Health and Energy: Minerals, Carbohydrates, Fats, and Oils

Chapter 7 Health and Energy: Minerals, Carbohydrates, Fats, and Oils

Review Questions

Carbohydrates are biochemical molecules containing the elements carbon, hydrogen, and oxygen in roughly a 1:2:1 atomic ratio. Most of the carbon atoms found in carbohydrates are chemically bonded to one hydroxyl group (-OH) and one hydrogen atom. Thus, carbohydrates are often referred to as polyhydroxy organic compounds.

Glucose is a carbohydrate because it contains the elements carbon, hydrogen, and oxygen in a 1:2:1 ratio. Glucose has the molecular formula C6H12O6, and a molecular structure resembling a six-member ring composed of five carbon atoms and one oxygen atom. Glucose belongs to an important subgroup of carbohydrates, known as sugars or saccharides.

Dextrose is called blood sugar because dextrose, also known as glucose, circulates in your blood in a concentration of about 0.1%. Glucose in the blood provides a rapid and critical energy source for the cells in your body.

Sugars are characteristically highly water-soluble (they dissolve in water), white in appearance, and sweet to the taste.

Both monosaccharides and disaccharides are members of the sugar subgroup of carbohydrates. Those sugar molecules containing one ring are called monosaccharides, and those containing two rings are called disaccharides.

Gestational diabetes is a medical condition in which diabetic symptoms, such as an elevated blood glucose level, appear in a woman during pregnancy. This condition usually disappears following delivery.

In type 1 diabetes, the body does not produce sufficient quantities of insulin. In type 2 diabetes, the body produces insulin, but the cells cannot use it properly. In gestational diabetes, the mother is unable to produce enough insulin to handle the increased glucose levels that result from the increased hormone secretions associated with pregnancy.

Both glucose and fructose have the formula C6H12O6. As compounds with the same chemical formula are called isomers, glucose and fructose are isomers. Unlike molecules of glucose, which exist in six-member ring structure with one side chain, fructose molecules consist of a five-member ring with two single-carbon side chains.

a) Sugar beets and sugar cane are sources of sucrose.

b) Raisins, grapes, and figs are sources of glucose.

c) Fruits and honey are sources of fructose.

d) Milk is a source of lactose.

e) Beans are a source of raffinose.

In general, the term hydrolysis reaction refers to the reaction of a substance with water. In saccharides, hydrolysis results in the addition of water to the C-O-C linkage.

The hydrolysis of sucrose results in the addition of water to the C-O-C linkage and produces equal amounts of glucose and fructose.

Three sweeteners that are “sugarless” are Sucralose™ (a molecule that is similar to sucrose, but with three of its –OH groups replaced with chlorine atoms), xylitol (a molecule with five carbon atoms each with an –OH group), and sorbitol (a molecule composed of six carbon atoms and six –OH groups).

Polyhydroxyl molecules are useful components of skin moisturizers because their multiple –OH groups can hydrogen bond to water molecules, thereby allowing water from the air to be attracted to them.

Lactose intolerance is a condition that results from the lack of an enzyme called lactase. Lactase is required for the hydrolysis of lactose to glucose and galactose. When individuals lacking this enzyme ingest lactose, it passes undigested in to the large intestine. Once there, bacteria convert it to carbon dioxide and hydrogen gas, which result in bloating, and lactic acid, which produces diarrhea.

Condensation reactions are those in which two or more molecules combine forming a larger molecule and, in the process, eliminate a small molecule, such as water. When two monosaccharides combine to form a disaccharide, a molecule of water is eliminated. Each of the monosaccharide components, however, still has several –OH groups that remain unreacted. Thus, the disaccharide could condense with another monosaccharide, eliminate a molecule of water, and form a trisaccharide. Similarly, repeated condensations would result in the formation of a condensation polymer called a polysaccharide.

Starch is depolymerized by enzyme-assisted (or enzyme catalyzed) hydrolysis reactions back to its monomer units, individual glucose molecules.
Starch consists of two glucose polymers, amylose and amylopectin. Amylose, composed of approximately 100 glucose monomers in a linear unbranched chain, comprises about 20% of the starch molecules. Because of the large number of free –OH groups, and the linear arrangement of the glucose monomers, amylose is soluble in water.

Unlike amylose, amylopectin is composed of thousands of glucose molecules in highly branched chains. Amylopectin, comprising about 80% of the starch molecules, is water insoluble.

When there is an excess of glucose in your body, a small amount is polymerized into a highly branched molecule called glycogen. Glycogen, stored in the muscles and liver, can be quickly depolymerized back to glucose to provide energy.

To meet the long-term energy needs of the body, excess glucose (beyond that which can be stored as glycogen) is converted to fat and stored as a potential energy source.

Glucose molecules are composed of carbon atoms in a tetrahedral arrangement. As a result, glucose is a nonplanar molecule. When glucose rings are condensed, such as in the disaccharide sucrose or the polysaccharide starch, adjacent rings can have different three-dimensional orientations. The C-O-C linkage unit between the rings can exist parallel to the rings (in-plane) or above (or below) the rings (out-of-plane). Different geometrical orientations result in different properties.

When the oxygen atom of this linkage lies below one of the rings and in the plane of the other forming a “stepped” linkage arrangement, the rings are said to be in the alpha form. The glucose linkages in starch and the linkage between fructose and glucose in sucrose exist in the alpha form. In general, humans possess enzymes that can facilitate the hydrolysis these alpha linkages.

When the oxygen atom of the linkage lies in the plane of both rings, a beta linkage is formed. This arrangement is common in the polysaccharide cellulose. Humans generally do not possess enzymes that facilitate the hydrolysis of beta linkages.

Cellulose is produced in plants by the process known as photosynthesis. This process, the reverse of the combustion reaction, converts carbon dioxide, water, and energy to produce carbohydrates and oxygen. A general equation for this process is given below.

CO2 + H2O + energy (sunlight)  CH2O + O2

Insoluble fiber, such as cellulose, absorbs, but is insoluble, in water. Soluble fiber, which consists of polymers of monosaccharides in addition to glucose, is very good at binding to water.

An oil is the liquid counterpart of a solid fat. Oils have lower melting points than solid fats because they contain shorter chain saturated fatty acids and/or contain more double bonds between their carbon atoms (more unsaturated).

Paraffin wax consists of long chain hydrocarbons obtained from oil refining. It is the major component of most candles.

A triglyceride is a triester molecule resulting from the condensation of the three-carbon molecule glycerol with three fatty acids.

Saturated and unsaturated fatty acids differ in the nature of their carbon-carbon bonds. Fatty acids that have one or more carbon-carbon double bonds along the hydrocarbon chain are termed unsaturated. Unsaturated fatty acids generally have lower melting points then their saturated counterparts.

Three plant sources of fats and oils include olives, peanuts, and corn. Three animal sources include butterfat, beef fat, and tallow.

An omega-3 fatty acid is a polyunsaturated fatty acid, generally with 5 or 6 carbon-carbon double bonds, in which the last double bond in the hydrocarbon chain occurs between the third and fourth carbons from the end of the chain. (Note: The beginning of the chain, by convention, is the COOH group.) Since the last carbon of the chain is referred to as the omega carbon, the fourth carbon from the end is called the “omega minus three” or “omega-3” carbon. Fatty acids with this configuration of unsaturation are termed omega-3 fatty acids.

A trans-fatty acid is one in which the hydrocarbon units, or “R” groups, around the carbon-carbon double bond lie on different sides of the unsaturated bond.

Understanding Concepts

The three-dimensional structure of glucose is given below.

Like other sugars, glucose has several –OH groups that can form hydrogen bonds with water molecules. This makes glucose, and other sugars, soluble in water.

In the cells in the body, glucose, a six-carbon molecule, is first split into two three-carbon molecules and then gradually oxidized into carbon dioxide and water. The net chemical equation for this reaction is the same as that obtained for the combustion of glucose, but the result is different. The enzyme-catalyzed oxidation in the cells occurs at body temperature, does not produce a flame, and efficiently transforms the chemical energy of the glucose molecule into useful energy that the cell can use rather than converting it into heat.

The hydrolysis of sugars in the body can be performed without the use of acid because the availability of specific catalysts, called enzymes.

A number of conditions are required for the optimal binding of the sweet molecule and the receptor. First, the –OH group on the molecule must form a hydrogen bond with either an oxygen or nitrogen atom on the receptor. Second, another hydrogen bond between an oxygen atom of the molecule and a hydrogen bonded to either an oxygen or nitrogen atom on the receptor is required. Third, the hydrocarbon region behind the two hydrogen bonded oxygen atoms of the molecule must be hydrophobic. Lastly, the molecule must be small and fit into a specific location on the receptor.

The relationship between the structure of a compound and its sweetness can be explained by the receptor–molecule binding theory. According to this theory, a molecule triggers the sensation of sweetness when it fits into the receptor sites located in the taste buds of our mouths. In general, most of these compounds are small molecules that contain several hydroxyl, or –OH groups.

Carbohydrate loading is a process believed to temporarily double or triple the usual amount of glycogen available for immediate use by the body. Glycogen, the temporarily polymer of glucose stored in muscle and liver cells, can be rapidly depolymerized to glucose in order to provide energy to the body. Normally, about one day’s worth of energy is stored in the form of glycogen. Carbohydrate loading, practiced by some serious athletes, occurs when the glycogen supply is depleted by a regime of exercise and/or a diet low in carbohydrates over the course of several days. A few days before a competitive event, they consume a high-carbohydrate diet, which generates much more glucose than they can utilize. The excess glucose is converted to high levels of glycogen stores (sometimes up to 300 grams) which are believed to enhance short-term performance.

The better a molecule can fulfill the structural requirements described in question 34, the sweeter the compound is perceived to be. In most artificial sweeteners, the -OH group of the molecule attached to either an oxygen atom or nitrogen atom on the receptor is replaced by an N-H group.

37. As a result of their high oxygen content, carbohydrates are a relatively inefficient way to store energy. Unlike hydrocarbons, carbohydrates are partially oxidized and, therefore, produce less energy per gram when burned. Animal fat, a triester composed of three fatty acids and a glycerol backbone, is structurally similar to a hydrocarbon molecule.

Amylose is an unbranched polymeric chain consisting of approximately 100 glucose monomers. Amylopectin is a highly branched polymeric chain consisting of thousands of glucose monomers.

Hydrogenation is a chemical process in which hydrogen is added to a carbon-carbon double bond. This process results in a decrease in the level of unsaturation of common plant oils, and is commonly conducted until the desired “softness” characteristics are obtained (partial hydrogenation). Due to the heating required for this hydrogenation process, some of the remaining carbon-carbon double bonds undergo a change in their geometry. Many C=C bonds originally in the cis configuration (both hydrocarbon residues around the bond on the same side) are converted into the trans configuration (the hydrocarbon residues around the bond lie on opposite sides). Fatty acids containing these trans configurations are referred to as trans fatty acids.

Synthesizing Ideas

In the body, glucose is first split into two three-carbon molecules and then gradually oxidized into carbon dioxide and water. The net chemical equation for this reaction is the same as that obtained for the combustion of glucose, but the result is far more effective. The enzyme-catalyzed oxidation in the cells occurs at body temperature, does not produce a flame, and efficiently transforms the chemical energy of the glucose molecule into useful energy that the cell can use rather than converting it into heat. If glucose was combusted like wood, you would experience a rapid and adverse increase in body temperature and, because of the heat generated by the combustion process, you would not be able to harness all of the chemical energy of the glucose molecule and convert it into useful energy.

Diabetes is a chronic disease in associated with elevated levels of blood glucose. While the treatment for diabetes depends upon its type (I, II, or III), some diabetic patients who produce insulin, but can’t utilize it to control their blood glucose levels, can control their condition with diet. It is recommended that these individuals consume a diet that is low in fat, has only moderate amounts of protein, and is high in complex carbohydrates. Current research indicates that complex carbohydrates are absorbed more slowly in the digestive tract, thereby preventing spikes or surges in blood glucose levels.

The branched structure of glycogen is more effective as a storage molecule for two reasons. First, the highly branched structure limits the solubility of glycogen making it compatible with the fluid balance required for the cell to live. Also, the compact structure makes the enzyme-mediated hydrolysis process more efficient.

A low intake of meat is recommended in order to maintain a healthy lifestyle primarily because of the high fat content associated with meat products. Beef and other red meats contain animal fat consisting of about 50% saturated fatty acids. On average, citizens of developed Western countries consume 34-40% of their dietary energy in the form of fat. Research indicates that only 30% of our dietary energy should come from fat, and that only 1/3 of the fat consumed should be saturated.

a) alpha form:

b)beta form:

Due to the availability of specific enzymes in your digestive tract, you are only able to digest the alpha form.

a) Lactose (glucose + galactose)

_O_

G Ga

b) a trisaccharide composed of three glucose molecules

_O__O_

G G G

The upper and lower limits of melting point of this triglyceride would be 46oC and -75oC, respectively.

a) Starch is composed of two glucose polymers. The first, amylose, constitutes approximately 20% of the polymer molecules in starch, and consists of about 100 glucose monomer units linked in unbranched chains. The remainder of the polymer units exist as a material known as amylopectin, a water insoluble molecule consisting of thousands of glucose monomers in a highly branched structure. Glycogen, on the other hand, only consists of glucose monomers in a highly branched arrangement.

b) Amylose consists of about 100 glucose monomers linked in unbranched chains. Amylopectin is composed of thousands of glucose monomers in a highly branched structural arrangement. Amylose is soluble in water while amylopectin is not.

a) Oleic acid would be classified as an omega-9 fatty acid (structure below).

b) Linolenic acid would be classified as an omega-3 fatty acid (structure below).

In comparing triglycerides composed of fatty acids of identical size, but differing degrees of unsaturation, the melting points of the triglycerides decrease as the number of the C=C bonds increase. Thus, the order of melting points, from lowest to highest, would be polyunsaturated, mono-unsaturated, and saturated.

The complete hydrogenation of one molecule of linolenic acid would require three molecules of H2. There are three double bonds in each molecule of linolenic acid, and each double bond requires one molecule of H2 to become saturated. The structure of the saturated fatty acid resulting from this complete hydrogenation is given below.

Reaction for the complete combustion of glucose:

C6H12O6 + 6 O2 6 CO2 + 6 H2O

Reaction for the complete combustion of hydrocarbon:

C13H28 + 20 O2  13 CO2 + 14 H2O

The ratio of the number of molecules of O2 consumed by the hydrocarbon compared to the sugar in the above reactions is:

20 / 6 = 3.3

Thus, approximately 3.3 times as much heat is generated from the combustion of the hydrocarbon when compared to the combustion of glucose.