Cellular Respiration Intelligent Design by Owen Borville August 19, 2024 Lesson 7
Redox Reactions: Oxidation-Reduction reactions involve taking an electron or electrons from one compound and transferring them to another compound. These reactions help power energy conversions within cells. The move of an electron from one compound to another compound removes some potential energy from the first compound, the oxidized compound, and increases potential energy of the second compound, the reduced compound.
Electron carriers are compounds that act as electron shuttles along biochemical pathways.
RH (Reducing Agent) + NAD+(Oxidizing Agent) => NADH (Reduced) + R (Oxidized)
ATP Adenosine Triphosphate allows cells to use and store energy safely. ATP releases energy usually by removing a phosphate group from its structure.
ATP is one molecule of adenine bonded to a ribose molecule, a 5-carbon sugar found in RNA, and two more phosphate group molecules.
Dephosphorylation is the release of a phosphate group which releases energy.
Hydrolysis is the process of breaking complex macromolecules apart. ATP is continuously broken down to ADP (adenosine diphosphate) to perform life processes and water is split by hydrolysis. ATP is continuously regenerated by adding a phosphate back. These processes require energy and is provided by the metabolism of sugars.
Phosphorylation is the addition of a high energy phosphate to a compound.
Substrate-level Phosphorylation is the production of ATP from ADP using excess energy from a chemical reaction and a phosphate group from a reactant. (producing adenosine triphosphate ATP from adenosine diphosphate ADP by adding a phosphate group)
Chemiosmosis is a process in which there is a production of adenosine triphosphate (ATP) in cellular metabolism by the involvement of a proton gradient across a membrane
Oxidative Phosphorylation is the production of ATP using the process of chemiosmosis in the presence of oxygen; occurs in mitochondria in eukaryotes; occurs in plasma membrane in prokaryotes
Glycolysis is the process of breaking glucose down into two three-carbon molecules with the production of ATP and NADH. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. Glycolysis is anerobic, because it does not use oxygen directly. Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. GLUT Proteins are integral membrane proteins that transport glucose. Glucose is also transported by secondary active transport against the glucose concentration gradient. Glycolysis begins with the six-carbon ring shaped structure of a glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate.
Pyruvate is a three-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citric acid cycle under aerobic conditions, and the end product is glycolysis. There are two distinct parts of glycolysis: the first part splits the glucose molecule (energy-requiring steps) and the second part (energy-releasing steps) extracts and stores energy from the glucose molecules.
Glycolysis Steps First Half:
Step 1: Phosphorylation of 6-carbon sugar, catalyzed by the enzyme hexokinase using ATP, and produces glucose-6 phosphate
Step 2: An isomerase converts glucose-6 phosphate into its isomer fructose-6 phosphate (compound with same formula but different atomic arrangement and properties). Isomerase is an enzyme that converts a molecule into its isomer.
Step 3: Phosphorylation of fructose-6 phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6 phosphate, producing fructose-1, 6 bisphosphate.
Step 4: The enzyme aldolase to convert fructose-1, 6 bisphosphate into two 3-carbon isomers : dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
Step 5: An isomerase transforms dihydroxyacetone phosphate into its isomer, glyceraldehyde-3-phosphate.
Glycolysis Steps Second Half:
Step 6: Oxidation of glyceraldehyde-3-phosphate; Glyceraldehyde-3-phosphate dehydrogenase dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-bisphosphoglycerate.
Step 7: Catalyst enzyme (isomerase) phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP molecule and 3-phosphoglycerate (the isomer)
Step 8: The enzyme phosphoglycerate mutase relocates the remaining phosphate group from 3-phosphoglycerate from the 3rd carbon to the 2nd carbon to form 2-phosphoglycerate.
Step 9: The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvate acid (PEP).
Step 10: The enzyme pyruvate kinase transfers a phosphate group from phosphoenolpyruvate (PEP) to ADP to form pyruvic acid and ATP molecule.
Aerobic respiration is the process in which organisms convert energy in the presence of oxygen.
Oxidation and Breakdown of Pyruvate and the Citric Acid Cycle
Pyruvate is converted to an acetyl group that will be activated by coenzyme CoA, creating acetyl CoA.
Step 1: A carboxyl group is removed from pyruvate, releasing a carbon dioxide. A 2 carbon hydroxyethyl group is created.
Step 2: The hydroxylethyl group is oxidized into an acetyl group, and the electrons are taken by NAD+, forming NADH.
Step 3: The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA.
Acetyl CoA to CO2
With oxygen, acetyl COA sends its acetyl group (2C) group to a 4 carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with 3 carboxyl groups. This process is called the Citric Acid Cycle, the TCA Cycle (tricarboxylic acids), and the Krebs Cycle, after Hans Krebs, who first identified the steps in the cycle.
Citric Acid Cycle Steps: After pyruvic acid is converted to acetyl CoA,
Step 1: This condensation step combines the two-carbon acetyl group with a four-carbon oxaloacetate molecule to form a six-carbon molecule of citrate.
Step 2: Citrate loses one water molecule and gains another as citrate is converted into its isomer, isocitrate.
Step 3: Isocitrate is oxidized, producing a five-carbon molecule, α-ketoglutarate, along with a molecule of CO2 and two electrons, which reduce NAD+ to NADH.
Step 4: A succinyl group is the product of step four. CoA binds with the succinyl group to form succinyl CoA. The enzyme that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.
Step 5: A carboxyl group is substituted for coenzyme A, and a high-energy bond is formed. This energy is used in substrate-level phosphorylation (during the conversion of the succinyl group to succinate) to form either guanosine triphosphate (GTP) or ATP.
Step 6: is a dehydrogenation process that converts succinate into fumarate. Two hydrogen atoms are transferred to FAD, reducing it to FADH2.
Step 7: Water is added by hydration to fumarate during step seven, and malate is produced. The last step in the citric acid cycle regenerates oxaloacetate by oxidizing malate. Another molecule of NADH is then produced in the process.
Oxidative Phosphorylation is a cellular process that harnesses the reduction of oxygen to generate high-energy phosphate bonds in the form of adenosine triphosphate (ATP).
The Electron Transport Chain is the last component of aerobic respiration and is a series of redox reactions where the electrons are passed rapidly from one component to the next on the chain until the electrons reduce molecular oxygen, and along with associated proteins, produces water. Four complexes of proteins are produced, and these complexes together with associated mobile, accessory electron carriers, is the electron transport chain.
A series of redox reactions that take place in the inner mitochondrial membrane, where electrons pass through proteins and organic molecules and release energy. Electrons from NADH and FADH2 combine with oxygen, and the energy released drives the synthesis of ATP from ADP.
Complex 1: Two electrons are carried to the first complex by NADH. Complex 1 is composed of FMN and an iron-sulfur protein. FMN is prosthetic group, a non-protein molecule required for the activity of a protein.
Complex 2: Directly receives NADH2, skipping Complex 1. The compound linking the 1, 2, 3rd complexes in ubiquinone B. Q molecule (ubiquinone) is reduced to QH2. Q receives electrons from NADH and FADH2.
Complex 3: Cytochrome b (another Fe-S protein), 2Fe-2S center, and cytochrome c proteins (this complex is also called cytochrome oxidoreductase.
Complex 4: Cytochrome proteins c, a, a3.
Chemiosmosis: The electron transfer creates an electrochemical gradient by pumping protons into the mitochondrial intermembrane space. This gradient is then used to synthesize ATP. If oxygen isn't present to accept electrons, the ETC stops running and ATP production stops as well. Without enough ATP, cells can't function and may eventually die. Chemiosmosis is used to generate 90 percent of the ATP made during aerobic glucose catabolism.
The number of ATP molecules generated from the catabolism of glucose varies between species.
Metabolism without Oxygen: Fermentation processes use an organic molecule to regenerate NAD+ from NADH. However, some Electron Transport Chains (ETC) use an inorganic molecule as the final electron acceptor. This is called anaerobic cellular respiration. Both processes enable organisms to convert energy for their use without oxygen (anaerobic). Anaerobic respiration is used by some prokaryotes like bacteria and archaea.
Lactic acid fermentation is used by animals and certain bacteria, and the enzyme used for this reaction is lactate dehydrogenase.
Pyruvic acid + NADH => lactic acid + NAD+
Alcohol Fermentation
Pyruvic acid + H+ => CO2 + acetaldehyde + NADH + H+ => ethanol + NAD+
Other fermentation methods occur in bacteria and prokaryotes, and many prokaryotes can switch back and forth from aerobic respiration and fermentation.
Glycogen is a polymer of glucose and an energy storage molecule in animals. Sucrose is a disaccharide with a molecule of glucose and a molecule of fructose bonded together. Fructose is one of three dietary monosaccharides, in addition to glucose and galactose, and each produces the same number of ATP. Proteins are hydrolyzed by a variety of enzymes in cells, and amino acids are recycled into new proteins. Excess amino acids, however, can be used for glucose catabolism if needed.
Lipids connected to the glucose pathway include cholesterol and triglycerides. Cholesterol is a lipid that contributes to cell membrane flexibility and the creation of cholesterol begins with acetyl groups. Triglycerides are made from the bonding of glycerol and three fatty acids, and are form of long term energy storage in animals. Triglycerides can be created and broken down through parts of the glucose catabolism pathways.
Cellular respiration must be regulated in order to provide balanced amounts of energy in the form of ATP, and intermediate compounds must be generated for use in anabolism (creation of macromolecules and storage of energy) and catabolism (breakdown of macromolecules and release of energy). Living things are Intelligently Designed to do these processes.
Regulatory mechanisms used to control cellular respiration exist at each stage of glucose metabolism. GLUT (glucose transporter proteins) transport glucose molecules and regulate access of glucose to the cells of specific tissues. The regulation also involves different enzymes working together in each pathway. Nucleotides ATP, ADP, AMP, NAD+, and NADH are used to regulate the enzymes.
Regulation of glycolysis begins with the enzyme hexokinase. Then the enzyme phosphofructokinase is the main enzyme controlled in glycolysis. Finally, glycolysis is catalyzed by pyruvate kinase.
The citric acid cycle is controlled by enzymes that catalyze the reactions that make the first two molecules of NADH, which are enzymes isocitrate dehydrogenase, and alpha ketoglutarate.
In the Electron Transport Chain, the rate of electron transport through the pathway is affected by levels of ADP and ATP in a directly proportional relationship, so that when ATP useage decreases, ADP also decreases. Then ATP increases again by building up its supply, so that enough is produced, but not too much. The relative concentration of ADP to ATP is the signal to the cell to slow down the electron transport chain.
www.ncbi.nlm.nih.gov/books
Redox Reactions: Oxidation-Reduction reactions involve taking an electron or electrons from one compound and transferring them to another compound. These reactions help power energy conversions within cells. The move of an electron from one compound to another compound removes some potential energy from the first compound, the oxidized compound, and increases potential energy of the second compound, the reduced compound.
Electron carriers are compounds that act as electron shuttles along biochemical pathways.
RH (Reducing Agent) + NAD+(Oxidizing Agent) => NADH (Reduced) + R (Oxidized)
ATP Adenosine Triphosphate allows cells to use and store energy safely. ATP releases energy usually by removing a phosphate group from its structure.
ATP is one molecule of adenine bonded to a ribose molecule, a 5-carbon sugar found in RNA, and two more phosphate group molecules.
Dephosphorylation is the release of a phosphate group which releases energy.
Hydrolysis is the process of breaking complex macromolecules apart. ATP is continuously broken down to ADP (adenosine diphosphate) to perform life processes and water is split by hydrolysis. ATP is continuously regenerated by adding a phosphate back. These processes require energy and is provided by the metabolism of sugars.
Phosphorylation is the addition of a high energy phosphate to a compound.
Substrate-level Phosphorylation is the production of ATP from ADP using excess energy from a chemical reaction and a phosphate group from a reactant. (producing adenosine triphosphate ATP from adenosine diphosphate ADP by adding a phosphate group)
Chemiosmosis is a process in which there is a production of adenosine triphosphate (ATP) in cellular metabolism by the involvement of a proton gradient across a membrane
Oxidative Phosphorylation is the production of ATP using the process of chemiosmosis in the presence of oxygen; occurs in mitochondria in eukaryotes; occurs in plasma membrane in prokaryotes
Glycolysis is the process of breaking glucose down into two three-carbon molecules with the production of ATP and NADH. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. Glycolysis is anerobic, because it does not use oxygen directly. Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. GLUT Proteins are integral membrane proteins that transport glucose. Glucose is also transported by secondary active transport against the glucose concentration gradient. Glycolysis begins with the six-carbon ring shaped structure of a glucose molecule and ends with two molecules of a three-carbon sugar called pyruvate.
Pyruvate is a three-carbon sugar that can be decarboxylated and oxidized to make acetyl CoA, which enters the citric acid cycle under aerobic conditions, and the end product is glycolysis. There are two distinct parts of glycolysis: the first part splits the glucose molecule (energy-requiring steps) and the second part (energy-releasing steps) extracts and stores energy from the glucose molecules.
Glycolysis Steps First Half:
Step 1: Phosphorylation of 6-carbon sugar, catalyzed by the enzyme hexokinase using ATP, and produces glucose-6 phosphate
Step 2: An isomerase converts glucose-6 phosphate into its isomer fructose-6 phosphate (compound with same formula but different atomic arrangement and properties). Isomerase is an enzyme that converts a molecule into its isomer.
Step 3: Phosphorylation of fructose-6 phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-6 phosphate, producing fructose-1, 6 bisphosphate.
Step 4: The enzyme aldolase to convert fructose-1, 6 bisphosphate into two 3-carbon isomers : dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.
Step 5: An isomerase transforms dihydroxyacetone phosphate into its isomer, glyceraldehyde-3-phosphate.
Glycolysis Steps Second Half:
Step 6: Oxidation of glyceraldehyde-3-phosphate; Glyceraldehyde-3-phosphate dehydrogenase dehydrogenates and adds an inorganic phosphate to glyceraldehyde 3-phosphate, producing 1,3-bisphosphoglycerate.
Step 7: Catalyst enzyme (isomerase) phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP molecule and 3-phosphoglycerate (the isomer)
Step 8: The enzyme phosphoglycerate mutase relocates the remaining phosphate group from 3-phosphoglycerate from the 3rd carbon to the 2nd carbon to form 2-phosphoglycerate.
Step 9: The enzyme enolase removes a molecule of water from 2-phosphoglycerate to form phosphoenolpyruvate acid (PEP).
Step 10: The enzyme pyruvate kinase transfers a phosphate group from phosphoenolpyruvate (PEP) to ADP to form pyruvic acid and ATP molecule.
Aerobic respiration is the process in which organisms convert energy in the presence of oxygen.
Oxidation and Breakdown of Pyruvate and the Citric Acid Cycle
Pyruvate is converted to an acetyl group that will be activated by coenzyme CoA, creating acetyl CoA.
Step 1: A carboxyl group is removed from pyruvate, releasing a carbon dioxide. A 2 carbon hydroxyethyl group is created.
Step 2: The hydroxylethyl group is oxidized into an acetyl group, and the electrons are taken by NAD+, forming NADH.
Step 3: The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA.
Acetyl CoA to CO2
With oxygen, acetyl COA sends its acetyl group (2C) group to a 4 carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with 3 carboxyl groups. This process is called the Citric Acid Cycle, the TCA Cycle (tricarboxylic acids), and the Krebs Cycle, after Hans Krebs, who first identified the steps in the cycle.
Citric Acid Cycle Steps: After pyruvic acid is converted to acetyl CoA,
Step 1: This condensation step combines the two-carbon acetyl group with a four-carbon oxaloacetate molecule to form a six-carbon molecule of citrate.
Step 2: Citrate loses one water molecule and gains another as citrate is converted into its isomer, isocitrate.
Step 3: Isocitrate is oxidized, producing a five-carbon molecule, α-ketoglutarate, along with a molecule of CO2 and two electrons, which reduce NAD+ to NADH.
Step 4: A succinyl group is the product of step four. CoA binds with the succinyl group to form succinyl CoA. The enzyme that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.
Step 5: A carboxyl group is substituted for coenzyme A, and a high-energy bond is formed. This energy is used in substrate-level phosphorylation (during the conversion of the succinyl group to succinate) to form either guanosine triphosphate (GTP) or ATP.
Step 6: is a dehydrogenation process that converts succinate into fumarate. Two hydrogen atoms are transferred to FAD, reducing it to FADH2.
Step 7: Water is added by hydration to fumarate during step seven, and malate is produced. The last step in the citric acid cycle regenerates oxaloacetate by oxidizing malate. Another molecule of NADH is then produced in the process.
Oxidative Phosphorylation is a cellular process that harnesses the reduction of oxygen to generate high-energy phosphate bonds in the form of adenosine triphosphate (ATP).
The Electron Transport Chain is the last component of aerobic respiration and is a series of redox reactions where the electrons are passed rapidly from one component to the next on the chain until the electrons reduce molecular oxygen, and along with associated proteins, produces water. Four complexes of proteins are produced, and these complexes together with associated mobile, accessory electron carriers, is the electron transport chain.
A series of redox reactions that take place in the inner mitochondrial membrane, where electrons pass through proteins and organic molecules and release energy. Electrons from NADH and FADH2 combine with oxygen, and the energy released drives the synthesis of ATP from ADP.
Complex 1: Two electrons are carried to the first complex by NADH. Complex 1 is composed of FMN and an iron-sulfur protein. FMN is prosthetic group, a non-protein molecule required for the activity of a protein.
Complex 2: Directly receives NADH2, skipping Complex 1. The compound linking the 1, 2, 3rd complexes in ubiquinone B. Q molecule (ubiquinone) is reduced to QH2. Q receives electrons from NADH and FADH2.
Complex 3: Cytochrome b (another Fe-S protein), 2Fe-2S center, and cytochrome c proteins (this complex is also called cytochrome oxidoreductase.
Complex 4: Cytochrome proteins c, a, a3.
Chemiosmosis: The electron transfer creates an electrochemical gradient by pumping protons into the mitochondrial intermembrane space. This gradient is then used to synthesize ATP. If oxygen isn't present to accept electrons, the ETC stops running and ATP production stops as well. Without enough ATP, cells can't function and may eventually die. Chemiosmosis is used to generate 90 percent of the ATP made during aerobic glucose catabolism.
The number of ATP molecules generated from the catabolism of glucose varies between species.
Metabolism without Oxygen: Fermentation processes use an organic molecule to regenerate NAD+ from NADH. However, some Electron Transport Chains (ETC) use an inorganic molecule as the final electron acceptor. This is called anaerobic cellular respiration. Both processes enable organisms to convert energy for their use without oxygen (anaerobic). Anaerobic respiration is used by some prokaryotes like bacteria and archaea.
Lactic acid fermentation is used by animals and certain bacteria, and the enzyme used for this reaction is lactate dehydrogenase.
Pyruvic acid + NADH => lactic acid + NAD+
Alcohol Fermentation
Pyruvic acid + H+ => CO2 + acetaldehyde + NADH + H+ => ethanol + NAD+
Other fermentation methods occur in bacteria and prokaryotes, and many prokaryotes can switch back and forth from aerobic respiration and fermentation.
Glycogen is a polymer of glucose and an energy storage molecule in animals. Sucrose is a disaccharide with a molecule of glucose and a molecule of fructose bonded together. Fructose is one of three dietary monosaccharides, in addition to glucose and galactose, and each produces the same number of ATP. Proteins are hydrolyzed by a variety of enzymes in cells, and amino acids are recycled into new proteins. Excess amino acids, however, can be used for glucose catabolism if needed.
Lipids connected to the glucose pathway include cholesterol and triglycerides. Cholesterol is a lipid that contributes to cell membrane flexibility and the creation of cholesterol begins with acetyl groups. Triglycerides are made from the bonding of glycerol and three fatty acids, and are form of long term energy storage in animals. Triglycerides can be created and broken down through parts of the glucose catabolism pathways.
Cellular respiration must be regulated in order to provide balanced amounts of energy in the form of ATP, and intermediate compounds must be generated for use in anabolism (creation of macromolecules and storage of energy) and catabolism (breakdown of macromolecules and release of energy). Living things are Intelligently Designed to do these processes.
Regulatory mechanisms used to control cellular respiration exist at each stage of glucose metabolism. GLUT (glucose transporter proteins) transport glucose molecules and regulate access of glucose to the cells of specific tissues. The regulation also involves different enzymes working together in each pathway. Nucleotides ATP, ADP, AMP, NAD+, and NADH are used to regulate the enzymes.
Regulation of glycolysis begins with the enzyme hexokinase. Then the enzyme phosphofructokinase is the main enzyme controlled in glycolysis. Finally, glycolysis is catalyzed by pyruvate kinase.
The citric acid cycle is controlled by enzymes that catalyze the reactions that make the first two molecules of NADH, which are enzymes isocitrate dehydrogenase, and alpha ketoglutarate.
In the Electron Transport Chain, the rate of electron transport through the pathway is affected by levels of ADP and ATP in a directly proportional relationship, so that when ATP useage decreases, ADP also decreases. Then ATP increases again by building up its supply, so that enough is produced, but not too much. The relative concentration of ADP to ATP is the signal to the cell to slow down the electron transport chain.
www.ncbi.nlm.nih.gov/books