Question

Label each of the following statements about a fatty acid with lipid number \(18: 2(\omega-6)\) as true, false, or cannot be determined. (a) This fatty acid is polyunsaturated. (b) This is an essential fatty acid. (c) This is a trans fatty acid. (d) This fat has an even number of carbon atoms.

Short answer

(a) True, (b) True, (c) Cannot be determined, (d) True.

Step-by-step solution

Analyze the Lipid Number

The given fatty acid has the lipid number notation \(18:2(\omega-6)\). This breaks down as follows: the first number \(18\) represents the number of carbon atoms in the fatty acid chain. The second number \(2\) indicates there are two double bonds in the fatty acid. The \(\omega-6\) indicates the position of the first double bond when counted from the methyl end of the fatty acid.

Determine Saturation (Statement a)

A fatty acid is considered polyunsaturated if it contains more than one double bond. Since this fatty acid is labeled as \(18:2\), it has two double bonds, so statement (a) 'This fatty acid is polyunsaturated' is true.

Determine If Essential (Statement b)

Essential fatty acids are those that the body cannot synthesize and must be obtained through the diet. Linoleic acid is a well-known \(\omega-6\) essential fatty acid with the notation \(18:2(\omega-6)\). Therefore, statement (b) 'This is an essential fatty acid' is true.

Check for Trans Fatty Acid (Statement c)

The notation \(18:2(\omega-6)\) does not provide information about the geometry of the double bonds. The presence of cis or trans configurations cannot be determined just from this notation. Thus, statement (c) 'This is a trans fatty acid' cannot be determined.

Analyze Carbon Atoms (Statement d)

The number \(18\) in the fatty acid notation \(18:2(\omega-6)\) specifies the number of carbon atoms, which is 18, an even number. Therefore, statement (d) 'This fat has an even number of carbon atoms' is true.

Key concepts

Lipid Number Notation

Understanding lipid number notation is key to analyzing the structure and properties of fatty acids. This notation typically includes two main numbers and sometimes additional information about the position of double bonds. For example, in the notation \(18:2(\omega-6)\):

• The first number, \(18\), indicates the total number of carbon atoms in the fatty acid chain.
• The second number, \(2\), shows the number of double bonds present. If this number is greater than one, the fatty acid is polyunsaturated.
• The \(\omega-6\) signifies the position of the first double bond from the methyl end of the chain. This particular position helps in classifying different types of fatty acids, like omega-3 or omega-6, which have distinct roles and benefits.

This method of notation offers a compact way to understand essential aspects of fatty acids without delving into complex molecular structures. It is a linchpin for identifying traits like saturation, potential dietary essentiality, and even aspects like chain length, which can affect biological functions.

Polyunsaturated Fatty Acids

Polyunsaturated fatty acids (PUFAs) are essential components of a healthy diet. They have more than one double bond in their hydrocarbon chains. In lipid notation, the number of double bonds is shown as the second number. For instance, in the notation \(18:2\), the digit \(2\) indicates two double bonds, classifying it as polyunsaturated.

• This structure is essential because it influences the fluidity and flexibility of cell membranes.
• They are also precursors to various important signaling molecules in the body.
• Common polyunsaturated fatty acids include omega-3 and omega-6 fatty acids, which are crucial in maintaining cardiovascular health and supporting brain function.

Incorporating adequate amounts of PUFAs from sources like fish, nuts, and seeds can help reduce the risk of chronic diseases and support overall well-being.

Essential Fatty Acids

Essential fatty acids are vital as our bodies cannot produce them, meaning they must come through our diet. The need for these healthy fats is universal:

• Linoleic acid, an example, is a prominent \(\omega-6\) essential fatty acid, denoted as \(18:2(\omega-6)\).
• These fats are necessary for brain function, cell growth, and the production of eicosanoids, which are molecules involved in inflammatory and immune responses.
• A deficiency in essential fatty acids can lead to symptoms such as dry skin, poor healing, and an increased risk of infection.

Ensuring a balanced diet with sources such as plant oils, seeds, and marine products is crucial for acquiring these indispensable nutrients.

Trans Fatty Acids

Trans fatty acids are a specific type of unsaturated fat with at least one double bond in a trans configuration. Unlike the cis configuration, where chains repel and are slightly kinked, trans forms stick straight, mimicking saturated fats. Despite the lipid number notation \(18:2(\omega-6)\) not revealing the geometric configuration of its double bonds, here's why trans fats are important:

• They occur naturally in small amounts but are mostly found in processed foods where oils are partially hydrogenated.
• Trans fats are associated with increased risk factors for cardiovascular disease, by elevating LDL cholesterol and lowering HDL cholesterol.
• Their consumption is widely discouraged due to these negative health impacts; hence, many countries impose regulations to limit these in foods.

Being aware of trans fat content is key to maintaining a healthy heart, making it a crucial consideration when interpreting food labels and making dietary choices.