Photosynthesis And Respiration-Respiration Topic
Photosynthesis and Respiration-Respiration
Glycolysis
Reactions of glycolysis:
- Phosphorylation of glucose to form glucose-6-phosphate (G-6-P) by hexokinase.
- Isomerization of G-6-P to fructose-6-phosphate (F-6-P) by phosphoglucose isomerase.
- Phosphorylation of F-6-P to fructose-1,6-bisphosphate (F-1,6-BP) by phosphofructokinase-1 (PFK-1).
- Cleavage of F-1,6-BP into glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) by aldolase.
- Isomerization of DHAP to GAP by triose phosphate isomerase.
- Oxidation of GAP to 1,3-bisphosphoglycerate (1,3-BPG) by glyceraldehyde-3-phosphate dehydrogenase (GAPDH).
- Phosphorylation of 1,3-BPG to 3-phosphoglycerate (3-PG) by phosphoglycerate kinase.
- Isomerization of 3-PG to 2-phosphoglycerate (2-PG) by phosphoglyceromutase.
- Dehydration of 2-PG to phosphoenolpyruvate (PEP) by enolase.
- Transfer of phosphate from PEP to ADP to form ATP by pyruvate kinase.
Energy yield of glycolysis:
- 2 molecules of ATP are produced for each molecule of glucose undergoing glycolysis.
- 2 molecules of NADH are also produced for each molecule of glucose undergoing glycolysis.
Regulation of glycolysis:
- Glycolysis is regulated at multiple points, including:
- Phosphorylation of glucose to G-6-P by hexokinase.
- Phosphorylation of F-6-P to F-1,6-BP by phosphofructokinase-1 (PFK-1).
- Phosphorylation of PEP to ATP by pyruvate kinase.
Significance of glycolysis:
- Glycolysis is the first stage of respiration and provides the starting point for the Krebs cycle and the electron transport chain.
- Glycolysis also produces ATP and NADH, which are used for energy production.
Krebs Cycle (Citric Acid Cycle)
Reactions of the Krebs cycle:
- Condensation of acetyl-CoA with oxaloacetate to form citrate by citrate synthase.
- Isomerization of citrate to isocitrate by aconitase.
- Oxidation of isocitrate to α-ketoglutarate by isocitrate dehydrogenase.
- Decarboxylation of α-ketoglutarate to succinyl-CoA by α-ketoglutarate dehydrogenase.
- Transfer of CoA from succinyl-CoA to GDP to form GTP by succinyl-CoA synthetase.
- Oxidation of succinate to fumarate by succinate dehydrogenase.
- Hydration of fumarate to malate by fumarase.
- Oxidation of malate to oxaloacetate by malate dehydrogenase.
Energy yield of the Krebs cycle:
- 2 molecules of ATP (or GTP) are produced for each molecule of acetyl-CoA entering the Krebs cycle.
- 3 molecules of NADH and 2 molecules of FADH2 are also produced for each molecule of acetyl-CoA entering the Krebs cycle.
Regulation of the Krebs cycle:
- The Krebs cycle is regulated at multiple points, including:
- Condensation of acetyl-CoA with oxaloacetate to form citrate by citrate synthase.
- Oxidation of isocitrate to α-ketoglutarate by isocitrate dehydrogenase.
- Decarboxylation of α-ketoglutarate to succinyl-CoA by α-ketoglutarate dehydrogenase.
Significance of the Krebs cycle:
- The Krebs cycle is a central metabolic pathway that provides energy and intermediates for many other biochemical processes.
- The Krebs cycle also produces ATP, NADH, and FADH2, which are used for energy production.
Electron Transport Chain (ETC)
Components of the ETC:
- The ETC is composed of a series of protein complexes located in the inner mitochondrial membrane.
- The complexes are:
- NADH dehydrogenase (Complex I)
- Succinate dehydrogenase (Complex II)
- Cytochrome b-c1 complex (Complex III)
- Cytochrome c oxidase (Complex IV)
Reactions of the ETC:
- Electrons are passed from NADH and FADH2 to oxygen through the ETC.
- The electrons are passed through a series of redox reactions, which release energy.
- The energy released is used to pump protons across the inner mitochondrial membrane, creating a proton gradient.
Energy yield of the ETC:
- The ETC produces ATP by oxidative phosphorylation.
- Oxidative phosphorylation is the process of synthesizing ATP from ADP using the energy released from the proton gradient.
Regulation of the ETC:
- The ETC is regulated at multiple points, including:
- The availability of NADH and FADH2.
- The proton gradient across the inner mitochondrial membrane.
Significance of the ETC:
- The ETC is the final stage of respiration and produces the majority of ATP used for energy production.
Oxidative Phosphorylation
Mechanism of oxidative phosphorylation:
- Oxidative phosphorylation is the process of synthesizing ATP from ADP using the energy released from the proton gradient.
- The proton gradient is created by the electron transport chain (ETC).
- The protons flow back down the proton gradient through ATP synthase, an enzyme that synthesizes ATP from ADP.
ATP synthesis during oxidative phosphorylation:
- As protons flow through ATP synthase, they cause a conformational change in the enzyme.
- This conformational change drives the synthesis of ATP from ADP and inorganic phosphate (Pi).
Regulation of oxidative phosphorylation:
- Oxidative phosphorylation is regulated at multiple points, including:
- The availability of NADH and FADH2.
- The proton gradient across the inner mitochondrial membrane.
- The activity of ATP synthase.
Significance of oxidative phosphorylation:
- Oxidative phosphorylation is the final stage of respiration and produces the majority of ATP used for energy production.
Respiratory Quotient (RQ)
Definition of respiratory quotient:
- The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration.
RQ values for different respiratory substrates:
- The RQ varies depending on the respiratory substrate used.
- For example, the RQ for glucose is 1.0, the RQ for fatty acids is 0.7, and the RQ for proteins is 0.8.
Significance of respiratory quotient:
- The RQ can be used to determine the type of respiratory substrate being used.
- The RQ can also be used to calculate the energy yield of respiration.
Anaerobic Respiration
Types of anaerobic respiration:
- There are two main types of anaerobic respiration:
- Alcoholic fermentation
- Lactic acid fermentation
Reactions of anaerobic respiration:
- Alcoholic fermentation:
- Glucose is converted to ethanol and carbon dioxide.
- Lactic acid fermentation:
- Glucose is converted to lactic acid.
Energy yield of anaerobic respiration:
- The energy yield of anaerobic respiration is lower than the energy yield of aerobic respiration.
- For example, the energy yield of alcoholic fermentation is only 2 ATP molecules per molecule