ATP synthesis in plants | The procedure of formation of ATP in plants. | Dr MALIK |

ATP synthesis in plants 

 ATP (the adenosine tri-phosphate) is formed in the light reaction of photosynthesis through ADP (adenosine diphosphate) by the process of phosphorylation.

ATP can be formed by three methods:

1. Direct synthesis
2. Photo phosphorylation
3. Oxidative phosphorylation

In plants, the photophosphorylation process can be seen. It occurs in the chloroplast of a plant’s cell.

We must fulfill four conditions for the process of photophosphorylation. These conditions are:

1. The number of hydrogen ions between the inner side of the thylakoid and the outer side of the thylakoid must have a great difference.
2. Hydrogen ions cannot pass from the membrane of the thylakoid freely.
3. Hydrogen ions must pass through special channels called F not channels.
4. There must be a proton pump, that pushes hydrogen ions inside the thylakoid membrane, as they pass out from special channels. 

The procedure of formation of ATP in plants.

• ATP is formed in the chloroplast of the plant’s cell.
• Chloroplast has thylakoids that are involved in the process of photosynthesis.
• The inner side of the thylakoid can be said as lumen while the outer side is the stroma that is part of the chloroplast.
• We must have hydrogen ions concentration more in the lumen and lower in the stroma.
• This difference in the concentration helps in the movement of hydrogen ions, which is very important for the synthesis of ATP.
• On the membrane of the thylakoid, a special structure of channels is formed, which is called F not.
• On the outer side of this channel, a head-like structure appears which is called F1. This head-like structure is moveable.
• Both f not and f1 form a structure that we call ATP synthase.
• Hydrogen ions move out through these special channels and this movement of hydrogen ions moves to F1. When F1 is moved, it will produce ATP.
• ADP molecules are attached to ATP synthase and when a proton is passed through it, the ATP synthase shows some movement. When it moves, a phosphate group is combined with ADP and forms an ATP molecule.

Now, the question is how the concentration of hydrogen ions increases in the lumen.

The concentration of hydrogen ions can be maintained in three ways:

1. Increase the number of hydrogen ions in the lumen.
2. Decrease the number of hydrogen ions in the stroma.
3. Move the hydrogen ion inside the lumen.

Now, how these three conditions can be satisfied?

• The first condition increases the number of hydrogen ions inside the lumen can be satisfied through the process of photolysis. We learn in the light reaction of photosynthesis that photolysis is the breakdown of water in the presence of light and it occurs in photosystem 2.
• If the process of photolysis occurs inside the lumen then the first condition will be satisfied and the number of hydrogen ions inside the lumen will be increased because when a molecule of water breaks, it releases hydrogen ions plus oxygen.

Now, we are going to satisfy the second condition which is to decrease the number of hydrogen ions in the stroma.

• We also learn in the light reaction of photosynthesis that NADP+ uses hydrogen ions and electrons to make NADPH.
• If NADP uses hydrogen ions from the stroma then the second condition will also be completed and the number of hydrogen ions in the stroma is reduced.

• Now the third and last condition to move hydrogen ions inside the lumen is satisfied when an electron moves from photosystem 2 to photosystem 1 through the electron transport chain, then it pushes a hydrogen ion inside the lumen. This is done by a hydrogen carrier that is plasto quinine and we learn in light reaction of photosynthesis that plasto quinine takes an electron from the primary acceptor. Plastic quinine (Pq) pushes a hydrogen ion inside the lumen when it is passing its electron to cytochrome.

In this way, the concentration of hydrogen ions is increased inside the lumen.
But the point to be remembered is that our main goal is to make a difference in the concentration of hydrogen ions between the lumen and stroma, not to make higher numbers of hydrogen ions in the lumen. But the concentration of hydrogen ions in the lumen is also very essential because it runs a proton pump.

 

Once all the conditions are fully satisfied, the synthesis of ATP is started from ATP synthase.

This ATP is used in the dark reaction of photosynthesis.

Related Articles.

Light reaction of photosynthesis

The dark reaction of photosynthesis