Question

Fatty acids enter the catabolic pathway in the form of: (A) glycerol. (B) adipose tissue. (C) acetyl-CoA. (D) ketone bodies.

Short answer

C: acetyl-CoA

Step-by-step solution

Understand the question

Identify what is being asked. The question queries the form in which fatty acids enter the catabolic pathway.

Review catabolic processes

Recall that catabolic pathways involve the breakdown of molecules to release energy. Fatty acids undergo a process called beta-oxidation in the mitochondria.

Analyze the options

Examine the multiple choice options:(A) glycerol – a component of fats but not directly involved in the main catabolic entry of fatty acids.(B) adipose tissue – stores fats but is not the immediate form in the catabolic pathway.(C) acetyl-CoA – a key molecule produced from beta-oxidation of fatty acids for entry into the citric acid cycle.(D) ketone bodies – produced from fatty acids during prolonged fasting but not the direct form in the catabolic pathway.

Determine the correct answer

Given that beta-oxidation of fatty acids produces acetyl-CoA, the correct form in which fatty acids enter the catabolic pathway is acetyl-CoA.

Key concepts

beta-oxidation

Beta-oxidation is a crucial metabolic process that breaks down fatty acids in the mitochondria. This pathway helps our bodies extract energy from fats.
In beta-oxidation, fatty acids are broken down into two-carbon units, producing acetyl-CoA. Each round of beta-oxidation removes two carbon atoms from the fatty acid, converting them to acetyl-CoA.
The process includes several steps:

• Activation: Fatty acids are activated by combining with CoA to form fatty acyl-CoA.
• Transport: Fatty acyl-CoA is transported into the mitochondria by a special carrier called carnitine.
• Cycle Reactions: Inside the mitochondria, the fatty acyl-CoA undergoes multiple reactions to produce acetyl-CoA.

Beta-oxidation is essential for converting stored fat into energy, especially during prolonged exercise or fasting when glucose levels are low.

acetyl-CoA

Acetyl-CoA is a vital molecule in metabolism. It acts as a convergence point for various catabolic pathways.
Acetyl-CoA is formed through beta-oxidation of fatty acids, glycolysis, and the breakdown of amino acids.
Apart from being a product of these catabolic processes, acetyl-CoA is also a crucial substrate for the citric acid cycle (Krebs cycle).
Here’s why acetyl-CoA is important:

• Energy Production: It enters the citric acid cycle to produce ATP.
• Biosynthesis Precursor: It serves as a building block for creating fatty acids and cholesterol.
• Regulation: Acetyl-CoA levels influence key metabolic pathways, ensuring the balance between energy production and storage.

Understanding the role of acetyl-CoA helps in grasping how the body efficiently manages its energy resources.

catabolic pathways

Catabolic pathways are the processes that break down large molecules into smaller ones, releasing energy.
These pathways are essential for providing the energy required for various cellular activities.
Examples include glycolysis (breaking down glucose), beta-oxidation (breaking down fatty acids), and protein catabolism (breaking down proteins into amino acids).
Key characteristics of catabolic pathways:

• Energy Release: They produce ATP and other high-energy molecules.
• Interconnected Processes: Different catabolic pathways often intersect, sharing intermediates like acetyl-CoA.
• Regulation: Enzymes control these pathways, responding to the body's energy needs.

By understanding catabolic pathways, students can appreciate how our bodies use different nutrients to sustain life and maintain cellular function.

citric acid cycle

The citric acid cycle, also known as the Krebs cycle, is a central part of cellular respiration occurring in the mitochondria.
It processes acetyl-CoA to produce high-energy molecules that power the cell.
Major steps in the citric acid cycle:

• Acetyl-CoA combines with oxaloacetate to form citrate.
• Citrate undergoes a series of enzymatic reactions, regenerating oxaloacetate and producing ATP, NADH, and FADH2.
• NADH and FADH2 are essential for the electron transport chain, which further produces ATP.

The citric acid cycle is vital because:

• Energy Production: It generates ATP and high-energy electron carriers.
• Metabolic Hub: It connects to various metabolic pathways, including those of proteins, fats, and carbohydrates.
• Regulation: The cycle is tightly regulated and adapts to cellular energy demands.

Mastering the citric acid cycle provides deeper insights into how cells harness energy from nutrients.