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