Some of the remaining double bonds are isomerized to trans in this operation. These saturated and trans-fatty acid glycerides in the diet have been linked to long-term health issues such as atherosclerosis. Triglycerides having three identical acyl chains, such as tristearin and triolein above , are called "simple", while those composed of different acyl chains are called "mixed".
The hydrogenation of vegetable oils to produce semisolid products has had unintended consequences. Although the hydrogenation imparts desirable features such as spreadability, texture, "mouth feel," and increased shelf life to naturally liquid vegetable oils, it introduces some serious health problems.
These occur when the cis-double bonds in the fatty acid chains are not completely saturated in the hydrogenation process. The catalysts used to effect the addition of hydrogen isomerize the remaining double bonds to their trans configuration. These unnatural trans-fats appear to to be associated with increased heart disease, cancer, diabetes and obesity, as well as immune response and reproductive problems.
Waxes are esters of fatty acids with long chain monohydric alcohols one hydroxyl group. Natural waxes are often mixtures of such esters, and may also contain hydrocarbons. The formulas for three well known waxes are given below, with the carboxylic acid moiety colored red and the alcohol colored blue. Waxes are widely distributed in nature.
The leaves and fruits of many plants have waxy coatings, which may protect them from dehydration and small predators. The feathers of birds and the fur of some animals have similar coatings which serve as a water repellent. Carnuba wax is valued for its toughness and water resistance. Phospholipids are the main constituents of cell membranes.
They resemble the triglycerides in being ester or amide derivatives of glycerol or sphingosine with fatty acids and phosphoric acid. The phosphate moiety of the resulting phosphatidic acid is further esterified with ethanolamine, choline or serine in the phospholipid itself. The following diagram shows the structures of some of these components.
Clicking on the diagram will change it to display structures for two representative phospholipids. To see a model of a phospholipid Click Here. As ionic amphiphiles, phospholipids aggregate or self-assemble when mixed with water, but in a different manner than the soaps and detergents.
Because of the two pendant alkyl chains present in phospholipids and the unusual mixed charges in their head groups, micelle formation is unfavorable relative to a bilayer structure. If a phospholipid is smeared over a small hole in a thin piece of plastic immersed in water, a stable planar bilayer of phospholipid molecules is created at the hole. As shown in the following diagram, the polar head groups on the faces of the bilayer contact water, and the hydrophobic alkyl chains form a nonpolar interior.
The phospholipid molecules can move about in their half the bilayer, but there is a significant energy barrier preventing migration to the other side of the bilayer. To see an enlarged segment of a phospholipid bilayer Click Here.
This bilayer membrane structure is also found in aggregate structures called liposomes. Liposomes are microscopic vesicles consisting of an aqueous core enclosed in one or more phospholipid layers. They are formed when phospholipids are vigorously mixed with water. Unlike micelles, liposomes have both aqueous interiors and exteriors. A cell may be considered a very complex liposome. The bilayer membrane that separates the interior of a cell from the surrounding fluids is largely composed of phospholipids, but it incorporates many other components, such as cholesterol, that contribute to its structural integrity.
Protein channels that permit the transport of various kinds of chemical species in and out of the cell are also important components of cell membranes. A very nice dynamic display of the gramicidin channel has been created by a collaboration of Canadian, French, Spanish and US scientists, and may be examined by Clicking Here.
The interior of a cell contains a variety of structures organelles that conduct chemical operations vital to the cells existence. Molecules bonded to the surfaces of cells serve to identify specific cells and facilitate interaction with external chemical entities. The sphingomyelins are also membrane lipids. They are the major component of the myelin sheath surrounding nerve fibers.
Multiple Sclerosis is a devastating disease in which the myelin sheath is lost, causing eventual paralysis. The members of this group of structurally related natural hormones have an extraordinary range of biological effects.
They can lower gastric secretions, stimulate uterine contractions, lower blood pressure, influence blood clotting and induce asthma-like allergic responses. Because their genesis in body tissues is tied to the metabolism of the essential fatty acid arachadonic acid 5,8,11,eicosatetraenoic acid they are classified as eicosanoids.
Many properties of the common drug aspirin result from its effect on the cascade of reactions associated with these hormones. The metabolic pathways by which arachidonic acid is converted to the various eicosanoids are complex and will not be discussed here. A rough outline of some of the transformations that take place is provided below. It is helpful to view arachadonic acid in the coiled conformation shown in the shaded box. Leukotriene A is a precursor to other leukotriene derivatives by epoxide opening reactions.
The prostaglandins are given systematic names that reflect their structure. The initially formed peroxide PGH 2 is a common intermediate to other prostaglandins, as well as thromboxanes such as TXA 2.
Compounds classified as terpenes constitute what is arguably the largest and most diverse class of natural products. A majority of these compounds are found only in plants, but some of the larger and more complex terpenes e.
Terpenes incorporating most of the common functional groups are known, so this does not provide a useful means of classification.
Instead, the number and structural organization of carbons is a definitive characteristic. Terpenes may be considered to be made up of isoprene more accurately isopentane units, an empirical feature known as the isoprene rule.
Because of this, terpenes usually have 5n carbon atoms n is an integer , and are subdivided as follows:. Classification Isoprene Units. Isoprene itself, a C 5 H 8 gaseous hydrocarbon, is emitted by the leaves of various plants as a natural byproduct of plant metabolism. Next to methane it is the most common volatile organic compound found in the atmosphere.
Examples of C 10 and higher terpenes, representing the four most common classes are shown in the following diagram. The initial display is of monoterpenes; larger terpenes will be shown by clicking the " Toggle Structures " button under the diagram.
Most terpenes may be structurally dissected into isopentane segments. To see how this is done click directly on the structures in the diagram. Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail. Cholesterol is a steroid.
Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It is also the precursor of vitamins E and K.
Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells.
Waxes are made up of a hydrocarbon chain with an alcohol —OH group and a fatty acid. Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out. Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules.
Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly. They are all, however, polymers of amino acids, arranged in a linear sequence.
The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. For example, proteins can function as enzymes or hormones.
Enzymes , which are produced by living cells, are catalysts in biochemical reactions like digestion and are usually proteins. Each enzyme is specific for the substrate a reactant that binds to an enzyme upon which it acts.
Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds. An example of an enzyme is salivary amylase, which breaks down amylose, a component of starch. Hormones are chemical signaling molecules, usually proteins or steroids, secreted by an endocrine gland or group of endocrine cells that act to control or regulate specific physiological processes, including growth, development, metabolism, and reproduction.
For example, insulin is a protein hormone that maintains blood glucose levels. Proteins have different shapes and molecular weights; some proteins are globular in shape whereas others are fibrous in nature.
For example, hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein. Protein shape is critical to its function. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation to be discussed in more detail later.
All proteins are made up of different arrangements of the same 20 kinds of amino acids. Amino acids are the monomers that make up proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom bonded to an amino group —NH 2 , a carboxyl group —COOH , and a hydrogen atom.
Every amino acid also has another variable atom or group of atoms bonded to the central carbon atom known as the R group. The R group is the only difference in structure between the 20 amino acids; otherwise, the amino acids are identical. The chemical nature of the R group determines the chemical nature of the amino acid within its protein that is, whether it is acidic, basic, polar, or nonpolar. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond, which is formed by a dehydration reaction.
The carboxyl group of one amino acid and the amino group of a second amino acid combine, releasing a water molecule. The resulting bond is the peptide bond. The products formed by such a linkage are called polypeptides. While the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically a polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have combined together, have a distinct shape, and have a unique function.
The Evolutionary Significance of Cytochrome cCytochrome c is an important component of the molecular machinery that harvests energy from glucose. For example, scientists have determined that human cytochrome c contains amino acids. For each cytochrome c molecule that has been sequenced to date from different organisms, 37 of these amino acids appear in the same position in each cytochrome c.
This indicates that all of these organisms are descended from a common ancestor. On comparing the human and chimpanzee protein sequences, no sequence difference was found. When human and rhesus monkey sequences were compared, a single difference was found in one amino acid. In contrast, human-to-yeast comparisons show a difference in 44 amino acids, suggesting that humans and chimpanzees have a more recent common ancestor than humans and the rhesus monkey, or humans and yeast.
As discussed earlier, the shape of a protein is critical to its function. To understand how the protein gets its final shape or conformation, we need to understand the four levels of protein structure: primary, secondary, tertiary, and quaternary. The unique sequence and number of amino acids in a polypeptide chain is its primary structure. The unique sequence for every protein is ultimately determined by the gene that encodes the protein.
Any change in the gene sequence may lead to a different amino acid being added to the polypeptide chain, causing a change in protein structure and function. What is most remarkable to consider is that a hemoglobin molecule is made up of two alpha chains and two beta chains that each consist of about amino acids.
The molecule, therefore, has about amino acids. The structural difference between a normal hemoglobin molecule and a sickle cell molecule—that dramatically decreases life expectancy in the affected individuals—is a single amino acid of the This can lead to a myriad of serious health problems, such as breathlessness, dizziness, headaches, and abdominal pain for those who have this disease.
Folding patterns resulting from interactions between the non-R group portions of amino acids give rise to the secondary structure of the protein. Both structures are held in shape by hydrogen bonds. In the alpha helix, the bonds form between every fourth amino acid and cause a twist in the amino acid chain. The R groups are attached to the carbons, and extend above and below the folds of the pleat. The pleated segments align parallel to each other, and hydrogen bonds form between the same pairs of atoms on each of the aligned amino acids.
The unique three-dimensional structure of a polypeptide is known as its tertiary structure. This structure is caused by chemical interactions between various amino acids and regions of the polypeptide.
Primarily, the interactions among R groups create the complex three-dimensional tertiary structure of a protein. There may be ionic bonds formed between R groups on different amino acids, or hydrogen bonding beyond that involved in the secondary structure.
When protein folding takes place, the hydrophobic R groups of nonpolar amino acids lay in the interior of the protein, whereas the hydrophilic R groups lay on the outside. The former types of interactions are also known as hydrophobic interactions.
Natural oils, fats and waxes are primarily obtained from either plant or animal sources, including sunflower, oilseed rape, oil palm, beef tallow, lanolin and beeswax. However, in recent years, algae oil has made an appearance as an attractive alternative for use in cosmetic and toiletry products. Oils and fats are organic compounds comprised of esters of glycerine and fatty acids. Glycerine is a trihydric alcohol which forms triesters with the fatty acids.
The fatty acids comprise a straight carbon backbone usually with an even number of carbon atoms and a carboxyl group at one end. The carbon chains can be saturated or unsaturated and vary in length from six to The diagram in figure 1 shows the structure of fatty acids. Glycerine and fatty acids together form triglycerides and this is presented in figure 2. The different types of triglyceride present give oils and fats their various properties.
For example, whether the triglycerides are saturated or unsaturated affects the melting point, unsaturated triglycerides having a lower melting point than saturated triglycerides with the same carbon chain length. Waxes are also comprised of esters. However, they mainly consist of monoesters, which are formed between a fatty alcohol molecule and a fatty acid molecule.
Essentially, the same method of extraction is used for the majority of vegetable oils and fats. This involves a process of pressing, cooking and solvent extraction. The material is then heated, to further facilitate oil and fat extraction, then passed through a screw press, which squeezes out the oil. Additional oil can then be extracted from the remaining material, the oil cake, via solvent extraction using a volatile hydrocarbon, normally hexane.
The oil is finally separated from the solvent by distillation and can then be refined: heated and mixed with alkaline substances to remove undesired fatty acids, degummed, bleached and deodorised figure 3. Animal fats, oils and waxes are mainly produced by rendering, which is the thermal processing operation that breaks down the cellular structures to release triacylglycerols from animal by-products and underutilised fish species.
Wet rendering employs the use of a steam injection. The fats, oils and waxes sink to the bottom of the vat and can be run off. Wet rendering can be preferable as it produces higher quality extracts, but it is more time consuming.
Other natural waxes, including beeswax, candelilla wax, carnauba wax, berry wax, sunflower wax, Myrica fruit wax, rice bran wax, lanolin and jojoba oil, have distinct processing methods. Beeswax is extracted by melting the combs using either boiling water, steam or heat; it can then be separated either by skimming off, running off or centrifugal extraction.
In cosmetics, natural derivatives, made from oils and fats, including beef tallow, rapeseed, soybean, coconut palm and oil palm, and the wax lanolin, are incredibly useful raw materials. They can better harness the desired properties of their parent materials, or can provide new functions which were previously unavailable.
Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out. Figure 5. Steroids such as cholesterol and cortisol are composed of four fused hydrocarbon rings. 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. Their basic structure has four fused carbon rings.
Cholesterol is a type of steroid and is an important constituent of the plasma membrane, where it helps to maintain the fluid nature of the membrane. It is also the precursor of steroid hormones such as testosterone. Answer the question s below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times. Use this quiz to check your understanding and decide whether to 1 study the previous section further or 2 move on to the next section.
Privacy Policy. Skip to main content. Module 3: Important Biological Macromolecules. Search for:. In this outcome, we will discuss lipids and the role they plan in our bodies. Learning Outcomes Distinguish between the different kinds of lipids Identify several major functions of lipids.
For an additional perspective on lipids, explore this interactive animation. In Summary: Lipids Lipids are a class of macromolecules that are nonpolar and hydrophobic in nature.
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