chemiosmotic hypothesis class 11 malayalam

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Chemiosmotic hypothesis

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Introduction

The chemiosmotic hypothesis is a widely accepted model. It describes how energy from electron transfer reactions is converted into ATP synthesis in living organisms. The hypothesis was first proposed by Peter Mitchell in 1961. It revolutionized our understanding of how cells generate ATP, the universal energy currency of living systems. This study note will explore the chemiosmotic hypothesis in detail.

Historical context

Before the chemiosmotic hypothesis, the prevailing theory for ATP synthesis was known as the “substrate-level phosphorylation” model. This model suggested that ATP was produced by directly transferring a phosphate group from a substrate molecule to ADP. However, experimental evidence did not fully support this model, and many scientists recognized that there must be an alternative mechanism for ATP synthesis.

In 1961, Peter Mitchell proposed the chemiosmotic hypothesis, which provided a new explanation for how ATP is synthesized in living systems. The hypothesis was initially met with skepticism, but as more evidence was accumulated, it gradually became accepted as a fundamental principle of bioenergetics.

Key components of the chemiosmotic hypothesis

The chemiosmotic hypothesis involves several key components, including electron transport chains, proton gradients, ATP synthase, and the mitochondrial inner membrane.

Electron transport chains

Electron transport chains are a series of membrane-bound proteins that transfer electrons from one molecule to another. In eukaryotic cells, electron transport chains are found in the inner mitochondrial membrane. In prokaryotic cells, they are located in the plasma membrane.

During electron transport, electrons are passed from one electron carrier to the next, releasing energy at each step. This energy is used to pump protons (H+) across the membrane, creating a proton gradient.

Proton gradients

Proton gradients are created when protons are pumped across a membrane, generating a difference in proton concentration (pH) and charge (electric potential) across the membrane. The chemiosmotic hypothesis proposes that this gradient can be used to generate ATP.

ATP synthase

ATP synthase is an enzyme complex that spans the mitochondrial inner membrane in eukaryotic cells. It consists of two major components: a proton channel, which allows protons to flow down their electrochemical gradient, and a catalytic domain, which synthesizes ATP from ADP and inorganic phosphate (Pi) using the energy from the proton gradient.

Mitochondrial inner membrane

The mitochondrial inner membrane is a highly impermeable membrane that separates the mitochondrial matrix from the intermembrane space. It contains electron transport chains and ATP synthase, which are the key components involved in the chemiosmotic hypothesis.

Mechanism of ATP synthesis

The chemiosmotic hypothesis proposes that ATP is synthesized when protons flow back across the mitochondrial inner membrane through the ATP synthase complex. This process is known as oxidative phosphorylation and can be divided into two main stages: electron transport and ATP synthesis.

Electron transport

During electron transport, electrons are passed from one electron carrier to the next, releasing energy at each step. This energy is used to pump protons across the mitochondrial inner membrane, creating a proton gradient. The proton gradient consists of a difference in proton concentration (pH) and charge (electric potential) across the membrane.

ATP synthesis

In the second stage of oxidative phosphorylation, protons flow back across the mitochondrial inner membrane through the ATP synthase complex. As the protons flow through the channel, they release energy. That energy is used to drive the synthesis of ATP from ADP and Pi. This process is known as chemiosmotic coupling, as it links the flow of protons down their electrochemical gradient to the synthesis of ATP.

Importance of the chemiosmotic hypothesis in cellular metabolism

The chemiosmotic hypothesis is a fundamental principle of bioenergetics and plays a crucial role in cellular metabolism. It explains how the energy stored in electron transfer reactions can be harnessed to generate ATP, the universal energy currency of living systems.

The chemiosmotic hypothesis is also relevant in the context of mitochondrial diseases. Mitochondria are the powerhouses of the cell. Disruptions to their function can lead to a range of diseases, including neurological disorders and muscle wasting. Many mitochondrial diseases are caused by defects in the electron transport chain or ATP synthase. And these highlight the importance of the chemiosmotic hypothesis in understanding these conditions.

The chemiosmotic hypothesis is a widely accepted model that describes how energy from electron transfer reactions is converted into ATP synthesis in living organisms. The hypothesis was first proposed by Peter Mitchell in 1961 and has since become a fundamental principle of bioenergetics. It involves several key components, including electron transport chains, proton gradients, ATP synthase, and the mitochondrial inner membrane. The chemiosmotic hypothesis is crucial for understanding how cells generate energy and how disruptions to this process can lead to disease.

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Chemiosmotic Hypothesis

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NCERT Solution

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• NCERT Solutions Chapter 11 of Class 11 Biology - Photosynthesis in Higher Plants
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• NCERT Solutions Class 11 Biology Chapter 15 Body Fluids and Circulation
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• NCERT Solutions for Class 11 Biology Chapter 17 Locomotion and Movement
• NCERT Solutions Class 11 Biology Chapter 18: Neural Control and Coordination
• NCERT Solutions for Class 11 Biology Chapter 19 - Chemical Coordination and Integration

The process through which a plant transforms light energy into chemical energy to produce food is known as photosynthesis . In the presence of chlorophyll, plants use water, carbon dioxide, and sunlight to make food or energy in the form of sugar, and as a by-product, they release oxygen. This suggests that light energy is used as a catalyst in chemical synthesis or reaction. Certain bacteria and prokaryotes also use this to prepare their food; it is not just for green plants. The chloroplast, a crucial organelle in green plants and algae that contains the pigment chlorophyll , is where synthesis occurs. The leaves, flowers, stems, sepals, and plastids all contain chlorophyll.

Chemiosmosis

Chemiosmosis refers to the process by which ions move over a semi-permeable membrane , such as the membrane within mitochondria . Molecules containing a net electric charge are called ions. Examples include the specialized usage of Na + , Cl – , and H + in chemiosmosis to generate energy. During chemiosmosis, ions move along an electrochemical gradient or a gradient of electrochemical potential (a form of potential energy). Chemiosmosis is a type of diffusion, and it causes ions to move from areas of high concentration to areas of low concentration across a membrane. Ions also move to balance the electric charge across a membrane.

The biological process by which ATP synthase produces ATP molecules is known as this process. An explanation of how energy molecules (ATP: Adenosine triphosphate) are produced during photosynthesis is provided by the Chemiosmotic theory, which was put forth by a British biochemist by the name of Peter Dennis Mitchell in 1961. Because of the improved understanding, it gave off the entire process of ATP generation within chloroplasts, his study was awarded the Nobel Prize. Nicotinamide adenine dinucleotide phosphate, often known as NADP or NADP + , is created with ATP during the light reaction or photochemical phase. These constitute the essential components of photosynthesis . They are used to produce sugar molecules throughout the dark reaction or Calvin cycle .

Chemiosmotic Hypothesis Process

The proton gradient that exists across the thylakoid membrane is what causes the ATP- Adenosine Triphosphates to be created in this process. The proton gradient, ATP synthase, and proton pump are important elements required for the chemiosmosis process. ATP synthase is the name of the enzyme that is necessary for the synthesis of ATP molecules. Two subunits designated F0 and F1, make up the enzyme ATP synthase. To move protons across the membrane, the F0 subunit is necessary. This alters the F1 subunit’s conformation, which activates enzymes . By adding a phosphate group to ADP, the enzyme phosphorylates it, turning it into ATP. Across the membrane, there is a proton gradient, which acts as ATP synthase’s main propulsion source.

Chlorophyll absorbs light with the aid of photosystems during the light response stage of photosynthesis. As a result, the water molecules split, releasing protons and electrons in the process. This is known as hydrolysis. The electron transport system carries the liberated electrons as they become energized and proceed to a higher energy level.

In the meantime, the stroma’s released protons start assembling inside the membrane. As a result, a proton gradient is produced, which is a by-product of the electron transport chain. Photosystem I use the few remaining protons to convert NADP+ to NADPH using electrons from the photolysis of water. The proton gradient eventually collapses, releasing energy and protons that are then transported back to the stroma by ATP synthase F0. ADP is converted to ATP by the ATP synthase when the F­1 conformation is altered by the resulting energy.

FAQs on Chemiosmosis Hypothesis

Question 1: What ion undergoes chemiosmosis as part of the production of ATP?

The process by which protons (H+) move down a proton gradient during cellular respiration is known as chemiosmosis. Adenosine diphosphate (ADP) and a phosphate group are joined by the enzyme ATP synthase as a result, creating ATP.

Question 2: What molecule is produced by chemiosmosis, and who proposed the chemiosmotic hypothesis?

ATP synthase’s role in the creation of ATP molecules naturally. The Chemiosmotic theory describes how energy molecules (ATP: adenosine triphosphate) are produced during photosynthesis and was put out by a British biochemist by the name of Peter Dennis Mitchell in 1961. He received the Nobel Prize for his contribution to the discovery of this idea.

Question 3: What cell organelle is capable of chemiosmosis?

During cellular respiration in the mitochondria and photosynthesis in the chloroplasts, chemiosmosis takes place. These two procedures both produce ATP.

Question 4: Exactly what does the chemiosmotic theory entail?

A British biochemist by the name of Peter Dennis Mitchell first put forth the chemiosmotic idea in 1961. The chemiosmotic theory proposes that energy is released through a series of oxidation-reduction events when electrons are transported through an electron transport system. This energy can be used by specific chain carriers to move hydrogen ions (H+ or protons) through a membrane.

Question 5: Where does chemiosmosis take place in the mitochondria?

Within the inner mitochondrial membrane. The efficiency of chemiosmosis is determined by the electron transport chain (ETC), which is situated in the inner mitochondrial membrane. A group of proteins known as the ETC cooperate and pass electrons back and forth like a hot potato. As ion pumps for hydrogen ions, the ETC contains three proteins.

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Photosynthesis and Chemiosmotic Hypothesis

Chemiosmotic hypothesis.

A chemiosmotic hypothesis is a biological process that was theorized in 1961 by a British biochemist known by the name Peter Dennis Mitchell. It is a process by which ATP molecules are produced through the action of ATP synthase. ATP is the abbreviation that is used for adenosine triphosphate. As theorized by Peter Dennis Mitchell, it is a process that describes the way in which the ATP molecules or the energy molecules are produced as a result of the process of photosynthesis. The biochemist was awarded the Nobel prize for his significant contributions to the field of Biology as his work provided a deeper insight into the entire process of the Chemiosmotic hypothesis.

NADP or Nicotinamide adenine dinucleotide phosphate (NADP+) is produced together with ATP throughout the light or photochemical reactions taking place during the process of photosynthesis. These are all the essential components involved in the process of photosynthesis. During the process, they are used for the dark reaction or in the Calvin Cycle for the production of sugar molecules, which is actually the final product.

What is Photosynthesis?

Photosynthesis is a technique used among the plant kingdom, algae and other bacteria to absorb energy obtained from exposure to sunlight and convert it into chemical energy.

(Image to be added soon)

What Happens During Photosynthesis?

The definition of photosynthesis describes it as the process which occurs in chloroplasts of green plants via photosynthetic pigments known as chlorophyll a, chlorophyll b, carotene, and xanthophyll. All green plants and trees and a few other autotrophic organisms utilize photosynthesis to produce nutrients utilizing carbon dioxide, water, and sunlight available. The products generated in the chemical reaction of photosynthesis are glucose and oxygen.

The process needs the green plants and trees to generate glucose, which can then be used by the plant to generate the chemicals needed for its growth. But it could also be deposited as starch and reconfigured into glucose whenever the plant needs energy. It could be used in the process of cellular respiration, thus, in turn, releasing the stored energy within molecules.

Chemiosmotic Hypothesis: The Process 

Throughout this procedure, ATP - Adenosine triphosphate molecules are generated as a result of the proton gradient that continues to exist around the thylakoid membrane. The essential components required for the chemiosmosis process are the ATP synthase proton gradient, and proton pump. The enzyme needed for the production of ATP molecules is known as ATP synthase.

The ATP synthase enzyme comprises 2 subunits, which include: F 0 and F 1 . The F 0 subunit is involved in the transfer of protons through all the membrane, which causes modifications in the F 1 configuration, and it leads to the activation of enzymes. The enzyme phosphorylates ADP converts ADP molecules into the ATP molecules. The gradient of the proton that exists across the membrane is the primary influence of the ATP synthase. 

In the light reaction step or light reaction phase of photosynthesis, chlorophyll, with the aid of photosystems, absorbs the light. It leads to the phenomenon of hydrolysis, in which the water molecules are separated, producing electrons and protons throughout the process. Released electrons are excited and travel to a higher level of energy and are transported by an electron transport system. Meanwhile, the protons released from the stroma begin to accumulate into the membrane. This process is what results in the production of the essential proton gradient, which is actually a product as a result of the functions carried out by the electron transport chain. 

The tiny quantity of the resultant protons is utilized by the photosystem to reduce NADP+ to NADPH by the electrons obtained from water photolysis. Ultimately, the proton gradient falls and releases heat, energy, and protons back to the stroma through the ATP synthase F 0 . This resulting energy causes alterations throughout the configuration of F-1, and this, in turn, stimulates the ATP synthase that transforms the ADP.

FAQs on Photosynthesis and Chemiosmotic Hypothesis

1. What is The Difference Between ATP and ADP?

Adenosine triphosphate (ATP) molecule is a nucleotide recognized in biology as the powerhouse of intracellular transfer of energy. It is capable of storing and transmitting chemical energy into the cells. In the process of nucleic acid synthesis, a major role is played by the ATP molecules. ATP captures the chemical energy generated through the breakdown of molecules of food and discharges it to support and boost other processes taking place within the cell.  

ADP is the abbreviation for adenosine diphosphate. It is not only amongst the most significant molecules of the body, but also one of the highest in number. It is an element of DNA and is very important for the contraction of muscles. It also promotes healing when a blood vessel is broken due to an injury.  Even with all these roles, the most important tole of ADP is during the process of conservation and release of energy within an organism.

2. What is Produced During Photosynthesis, and What is Photosynthesis in Biology? What are Anoxygenic and Oxygenic Bacteria?

The details of what is meant by photosynthesis are already mentioned above but let us now look at the process of photosynthesis through the chemical reactions that take place. 

The meaning of the word Phos is “light,” and the meaning of the word synthesis is “combining together.” 

The chemical reaction of photosynthesis can be written as follows: 

6H 2 O + 6CO 2   ------> 6O 2 + C 6 H 12 O 6   (glucose)

CO 2  = carbon dioxide H 2 O = water Light energy is required C 6 H 12 O 6  = glucose O 2  = oxygen

(Carbon dioxide) + (water) combine in the presence of sunlight to produce (glucose) + (oxygen) as products.

So, glucose and oxygen are produced as by-products as a result of the chemical reaction of photosynthesis in green plants. This is the answer to the question of what is produced during photosynthesis. 

Certain bacteria that do not perform photosynthesis will not generate oxygen as a by-product of the chemical reaction of photosynthesis. These types of bacteria are actually known as anoxygenic photosynthetic bacteria, as they do not generate oxygen. Bacteria that generate oxygen as a by-product of the chemical reaction of photosynthesis are known as oxygenic photosynthetic bacteria.

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Chemiosmotic Hypothesis – Class 11 | Chapter – 13 | Biology Short Notes Series PDF

• January 17, 2023

Chemiosmotic Hypothesis: The chemiosmotic hypothesis is a biological mechanism proposed in 1961 by a British biochemist  named Peter Dennis Mitchell.

• It is the mechanism by which  ATP  molecules are synthesised by the activity of  ATP  synthase.
• It is a process that describes how  ATP  molecules or energy molecules are formed as a result of the process of photosynthesis.
• The Nobel Prize in Chemistry was granted to the biochemist for his important contributions to the discipline of Biology, since his study gave a clearer understanding of the complete process of the Chemiosmotic hypothesis.

The Process of Chemiosmotic Hypothesis

The  proton  gradient that prevails across the thylakoid membrane causes  ATP: Adenosine triphosphates  to be generated throughout this process. Proton gradient, ATP synthase, and proton pump are three essential components for the chemiosmosis process. ATP synthase is the  enzyme  that is needed for the formation of ATP molecules.

F0 and F1 are the 2 subunits of the  ATP  synthase enzyme. The F0 subunit is implicated in proton transport across the membrane, which results in changes in F1 structure and  enzyme  activation. The enzyme phosphorylates ADP (adding a phosphate group) and transforms ADP to ATP. ATP synthase is primarily driven by the proton gradient that develops throughout the membrane.

Photosystems assist  chlorophyll  absorb  light  during the light response phase of photosynthesis. This causes  hydrolysis , in which water molecules are torn apart, releasing  electrons  and protons. The liberated electrons are energised and proceed to a higher energy level, where the electron transport system gives them away.

Meanwhile, the stroma’s discharged protons begin to accumulate within the membrane. As a result, a proton gradient is created, which is a product of the electron transport chain. Photosystem I use a little amount of the resulting protons to convert NADP+ to NADPH using electrons obtained from water photolysis. The proton gradient eventually collapses, releasing energy and protons that are transported back to the stroma via ATP synthase F0. The energy released causes changes in F1 conformation, which initiates the ATP synthase, which transforms ADP to ATP.

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Photosynthesis and Chemiosmotic Hypothesis – Definition and Process

Table of Contents

Chemiosmotic Hypothesis

The chemiosmotic hypothesis is a scientific theory that proposes that the energy used to create the proton gradient across the mitochondrial membrane is used to produce ATP. The chemiosmotic hypothesis was proposed by Peter Mitchell in 1961. The chemiosmotic hypothesis is a model that helps to explain how energy is transferred within cells. The model suggests that energy is transferred by means of a proton gradient that is created by the interaction of enzymes and ions. The proton gradient is then used to power the production of ATP, which is a molecule that provides energy to cells.

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What is Photosynthesis?

Photosynthesis is the process that produces organic molecules from simple inorganic molecules from the sun’s energy. Chloroplasts in photosynthesis use light energy to convert carbon dioxide and water into glucose and oxygen gas. The glucose is used by the plant to create energy rich molecules such as starch and sucrose which are used for growth. Oxygen gas is a byproduct of photosynthesis and is released into the atmosphere.

What Happens During Photosynthesis?

In photosynthesis, light energy is converted into useful chemical energy in the form of glucose. This process occurs in the chloroplasts of photosynthetic cells.

The light energy liberates electrons from water molecules, which combine with CO 2 to form O2 in photosynthesis.

Chemiosmotic Hypothesis: The Process of Respiration

The chemiosmotic hypothesis is a theory that explains the process of respiration. The theory states that respiration is driven by the transfer of energy from organic molecules to inorganic molecules. This energy is transferred through the creation of a proton gradient across a membrane. The proton gradient is created by the movement of protons through ATP synthase, a protein that is embedded in the membrane. The energy stored in the proton gradient is used to create ATP, the energy currency of the cell.

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• MCQ on Chemiosmotic Hypothesis

MCQs on Chemiosmotic Hypothesis

The chemiosmotic hypothesis explains the synthesis of ATPs driven by proton gradient present across the membranes of mitochondria during respiration and thylakoid membranes during photosynthesis. Peter Mitchell proposed this hypothesis of ATP synthesis. ATP synthesis is coupled with the electron transport chain and generation of the proton gradient. He explained that if there is some other mechanism to generate pH gradient then electron transport is not necessary.

1. Proton concentration is highest in which part of the chloroplast?

(b) Intermembrane space

(c) Lumen of thylakoids

(d) Antennae complex

Answer: (c)

2. Cyclic photophosphorylation is associated with the production of

(d) All of the above

Answer: (a)

3. During cellular respiration, chemiosmosis occurs in

(a) Chloroplast

(b) Mitochondria

(c) Peroxisome

(d) Nucleoplasm

Answer: (b)

4. Which of the following is necessary for chemiosmosis?

(a) Proton gradient

(b) Membrane

(c) Proton pump

Answer: (d)

5. Which of the following processes is responsible for generating a proton gradient across the thylakoid membrane?

(a) Proton carrier transport H + from stroma to lumen

(b) Splitting of water on the inner side of the membrane

(c) NADP reductase enzyme present at the stroma side, removes proton by reducing NADP +

6. Proton concentration is highest in which part of the mitochondria?

(b) Inner membrane

(c) Outer membrane

(d) Intermembrane space

7. Which part of ATP synthase forms the transmembrane channel?

(d) None of the above

8. The ATP synthesised by ATP synthase present in the thylakoid membrane is released towards

(c) inner membrane

(d) outer membrane

9. ATP synthesis by ATP synthase is driven by the movement of

(a) protons

(c) electrons

10. Who proposed the chemiosmotic hypothesis of ATP synthesis?

(a) Francis Crick

(b) H G Khorana

(c) Peter Mitchell

(d) J D Watson

These were some MCQs on Chemiosmotic Hypothesis. Learn MCQs on related topics for NEET , at BYJU’S.

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