Respiratory Balance Sheet: Assumptions, Efficiency, and Respiratory Quotient
Definition Of Respiratory Balance Sheet
A respiratory balance sheet is simply a summary of the input and products of cellular respiration including the amount of ATP produced and used up, together with its relation to main metabolic intermediates. Much of the importance attached to a respiratory balance sheet should deal with appreciating efficiency and the regulation involved in cellular respiration—the process whereby cells convert glucose and oxygen into energy, carbon dioxide, and water. Cellular respiration comprises the processes of glycolysis, the citric acid cycle, and oxidative phosphorylation—all examples of biochemical pathways that support energy production in the cell.
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Cellular Respiration: An Overview
One such metabolic process is cell respiration, which converts glucose and oxygen into energy in the form of ATP, carbon dioxide, and water. It is a very important process for the survival of aerobic organisms because it yields all the required energy for several other cellular activities.
Stages:
Glycolysis: Glucose Degradation to pyruvate that turns into limited amounts of ATP and NADH.
Krebs Cycle (Citric Acid Cycle): The further degradation of pyruvate into ATP, NADH, and FADH2 with the concomitant release of carbon dioxide.
Electron Transport Chain: Passed on to the ETC are electrons from NADH and FADH2, driving a great quantity of ATP production via oxidative phosphorylation.
Importance Of ATP
ATP is the main energy equivalent or, in other words, the energy currency of the cell and is always required to drive every biochemical reaction or activity of the cell which makes life possible.
Respiratory Balance Sheet: Detailed Analysis
The detailed analysis is given below:
ATP Yield per Glucose Molecule
Glycolysis: The place is in the cytoplasm. It breaks one glucose molecule into two pyruvate molecules. The process directly yields 2 ATP molecules while generating 2 NADH molecules.
Krebs Cycle (Citric Acid Cycle): In the mitochondrial matrix, this is where the process whereby each pyruvate undergoes conversion to Acetyl-CoA and enters the Krebs cycle. The Krebs cycle happens twice per every glucose molecule to produce 6 NADH and 2 FADH₂, along with 2 net ATPs.
Electron transport chain with Oxidative Phosphorylation: It is located in the mitochondrial inner membrane. NADH and FADH₂ are oxidized, electrons donate their energy in the production of ATP through the process of chemiosmosis.
ATP Production Summary
Glycolysis: 2 ATP (net) + 2 NADH (which will generate additional ATP in ETC)
Krebs Cycle: 2 ATP + 6 NADH + 2 FADH₂
ETC and Oxidative Phosphorylation: The ATP production from NADH and FADH₂ will be discussed below.
NADH And FADH2 Contribution To ATP Production
NADH
Each NADH molecule can produce approximately 2.5 ATPs in the ETC.
FADH₂
Each FADH₂ molecule can produce approximately 1.5 ATPs in the ETC.
Calculation of ATP Contribution
From Glycolysis: 2 NADH × 2.5 ATP/NADH = 5 ATP
From Krebs Cycle: 6 NADH × 2.5 ATP/NADH = 15 ATP
From Krebs Cycle: 2 FADH₂ × 1.5 ATP/FADH₂ = 3 ATP
Energy Yield In Different Stages
The energy yield is given below:
Glycolysis
ATP: 2 (net gain)
NADH: 2 (contributing to ETC)
Krebs Cycle
ATP: 2 (one per cycle, two cycles per glucose molecule)
NADH: 6
FADH₂: 2
Electron Transport Chain
Total ATP Production from NADH and FADH₂:
NADH: 8 × 2.5 ATP = 20 ATP
FADH₂: 2 × 1.5 ATP = 3 ATP
Total ATP Calculation
From Glycolysis:
2 ATP (direct) + 5 ATP (from NADH) = 7 ATP
From Krebs Cycle:
2 ATP (direct) + 15 ATP (from NADH) + 3 ATP (from FADH₂) = 20 ATP
Overall Total ATP Yield:
Total from Glycolysis and Krebs Cycle = 7 ATP + 20 ATP = 27 ATP
Calculation Of Total ATP Yield
Direct ATP Production:
Glycolysis: 2 ATP
Krebs Cycle: 2 ATP
Total Direct ATP: 4 ATP
ATP from NADH:
8 NADH × 2.5 ATP/NADH = 20 ATP
ATP from FADH₂:
2 FADH₂ × 1.5 ATP/FADH₂ = 3 ATP
Total ATP Yield per Glucose Molecule:
Direct ATP + ATP from NADH + ATP from FADH₂ = 4 ATP + 20 ATP + 3 ATP = 27 ATP
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Frequently Asked Questions (FAQs)
The respiratory balance sheet is the statement giving details of this energy production during cellular respiration. It gives the exact amount of ATP produced by the complete oxidation of a single glucose molecule.
A balance sheet would provide details on the following: • Amount of ATP produced in each of the three phases: glycolysis, Krebs cycle, and electron transport chain. • Contribution of the reduced co-enzymes NADH and FADH₂ as electron carriers in terms of ATP produced. Total ATP yield by adding direct ATP production to ATP produced from electron carriers.
Oxygen is important in ETC because the latter cannot take place without oxygen being the last electron acceptor; the reasons for this are explained below.
Electron Transfer: During the mechanism of ETC, the transfer of electrons from one electron carrier to another occurs down their electrochemical gradient in a series of protein complexes within the inner mitochondrial membrane.
Proton Gradient: Electron transport drives the pumping of protons—H⁺ ions—across the membrane, ultimately forming a proton gradient that will drive ATP generation.
Role of Oxygen: At the end of the ETC, oxygen picks up those electrons and joins with H⁺ to form water, H₂O. Without oxygen, this chain cannot continue because the electrons would back up, thus ending the processes of proton pumping and ATP synthesis.
Prevention of Electron Buildup: Oxygen, on getting reduced, prevents the back buildup of electrons. It thereby allows the smooth flow and proper functioning of the ETC.
Aerobic Respiration:
Oxygen Requirement: Requires oxygen
ATP Yield: High yield of ATP (~ 27 ATP per glucose molecule)
Process: The process involves glycolysis, Krebs cycle, and electron transport chain (ETC)
By-products: Carbon dioxide CO₂ and water H₂O.
Anaerobic Respiration:
Oxygen Requirement: No oxygen is required.
ATP Yield: Low yield of ATP, approximately 2 ATP per glucose molecule.
Process: It involves glycolysis succeeded by fermentation.
Products:
In animal Systems: Lactic acid is formed.
In Yeast Systems: Ethanol and carbon dioxide are formed.
This would be the case for mitochondrial health. In that case, the key factors would be:
Mitochondrial Efficiency: Healthy mitochondria go through the complete cycles of Krebs and the electron transport chain, hence producing ATP optimally.
Oxidative Stress: If mitochondria are damaged, more ROS will be produced, which possibly inactivate ETC components and thus decrease yields of ATP.
Mitochondrial DNA: Its mutation or damage leads to impairment in the expression of critical proteins involved in the process of ATP synthesis.
Supply of Nutrients: The supply of nutrients to the mitochondria at an appropriate level is essential for energy production. Poor nutrition negatively impacts mitochondrial function.
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