Cellular Respiration: A Comprehensive Guide to Energy Production

Introduction

In this process, energy, in the form of adenosine triphosphate (ATP), is released and utilized by the cell for basic biological functions. This guide will delve into the intricacies of cellular respiration, exploring its different stages and the molecules involved.

Steps in Cellular Respiration

Oxidation-Reduction (Redox) Reactions

Electrons are transferred from one molecule to another, playing a pivotal role in cellular respiration.

ATP Synthesis Methods

• Substrate-Level Phosphorylation: Depends on the interaction between enzymes.
• Oxidative Phosphorylation: Powered by the proton motive force and occurs through the use of ATP Synthase.

Glycolysis

Glycolysis produces 4 ATP molecules, all formed through the use of a substrate-enzyme complex. This is the final step in glycolysis. Phosphoenolpyruvate binds to the active site on pyruvate kinase, and the phosphate group is transferred to ADP to make ATP.

Molecules Involved in Each Step

Glycolysis

Takes place in the cytoplasm and begins by priming glucose in preparation for splitting each molecule of glucose into two molecules of 3-carbon sugar phosphate. Each G3P compound is eventually converted into a pyruvate molecule, which will either enter the Krebs cycle in the presence of oxygen.

Pyruvate Oxidation

For every one molecule of glucose that enters glycolysis, there are two pyruvate molecules that result. These molecules are converted into acetyl CoA.

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle has three main segments:

• Segment A: Pyruvate from glycolysis is oxidized into an acetyl group that feeds into the cycle. The 2-carbon acetyl group combines with the 4-carbon oxaloacetate.
• Segment B: Oxidation reactions produce NADH. The loss of two CO2 molecules leaves a new 4-carbon compound.
• Segment C: Two additional oxidations generate another NADH and FADH2. The final yield of products for the Krebs cycle includes: 2 ATP, 2 FADH2, 6 NADH, and 4 CO2.

Types of Respiration

Aerobic Respiration

Oxygen is used as the final electron acceptor. This type of respiration needs oxygen to occur, hence the name aerobic respiration.

Equation: Glucose + Oxygen = Carbon dioxide + Water + Energy

Chemical Equation: C6H12O6 + 6O2 = 6CO2 + 6H2O + ATP + Heat

A major advantage of aerobic respiration is the amount of energy it releases. Without oxygen, organisms can only split glucose into two molecules of pyruvate. The final electron acceptor in aerobic respiration is oxygen.

Anaerobic Respiration

There are two types of fermentation:

• Alcoholic Fermentation: The process of converting glucose into ethanol.
• Lactic Acid Fermentation: What causes your muscles to “burn” when you exercise strenuously for an extended period. Lactic acid fermentation occurs in animals after glycolysis if there is not enough oxygen to perform aerobic respiration.

Specific Gravity (SG) Calculation: SG = Density of solution / Density of water

% Alcohol Calculation: % Alcohol = (SG1 - SGf) / 0.00736

Difference Between Fermentation and General Anaerobic Respiration

Fermentation extends glycolysis to produce usable energy, while anaerobic respiration uses molecules other than oxygen to complete the metabolic cycle.

Demonstration of Aerobic Respiration

When eukaryotic organisms respire, they release CO2, which can combine with H2O to form carbonic acid (H2CO3). Acidic solutions like H2CO3 (pH less than 7) have a larger concentration of H+ ions, while basic solutions (pH greater than 7) contain more OH- ions.