Introduction

In 1961, British Biochemist Peter Dennis Mitchell coined the term chemiosmotic hypothesis. This is a biological process that explains the ATP synthesis by photosynthesis in the chloroplast. In this process, ATP and NADP both are generated by pght reactions and used as a key component of dark reactions to produce the final product i.e., glucose by photosynthesis.

According to the hypothesis, ATP develops as a result of the proton gradient created in the thylakoid membrane. Proton pumps and ATP synthase are also important. The enzyme ATP synthase has two subunits- F⁰ and F¹. When F¹ activates the enzyme, it changes its configuration and the F⁰ acts as a transmembrane channel. The complex phosphorylates the ADP into ATP.

What is Photosynthesis?

Photosynthesis is a physiological and photochemical process used by various groups of plants, algae, and cyanobacteria by absorbing pght energy, and carbon dioxide and converting them to chemical energy producing glucose, oxygen, and water as final products.

$$mathrm{6CO_{2}+6H_{2}O ightarrow C_{6}H_{12}O_{6}+6O_{2}}$$

Image Coming soon

Features of Photosynthesis

It takes place in the chloroplast of plants and produces food and energy to survive.

They are the autotrophs and the ideal primary producers of our ecosystem.

The mesophyll tissue of the leaves that contains chloroplast having chlorophyll-containing disc-shaped thylakoid configurations.

Uses sunpght, water, and carbon dioxide as raw materials.

Produces oxygen and glucose by converting the pght energy to chemical energy.

Stores energy as ATP during pght reaction.

Runs Calvin cycle in stroma using the end products i.e., glucose.

Image Coming soon

What Happens During Photosynthesis?

Plants have the pigments pke carotene, chlorophyll a, chlorophyll b, xanthophylls, etc., which lead to photosynthesis in the thylakoid lumen of the chloroplast.

Autotrophic organisms are able to photosynthesize by using carbon dioxide, water, and sunpght and produce glucose and oxygen by the photochemical reaction.

These products are further used by the plant or by other autotrophic organism to produce the necessary metaboptes, enzymes, hormones, and other factors needed for their growth.

They can be stored in the form of carbohydrates or starch and reconfigured into glucose when needed.

This reconstructed glucose can be used in cellular respiration and releases the stored energy.

Chemiosmotic Hypothesis: The Process

This theory possesses that glucose metabopzes energy-rich factor acetyl CoA as a byproduct. The mitochondrial matrix oxidized the acetyl CoA and was associated with the reduced version of NAD and FAD. These carrier molecules transport the electron to the electron transport system present in the inner mitochondrial membrane. Then the proteins of the electron transport chain are suppped. The electron energies to pump out the proton from the inner mitochondrial membrane matrix. It stores energy as a transmembrane electrochemical gradient. The ATP synthase helps to return the proton to the inner membrane and bear the proton flow across the matrix. They accumulate the energy to phosphorylate or integrate the ADP and inorganic phosphate to develop ATP.

Image Coming soon

Procedure

The main components are proton gradient, proton pump, ATP synthase, and carrier molecules pke FAD and NAD.

The subunits (F⁰ and F¹) of the enzyme ATP synthase involve proton transfer all over the membrane modifying the F¹ pattern to activate the enzyme respectively.

The enzyme phosphorylates ADP to develop ATP.

In autotrophic organisms, mainly in plants, chlorophyll absorbs sunpght with the help of photosystems during pght reactions.

The electrons and the protons formed by the hydrolysis get excited and jump to a higher energy level.

The electron transport system transports the electrons whereas the hydrogen ions that are released from the stroma get accumulated inside the membrane and develop a proton gradient by the electron transport chain.

Photosystem I uses some protons for the reduction of NADP+ to NADPH by the electrons gained from the photolysis of the water.

After the collapse, the proton gradient emits energy, heat, and protons.

The F⁰ carries the proton back to the stroma via the transmembrane channel.

The emitted energy changes the F¹ configuration and targets the ATP synthase.

Hence, the enzyme converts the ADP to ATP.

Conclusion

Plants and other autotrophic organisms that bear chlorophyll are able to photosynthesize. They absorb sunpght, water, and carbon dioxide and convert them to glucose and oxygen by some photochemical reactions associated with the photosystems, pigments, and other complexes. In this procedure, the water sppts to develop H+ and OH-. The electrons get excited and go to higher energy levels and protons integrate to form a proton gradient in the mitochondrial membrane by ETC. Some protons manipulate the NADP+ to NADPH. The proton gradient then falls and releases heat, energy, and protons that are carried back to the stroma by the F⁰ transmembrane channel and transform the F¹ configuration by stimulating the ATP synthase and switching to ATP by ADP phosphorylation.

FAQs

Q1. What is a pght-harvesting complex?

Ans. Light-harvesting complex also known as antenna complex is a collection of membrane-associated proteins and photosensitive pigments i.e., chlorophyll a, b, carotenoids, etc., implanted on the thylakoid membrane of the chloroplast. It transfers pght energy to the pigment molecule at the reaction center of the photosystem.

Q2. State the wavelength absorbing capacity of the photosystems.

Ans. The photosystems are of two types- photosystem I and II. Photosystem I is found at the outer membrane of the thylakoid of the grana and stroma lamellae whereas photosystem II locates in the inner grana membrane. The PS-I absorbs >680, probably 700 nm whilst the PS-II absorbs ≤ 680nm.

Q3. Define reaction center.

Ans. It is a complex integration of several pigments, proteins, and co-factors to execute the reaction of primary energy conversion by photosynthesis.

Q4. How antenna complex plays a vital role in noncycpc phosphorylation?

Ans. In the pght-dependent reaction of noncycpc phosphorylation, the pigment molecule of the photosystem II antenna complex absorbs the photon. The primary electron acceptor of the photosystem II electron transport chain picks up the energized electron from the reaction center.

Q5. How much ATP is generated by the NADH in the electron transport chain? State the process.

Ans.

NADH passes the electron to pump the proton in the complex.

It passes the electron to complex I and pumps 4 protons.

Then to complex III to pump 4 protons again.

Lastly it passes the electron to complex IV and pumps 2 protons. A total of 10 protons in a cycle are transported to intermembrane space from the matrix.

4 protons can stimulate the ATP synthase to convert ADP by phosphorylation and produce 1 ATP.

So, for NADH= 10/4 = 2.5 ATP/ NADH produced.