9.1 and 9.2 Photosynthesis and ATP - 12 cards

Now what are the "Dark Phase Reactions" (aka CalvinCycle)? This is the cycle that converts CO2 into glucose. Sinceit utilizes the chemical energy in the ATP and NADPH, it does notrequire sunlight (hence the name). It is a complex cycle ofmostly phosphorylation (adding or removing phosphate) andoxidative (electron removal) chemical reactions whereby 6molecules of CO2 are converted into one molecule of glucose. Itrequires the energy-releasing cleavage of high energy bonds of 18ATPs and 12 NADPHs . The resulting 18 ADPs and 12 NADP+s are thenrestored by the Light Phase process to their high energy forms(ATP and NADPH).

ATP production during photosynthesis ..

The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions).

Photosynthesis, Respiration, and the ATP-ADP Cycle

A
similar activity can be used to create models of mitochondria.

Using tennis balls the students will play a game of catch to demonstrate
the loss of 1 phosphate to form ADP from ATP and the gain of one phosphate to
form ATP from ADP.

Photosynthesis, Respiration, and the ATP-ADP Cycle ..

To make a long story short, the primary function of ATP synthase in most organisms is ATP synthesis. Hence the name. However, in some cases the reverse reaction, i.e. transmembrane proton pumpingpowered by ATP hydrolysis is more important. A typical example: anaerobic bacteria produce ATP byfermentation, and ATP synthase uses ATP to generate protonmotive force necessary for ion transportand flagella motility.
Many bacteria can live both from fermentation and respiration or photosynthesis. In such case ATP synthasefunctions in both ways.
An important issue is to control ATP-driven proton pumping activity of ATP synthase in order to avoid wasteful ATP hydrolysis under conditions when no protonmotive force can be generated (e.g. leakydamaged membrane, uncoupler present, etc.). In such case ATP hydrolysis becomes a problem,because it can quickly exchaust the intecellular ATP pool. To avoid this situation,all ATP synthases are equipped with regulatory mechanisms that suppress the ATPaseactivity if no protonmotive force is present. The degree of ATP hydrolysis inhibitiondepend on the organism. In plants (in chloroplasts), where it is necessary to preserveATP pool through the whole night, the inhibition is very strong: the enzyme hardly has anyATPase activity. In contrast, in anaerobic bacteria where ATP synhase is the maingenerator of protonmotive force, such inhibition is very weak. Mitochondrial ATP synthase is somewhereinbetween.


The Light-Dependent Reactions of Photosynthesis

Photosynthesis converts these energy- depleted compounds (ADPand NADP+) back to the high energy forms (ATP and NADPH) and theenergy thus produced in this chemical form is utilized to drivethe chemical reactions necessary for synthesis of sugars andother carbon containing compounds (e.g., proteins, fats). Theproduction of high energy ATP and NADPH in plants occurs in whatis known as Light Phase Reactions (Z Scheme) (requiressunlight). The energy releasing reactions which converts themback to energy-depleted ADP and NADP is known as Dark PhaseReactions (Calvin Cycle) (does not require light) in whichthe synthesis of glucose and other carbohydrates occurs.

Its production leaves chlorophyll in ..

The Z Scheme diagram shows the pathway of an electron fromwater (lower right) to NADP+ (upper left). It also shows theenergy relationships which are measured as voltage potentialshown on the scaleon the right. To raise the energy of theelectrons derived from water (+0.82 volts) to the level necessaryto reduce NADP+ to NADPH (-0.32 volts), each electron must beboosted twice (vertical red arrows) by light energy absorbed inPhotosystems I and II. After each boosting , the energizedelectrons flow "downhill" (diagonal black lines) and inthe process transfer some of their energy to a series ofreactions which ultimately adds a phosporus to ADP to producehigh energy ATP and reduces NADP+ to NADPH. There is analternative shunt whereby the electron flow turns back tocytochrome b563 (green line)and this is called and it occurs when there is no need for NADPH, so onlyATP is produced.

35) Refer to the accompanying figure

The "" and "" indices denote the ositively and the egatively charged sides of thecoupling membrane.
The pH value is important: the pK value for 2-+i- is 7.2, while thecorresponding pK values for phosphate in ADP and ATP are close to 6.9.
This means that in the pH interval of 6.9-7.2 the prevailingreaction will not include trapping of protons:

How do we know the O 2 is derived from H 2 O during photosynthesis

So we can summarize by saying that the photosynthetic plantstrap solar energy to form ATP and NADPH (Light Phase) and thenuse these as the energy source to make carbohydrates and otherbiomolecules from carbon dioxide and water (Dark Phase),simultaneously releasing oxygen in to the atmosphere. Thechemoheterotrophic animals reverse this process by using theoxygen to degrade the energy-rich organic products ofphotosynthesis to CO2 and water in order to generate ATP fortheir own synthesis of biomolecules.