Chapter 3: The Molecules of Life

Monosaccahrides

Simple sugars, the monomers of carbohydrates (from the Greek "mono", simple, and "sacchar", sugar. Examples: glucose (found in sports drinks) fructose (found in fruit)

Hydrocarbon

Simplest carbon compounds, have only carbon and hydrogen atoms

What requirement did the FDA introduce in 2006 with regards to trans fats?

Since 2006, the U.S. Food and Drug Administration (FDA) has required trans fats to be listed on nutrition labels.

Describe the amino acid glycine's side group.

Some amino acids have very simple side groups; the amino acid glycine, for example, has a single hydrogen as its side group. Other amino acids have more complex side groups, some with branches or rings within them.

What is dietary fiber?

The cellulose in plant foods, which passes unchanged through our digestive tract, is commonly known as dietary fiber (your grandma might call it "roughage"). Because it remains undigested, fiber does not serve as a nutrient, but it does help keep your digestive system healthy. Among other benefits, the passage of cellulose stimulates cells lining the digestive tract to secrete mucus, which allows food to pass smoothly.

What are three categories of large biological molecules?

1. Carbohydrates (ex: found in starchy foods such as french fries and bagels) 2. Proteins (ex: enzymes and the components of your hair) 3. Nucleic acids (ex: DNA)

Two examples of functional groups?

1. Hydroxyl group (-OH) 2. Carboxyl group (-COOH)

The rapid conversion of glucose to cellular energy is the reason _____.

An aqueous solution of glucose (often called dextrose) is given as an IV to sick or injured patients; the glucose provides an immediate energy source to tissues in need of repair.

What foods are rich in fiber?

Foods rich in fiber include fruits and vegetables, whole grains, bran, and beans.

What are the major sources of starch in our diet?

Potatoes and grains, such as wheat, corn, and rice.

How do cells link amino acid monomers together?

Proteins as Polymers Cells link amino acid monomers together by-can you guess?-dehydration reactions.

Explain the molecular structure of an amino acid. What is the variable component that distinguishes one amino acid from another?

Each amino acid consists of a central carbon atom bonded to four covalent partners (carbon, remember, always forms four covalent bonds). Three of those attachments are common to all 20 amino acids: a carboxyl group (-COOH), an amino group (-NH2), and a hydrogen atom. The variable component of amino acids, the side group (also called an R group, or radical group), is attached to the fourth bond of the central carbon (Figure 3.16a}. Each type of amino acid has a unique side group, giving that amino acid its special chemical properties (Figure 3.16b).

How do you prevent lactose intolerance symptoms?

Eat lactose-free foods or take lactate as a pill

How do lipids react with water?

In contrast to most biological molecules, lipids are hydrophobic ("water-fearing"); they do not mix with water. You've probably seen this chemical behavior when you combine oil and vinegar: The oil, which is a type of lipid, separates from the vinegar, which is mostly water (Figure 3.10). If you shake vigorously, you can force a temporary mixture long enough to douse your salad, but what remains in the bottle will quickly separate.

Why are fluffy towels so absorbent?

In contrast, cellulose does not dissolve in water, but water can adhere to its surface, which is why a fluffy bath towel (high in cellulose) is so water absorbent. Thus, almost all carbohydrates are hydrophilic ("water-loving") molecules. Not all biological molecules share this property.

Is body fat normal? What kind of cells do we store body fat in, and what are some benefits of it?

It is important to understand that a reasonable amount of body fat is both normal and healthy as a fuel reserve. We stock these long-term food stores in specialized reservoirs called adipose cells, which swell and shrink when we deposit and withdraw fat from them. This adipose tissue, or "body fat," not only stores energy but also cushions vital organs and insulates us, helping maintain a warm body temperature even when the outside air is cold.

Why is milk healthy?

It's rich in protein, minerals, and vitamins

What is the main fuel for cellular work?

Monosaccahrides, particularly glucose. Like an automobile engine consuming gasoline, your cells break down glucose molecules and extract their stored energy, giving off carbon dioxide an "exhaust".

What are two monosaccharides, two disaccharides, and what do they dissolve in?

Monosaccharides (such as glucose or fructose) and disaccharides (such as sucrose or lactose) dissolve readily in water, forming sugary solutions.

The American natural "sweet tooth" persists in spite of what?

Our growing awareness about how sugar can negatively affect our health. Sugar is a major cause of tooth decay. Moreover, high sugar consumption tends to replace eating more varied and nutritious foods.

What type of fatty acids do most plants and fish have? Why are those fatty acids less likely to form solids than fatty acids found in most animal fats? Give examples.

Plant and fish fats are relatively high in unsaturated fatty acids. The bent shape of unsaturated fatty acids makes them less likely to form solids (imagine trying to build a wall using irregularly bent bricks!), so most un- saturated fats are liquid at room temperature. Foods that are primarily unsaturated include vegetable oils (such as corn and canola oil) and fish oils (such as cod liver oil).

Methane is produced by _____.

Prokaryotes that live in swamps and in the digestive tracts of grazing animals, such as cows.

How might a food manufacturer make vegetable oil solid?

Sometimes a food manufacturer wants to use a vegetable oil but needs the food product to be solid, as with margarine or peanut butter. To achieve this, the manufacturer can convert unsaturated fats to saturated fats by adding hydrogen, a process called hydrogenation. Unfortunately, hydrogenation also creates trans fats, a type of unsaturated fat that is particularly bad for your health.

What is the most common disaccharide?

Sucrose (table sugar), which consists of a glucose monomer linked to a fructose monomer. Sucrose is the main carbohydrate in plant sap, and it nourishes all the parts of the plant.

Why are proteins called macromolecules?

The Monomers of Proteins: Amino Acids All proteins are macromolecules, which are made by stringing together a common set of 20 kinds of amino acids.

How is it possible to make such a huge variety of proteins from just 20 kinds of amino acids?

The answer is arrangement. You know that you can make many different English words by varying the sequence of just 26 letters. Though the protein alphabet is slightly smaller (just 20 "letters"), the "words" are much longer, with a typical polypeptide being at least hundreds of amino acids in length. Just as each word is constructed from a unique succession of letters, each protein has a unique linear sequence of amino acids. This specific amino acid sequence-the "spelling" of a polypeptide is called the protein's primary structure (Figure 3.18).

What is a polypeptide?

The bond between adjacent amino acids is called a peptide bond (Figure 3.17). The resulting long chain of amino acids is called a polypeptide. A protein is a polymer consisting of one or more polypeptides.

Give an example of a hydrolysis reaction

The breakdown of lactose into its monomers by the enzyme lactate.

What are anabolic steroids?

The controversial drugs called anabolic steroids are synthetic variants of testosterone. In human males, testosterone causes buildup of muscle and bone mass during puberty and maintains masculine traits throughout life. Because anabolic steroids resemble testosterone, they mimic some of its effects. Anabolic steroids are prescribed to treat diseases that cause muscle wasting, such as cancer and AIDS. On the flip side, athletes can abuse anabolic steroids to build up their muscles quickly.

Why are hydrocarbons important fuels in your body?

The energy-rich parts of fat molecules have a hydrocarbon structure

How many grams of trans fats can a food product have if its label says 0g trans fats?

But even if a label on a hydrogenated product says 0 grams (g) of trans fats per serving, the product might still have up to 0.5 g per serving. Any product with partially hydrogenated vegetable oil contains trans fats. (See the Process of Science section in Chapter 1-"Are Trans Fats Bad for You?" -for an investigation of the health effects of trans fats.)

What can an unfavorable change in the surrounding environment do to a protein? What is that called?

A protein's shape is sensitive to the surrounding environment. An unfavorable change in temperature, pH, or some other quality of the environment can cause a protein to unravel and lose its normal shape. This is called denaturation of the protein. If you cook an egg. the transformation of the egg white from clear to opaque is caused by proteins in the egg white denaturing. As the proteins fall apart, they separate and form a white solid. One of the reasons why extremely high fevers are so dangerous is that some proteins in the body become denatured above 104°F.

Describe the molecular structure of a typical fat. What is it called?

A typical fat consists of a glycerol molecule joined with three fatty acid molecules via dehydration reactions (Figure 3.11 ). The resulting fat is called a triglyceride, a term you may see on food labels or in the results of a blood test.

Distinguish between a polypeptide chain and a protein.

At this point. you might be thinking that a polypeptide chain is the same thing as a protein, but that's not quite true. The distinction between the two is like the relationship between a long strand of yarn and a sweater that you could knit from the yarn. A functional protein is one or more polypeptide chains precisely twisted, folded. and coiled into a molecule of unique shape.

Carbohydrates

Commonly known as "carbs," they are a class of molecules including sugars and polymers of sugars. Some examples are small sugar molecules dissolved in energy drinks and the long starch molecules in spaghetti and bread. In animals, they are a primary source of dietary energy and raw material for manufacturing other kinds of organic compounds. In plants, they serve as a building material for much of the plant body.

What are polysaccharides? Give an example.

Complex carbohydrates, long chains of sugars-polymers of monosaccharides. One familiar example is starch, a storage polysaccharide found in plants.

What is lactose intolerance?

The inability to digest lactose, the main sugar found in milk. It can cause bloating, gas, and other discomforts.

Why do saturated fats tend to be solid at room temperature?

The linear shape of saturated fatty acids allows these molecules to stack easily (like bricks in a wall), so saturated fats tend to be solid at room temperature (Figure 3.12).

Why can animals digest starch?

Their digestive systems break the bonds between glucose monomers through hydrolysis reactions.

Despite the size of macromolecules, their structures can be easily understood because _____.

They are polymers, large molecules made by stringing together many smaller molecules called monomers (like a polymer pearl necklace made by joining together many pearl monomers)

Monosaccahrides are monomers because...

They cannot be broken down into smaller sugars.

Cells link monomers to form polymers through a _____.

dehydration reaction, a chemical reaction that removes a molecule of water (appears separately) For each monomer added to a chain, a water molecule (H2O) is formed by the release of two hydrogen atoms and one oxygen atom. The same dehydration reaction occurs regardless of the specific monomers and type of polymer the cell is producing

Organisms not only _____ organic molecules but also _____.

make, break them down. For example, many molecules in your food are macromolecules. You must digest these giant molecules to make their monomers available to your cells, which can then rebuild the monomers into macromolecules that make up your body.

In water, many monosaccahrides form _____.

rings, when one part of the molecule forms a bond with another part of the molecule

The United States in one of the world's leading markets for _____.

sweeteners, The average American consumes about 45 kilograms-a whopping 100 pounds-per year., mainly in the form of sucrose and high fructose corn syrup.

Converting macromolecules is like _____.

taking apart a car (food) made of new Legos and then using the Legos (monomers) to assemble a new car (macromolecule) of your own design

A cell is mostly _____, but the rest consists mainly of _____

water, carbon-based molecules

What treatment is there for lactose intolerance?

None

Differences in molecular shape

Are important, fructose is much sweeter than glucose

What are disaccharides? Give an example.

A double sugar constructed from two monosaccahrides by a dehydration reaction. Disaccharide latose is often called "milk sugar". Lactose is made from the monosaccharides glucose and galactose.

Hydrolysis

A process in which polymers are broken down. Hydrolysis means to break (lyse) with water (hydro). Cells break bonds between monomers by adding water to them, a process that is essentially the reverse of a dehydration reaction.

What is a protein?

A protein is a polymer of amino acid monomers. Proteins are the most elaborate and diverse of life's molecules. Proteins account for more than 50% of the dry weight of most cells, and they are instrumental in almost everything cells do (Figure 3.15). Chances are, if something is getting done in your body, there is a protein doing it.

What types of fats do tropical plants, such as cocoa butter, have? What delicious treat is cocoa butter found in? What is "mouth feel"?

Although plant oils tend to be low in saturated fat, tropical plant fats are an exception. Cocoa butter, a main ingredient in chocolate, contains a mix of saturated and unsaturated fat. This gives chocolate a melting point near body temperature. Thus, chocolate stays solid at room temperature but melts in the mouth. This pleasing "mouth feel" is one of the reasons chocolate is so appealing.

What are some fats that are not unhealthy?

Although saturated and trans fats should generally be avoided, it is not true that all fats are unhealthy. In fact, some fats perform impor- tant functions within the body andare beneficial and even essential to a healthy diet. For example, fats contain- ing omega-3 fatty acids have been shown to reduce the risk of heart disease and relieve the symptoms of arthritis and inflammatory bowel disease. Some sources of these beneficial fats are nuts and oily fish such as salmon.

How are steoids both similar and different from fats?

Although they are also hydrophobic, steroids are very different from fats in structure and function. All steroids have a carbon skeleton with four fused rings. Different steroids vary in the functional groups attached to this set of rings, and these chemical variations affect their function.

How does one amino acid differ from another at the molecular level?

Amino acids. The 20 amino acids vary only in their side groups, which give these monomers their unique properties.

Why are carbon atoms so versatile (able to do many different functions) as molecular ingredients?

An atom's bonding ability is related to the number of electrons it must share to complete its outer shell. Carbon has four atoms in its outer shell which holds eight. Since it can form four bonds, carbon can form an endless variety of carbon skeletons.

Glycogen

Animals store excess sugar in the form of a polysaccharide called glycogen. Like starch, glycogen is a polymer of glucose monomers, but glycogen is more extensively branched

Name two athletes mentioned in this chapter who admitted to using steroids. What happened to one of them?

Baseball player Jose Canseco (left), an admitted user of performance-enhancing steroids, testifies before Congress during an inquiry into the abuse of drugs by professional athletes. After admitting that she had taken performanceenhancing drugs, track-and-field star Marion Jones (right) was stripped of her five Olympic medals. Note the similarity in chemical structure of testosterone (shown above) and THG (shown here).

Glucose molecular formula

C6H12O6, Fructose has the same formula but its atoms are arranged differently.

What are the four organic molecules?

Carbohydrates, lipids, proteins (amino acids), and nucleic acids

Organic compounds

Carbon-based molecules

What is cellulose a polymer of?

Cellulose is also a polymer of glucose, but its glucose monomers are linked together in a unique way. Unlike the glucose linkages in starch and glycogen, those in cellulose cannot be broken by animals.

Cellulose

Cellulose, the most abundant organic compound on Earth, forms cable-like fibrils in the tough walls that enclose plant cells and is a major component of wood and other structural components of plants (Figure 3.9c) .

What is the impact of swapping a single amino acid in a protein?

Changing a single letter can drastically affect the meaning of a word-"tasty" versus "nasty," for instance. Similarly, even a slight change in primary structure can affect a protein's ability to function. For example, the substitution of one amino acid for another at a particular position in hemoglobin, the blood protein that carries oxygen, causes sickle-cell disease, an inherited blood disorder (Figure 3.19).

What is atherosclerosis? What types of diets promote it?

Diets rich in saturated fats may contribute to cardiovascular disease by promoting atherosclerosis. In this condition, lipid-containing deposits called plaque build up along the inside walls of blood vessels, reducing blood flow and increasing risk of heart attacks and strokes.

Why are trans fats becoming less common in manufactured food?

Due to the increased awareness of their unhealthy nature, trans fats are becoming less common as food manufacturers substitute other forms of fat.

What creatures are are able to derive nutrition from cellulose, and why?

Grazing animals and wood-eating insects such as termites are able to derive nutrition from cellulose because microorganisms inhabiting their digestive tracts break it down.

What are the simplest carbon compounds called?

Hydrocarbons

What determines how many levels of structure a protein has?

If we dissect the overall shape of a protein, we can recognize at least three levels of structure: primary. secondary, and tertiary. Proteins with more than one polypeptide chain have a fourth level: quaternary structure. Figure 3.20 shows how the levels of protein structure are related.

Functional groups

In an organic compound, the groups of atoms directly involved in chemical reactions. Each functional group plays a particular role during chemical reactions

How much energy does a pound of fat store, relative to a pound of carbohydrates? What is one downside of that?

In fact, a pound of fat packs more than twice as much energy as a pound of carbohydrate. The downside to this energy efficiency is that it is very difficult for a person trying to lose weight to "burn off' excess fat.

What is THG?

In recent years, the discovery that some athletes were using a performance-enhancing anabolic steroid called THG rocked the sports world. THG is a chemically modified ("designer") steroid intended to avoid detection by drug tests (hence its nickname, "the clear"). New tests revealed widespread use ofTHG and other steroids among athletes in many sports (Figure 3.14) and raised questions about the validity of home run records and other athletic accomplishments.

What enables a protein molecule to carry out its specific function?

It is a protein's three-dimensional shape that enables the molecule to carry out its specific function in a cell. In almost every case. a protein's function depends on its ability to recognize and bind to some other molecule. For example. the specific shape of lactase enables it to recognize and attach to lactose, its molecular target. With proteins,function follows form that is, what a protein does is a consequence of its shape (Figure 3.21 ).

How does lactose intolerance work?

Lactose enters the small intestine. Lactate, an enzyme (protein that helps drive chemical reactions) breaks lactose into smaller sugars. Lactose not broken down enters the large intestine where bacteria feed on it, resulting in uncomfortable symptoms.

What's the main molecule in the gasoline we burn in cars and other machines?

Larger hydrocarbons (such as octane, with eight carbons)

What does starch consist of?

Long strings of glucose monomers. Plant cells store starch, providing a sugar stockpile that can be broken down when needed.

What do biologists call the large biological molecules (carbohydrates, proteins, and nucleic acids)?

Macromolecules (macro means "big")

What's a common disaccharide (other than lactose)? How is it made?

Maltose, naturally found in germinating seeds. It is used in making beer, malt whiskey and liquor, malted milk shakes, and malted malt ball candy. A molecule of maltose consists of two glucose monomers joined together.

Why is the shape of molecules so important?

Many vital processes within living organisms rely on the ability of molecules to recognize one another based on their shape

_____ is one of the most abundant hydrocarbons in natural gas

Methane

What is the simplest hydrocarbon?

Methane: CH4, a single carbon atom bonded to four hydrogen atoms.

Isomers

Molecules with the same molecular formula but different structures. Isomers are like anagrams (heart and earth, same letters in a different order)

Why is cholesterol essential to your body?

One common steroid is cholesterol, which has a bad reputation because of its association with cardiovascular disease. However, cholesterol is an essential molecule in your body. It is a key component of the membranes that surround your cells. It is also the "base steroid" from which your body produces other steroids, such as the sex hormones estrogen and testosterone (Figure 3.13).

Do most americans get enough fiber in their diet?

Most Americans do not get the recommended levels of fiber in their diet.

What type of fatty acids do most animal fats (give examples) have?

Most animal fats, such as lard and butter, have a relatively high proportion of saturated fatty acids.

Why do most athletic organizations ban the use of anabolic steroids?

Most athletic organizations ban the use of anabolic steroids because of their many potential health hazards coupled with the unfairness of an artificial advantage.

Where is most of your glycogen stored?

Most of your glycoge is stored in liver and muscle cells, which break down the glycogen to release glucose when you need energy. This is why some athletes "carbo load," consuming large amounts of starchy foods the night before an athletic event. The starch is converted to glycogen, which is then available for rapid use during physical activity the next day.

Why is the description of sugar as "empty calories" accurate.

Most sweeteners contain only negligible amounts of nutrients other than carbohydrates. For good health, we also require proteins, vitamins, fats, and minerals. And we need to include complex amounts of complex carbohydrates-that is, polysaccharides-in our diet.

Explain the molecular difference between saturated fat and unsaturated fat.

Notice in Figure 3.1 lb that the bottom fatty acid bends where there is a double bond in the carbon skeleton. That fatty acid is said to be unsaturated because it has fewer than the maximum number of hydrogens at the double bond. The other two fatty acids in the fat molecule lack double bonds in their hydrocarbon portions. Those fatty acids are saturated, meaning that they contain the maximum number of hydrogen atoms, giving them a straight shape. A saturated fat is one with all three of its fatty acid tails saturated. If one or more of the fatty acids is unsaturated, then it's an unsaturated fat, like the one in Figure 3.11 b. A polyunsaturated fat has several double bonds within its fatty acids.

What is the major portion of a fatty acid? What does it store?

The major portion of a fatty acid is a long hydrocarbon that stores a lot of energy, like the hydrocarbons of gasoline.

How do sugar manufacturers extract sucrose?

The stems of sugarcane and the roots of sugar bees. However, sucrose is rarely used as a sweetener in processed foods in the United States. Much more common is high fructose corn syrup, made through a commercial process that converts natural glucose in corn syrup to the much sweeter fructose. If you read the label on a soft drink can or bottle, you're likely to find that high fructose corn syrup is one of the first ingredients listed.

What does the difference between testosterone and estrogen influence?

The subtle difference between testosterone and estrogen influences the development of the anatomical and physiological differences between male and female mammals, including lions and humans.

Are lipids macromolecules or polymers?

Unlike carbohydrates, proteins, and nucleic acids, lipids are neither macromolecules nor polymers. In fact, lipids are a diverse group of molecules made from different "building blocks." In this section, we'll look at two types of lipids: fats and steroids.

What are some unwelcome side effects of anabolic steroids?

Using anabolic steroids is indeed a fast way to increase body size beyond what hard work alone can produce. But at what cost? Steroid abuse can cause violent mood swings ("roid rage"), depression, liver damage, high cholesterol, shrunken testicles, reduced sex drive, and infertility. These last symptoms occur because artificial anabolic steroids often cause the body to reduce its output of natural sex hormones.

When do we take advantage of cellulose?

We take advantage of that structural strength when we use lumber as a building material.

How does the functional shape of a protein get formed?

When a cell makes a polypeptide, the chain usually folds spontaneously to form the functional shape for that protein.

The unique properties of an organic compound rely not only on its _____ but on the _____.

carbon skeleton, atoms attached to the skeleton

How many different kinds of proteins does your body have?

Your body has tens of thousands of different kinds of proteins.

How many proteins does our body have?

Your body has thousands of proteins, and each protein has a unique three-dimensional shape corresponding to a specific function.