Question

How many molecules of acetyl CoA are produced by catabolism of the following fatty acids, and how many passages of the \(\beta\) -oxidation pathway are needed? (a) Palmitic acid, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{14} \mathrm{CO}_{2} \mathrm{H}\) (b) Arachidic acid, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{18} \mathrm{CO}_{2} \mathrm{H}\)

Short answer

Palmitic acid produces 8 acetyl CoA and requires 7 β-oxidation passages; arachidic acid produces 10 acetyl CoA and requires 9 passages.

Step-by-step solution

Determine the Number of Carbons

To solve this problem, first determine the number of carbon atoms in the fatty acid chain. For palmitic acid, this is 16 carbon atoms, and for arachidic acid, it's 20 carbon atoms.

Calculate the Number of Acetyl CoA Molecules

Each acetyl CoA molecule is derived from a 2-carbon unit. Therefore, the number of acetyl CoA molecules produced is half the total number of carbons. So for palmitic acid, it is \( \frac{16}{2} = 8 \), and for arachidic acid, \( \frac{20}{2} = 10 \).

Calculate the Number of β-Oxidation Passages

The number of passages through the β-oxidation pathway is one less than the number of acetyl CoA molecules. This is because the last two carbons remain as one acetyl CoA after the last passage. Thus, for palmitic acid, the passages equal 8 - 1 = 7, and for arachidic acid, 10 - 1 = 9.

Key concepts

Acetyl CoA Production

Acetyl CoA is a crucial molecule in metabolism, vital for energy production. It is produced during the breakdown of fatty acids through a process called fatty acid catabolism. This process involves converting the carbon atoms in fatty acids into acetyl CoA units, each consisting of 2 carbon atoms.
To determine how many acetyl CoA molecules are produced, simply divide the number of carbon atoms in a fatty acid by 2.
This conversion allows these acetyl CoA molecules to enter the citric acid cycle, generating ATP and storing energy for the body to use later.

Beta-Oxidation Pathway

The beta-oxidation pathway is a metabolic process that breaks down fatty acids to produce acetyl CoA units. This multi-step pathway occurs in the mitochondria of cells. It involves the sequential removal of 2-carbon units from the fatty acid chain.

• The process starts by activating the fatty acid, converting it into a fatty acyl-CoA.
• Next, through a series of reactions, it breaks the bonds between the carbon atoms, releasing acetyl CoA.

The number of beta-oxidation cycles needed is one less than the total number of acetyl CoA units produced. This is because each cycle shortens the fatty acid by 2 carbon atoms until only 2-carbon units remain.
Understanding this pathway is essential for grasping how the body efficiently converts fats into usable energy.

Palmitic Acid

Palmitic acid is a common saturated fatty acid found in both animals and plants. It's made up of 16 carbon atoms. During the catabolism of palmitic acid, it produces 8 molecules of acetyl CoA because \( \frac{16}{2} = 8 \).
The process requires 7 passages of the beta-oxidation pathway. This is because 8 cycles reduce the chain to just acetyl CoA molecules, so only 7 passages are needed to cut it down to its final 2-carbon piece.
Palmitic acid serves as a prime example for exploring how saturated fatty acids are broken down within the body.

Arachidic Acid

Arachidic acid, another saturated fatty acid, consists of 20 carbon atoms. When metabolized, it produces 10 acetyl CoA molecules, calculated by \( \frac{20}{2} = 10 \).
For its complete breakdown, 9 passages through the beta-oxidation pathway are necessary. This results in the stepwise removal of carbon atoms down to acetyl CoA units.
Arachidic acid helps illustrate the energy potential stored in longer saturated fatty acids and the efficiency of the beta-oxidation pathway in processing them.