Energy Storage inform of Lipids
Lipids are a class of natural compounds that are hydrophobic in nature and consist of ketoacyl and isoprene groups. They include sterols, waxes, fats, glycerides, phospholids and fat soluble vitamins such as vitamins A, E and K. Lipids are structural compounds being components of the cell wall but also serve in energy storage and signaling. The signaling function of lipids results from their use in nerve cell axons and as bases for hormones. After digestion and absorption lipids are carried as lipoproteins by blood to the liver which regulates lipid levels in blood. Excess lipids are converted to adipose tissue for energy storage. Lipids have certain characteristics that make them excellent alternatives for energy storage compared to glycogen. First, lipids are structural compounds and they are easy to store in the adipose fat layer of the skin.
This fat layer serves other functions such as protection and insulation. When the blood has low lipid levels, the liver synthesizes lipids from carbohydrates or uses the existing adipose energy reserves (Stryer, Berg & Tymoczko, 2007). Although carbohydrates are provide more readily available energy compared to lipids, lipids are preferred due to their high caloric content. One gram of lipid gives 9 kcal of energy when fully oxidized compared too carbohydrates and proteins which gives 4 kcal (Bhagavan, 2002). The oxidation of lipids release more water than glycogen and desert animals such as camels use lipids to store water and energy. The compactness of lipids and their high energy content make them excellent food reserves for migrating birds which must fly for long periods without stopping for food and hibernating animals (Stryer, Berg & Tymoczko, 2007). The only downside of using lipids as an energy source is that they are not readily available as energy sources because they have to be broken down before they can enter into the regular citric acid cycle to generate energy in the form of ATP which can be used to power living organisms.
Saturated versus unsaturated fatty acids
Fatty acids are lipids whose hydrocarbon chain terminates in a carboxylic acid group. Fatty acids have one polar, hydrophilic end, while the other end is non-polar and hydrophobic. Fatty acids can be saturated or unsaturated. Saturated fatty acids have no carbon-carbon double or triple bonds in their hydrocarbon chain while unsaturated fatty acids have at least one double or triple carbon-carbon bond. Saturated fatty acids are rich in cholesterol and not recommended in large amounts unlike unsaturated fatty acids which are rich in high density lipoproteins and do not cause cardiovascular disease. This is because saturated fatty acids are compact and solid at body temperature and can easily clog arteries while unsaturated fatty acids are liquids at body temperature and are not deposited along arteries.
3D Structure of Saturated and Unsaturated Fatty Acids
Saturated and unsaturated fatty acids differ in that saturated fatty acids have single bonds in the hydrocarbon chain while unsaturated fatty acids have at least one double or triple bond in the hydrocarbon chain. This double or triple bonds cause unsaturated fatty acids to exhibit cis-trans isomerism and to have bends. This can be demonstrated by comparing the 3D structures of Palmitic acid and linoleic acid as given in the figure below. Palmitic acid is a saturated fatty acid with a fifteen carbon chain while linoleic acid is an unsaturated fatty acid with a 15 carbon chain too. Linoleic acid has two double bonds on the sixth and ninth carbon atoms. The stable structure of linoleic acid is the cis isomer and as the 3D structure show, linoleic acid has bends while palmitic acid is a straight chain molecule.
Role of Fatty Acids in the Body
Fatty acids are synthesized in large amounts though the fatty acid synthesis process due to their various roles in the body. Their ability to have functional groups containing oxygen, halogens, nitrogen and sulfur give them varied properties making them ideal for various functions in the body. The main purpose of fatty acids in the body is serving as building blocks for other lipids in the body. This is because the fatty acids structure is a basic structure from which other molecules can be formed. Fatty acids are also metabolized as a source of energy just like glucose. In addition fatty acids serve as energy storage mediums because of their compact nature and energy rich molecules compared to glycogen. Fatty acids also serve as structural compounds for the formation of cell membrane
Structure of cell membrane
The cell membrane separates the interior environment of a cell from the exterior environment and controls movement of substances into and out of cells. According to the fluid mosaic model of a cell membrane advanced by Singer and Nicolson, the cell membrane is a two dimensional liquid with proteins and lipids diffusing freely (Sherwood, 2008). Integral membrane proteins are embedded in the lipid bi-layer while peripheral membrane proteins are partially submerged in the lipid bi-layer. Different lipid-proteins ratios give the cell membrane different characteristics such as permeability. The hydrophobic tail of lipids which make the cell membrane is isolated from the aqueous environment by hydrophobic integrations.
Effect of no-fat Diet on the Biochemical functioning of the Body
Most lipids found in food occur as triglycerids, chorestrol and phospholipids. In the body, this are digested to their basic building blocks such as fatty acids and transported to the liver where specialty lipids such as adipose are synthesized. However, some people adopt a fat free diet due to the increased risk of cardiovascular disease, obesity and diabetes posed by trans-fats, chorestrol and partially hydrogenated vegetable oils (Micha & Mozaffarian, 2008). Adipose fat is more compact than glycogen and to store the same amount of energy contained in the adipose fat layer as glycogen would need an increase in weight for individuals due to having more glycogen.
A fat free diet would affect the biochemical functioning of the body significantly. Some fatty acids such as linolenic acid (omega-6 fatty acid) and alpha-linolenic acid (omega-3 fatty acid) can not be synthesized from simple precursors and must be supplied through food (Stryer, Berg & Tymoczko, 2007). These essential fatty acids are important in maintaining good health in the body. Research shows that these omega-3 fatty acids have positive health benefits in infant development, cancer, mental illnesses and cardiovascular disease (Riediger, Othman, Suh & Moghadasian, 2009). Lipids serve as energy sources and water when they are metabolized. Without them in the diet, the body would generate less energy and water from the citric acid cycle which is the typical metabolic pathway.
Bhagavan, N. V. (2002) Medical Biochemistry. San Diego: Harcourt/Academic Press.
Micha R, Mozaffarian D (2008). "Trans fatty acids: effects on cardiometabolic health and implications for policy". Prostaglandins, Leukotrienes, and Essential Fatty Acids 79 (3–5): 147–52.
Riediger ND, Othman RA, Suh M, Moghadasian MH (2009). "A systemic review of the roles of n-3 fatty acids in health and disease". Journal of the American Dietetic Association 109 (4): 668–79.
Sherwood, L. (20080. Human Physiology: From Cells to Systems. New York, NY: Cengage Learning.
Stryer, L., Berg, J. M., & Tymoczko, J. L. (2007). Biochemistry (6th ed.). San Francisco: W.H. Freeman.