8.3 Cellular Respiration
3 min read•june 18, 2024
Cellular respiration is the powerhouse of energy production in living cells. It's a complex process that involves breaking down nutrients to generate ATP, the energy currency of life. The plays a crucial role in this process.
At its core, cellular respiration is all about harvesting energy from food molecules. Through a series of chemical reactions, cells convert glucose and other nutrients into usable energy, powering everything from muscle contractions to brain function.
Electron Transport and Energy Production
Electron transport system in cells
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- Function of the
- Generates a across a membrane by pumping protons (H+) from the matrix to the intermembrane space
- Drives ATP synthesis through by harnessing the energy of the proton gradient
- Location of the ETS
- Prokaryotic cells (bacteria)
- Embedded in the cytoplasmic membrane as part of the cell membrane
- Eukaryotic cells (animals, plants, fungi)
- Embedded in the inner mitochondrial membrane as part of the
- Prokaryotic cells (bacteria)
Substrate-level vs oxidative phosphorylation
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- ATP is generated directly by the transfer of a phosphate group from a high-energy intermediate (such as or ) to ADP
- Occurs during (cytoplasm) and the (mitochondrial matrix)
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- ATP is generated indirectly through the ETS and by utilizing the energy of the proton gradient
- Requires oxygen as the final electron acceptor to generate the proton gradient
- Produces the majority of ATP (34 out of 38 ATP) in
- Utilizes electron carriers like NADH and FADH2 to transfer electrons to the ETS
Chemiosmosis and proton motive force
- Chemiosmosis
- The process by which ATP is generated using the energy of a proton gradient established by the ETS
- Protons flow down their concentration gradient through , driving the synthesis of ATP
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- The combination of the proton concentration gradient (pH gradient) and the electrical potential difference (membrane potential) across a membrane
- Drives protons through , enabling ATP production by providing the necessary energy
ATP synthase in cellular respiration
- Role of ATP synthase
- Catalyzes the synthesis of ATP from ADP and inorganic phosphate (Pi) by harnessing the energy of the proton gradient
- Utilizes the proton gradient generated by the ETS to drive the rotation of its subunits and facilitate ATP synthesis
- Placement of ATP synthase
- Prokaryotic cells (bacteria)
- Embedded in the cytoplasmic membrane, associated with the ETS components
- Eukaryotic cells (animals, plants, fungi)
- Embedded in the inner mitochondrial membrane, associated with the ETS components in the cristae
- Prokaryotic cells (bacteria)
Aerobic and Anaerobic Respiration
Aerobic vs anaerobic respiration
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- Utilizes oxygen (O2) as the final electron acceptor in the ETS
- Includes glycolysis (cytoplasm), Krebs cycle (mitochondrial matrix), and (inner mitochondrial membrane)
- Produces the most ATP per molecule of glucose ( ATP) due to the efficiency of the ETS and oxidative phosphorylation
-
- Uses alternative final electron acceptors, such as nitrate (NO3-), sulfate (SO42-), or fumarate, in the absence of oxygen
- Includes glycolysis (cytoplasm) and or alternative electron transport chains (cytoplasmic membrane)
- Produces less ATP than aerobic respiration due to the lower energy yield of alternative electron acceptors
- Fermentation
- A type of that regenerates NAD+ without an electron transport chain by using organic compounds as electron acceptors
- Examples include (lactate as the final product) and (ethanol and CO2 as the final products)
Key metabolic intermediates in cellular respiration
- : The end product of glycolysis, which enters the mitochondria for further oxidation in aerobic respiration
- : Formed from pyruvate, it enters the Krebs cycle (also known as the cycle) for complete oxidation
- Citric acid: The first compound formed in the Krebs cycle, from which subsequent reactions produce reduced electron carriers and CO2
Key Terms to Review (35)
1,3-bisphosphoglycerate: 1,3-bisphosphoglycerate is a key intermediate in the glycolysis pathway, which is the first stage of cellular respiration. It is an important high-energy compound that links the energy-releasing reactions of glycolysis to the energy-storing reactions of the citric acid cycle and electron transport chain.
Acetyl-CoA: Acetyl-CoA is a crucial metabolic intermediate that serves as a central hub, linking the catabolism of carbohydrates, lipids, and proteins to the cellular respiration process. It is the primary entry point for the citric acid cycle, also known as the Krebs cycle, which is the final common pathway for the oxidation of these macromolecules to generate energy in the form of ATP.
Aerobic respiration: Aerobic respiration is a metabolic process in which cells convert glucose and oxygen into energy, carbon dioxide, and water. It occurs in the mitochondria of eukaryotic cells.
Aerobic Respiration: Aerobic respiration is a metabolic process that utilizes oxygen to efficiently convert the chemical energy stored in organic molecules, such as glucose, into adenosine triphosphate (ATP), the primary energy currency of the cell. This process is a key component of cellular respiration and is essential for the survival and growth of aerobic organisms.
Anaerobic respiration: Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen, using other electron acceptors to produce energy. This process is essential for certain microorganisms in oxygen-depleted environments.
Anaerobic Respiration: Anaerobic respiration is a metabolic process that produces energy without the use of oxygen. It is an alternative pathway for energy production in organisms that can occur when oxygen is limited or unavailable, in contrast to the more efficient aerobic respiration.
ATP synthase: ATP synthase is an enzyme that synthesizes adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate during cellular respiration. It is located in the inner mitochondrial membrane in eukaryotes and the plasma membrane of prokaryotes.
ATP Synthase: ATP synthase is a large enzyme complex that is responsible for the final step of cellular respiration, the production of ATP, the primary energy currency of the cell. It is located in the inner membrane of mitochondria and uses the electrochemical gradient generated by the electron transport chain to drive the synthesis of ATP from ADP and inorganic phosphate.
Chemiosmosis: Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient. In cellular respiration, it is crucial for ATP synthesis in the mitochondria.
Chemiosmosis: Chemiosmosis is a key process in cellular respiration and other environmental conditions that affect microbial growth. It is the movement of protons (H+ ions) across a selectively permeable membrane, down their electrochemical gradient, to drive the synthesis of ATP, the energy currency of the cell.
Citric Acid: Citric acid is a weak organic acid found naturally in citrus fruits, such as lemons, limes, and oranges. It is a key compound in the citric acid cycle, a central metabolic pathway in cellular respiration that generates energy for the cell.
Cytochrome: Cytochrome is a class of heme-containing proteins involved in electron transport and redox reactions. They play a crucial role in the electron transport chain during cellular respiration.
Cytochrome oxidase: Cytochrome oxidase is an enzyme found in the mitochondria that plays a key role in the electron transport chain by facilitating the transfer of electrons to oxygen. This process is crucial for the production of ATP during cellular respiration.
Electron Transport System: The electron transport system, also known as the respiratory chain, is a series of protein complexes embedded in the inner membrane of mitochondria that are responsible for the final stages of cellular respiration. It is the process by which electrons are passed through a series of redox reactions, generating a proton gradient that drives the synthesis of ATP, the primary energy currency of the cell.
Electron transport system (ETS): The electron transport system (ETS) is a series of protein complexes located in the inner mitochondrial membrane that transfer electrons through redox reactions. This process helps generate a proton gradient that drives ATP synthesis.
Ethanol Fermentation: Ethanol fermentation is a metabolic process in which glucose is converted into ethanol and carbon dioxide by certain microorganisms, such as yeast, in the absence of oxygen. This anaerobic process is a crucial part of cellular respiration and is widely used in various industries, including the production of alcoholic beverages and biofuels.
FAD/FADH2: FAD (Flavin Adenine Dinucleotide) and FADH2 (Reduced Flavin Adenine Dinucleotide) are important cofactors involved in cellular respiration, a series of metabolic processes that convert the chemical energy stored in nutrients into ATP, the universal energy currency of the cell.
Fermentation: Fermentation is a metabolic process in which an organism converts carbohydrates, such as sugars, into acids, gases, or alcohol. It is a crucial biological process that has been utilized by our ancestors for centuries and continues to play a vital role in various aspects of microbiology, from the production of food and beverages to the generation of energy in certain microorganisms.
The term 'fermentation' connects to the topics of 1.1 What Our Ancestors Knew, 1.3 Types of Microorganisms, 4.1 Prokaryote Habitats, Relationships, and Microbiomes, 8.2 Catabolism of Carbohydrates, 8.3 Cellular Respiration, 8.4 Fermentation, and 9.2 Oxygen Requirements for Microbial Growth, as it represents an ancient and widely-employed metabolic strategy employed by diverse microorganisms to derive energy from organic compounds in the absence of oxygen or under limited oxygen conditions.
Flavoprotein: Flavoproteins are a group of proteins that contain a nucleic acid derivative of riboflavin, such as FAD or FMN, and play crucial roles in redox reactions. They are essential in the electron transport chain and various other metabolic pathways.
Glycolysis: Glycolysis is the metabolic pathway that converts glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound. This process is the first stage of cellular respiration and occurs in the cytoplasm of cells, providing a crucial source of energy for the cell.
Iron-sulfur protein: Iron-sulfur proteins are a group of proteins that contain iron-sulfur clusters and play crucial roles in electron transfer processes within cellular respiration. These proteins are essential in the electron transport chain, facilitating the transfer of electrons between different molecules.
Krebs Cycle: The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is a key part of cellular respiration, which is the process of converting the chemical energy stored in organic molecules, such as glucose, into a form that can be used by the cell, known as adenosine triphosphate (ATP).
Lactic Acid Fermentation: Lactic acid fermentation is a metabolic process in which glucose or other sugars are converted into lactic acid as the end product, typically occurring in the absence of oxygen. This anaerobic process is an important part of cellular respiration and is commonly observed in certain bacteria and in the muscle cells of animals.
Mitochondrial Cristae: Mitochondrial cristae are the internal folds or invaginations of the inner membrane of a mitochondrion. These specialized structures are critical for the process of cellular respiration, as they provide a large surface area for the enzymes and proteins involved in the electron transport chain and ATP synthesis.
Oxidative phosphorylation: Oxidative phosphorylation is the process by which cells generate ATP through the electron transport chain and chemiosmosis in the mitochondria. It is the final stage of cellular respiration, involving oxygen as the final electron acceptor.
Oxidative Phosphorylation: Oxidative phosphorylation is the process by which cells use enzymes and electron transport chains to generate large amounts of adenosine triphosphate (ATP) from the oxidation of nutrients, primarily glucose. It is a crucial component of cellular respiration and the final stage of carbohydrate catabolism.
Phosphoenolpyruvate: Phosphoenolpyruvate (PEP) is a key intermediate in the glycolytic pathway, the first stage of cellular respiration. It is a high-energy phosphate compound that serves as a crucial link between carbohydrate metabolism and energy production within the cell.
Proton Gradient: A proton gradient is a difference in the concentration of hydrogen ions (protons) across a membrane, typically the inner membrane of a mitochondrion or the thylakoid membrane of a chloroplast. This gradient is an essential component of the chemiosmotic process, which is the primary mechanism of ATP synthesis in cellular respiration and photosynthesis.
Proton motive force: Proton motive force (PMF) is the potential energy stored across a membrane due to the difference in proton concentration and electrical charge. It is essential for ATP synthesis during cellular respiration.
Proton Motive Force: Proton motive force (PMF) is a fundamental concept in cellular respiration that describes the electrochemical gradient of protons (H+ ions) across a membrane, which drives the synthesis of ATP through the process of chemiosmosis. This gradient is established by the transport of protons across the membrane during the electron transport chain, creating a proton-motive force that powers the ATP synthase enzyme.
Pseudomonas aeruginosa: Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that can cause serious infections in humans. It is known for its resistance to antibiotics and ability to thrive in various environments.
Pyruvate: Pyruvate is a key metabolic intermediate produced during the breakdown of glucose and other carbohydrates. It serves as a central molecule in several important cellular processes, including cellular respiration and fermentation.
Quinone: Quinone is a class of organic compounds that play a crucial role as electron carriers in cellular respiration. They are essential for the electron transport chain, especially within the mitochondria and certain bacteria.
Redox potential: Redox potential, also known as oxidation-reduction potential (ORP), measures the tendency of a chemical species to acquire electrons and thereby be reduced. It is expressed in volts (V) or millivolts (mV).
Substrate-Level Phosphorylation: Substrate-level phosphorylation is a metabolic process in which the energy released from a chemical reaction is used to directly transfer a phosphate group to a molecule, resulting in the production of ATP without the involvement of the electron transport chain or oxidative phosphorylation. This process is a key step in both cellular respiration and fermentation pathways.