What is Fatty acids?
Fatty acids are made up of hydrocarbon chains that end with carboxylic acid groups. Fatty acids and their associated derivatives are the main components of lipids. The length and degree of saturation of the hydrocarbon chain are highly variable between each fatty acid and dictates the associated physical properties (eg, melting point and fluidity). Furthermore, fatty acids are responsible for the hydrophobic (water-insoluble) properties exhibited by lipids.
The role of fatty acids
Fatty acids play important roles in
- Signal transduction pathways
- Sources of cellular fuel
- The composition of hormones and lipids
- Protein modification, and
- Energy storage within adipose tissue (specialized fat cells) in the form of triacylglycerols.
Fatty acids are involved in a wide range of biological signaling pathways. After dietary intake of polyunsaturated lipids, the products of lipid peroxidation can function as precursors to powerful signaling mediators. Some examples of such signaling include eicosanoid production, LDL peroxidation, and modulation of metabolic and neurological pathways.
Of particular importance is the role of fatty acids in the formation of eicosanoids, which are a group of signaling molecules involved in the immune response. Eicosanoids consist of 20-carbon polyunsaturated fatty acids that form the precursors of various molecules responsible for platelet aggregation, chemotaxis, and growth factors. Dietary intake of polyunsaturated fatty acids can also cause LDL peroxidation. When peroxidized LDL is engulfed by macrophages, the resulting immune activation can lead to the development of atherosclerosis. Furthermore, increased intake of cholesterol, saturated, and trans-fatty acids have been linked to the development of various cardiovascular diseases.
Unlike the negative effects of LDL cholesterol, saturated and trans-fatty acids, the intake of monounsaturated and polyunsaturated fatty acids ω-3 and ω-6 is associated with anti-inflammatory effects. In particular, these fatty acids increase the absorption of circulating LDL by the liver and reduce leukocyte activation and platelet reactivity, lymphocyte proliferation, and blood pressure. Also, polyunsaturated fats are also necessary for normal growth and development, as well as for the regulation of visual acuity and cognition in the central nervous system. Other beneficial effects of polyunsaturated fatty acids to inhibition of cancer cell proliferation and antitumor effects have been observed in animal models.
Fatty acid metabolism as a fuel source
Fatty acid metabolism involves the absorption of free fatty acids by cells through fatty acid-binding proteins that transport fatty acids intracellularly from the plasma membrane. Free fatty acids are activated through acyl-CoA and transported to 1) the mitochondria or peroxisomes to convert them to ATP and heat as a form of energy; 2) facilitate gene expression by binding to transcription factors, or 3) the endoplasmic reticulum for esterification into various classes of lipids that can be used as energy storage.
When used as an energy source, fatty acids are released from triacylglycerol and processed into two-carbon molecules identical to those formed during the breakdown of glucose; Furthermore, the two-carbon molecules generated by the breakdown of fatty acids and glucose are used to generate energy through the same pathways. Glucose can also be converted to fatty acids under conditions of excess glucose or energy within a cell.
Fatty acids are also used as a form of energy storage as fat droplets made up of hydrophobic triacylglycerol inside specialized fat cells called adipocytes. When stored in this form, fatty acids are important sources of thermal and electrical insulation, as well as protection against mechanical compression. Fatty acids are the preferred form of energy storage for glucose because they produce approximately six times the amount of usable energy. Storage in the form of triacylglycerol molecules consists of three fatty acid chains attached to one glycerol molecule.
Cell membrane formation
One of the most critical functions of fatty acids is the formation of the cell membrane, which envelops all cells and associated intracellular organelles. In particular, cell membranes are made up of a phospholipid bilayer consisting of two fatty acid chains attached to glycerol and a hydrophilic phosphate group attached to a smaller hydrophilic compound (eg, choline). Therefore, each phospholipid molecule has a hydrophobic tail made up of two fatty acid chains and a hydrophilic head made up of the phosphate group. Cell membranes are formed when two phospholipid monolayers associate with the tails that unite in an aqueous solution to create a phospholipid bilayer.
An important characteristic of cell membranes is the fluidity of the membrane, which refers to the viscosity of the lipid membrane. Membrane fluidity is influenced by the diversity of the lipid chains that comprise the cell membrane, including the length of the chains and the level of saturation. When the fluidity of the membrane changes, the function and physical characteristics of the membrane are also altered.
For example, increased consumption of ω-3 fatty acids can increase the level of EPA and DHA in cell membranes. When such incorporation occurs in the cell membranes of retinal cells, there is an improvement in light transduction. Furthermore, increased accumulation of ω-3 fatty acids in red blood cell membranes results in increased membrane flexibility, which can result in better microcirculation.
Fatty acids play several critical roles through their interaction with various proteins. Protein acylation is an important function of polyunsaturated fatty acids, as it is essential for the anchorage, folding and function of multiple proteins. Furthermore, fatty acids can also interact with various nuclear receptor proteins and promote gene expression, since various complexes of fatty acids and proteins function as transcription factors. In this way, fatty acids have been found to regulate gene transcription related to metabolism, cell proliferation, and apoptosis.
Types of fatty acids
- Unsaturated fatty acids
- Saturated fatty acids
Unsaturated fatty acids
Monounsaturated fatty acids contain a carbon-carbon double bond, which can be found at different positions along the fatty acid chain. Most monounsaturated fatty acids are between 16 and 22 carbons in length and contain a cis double bond, which means that the hydrogen atoms are oriented in the same direction, which introduces a curve in the molecule. Furthermore, the cis configuration is associated with thermodynamic instability and, therefore, a lower melting point compared to trans and saturated fatty acids.
Polyunsaturated fatty acids contain more than one double bond. When the first double bond is located between the third and fourth or sixth and seventh carbon atoms of the carbon-oxygen bond, they are called ω-3 and ω-6 fatty acids, respectively. Polyunsaturated fatty acids are produced only by plants and phytoplankton and are essential for all higher organisms.
Saturated fatty acids
Saturated fatty acids are saturated with hydrogen, and most are linear hydrocarbon chains with an even number of carbon atoms. The most common fatty acids contain 12–22 carbon atoms.
Long-chain fatty acids
Long-chain fatty acids (C16 and higher) can be saturated or mono/polyunsaturated depending on the presence of one or more double bonds in the carbon chain. Oleate is the most abundant long-chain monounsaturated fatty acid, with a chain length of 18 carbons and a double bond located between C9 and C10 from the methyl end (C18: 1n-9). In addition, long-chain fatty acids are insoluble in water and circulate through plasma as an esterified complex, triacylglycerols, or unesterified forms freely bound to albumin.
Short-chain fatty acids
Short-chain fatty acids are the main end products of bacterial metabolism in the human large intestine. Furthermore, while short-chain fatty acids are formed from various precursors by anaerobic microorganisms, carbohydrates are the most common progenitors of short-chain fatty acids.
Fatty acid structure
Fatty acids are made up of carbon chains that contain a methyl group at one end and a carboxyl group at the other. The methyl group is called the omega (ω) and the carbon atom next to the carboxyl group is called the “α” carbon, followed by the “β” carbon, etc. Fatty acid molecules also have two chemically distinct regions: 1) a long hydrophobic hydrocarbon chain, which is not highly reactive; and 2) a carboxyl group (-COOH), which is hydrophilic and highly reactive. At the cell membrane, practically all fatty acids form covalent bonds with other molecules through carboxylic acid groups.
As described above, fatty acids can contain double bonds (unsaturated fatty acids) or non-double bonds (saturated fatty acids) in the hydrocarbon chains. The presence of double bonds results in the formation of kinks or kinks in the molecules and impacts the ability of fatty acid chains to accumulate. Other differences between fatty acids include the length of the hydrocarbon chains, as well as the number and position of the double bonds. The presence of the double bond will also influence the melting point since unsaturated fatty acids have a lower melting point than saturated fatty acids. The melting point is also influenced by whether there is an odd or even number of carbon atoms; an odd number of carbons is associated with a higher melting point. Furthermore, saturated fatty acids are highly stable, while unsaturated fatty acids are more susceptible to oxidation.
Fatty Acids, Role, Types ,Unsaturated And Saturated