High energy compounds involved in light reaction b.

Glycerate 3-phosphate is reduced during the reduction reactions to a three-carbon sugar called triose phosphate. Energy and hydrogen is needed for the reduction and these are supplied by ATP and NADPH + H+ (both produced during light-dependent reactions) respectively. Two triose phosphate molecules can then react together to form glucose phosphate. The condensation of many molecules of glucose phosphate forms starch which is the form of carbohydrate stored in plants. However, out of six triose phosphates produced during the reduction reactions, only one will be used to synthesise glucose phosphate. The five remaining triose phosphates will be used to regenerate RuBP.

ATP and NADPH are formed during the light reactions 6.

Photosynthesis consists of light-dependent and light-independent reactions.

of the Calvin cycle, light-independent reactions are ..

These two stages of photosynthesis are known as the (the photo part of photosynthesis) and the (the synthesis part) (FIGURE 10-4).

of light-independent reactions of photosynthesis.

use sunlight as a source of energy and through the process of photosynthesis, reduce carbon dioxide to form carbohydrates such as glucose. The radient energy is converted to the chemical bond energy within glucose and other organic molecules.

Light reactions (light dependent reactions) - in grana of chloroplasts

Stages of Photosynthesis | The Light Reactions

1. To begin the Calvin cycle, a molecule of CO2 reacts with a five-carbon compound called ribulose bisphosphate (RuBP) producing an unstable six-carbon intermediate which immediately breaks down into two molecules of the three-carbon compound phosphoglycerate (PGA). The carbon that was a part of inorganic CO2 is now part of the carbon skeleton of an organic molecule. The enzyme for this reaction is ribulose bisphosphate carboxylase or Rubisco. A total of six molecules of CO2 must be fixed this way in order to produce one molecule of the six-carbon sugar glucose.

in the light-independent reactions

2. The energy from ATP and the reducing power of NADPH (both produced during the light-dependent reactions) is now used to convert the molecules of PGA to glyceraldehyde-3-phosphate (G3P), another three-carbon compound. For every six molecules of CO2 that enter the Calvin cycle, two molecules of G3P are produced. Most of the G3P produced during the Calvin cycle - 10 of every 12 G3P produced - are used to regenerate the RuBP in order for the cycle to continue. Some of the molecules of G3P, however, are used to synthesize glucose and other organic molecules. Two molecules of the three-carbon G3P can be used to synthesize one molecule of the six-carbon sugar glucose. The G3P is also used to synthesize the other organic molecules required by photoautotrophs.

Light energy is absorbed by pigments and drives the reactions of photosynthesis 5.

Photosynthesis - California Polytechnic State University

Photophosphorylation is the production of ATP using the energy of sunlight. Photophosphorylation is made possible as a result of chemiosmosis. Chemiosmosis is the movement of ions across a selectively permeable membrane, down their concentration gradient. During photosynthesis, light is absorbed by chlorophyll molecules. Electrons within these molecules are then raised to a higher energy state. These electrons then travel through Photosystem II, a chain of electron carriers and Photosystem I. As the electrons travel through the chain of electron carriers, they release energy. This energy is used to pump hydrogen ions across the thylakoid membrane and into the space within the thylakoid. A concentration gradient of hydrogen ions forms within this space. These then move back across the thylakoid membrane, down their concentration gradient through ATP synthase. ATP synthase uses the energy released from the movement of hydrogen ions down their concentration gradient to synthesise ATP from ADP and inorganic phosphate.

In this cycle the end products of the light-dependent reaction are used.

Light-independent reactions - Wikipedia

To begin the Calvin cycle, a molecule of CO2 reacts with a five-carbon compound called ribulose bisphosphate (RuBP) producing an unstable six-carbon intermediate which immediately breaks down into two molecules of the three-carbon compound phosphoglycerate (PGA) (see Fig. 1). The carbon that was a part of inorganic CO2 is now part of the carbon skeleton of an organic molecule. The enzyme for this reaction is ribulose bisphosphate carboxylase or Rubisco. A total of six molecules of CO2 must be fixed this way in order to produce one molecule of the six-carbon sugar glucose.

The reducing power is provided by NADPH, which acquired energized electrons in the light reactions.

Photosynthesis occurs in two stages in a cell

Light reactions occur in the grana
Dark reactions occur in the stroma : An essay on the significance of photosynthesis on livingorganism, especially humans
from Newton's Apple
:An excellent review
: Advanced information

: Detailed but most useful
: Detailed but most useful


Last revised :Aug 11, 1998, Straney