7.2.2.2.2. Krebs cycle

Krebs cycle

The Krebs cycle (cycle citric acid or cycle of tricarboxylic acids) is a metabolic pathway, that is, a succession of chemical reactions, which is part of cellular respiration in all aerobic cells. In eukaryotic cells it is carried out in the mitochondrial matrix. In prokaryotes, the Krebs cycle occurs in the cytoplasm.

In the Krebs cycle, a series of chemical reactions take place in which, in each of which, a specific enzyme intervenes, which lead to the total oxidation of acetyl-CoA to CO₂. The electrons that are released in this oxidation are accepted by the coenzymes NAD⁺ and FAD, which are reduced in the form of NADH and FADH₂.

The acetyl-CoA that is introduced into the cycle and is oxidized to CO₂ comes from the degradation of immediate principles, through the β-oxidation of fatty acids and the glycolysis of carbohydrates.

The Krebs cycle begins when the acetyl group of two carbons is combined with one molecule of four carbons (oxaloacetic acid) to produce a compound of six carbons (citric acid). After going through this cycle, two of the six carbons are oxidized to CO ₂ (removed) and the oxaloacetic acid is regenerated, making it available to bind again with another acetyl-CoA molecule. Therefore, two rounds of the cycle are necessary to fully oxidize a glucose molecule, since, in glycolysis, of each glucose molecule glucose formed two of pyruvic acid.

The energy that has been released by the oxidation of the carbon-hydrogen and carbon-carbon bonds is used to produce ATP (one molecule per cycle) from ADP, and to produce NADH from NAD⁺ (three molecules per cycle). It is also used to reduce another electron carrier, flavin adenine dinucleotide (FAD), obtaining a FADH₂ molecule from FAD in each cycle.

O ₂ is not needed directly in the Krebs cycle, since all electrons and protons released in carbon oxidation are accepted by NAD⁺ and FAD. However, oxygen is required in the electron transport chain, the next stage of respiration.

Therefore, the Krebs cycle is the metabolic (catabolic) route in which the total degradation of organic matter occurs to transform it into inorganic, obtaining energy directly (only 1 ATP per turn) or reoxidating the reduced coenzyme in the transport chain electron cells from the inner mitochondrial membrane.

Although the Krebs cycle is catabolic, some of its intermediate molecules can also be precursors to other anabolic processes that occur in the cytosol. That is why it is considered an amphibolic pathway, that is, catabolic and anabolic at the same time .

By Narayanese, WikiUserPedia, YassineMrabet, TotoBaggins [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Krebs cycle energy balance

At each turn of the cycle, the following is generated:

A molecule of GTP (convertible to ATP).
Three from NADH and one from FADH₂. These molecules, by oxidative phosphorylation, will form ATP molecules in the electron transport chain.
Two CO₂ molecules, which correspond to the two carbons of a fully oxidized acetyl-CoA molecule. CO₂ leaves the cell.

Therefore, in the Krebs cycle, from a glucose molecule (two rounds of the cycle), two GTP molecules are formed, six of NADH and two of FADH₂. The GTP transfers its phosphate group to the ADP, while producing a molecule of ATP. Although the Krebs cycle does not have a great energy yield in the form of ATP, it does obtain reduced nucleotides from which you will obtain more ATP later.

Krebs cycle:

Acetyl-CoA + GDP + Pi + 3 NAD⁺ + FAD → 2 CO ₂ + CoA + GTP + 3 NADH + FADH₂

Biological music: Rap of the Krebs Cycle .

Documentary: Krebs Cycle, looks old but is very good (9:39).

Animation: Reactions of the Krebs cycle.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Madrid, June 2017, option A, question 5.

Regarding cell metabolism:

a) Briefly explain the meaning of the amphibole character of the Krebs Cycle. Indicate the initial and final products of that cycle (1.5 points).

b) State the role of the ATP molecule in cell metabolism (0.5 points).

Cantabria, July 2019, option 1, question 2.

Define the concept of "Krebs Cycle". Discuss its biological function in the cell. (1.5 points)

Castilla y León, July 2019, option A, question 3.

Related to cell metabolism:

a) List the initial molecules and the end products of glycolysis. (0,6)
b) Name three routes from which acetyl-CoA that is incorporated into the Krebs cycle can come. (0,3)
c) In which organelle and in what part of it does the Krebs cycle take place? List the coenzymes that originate at this stage and indicate their destination. (0.85)

Castilla La Mancha, June 2021, question 2.4.

In his Nobel Prize speech, Hans Krebs said: "... the citric acid cycle (of carbohydrate oxidation) also plays an important role in the stages after beta oxidation of fatty acids."

a. In which cell organelle and in which part of said organelle does the Krebs cycle take place?
b. What is the metabolic function of the Krebs cycle? List TWO of your final products.
c. In which molecule, which is incorporated into the Krebs cycle, does the oxidation of carbohydrates and fatty acids converge?
Justify your answer.

Fundamental ideas about the Krebs cycle

The Krebs cycle

The Krebs cycle is a metabolic pathway that is part of cellular respiration in all aerobic cells.
- In eukaryotic cells it is carried out in the mitochondrial matrix.
- In prokaryotes, the Krebs cycle occurs in the cytoplasm.
- It is an amphibolic, catabolic and anabolic pathway at the same time, since some of its intermediate molecules can also be precursors of other anabolic processes that occur in the cytosol.
Energy is obtained from the oxidation of acetyl-CoA. proceeding comes from the degradation of immediate principles, through the β-oxidation of fatty acids and the glycolysis of carbohydrates and proteins, to CO₂ and ATP.
The acetyl group of two carbons is combined with one molecule of four carbons (oxaloacetic acid) to produce a compound of six carbons (citric acid).
- After going through this cycle, two of the six carbons are oxidized to CO₂ (removed) and the oxaloacetic acid is regenerated, making it available to bind again with another acetyl-CoA molecule. Therefore, two rounds of the cycle are necessary to fully oxidize a glucose molecule, since, in glycolysis, two of pyruvic acid were formed from each glucose molecule.
- ATP is obtained (one molecule per cycle), NADH (three molecules per cycle) and one FADH₂ molecule in each cycle.
- You do not need O₂ directly, although you do need O₂ in the electron transport chain, the next stage of respiration.
At each turn of the Krebs cycle, the following is generated:
- A molecule of GTP (convertible to ATP).
- Three from NADH and one from FADH₂ .
- Two CO₂ molecules.
For each glucose molecule (two rounds of the cycle), two GTP molecules are formed , six of NADH and two of FADH₂ .
Krebs cycle: Acetyl-CoA + GDP + Pi + 3NAD⁺ + FAD → 2CO₂ + CoA + GTP + 3 NADH + FADH₂

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Skip navigation Biology 2nd Baccalaureate Biology 2nd Bac. 1. Bioelements and biomolecules. Water and mineral salts 1.1. Chemical bonds in biology 1.1.1. Intramolecular bonds 1.1.1.1. Covalent bond 1.1.1.2. Ionic bond 1.1.2. Intermolecular bonds 1.1.2.1. Van der Waals forces 1.1.2.2. Hydrogen bonds 1.2. The chemical basis of life: inorganic and organic components 1.2.1. Primary bioelements 1.2.2. Secondary bioelements 1.2.3. Trace elements 1.3. The immediate principles or biomolecules 1.3.1. Water 1.3.1.1. Chemical structure of water 1.3.1.2. Properties and functions of water 1.3.2. Mineral salts 1.3.2.1. Functions of salts in solution 1.3.2.2. Colloidal solutions and dispersions 1.3.2.3. Properties of colloidal dispersions 1.3.2.4. Diffusion, osmosis and dialysis 1.3.2.4.1. Diffusion 1.3.2.4.2. Osmosis 1.3.2.4.3. Dialysis 1.4. Bibliography 2. Glucides 2.1. Glucid concept 2.2. Classification of carbohydrates 2.3. Monosaccharides 2.3.1. Trioses 2.3.1.1. Spatial isomerism or stereoisomerism 2.3.2. Tetroses 2.3.3. Pentoses 2.3.3.1. Monosaccharide cyclization 2.3.4. Hexoses 2.4. The N-glucosidic and O-glucosidic bonds 2.4.1. Substances derived from monosaccharides 2.5. Disaccharides 2.6. Polysaccharides 2.6.1. Homopolysaccharides 2.6.1.1. Reserve homopolysaccharides 2.6.1.2. Structural homopolysaccharides 2.6.2. Heteropolysaccharides 2.6.3. Heterosides 2.7. General functions of glucides 2.8. Bibliography 3. Lipids 3.1. Lipid concept 3.2. Classification of lipids 3.2.1. Fatty acids 3.2.1.1. Saturated and unsaturated fatty acids 3.2.1.2. Chemical properties of fatty acids 3.2.1.3. Physical properties of fatty acids 3.2.1.4. Fatty Acid Functions 3.2.2. Saponifiable lipids or with fatty acids 3.2.2.1. Simple lipids 3.2.2.1.1. Acylglycerides 3.2.2.1.2. Cerides 3.2.2.2. Complex lipids 3.2.2.2.1. Phospholipids 3.2.2.2.2. Glycolipids 3.2.3. Unsaponifiable lipids or without fatty acids 3.3. Lipid functions 3.4. Bibliography 4. Proteins 4.1. Introduction to proteins 4.2. Amino acids 4.2.1. Classification of amino acids 4.2.2. Properties of amino acids 4.3. The peptide bond 4.4. Protein 4.4.1. Protein structure 4.4.1.1. Primary structure of proteins 4.4.1.2. Secondary structure of proteins 4.4.1.3. Tertiary structure of proteins 4.4.1.4. Quaternary structure of proteins 4.4.2. Protein properties 4.4.3. Classification of proteins 4.4.3.1. Holoproteins 4.4.3.2. Heteroproteins 4.4.4. Protein functions 4.5. Enzymes 4.5.1. Structure of enzymes 4.5.2. The active center of enzymes 4.5.3. General Mechanism of Enzyme Catalysis 4.5.4. Regulation of enzyme activity 4.5.5. Allosteric enzymes 4.5.6. Nomenclature and classification of enzymes 4.6. The vitamins 4.6.1. Fat-soluble vitamins 4.6.2. Water soluble vitamins 4.7. Bibliography 5. Nucleotides and nucleic acids 5.1. The chemical composition of nucleic acids 5.1.1. Components of nucleic acids 5.1.2. Concept, types and functions of nucleic acids 5.1.3. Nucleosides 5.1.4. Nucleotides 5.1.4.1. Nucleotide functions 5.1.5. Nucleic acids 5.2. Deoxyribonucleic acid (DNA) 5.2.1. DNA structure 5.2.1.1. Primary structure of DNA 5.2.1.2. Secondary structure of DNA 5.2.1.3. Tertiary structure of DNA 5.2.1.3.1. Tertiary structure of DNA in prokaryotes 5.2.1.3.2. Tertiary structure of DNA in eukaryotes 5.2.1.4. Quaternary structure of DNA 5.2.2. DNA types 5.2.3. Genetic material: chromatin and chromosomes 5.2.3.1. Karyotype and karyogram 5.3. Ribonucleic acid (RNA) 5.3.1. RNA types 5.3.1.1. Transfer RNA 5.3.1.2. Messenger RNA 5.3.1.3. Ribosomal RNA 5.3.1.4. Nucleolar RNA 5.3.1.5. Small nuclear RNA 5.3.2. Functions of ribonucleic acids 5.4. Bibliography 6. Cell morphology 6.1. Cell concept 6.1.1. Cell history 6.1.2. Cell theory 6.2. Levels of cellular organization 6.2.1. General characteristics of cells 6.2.2. Prokaryotic cells 6.2.2.1. Prokaryotic cell morphology 6.2.2.2. Structure of prokaryotes 6.2.2.2.1. Bacterial capsule 6.2.2.2.2. Bacterial wall 6.2.2.2.3. Plasma membrane 6.2.2.2.4. Cytoplasm-Ribosomes-Inclusions 6.2.2.2.5. Bacterial DNA 6.2.2.2.6. Bacterial appendages 6.2.2.3. Bacteria Physiology 6.2.3. Eukaryotic cells 6.2.3.1. Animal and plant cell 6.2.3.1.1. Animal eukaryotic cell 6.2.3.1.2. Plant eukaryotic cell 6.2.3.2. Cell Evolution: Endosymbiont Theory 6.3. Size, shape and quantity 6.4. The plasma membrane 6.4.1. Chemical composition of the membrane 6.4.2. The structure of the membrane. The fluid mosaic model 6.4.3. Functions of the plasma membrane 6.4.4. Transport across the membrane 6.4.4.1. Small molecule transport 6.4.4.2. Macromolecule transport 6.4.5. Plasma membrane differentiations 6.5. The cell wall of plant cells 6.5.1. Chemical composition of the cell wall 6.5.2. Cell wall structure 6.5.3. Cell wall differentiations 6.5.4. Cell wall functions 6.6. Extracellular matrix or glucocalyx 6.7. Cytosol or hyaloplasm 6.8. The cytoskeleton 6.8.1. Microfilaments or actin filaments 6.8.2. Intermediate filaments 6.8.3. Microtubules 6.9. Cell membrane and organelle systems 6.9.1. Membrane systems 6.9.1.1. The endoplasmic reticulum 6.9.1.2. Golgi apparatus 6.9.2. Cell organelles 6.9.2.1. Lysosomes 6.9.2.2. Peroxisomes 6.9.2.3. Vacuoles 6.9.2.4. Mitochondria 6.9.2.4.1. Functions of the mitochondria 6.9.2.5. Plastids 6.9.2.5.1. Chloroplasts 6.9.2.6. Ribosomes 6.9.2.7. Centrosome 6.9.2.8. Cilia and flagella 6.10. Cell motility 6.11. The cell nucleus 6.11.1. Characteristics of the cell nucleus 6.11.2. The interphase nucleus 6.11.3. The mitotic nucleus or nucleus in division 6.12. Bibliography 7. Metabolism 7.1. Metabolism 7.1.1. Energetic Aspects of Cellular Chemical Reactions 7.2. Catabolism 7.2.1. Catabolism and obtaining energy 7.2.2. Carbohydrate catabolism 7.2.2.1. Glycolysis 7.2.2.2. Cellular respiration 7.2.2.2.1. Oxidative decarboxylation 7.2.2.2.2. Krebs cycle 7.2.2.2.3. Electron transport chain 7.2.2.2.4. Energy balance of cellular respiration 7.2.2.3. Fermentations 7.2.2.3.1. Alcoholic or ethyl fermentation 7.2.2.3.2. Lactic fermentation 7.2.2.3.3. Other types of fermentations 7.3. Anabolism 7.3.1. Autotrophic anabolism 7.3.2. Photosynthesis 7.3.2.1. Photochemical or light phase 7.3.2.1.1. Photosystems 7.3.2.1.2. Photophosphorylation 7.3.2.1.2.1. Non cyclic photophosphorylation 7.3.2.1.2.2. Cyclic photophosphorylation 7.3.2.2. Biosynthetic or dark phase 7.3.2.3. Factors influencing photosynthesis 7.3.2.4. Products of photosynthesis 7.3.3. Chemosynthesis 7.4. Bibliography 8. Cell reproduction 8.1. The cell cycle 8.1.1. Interphase 8.1.2. Cellular division 8.2. Cellular division 8.2.1. Mitosis 8.2.1.1. Prophase 8.2.1.2. Metaphase 8.2.1.3. Anaphase 8.2.1.4. Telophase 8.2.1.5. Cytokinesis 8.2.1.6. More on mitosis 8.2.2. Meiosis 8.2.2.1. Meiosis I 8.2.2.2. Meiosis II 8.2.3. Meiosis and sexual reproduction 8.2.4. Meiosis and life cycle 8.2.5. Biological importance of meiosis 8.3. Differences and similarities between mitosis and meiosis 8.4. Bibliography 9. Classical genetics 9.1. Genetics basics 9.2. Mendelian genetics 9.2.1. The method 9.2.2. Mendel's Laws 9.2.2.1. Mendel's first law or principle of uniformity in the first generation 9.2.2.2. Mendel's second law or principle of segregation 9.2.2.2.1. Backcross and test crossover 9.2.2.3. Mendel's third law or principle of independent combination 9.3. Gene interaction 9.3.1. Gene interaction between allelic genes 9.3.2. Gene interaction between non-allelic genes that influence for the same trait 9.4. Chromosomal theory of heredity 9.5. Ligation and recombination 9.6. Complex mendelism 9.6.1. Multiple allelism 9.6.1.1. Lethal genes 9.6.2. Pleiotropy 9.6.3. Expressiveness and genetic penetrance 9.7. Sex-linked inheritance 9.7.1. Y-linked inheritance 9.7.2. X-linked inheritance 9.8. Heredity influenced by sex 9.9. Bibliography 10. Molecular genetics 10.1. DNA as hereditary material 10.2. DNA replication 10.2.1. The need for DNA replication 10.2.2. First hypotheses about DNA duplication 10.2.3. Meselson and Stahl experiment 10.2.4. The sense of growth of the new strands 10.2.5. Mechanism of DNA replication 10.2.5.1. Replication in prokaryotes 10.2.5.2. Replication in eukaryotes 10.2.6. Error correction 10.2.7. Enzymes involved in replication 10.3. Gene concept 10.4. "One gene-one enzyme" theory 10.5. Transcription 10.5.1. Mechanism of transcription 10.5.1.1. Transcription in prokaryotes 10.5.1.2. Eukaryotic transcription 10.6. Translation or protein biosynthesis 10.6.1. The genetic code 10.6.2. Mechanism of translation of RNA to proteins 10.6.2.1. Translation in eukaryotes 10.7. Regulation of gene expression 10.8. Bibliography 11. Genetics and evolution 11.1. Mutations 11.2. Types of mutations 11.2.1. Gene or point mutation 11.2.2. Chromosomal or structural mutation 11.2.3. Mutation at the genomic level 11.3. Causes of mutations 11.4. Evolutionary implications of mutations 11.5. Metabolic implications of mutations 11.6. Bibliography 12. Microbiology and biotechnology 12.1. Microbiology 12.2. Viruses 12.2.1. Viral morphology 12.2.2. Viral physiology 12.2.2.1. Lytic cycle 12.2.2.2. Lysogenic cycle 12.2.2.3. Cycles of viruses of special interest 12.2.2.3.1. Flu virus life cycle 12.2.2.3.2. Life cycle of the AIDS virus 12.3. Other acellular forms 12.3.1. Viroids 12.3.2. Prions 12.4. Biotechnology 12.5. Bibliography 13. Immunology 13.1. Infection concept 13.2. Defense mechanisms against infections 13.2.1. Nonspecific mechanisms 13.2.1.1. Primary barriers: external defenses 13.2.1.2. Secondary barriers: internal defenses 13.2.2. Specific mechanisms 13.3. Immunity and immune system 13.3.1. Components of the immune system 13.3.2. Concept and nature of antigens 13.4. The immune response 13.4.1. Humoral immune response: the antibodies 13.4.1.1. Antibody-producing cells: B lymphocytes 13.4.1.2. Antibodies 13.4.1.2.1. Types of antibodies 13.4.1.2.2. Antigen-antibody reaction 13.4.1.3. Immune memory: primary and secondary responses 13.4.2. Cellular immune response: T lymphocytes 13.5. Types of immunity 13.5.1. Natural immunity 13.5.2. Artificial immunity 13.6. Immune system disorders 13.6.1. Autoimmunity 13.6.2. Hypersensitivity 13.6.3. Immunodeficiency 13.6.4. Transplants and the phenomenon of rejections 13.7. Bibliography « Previous \| Next » 7.2.2.2.2. Krebs cycle Krebs cycle The Krebs cycle (cycle citric acid or cycle of tricarboxylic acids) is a metabolic pathway, that is, a succession of chemical reactions, which is part of cellular respiration in all aerobic cells. In eukaryotic cells it is carried out in the mitochondrial matrix. In prokaryotes, the Krebs cycle occurs in the cytoplasm. In the Krebs cycle, a series of chemical reactions take place in which, in each of which, a specific enzyme intervenes, which lead to the total oxidation of acetyl-CoA to CO₂. The electrons that are released in this oxidation are accepted by the coenzymes NAD⁺ and FAD, which are reduced in the form of NADH and FADH₂. The acetyl-CoA that is introduced into the cycle and is oxidized to CO₂ comes from the degradation of immediate principles, through the β-oxidation of fatty acids and the glycolysis of carbohydrates. The Krebs cycle begins when the acetyl group of two carbons is combined with one molecule of four carbons (oxaloacetic acid) to produce a compound of six carbons (citric acid). After going through this cycle, two of the six carbons are oxidized to CO ₂ (removed) and the oxaloacetic acid is regenerated, making it available to bind again with another acetyl-CoA molecule. Therefore, two rounds of the cycle are necessary to fully oxidize a glucose molecule, since, in glycolysis, of each glucose molecule glucose formed two of pyruvic acid. The energy that has been released by the oxidation of the carbon-hydrogen and carbon-carbon bonds is used to produce ATP (one molecule per cycle) from ADP, and to produce NADH from NAD⁺ (three molecules per cycle). It is also used to reduce another electron carrier, flavin adenine dinucleotide (FAD), obtaining a FADH₂ molecule from FAD in each cycle. O ₂ is not needed directly in the Krebs cycle, since all electrons and protons released in carbon oxidation are accepted by NAD⁺ and FAD. However, oxygen is required in the electron transport chain, the next stage of respiration. Therefore, the Krebs cycle is the metabolic (catabolic) route in which the total degradation of organic matter occurs to transform it into inorganic, obtaining energy directly (only 1 ATP per turn) or reoxidating the reduced coenzyme in the transport chain electron cells from the inner mitochondrial membrane. Although the Krebs cycle is catabolic, some of its intermediate molecules can also be precursors to other anabolic processes that occur in the cytosol. That is why it is considered an amphibolic pathway, that is, catabolic and anabolic at the same time . By Narayanese, WikiUserPedia, YassineMrabet, TotoBaggins [GFDL or CC-BY-SA-3.0], via Wikimedia Commons Krebs cycle energy balance At each turn of the cycle, the following is generated: A molecule of GTP (convertible to ATP). Three from NADH and one from FADH₂. These molecules, by oxidative phosphorylation, will form ATP molecules in the electron transport chain. Two CO₂ molecules, which correspond to the two carbons of a fully oxidized acetyl-CoA molecule. CO₂ leaves the cell. Therefore, in the Krebs cycle, from a glucose molecule (two rounds of the cycle), two GTP molecules are formed, six of NADH and two of FADH₂. The GTP transfers its phosphate group to the ADP, while producing a molecule of ATP. Although the Krebs cycle does not have a great energy yield in the form of ATP, it does obtain reduced nucleotides from which you will obtain more ATP later. Krebs cycle: Acetyl-CoA + GDP + Pi + 3 NAD⁺ + FAD → 2 CO ₂ + CoA + GTP + 3 NADH + FADH₂ Biological music: Rap of the Krebs Cycle . Documentary: Krebs Cycle, looks old but is very good (9:39). Animation: Reactions of the Krebs cycle. Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU) Madrid, June 2017, option A, question 5. Regarding cell metabolism: a) Briefly explain the meaning of the amphibole character of the Krebs Cycle. Indicate the initial and final products of that cycle (1.5 points). b) State the role of the ATP molecule in cell metabolism (0.5 points). Cantabria, July 2019, option 1, question 2. Define the concept of "Krebs Cycle". Discuss its biological function in the cell. (1.5 points) Castilla y León, July 2019, option A, question 3. Related to cell metabolism: a) List the initial molecules and the end products of glycolysis. (0,6) b) Name three routes from which acetyl-CoA that is incorporated into the Krebs cycle can come. (0,3) c) In which organelle and in what part of it does the Krebs cycle take place? List the coenzymes that originate at this stage and indicate their destination. (0.85) Castilla La Mancha, June 2021, question 2.4. In his Nobel Prize speech, Hans Krebs said: "... the citric acid cycle (of carbohydrate oxidation) also plays an important role in the stages after beta oxidation of fatty acids." a. In which cell organelle and in which part of said organelle does the Krebs cycle take place? b. What is the metabolic function of the Krebs cycle? List TWO of your final products. c. In which molecule, which is incorporated into the Krebs cycle, does the oxidation of carbohydrates and fatty acids converge? Justify your answer. Fundamental ideas about the Krebs cycle The Krebs cycle The Krebs cycle is a metabolic pathway that is part of cellular respiration in all aerobic cells. In eukaryotic cells it is carried out in the **mitochondrial matrix*. In prokaryotes, the Krebs cycle occurs in the cytoplasm. It is an amphibolic, catabolic and anabolic pathway* at the same time, since some of its intermediate molecules can also be precursors of other anabolic processes that occur in the cytosol. Energy is obtained from the oxidation of acetyl-CoA. proceeding comes from the degradation of immediate principles, through the β-oxidation of fatty acids and the glycolysis of carbohydrates and proteins, to CO₂ and ATP. The acetyl group of two carbons is combined with one molecule of four carbons (oxaloacetic acid) to produce a compound of six carbons (citric acid). After going through this cycle, two of the six carbons are oxidized to CO₂ (removed) and the oxaloacetic acid is regenerated, making it available to bind again with another acetyl-CoA molecule. Therefore, two rounds of the cycle are necessary to fully oxidize a glucose molecule, since, in glycolysis, two of pyruvic acid were formed from each glucose molecule. ATP is obtained (one molecule per cycle), NADH (three molecules per cycle) and one FADH₂ molecule in each cycle. You do not need O₂ directly, although you do need O₂ in the electron transport chain, the next stage of respiration. At each turn of the Krebs cycle, the following is generated: A molecule of GTP (convertible to ATP). Three from NADH and one from FADH₂ . Two CO₂ molecules. For each glucose molecule (two rounds of the cycle), two GTP molecules are formed , six of NADH and two of FADH₂ . Krebs cycle: Acetyl-CoA + GDP + Pi + 3NAD⁺ + FAD → 2CO₂ + CoA + GTP + 3 NADH + FADH₂ Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » These pages are semi-automatically translated from the web Biology 2nd Baccalaureate. Biología de 2º de Bachillerato (biologia-geologia.com). You can make any suggestion, question, comment, ..., in our forum 2º Bachillerato Biología - Foro de biologia-geologia.com
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Krebs cycle

Krebs cycle energy balance

The Krebs cycle