Energetics of Anaerobic Glycolysis

Introduction

One glucose molecule is broken down into two pyruvate molecules during the glycolysis process. Pyruvate has different fates depending on the microcellular environment (particularly, energy demand, oxygen availability, and the presence or absence of mitochondria).

Pyruvate can enter the citric acid cycle within the matrix of mitochondria and undergo oxidative phosphorylation in mitochondria-containing cells. Oxidative phosphorylation gets its name from the fact that it requires oxygen as the final electron acceptor because it would not be possible without it.

Pyruvate remains within the cytoplasm of erythrocytes and oxygen-depleted tissue, where it transforms to lactate via anaerobic glycolysis. This final step allows for the regeneration of NAD+, a cofactor that must be present in sufficient intracellular concentrations for the earlier glycolysis events to function properly.

On the other hand, Anaerobic glycolysis is substantially less efficient than oxidative phosphorylation, producing only 2 ATP per glucose molecule (versus 32 ATP per glucose molecule produced during oxidative phosphorylation).

Table of Contents

• Overview of Glycolysis
• Anaerobic Glycolysis
• Energetics of Anaerobic Glycolysis
• Frequently Asked Questions (FAQs)

Overview of Glycolysis

Glycolysis is the process of breaking down glucose into pyruvate within a cell’s cytoplasm. Pyruvate can diffuse into mitochondria under aerobic conditions, where it enters the citric acid cycle and produces reducing equivalents like NADH and FADH2.

The electron transport chain then accepts these reducing equivalents, forming 32 ATP per molecule of glucose. Inadequate tissue oxygenation limits the process of oxidative phosphorylation since the electron transport chain requires oxygen as the final electron acceptor.

Glycolysis is the first phase of cellular respiration, which takes place in all living things. During aerobic respiration, Glycolysis is preceded by the Krebs cycle. The cells produce small amounts of ATP in the absence of oxygen by glycolysis, which is followed by fermentation.

The EMP route (Embden–Meyerhof–Parnas) was identified by three German biochemists, Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas, in the early nineteenth century.

Like all biochemical processes, Glycolysis follows a pathway, a series of chemical processes, each mediated by a different enzyme.

Points to Remember in Glycolysis

• It is the process that breaks a glucose molecule into two pyruvate molecules.
• Plant and animal cells undergo the procedure in their cytoplasm.
• The process is carried out by six enzymes.
• Two pyruvate, two ATP, and two NADH molecules are the end products of the process.

Anaerobic Glycolysis

When there is a lack of oxygen during exercise, anaerobic glycolysis is the primary metabolic route. It’s utilised for high-intensity, sustained isometric muscular contractions. From an energy aspect, it is inefficient, producing only two ATP molecules per glucose molecule, which is 19 times less than the entire energy potential of a glucose molecule.

Anaerobic glycolysis is the conversion of glucose to lactate when oxygen (O₂) is insufficient. It is assumed to have been the predominant source of energy in earlier organisms before the presence of significant levels of oxygen in the environment, and hence represents a more primitive form of energy production in cells.

It is a fast process, around 100 times faster than oxidative phosphorylation, despite its inefficiency. The conversion of pyruvate to lactate is the final stage in the pathway, which results in the formation of lactic acid.

The Cori cycle in animals allows lactate to be converted back to glucose by the liver.

Lactate dehydrogenase is the enzyme that converts lactate to pyruvate. Under anaerobic conditions, pyruvate metabolites are as follows:

1. When there is insufficient oxygen in the muscle cells for continued oxidation of pyruvate and NADH created during glycolysis, NAD+ is regenerated from NADH by reducing pyruvate to lactate. Lactate dehydrogenase is the enzyme that converts lactate to pyruvate. The reaction’s standard free energy change is -25.1 kJ/mol.
2. Fermentation of ethanol

Instead of pyruvate, yeast and other anaerobic microbes convert glucose to ethanol and CO₂. In the presence of Thiamine pyrophosphate and Mg++, the enzyme pyruvate decarboxylase converts pyruvate to acetaldehyde. During this reaction, carbon dioxide is produced. Alcohol dehydrogenase converts acetaldehyde to ethanol. During this process, NADH is oxidised to NAD+.

Energetics of Anaerobic Glycolysis

The anaerobic glycolysis pathway occurs when there is no oxygen, when there is insufficient oxygen, and when there is a strong demand for energy in the muscles. Because RBCs lack mitochondria, they rely on lactic acid fermentation for energy.

Anaerobic glycolysis is used to provide energy in cells that cannot produce enough by oxidative phosphorylation. By diverting pyruvate away from mitochondria and through the lactate dehydrogenase process, glycolysis creates 2 ATP in low-oxygenated tissue.

Anaerobic glycolysis provides for faster ATP generation in rapidly contracting skeletal muscle cells with energy demands surpassing what can be met by oxidative phosphorylation alone.

Because mature erythrocytes lack mitochondria, they rely only on anaerobic glycolysis to generate ATP. Despite the presence of mitochondria, other tissues, such as the cornea and lens of the eye and the inner medulla of the kidney, are weakly vascularized and rely primarily on anaerobic glycolysis.

Read Also:

• MCQs on EMP Pathway For NEET
• Life Processes MCQs for NEET
• Significance of Glycolysis
• Metabolism and Metabolic Pathways