP+ to NADPH + H+.

► Photosystem II uses light energy to oxidize water molecules, producing electrons, protons (H+), and O2.

The reaction center for photosystem I contains a chlorophyll a molecule called P700 because it can best absorb light of wavelength 700 nm. The reaction center for photosystem II contains a chlorophyll a molecule called P680 because it absorbs light maximally at 680 nm. Thus photosystem II requires photons that are somewhat more energetic (i.e., shorter wavelengths) than those required by photosystem I. To keep noncyclic electron transport going, both photosystems I and II must constantly be absorbing light, thereby boosting electrons to higher orbitals from which they may be captured by specific oxidizing agents.

P700*, which then leads to the reduction of an oxidizing agent called ferredoxin (Fd) and the production of P700+. Then P700+ returns to the ground state by accepting electrons passed through the redox chain from photosystem II.

With this accounting for the source of the electrons entering photosystem II, we can now consider the fate of the electrons from photosystem I. These electrons are used in the last step of noncyclic electron transport, in which two electrons and two protons are used to reduce a molecule of NADP+ to NADPH + H+. In summary:

► Noncyclic electron transport uses a molecule of water, four photons (two each absorbed by photosystems I and II), one molecule each of NADP+ and ADP, and one Pi.

► Noncyclic electron transport produces NADPH + H+ and ATP and half a molecule of oxygen (1/2 O2).

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Responses

  • natsnet
    Is water an oxidizing agent in noncyclic electron transport?
    8 years ago
  • ANNE KOHL
    How are nadph and atp formed in noncyclic electron transport?
    8 years ago
  • ian smith
    What is the final oxidizing agent in the noncyclic electron transport chain?
    8 years ago
  • Flavus
    What does the non cyclic electron transport produce?
    8 years ago
  • TONY
    What does the final oxidizing agent in the noncyclic electron transport chain produce?
    8 years ago
  • Tuomo
    Which photosystem reduces nadp?
    8 years ago
  • Kay Gilreath
    Which photosystem produces atp?
    7 years ago
  • ANNABELLA FOLLIERO
    Which photosystem produces both ATP and NADPH?
    7 years ago
  • malachy donaldson
    Which photosystem is used in noncyclic electron pathway?
    7 years ago
  • kathryne
    How is ADP, ATP, NADP , and NADPH used?
    7 years ago
  • sakari
    What are the electrons excited in photosystem I used for?
    7 years ago
  • vanessa
    What are two steps in the electron transport chain producing NADPH?
    5 years ago
  • landolfo
    How many ATP are produced per molecule of oxygen liberated during non cyclic electron transport?
    3 years ago
  • alida
    What is NADPH in electron transport system?
    3 years ago
  • Saverio
    How many atp form from non cyclic reaction?
    2 years ago
  • holfast
    Who much nadph is produced atp?
    2 years ago
  • Josefiina
    How many ATP is produce in from one NADPH through ETC?
    1 year ago
  • amanda
    How many atp are produced in noncyclic electron flow?
    1 year ago

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