Waxes are made up of long fatty acid chains esterified to long-chain alcohols. Phospholipids are major constituents of the plasma membrane, the outermost layer of animal cells. Like fats, they are composed of fatty acid chains attached to a glycerol or sphingosine backbone.
Instead of three fatty acids attached as in triglycerides, however, there are two fatty acids forming diacylglycerol, and the third carbon of the glycerol backbone is occupied by a modified phosphate group Figure 8. Figure 8. A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone.
The phosphate may be modified by the addition of charged or polar chemical groups. Two chemical groups that may modify the phosphate, choline and serine, are shown here. Both choline and serine attach to the phosphate group at the position labeled R. A phosphate group alone attached to a diaglycerol does not qualify as a phospholipid; it is phosphatidate diacylglycerol 3-phosphate , the precursor of phospholipids. The phosphate group is modified by an alcohol.
Phosphatidylcholine and phosphatidylserine are two important phospholipids that are found in plasma membranes. A phospholipid is an amphipathic molecule, meaning it has a hydrophobic and a hydrophilic part.
The fatty acid chains are hydrophobic and cannot interact with water, whereas the phosphate-containing group is hydrophilic and interacts with water Figure 9.
Figure 9. The phospholipid bilayer is the major component of all cellular membranes. The hydrophilic head groups of the phospholipids face the aqueous solution. The hydrophobic tails are sequestered in the middle of the bilayer. The head is the hydrophilic part, and the tail contains the hydrophobic fatty acids. In a membrane, a bilayer of phospholipids forms the matrix of the structure, the fatty acid tails of phospholipids face inside, away from water, whereas the phosphate group faces the outside, aqueous side Figure 9.
Phospholipids are responsible for the dynamic nature of the plasma membrane. If a drop of phospholipids is placed in water, it spontaneously forms a structure known as a micelle, where the hydrophilic phosphate heads face the outside and the fatty acids face the interior of this structure. Unlike the phospholipids and fats discussed earlier, steroids have a fused ring structure. Although they do not resemble the other lipids, they are grouped with them because they are also hydrophobic and insoluble in water.
All steroids have four linked carbon rings and several of them, like cholesterol, have a short tail Figure Many steroids also have the —OH functional group, which puts them in the alcohol classification sterols. Figure Steroids such as cholesterol and cortisol are composed of four fused hydrocarbon rings. Cholesterol is the most common steroid.
Cholesterol is mainly synthesized in the liver and is the precursor to many steroid hormones such as testosterone and estradiol, which are secreted by the gonads and endocrine glands. It is also the precursor to Vitamin D.
Cholesterol is also the precursor of bile salts, which help in the emulsification of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms by lay people, it is necessary for proper functioning of the body. It is a component of the plasma membrane of animal cells and is found within the phospholipid bilayer.
Being the outermost structure in animal cells, the plasma membrane is responsible for the transport of materials and cellular recognition and it is involved in cell-to-cell communication. Lipids are a class of macromolecules that are nonpolar and hydrophobic in nature. Major types include fats and oils, waxes, phospholipids, and steroids.
Fats are a stored form of energy and are also known as triacylglycerols or triglycerides. Fats are made up of fatty acids and either glycerol or sphingosine. Fatty acids may be unsaturated or saturated, depending on the presence or absence of double bonds in the hydrocarbon chain.
If only single bonds are present, they are known as saturated fatty acids. Unsaturated fatty acids may have one or more double bonds in the hydrocarbon chain. Phospholipids make up the matrix of membranes. They have a glycerol or sphingosine backbone to which two fatty acid chains and a phosphate-containing group are attached.
Steroids are another class of lipids. A cis double bond causes a kink in the chain. In the food industry, oils are artificially hydrogenated to make them semi-solid and of a consistency desirable for many processed food products.
During this hydrogenation process, gas is bubbled through oils to solidify them, and the double bonds of the cis-conformation in the hydrocarbon chain may be converted to double bonds in the trans-conformation. Margarine, some types of peanut butter, and shortening are examples of artificially-hydrogenated trans fats. Many fast food restaurants have recently banned the use of trans fats, and food labels are required to display the trans fat content.
Essential fatty acids are fatty acids required for biological processes, but not synthesized by the human body. Consequently, they have to be supplemented through ingestion via the diet and are nutritionally very important.
Omega-3 fatty acid, or alpha-linoleic acid ALA , falls into this category and is one of only two fatty acids known to be essential for humans the other being omega-6 fatty acid, or linoleic acid. These polyunsaturated fatty acids are called omega-3 because the third carbon from the end of the hydrocarbon chain is connected to its neighboring carbon by a double bond. Salmon, trout, and tuna are good sources of omega-3 fatty acids.
Research indicates that omega-3 fatty acids reduce the risk of sudden death from heart attacks, reduce triglycerides in the blood, lower blood pressure, and prevent thrombosis by inhibiting blood clotting. They also reduce inflammation and may help reduce the risk of some cancers in animals. Omega Fatty Acids : Alpha-linolenic acid is an example of an omega-3 fatty acid. It has three cis double bonds and, as a result, a curved shape. For clarity, the carbons are not shown. Each singly bonded carbon has two hydrogens associated with it, also not shown.
Waxes are nonpolar lipids that plants and animals use for protection and have many functions in society. Waxes are a type of long chain nonpolar lipid. Natural waxes are typically esters of fatty acids and long chain alcohols.
Waxes are synthesized by many animals and plants. Animal wax esters are typically derived from a variety of carboxylic acids and fatty alcohols.
The composition of a wax depends not only on the species, but also on the geographic location of the organism. The best known animal wax is beeswax, but other insects secrete waxes as well.
A major component of beeswax is the ester myricyl palmitate, which bees use for constructing honeycombs. One of its main constituents is cetyl palmitate, an ester of a fatty acid and fatty alcohol.
Plant waxes are derived from mixtures of long-chain hydrocarbons containing functional groups such as alkanes, fatty acids, alcohols, diols, ketones, and aldehydes. Plants also use waxes as a protective coating to control evaporation and hydration and to prevent them from drying out.
Waxes are valuable to both plants and animals because of their hydrophobic nature. This makes them water resistant, which prevents water from sticking on surfaces. Plant Waxes : Waxy coverings on some leaves are used as protective coatings. Unlike most natural waxes, which are esters, synthetic waxes consist of long-chain hydrocarbons lacking functional groups.
Paraffin wax is a type of synthetic wax derived from petroleum and refined by vacuum distillation. Synthetic waxes may also be obtained from polyethylene. Millions of of these waxes are produced annually, and they are used in adhesives, cosmetics, sealants and lubricants, insecticides, and UV protection. They are also used in foods like chewing gum. Generic structure formula of bee waxes : Ester myricyl palmitate is a major component of beeswax.
Phospholipids are amphipathic molecules that make up the bilayer of the plasma membrane and keep the membrane fluid. Phospholipids are major components of the plasma membrane, the outermost layer of animal cells.
Like fats, they are composed of fatty acid chains attached to a glycerol backbone. Unlike triglycerides, which have three fatty acids, phospholipids have two fatty acids that help form a diacylglycerol. The third carbon of the glycerol backbone is also occupied by a modified phosphate group. However, just a phosphate group attached to a diacylglycerol does not qualify as a phospholipid. This would be considered a phosphatidate diacylglycerol 3-phosphate , the precursor to phospholipids. To qualify as a phospholipid, the phosphate group should be modified by an alcohol.
Phosphatidylcholine and phosphatidylserine are examples of two important phospholipids that are found in plasma membranes. Phospholipid Molecule : A phospholipid is a molecule with two fatty acids and a modified phosphate group attached to a glycerol backbone. The phosphate may be modified by the addition of charged or polar chemical groups.
Two chemical groups that may modify the phosphate, choline and serine, are shown here. Both choline and serine attach to the phosphate group at the position labeled R via the hydroxyl group indicated in green.
A phospholipid is an amphipathic molecule which means it has both a hydrophobic and a hydrophilic component. Some lipid tails consist of saturated fatty acids and some contain unsaturated fatty acids. It is to store biochemical energy for later metabolic use. Lipogenesis includes 1 fatty acid synthesis and 2 triglyceride synthesis.
Fatty acid synthesis occurs in the cytoplasm and characterized by the repeated addition of two-carbon units to acetyl-CoA. In triglyceride synthesis, three fatty acids are esterified to a glycerol in the endoplasmic reticulum. The cells that carry out lipogenesis are mostly adipocytes and liver cells. The liver cells, though, release triglycerides in the form of very-low-density lipoproteins VLDL into the bloodstream. Apart from biosynthesis, lipids may also be obtained from the diet. Furthermore, animals that consume carbohydrates in excess tend to convert the carbohydrates into trigylcerides.
The process wherein lipid is broken down to extract energy is called lipolysis. Lipolysis is activated when the circulating insulin level is low whereas the circulating epinephrine is high. Fatty acids may be further degraded in the mitochondria or in the peroxisome, producing acetyl-CoA. This metabolic process in which fatty acids are degraded resulting in the formation of acetyl-coA is called beta oxidation. The acetyl-coA, in turn, may enter the citric acid cycle and degraded ultimately into CO 2 and water molecules, with the concomitant generation of ATP.
The major biological functions of lipids involve energy storage, structural component of cell membrane , and cell signaling. In biological membranes, the lipid component has a hydrophilic head that may be a glycolipid, a phospholipid, or a sterol e. Plants are responsible for incredible feats of molecular transformation.
Plant processes, such as photosynthesis, photophosphorylation, chemiosmosis, carbon fixing reactions, respiration, are presented in this tutorial Read More. A typical eukaryotic cell is comprised of cytoplasm with different organelles, such as nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, and so on.
The cellular contents are surrounded by a double layer, cell membrane. These cellular structures and cell junctions are elaborated in this tutorial Molecules move within the cell or from one cell to another through different strategies.
Transport may be in the form of simple diffusion, facilitated diffusion, active transport, osmosis, endocytosis, exocytosis, epithelial transport, or glandular secretion. This tutorial provides elaborate details on each of these mechanisms. Find out how. The gastrointestinal system breaks down particles of ingested food into molecular forms by enzymes through digestion and then transferred to the internal environment by absorption.
Find out more about these processes carried out by the gastrointestinal system through this tutorial Physiology is the study of how living organisms function.
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