Question

Which pathways are involved in the anaerobic metabolism of glucose? Which pathways are involved in the aerobic metabolism of glucose?

Short answer

Anaerobic metabolism involves glycolysis and fermentation. Aerobic metabolism involves glycolysis, the citric acid cycle, and the electron transport chain.

Step-by-step solution

- Understand Metabolism

Metabolism refers to all the biochemical processes that occur within a living organism to sustain life. These processes are divided into two categories: catabolism (breaking down molecules to generate energy) and anabolism (building complex molecules from simpler ones).

- Define Anaerobic Metabolism

Anaerobic metabolism occurs in the absence of oxygen. This type of metabolism primarily includes glycolysis followed by fermentation.

- Glycolysis

Glycolysis is the breakdown of glucose into pyruvate, yielding 2 ATP molecules. The process occurs in the cytoplasm of the cell and does not require oxygen.

- Fermentation

After glycolysis, in the absence of oxygen, the pyruvate undergoes fermentation to regenerate NAD+. Common types of fermentation include lactic acid fermentation (used by muscle cells) and alcoholic fermentation (used by yeast).

- Define Aerobic Metabolism

Aerobic metabolism occurs in the presence of oxygen. This type of metabolism includes glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain (ETC).

- Citric Acid Cycle

In aerobic conditions, pyruvate from glycolysis is converted to acetyl-CoA, which enters the citric acid cycle. This cycle takes place in the mitochondria and generates NADH and FADH2 by oxidizing acetyl-CoA.

- Electron Transport Chain

NADH and FADH2 produced in the citric acid cycle donate electrons to the electron transport chain located in the inner mitochondrial membrane. The ETC uses these electrons to create a proton gradient that drives ATP synthesis, producing 34 ATP molecules.

Key concepts

anaerobic metabolism

Anaerobic metabolism happens when there's no oxygen present. It allows cells to generate energy quickly, albeit less efficiently. This process is vital for activities that require immediate energy, like sprinting. Anaerobic metabolism primarily involves two pathways: glycolysis and fermentation.
Here is how it works in a nutshell:
First, glucose is broken down into pyruvate through glycolysis. Secondly, since there's no oxygen for aerobic respiration, pyruvate undergoes fermentation to produce ATP.

aerobic metabolism

Aerobic metabolism occurs in the presence of oxygen and is more efficient than anaerobic metabolism. It includes three main steps: glycolysis, the citric acid cycle, and the electron transport chain.
This type of metabolism supplies long-lasting energy and is crucial for endurance activities. It occurs in the mitochondria of cells and results in the production of a significant amount of ATP. Let's explore each of these steps in detail to understand the complete process.

glycolysis

Glycolysis is the first step in both anaerobic and aerobic metabolism. It's a series of ten enzyme-driven steps that happen in the cell's cytoplasm. During glycolysis:

• One molecule of glucose (6-carbons) is broken down into two molecules of pyruvate (3-carbons each).
• This process generates a net gain of 2 ATP molecules and 2 NADH molecules.

Glycolysis doesn't require oxygen. However, what happens next (fermentation or further aerobic processes) depends on the availability of oxygen.

fermentation

In the absence of oxygen, cells undergo fermentation to regenerate NAD+, which is essential for glycolysis to continue. Fermentation doesn't produce more ATP; it allows cells to keep generating energy anaerobically. There are two primary types:

• Lactic Acid Fermentation: Occurs in muscle cells and some bacteria. Pyruvate is converted to lactic acid.
• Alcoholic Fermentation: Occurs in yeast and some types of bacteria. Pyruvate is broken down into ethanol and carbon dioxide.

These processes help cells survive short periods of low oxygen availability.

citric acid cycle

Under aerobic conditions, pyruvate from glycolysis is converted to acetyl-CoA, which enters the citric acid cycle (also known as the Krebs cycle). This cycle occurs in the mitochondria and involves multiple steps:

• Acetyl-CoA combines with oxaloacetate to form citrate.
• Through a series of reactions, citrate is converted back to oxaloacetate.
• This cycle produces 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA molecule.

The high-energy electrons carried by NADH and FADH2 move on to the next stage, the electron transport chain.

electron transport chain

The electron transport chain (ETC) is the final step of aerobic metabolism. It occurs in the inner mitochondrial membrane and involves the transfer of electrons from NADH and FADH2 to oxygen.
Here's how it works:

• Electrons pass through a series of protein complexes and coenzymes in the membrane.
• This transfer creates a proton gradient across the membrane.
• The energy from this gradient drives ATP synthesis by ATP synthase.

This process produces about 34 ATP molecules per glucose molecule, making it the most efficient way to produce energy.