Question

With which of the following fatty acid the value of \(\mathrm{RQ}\) is one? (a) Acetic acid (b) Oleic acid (c) Stearic acid (d) Palmitic acid

Short answer

The fatty acid among the given options having an RQ value of 1 is (a) Acetic acid.

Step-by-step solution

Evaluation of the given fatty acids

Among the given options, acetic acid is not a fatty acid but still we will consider it for evaluation. Oleic acid, stearic acid and palmitic acid are all fatty acids. Each of these substances will have different RQ values, depending on their chemical make-up.

Determination of the RQ

As a rule, carbohydrates have an RQ=1, while fatty acids have RQ<1. However, acetic acid, being a two-carbon compound is an exception and it is completely metabolised to CO2 and H2O similar to carbohydrates. Thus its RQ=1(changed into CO2 / O2 used).

Conclusion

Even though acetic acid is not a fatty acid, among the given options, it is the only substance having an RQ=1. Therefore, the answer is (a) Acetic acid.

Key concepts

Fatty Acids

Fatty acids are an essential part of biology, playing a pivotal role in energy storage and cellular structure. They are typically long hydrocarbon chains with a carboxylic acid group at one end. When metabolized, fatty acids usually yield more energy per gram than carbohydrates. However, they often require more oxygen for oxidation, resulting in a respiratory quotient (RQ) of less than 1. This lower RQ indicates that less carbon dioxide is produced per unit of oxygen consumed, compared to carbohydrates. This makes fatty acids a more oxygen-intensive energy source and impacts how the body balances oxygen and energy needs.

Acetic Acid

Acetic acid is a simple, two-carbon carboxylic acid, commonly known as vinegar when diluted. It's not traditionally classified as a fatty acid due to its short chain length, but it can still be involved in metabolic processes. What's unique about acetic acid is that it is completely oxidized to carbon dioxide and water, similar to carbohydrates, hence it has a respiratory quotient (RQ) of 1. This is an exception among acids and is important in certain metabolic pathways, making acetic acid connect closely to both fat and carbohydrate metabolism.

Biological Metabolism

Biological metabolism refers to the complex array of chemical reactions occurring within living organisms to sustain life. It encompasses the conversion of nutrients into energy, building blocks for macromolecules, and the removal of waste products. Metabolism is broadly categorized into two types: catabolism, which breaks down molecules to release energy, and anabolism, which constructs molecules using energy. Fatty acids and carbohydrates play significant roles here, with fatty acids often used for long-term energy storage and carbohydrates for short-term energy needs. The respiratory quotient (RQ) serves as an indicator of which substrate (fatty acids or carbohydrates) is predominantly being metabolized for energy.

Carbohydrates

Carbohydrates are the body's main energy source, easily used by cells for fuel. Structurally, they are composed of carbon, hydrogen, and oxygen. When metabolized, they tend to have a respiratory quotient (RQ) of 1, meaning the carbon dioxide produced equals the oxygen consumed. This is because carbohydrates are fully oxidized to carbon dioxide and water in aerobic respiration. Due to this straightforward breakdown into basic molecules, carbohydrates are often regarded as a rapid source of energy, especially for activities that demand immediate energy release.

Oleic Acid

Oleic acid is a monounsaturated fatty acid found naturally in various animal and vegetable fats and oils. It is an omega-9 fatty acid that is beneficial for heart health and is involved in various cellular processes. Oleic acid, like other fatty acids, will typically have an RQ of less than 1 due to requiring more oxygen for breakdown compared to what it releases as carbon dioxide. Despite its energy richness, oleic acid metabolism is more complex than that of carbohydrates, sometimes serving as an alternative fuel during prolonged, low-intensity exercise.

Stearic Acid

Stearic acid is a saturated fatty acid often found in animal fat and cocoa butter. In terms of structure, it is a long-chain fatty acid with 18 carbon atoms. It too shares the common attribute of fatty acids with an RQ of less than 1, indicating oxygen consumption that exceeds carbon dioxide output. Stearic acid is usually considered neutral concerning cardiovascular health and undergoes metabolic processes transforming it into energy storage forms or structural components in the body. Its role in energy metabolism is critical, particularly in providing a sustained energy release.

Palmitic Acid

Palmitic acid is another saturated fatty acid, quite abundant in both plant and animal sources. It consists of a 16-carbon chain and, like other fatty acids, has an RQ below 1. This fatty acid is involved not only in providing energy but also in the synthesis of longer-chain fatty acids and various regulatory molecules. Palmitic acid is a key player in the body’s lipid metabolism, contributing to long-term energy storage within fat cells. Its metabolism illustrates how the body balances different energy substrates under various conditions, particularly when carbohydrates are scarce.