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3.13: Case Study Diet Conclusion and Chapter Summary

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  • Case Study Conclusion: Diet Dilemma

    After reading this chapter, you should be able to see numerous connections between chemistry, human life, and health. In Joseph’s situation, chemistry is involved in the reasons why his father has diabetes, why his personal risk of getting diabetes is high, and the different dietary changes he is considering.

    Soy-whey-protein-diet
    Figure \(\PageIndex{1}\): (Public domain. Peggy Greb, from the Agricultural Research Service, the research agency of the US Department of Agriculture.; via wikimedia.org; Soy whey protein diet.jpg)

    For instance, type 2 diabetes is caused mainly by a lack of response in the body to the hormone insulin, which causes problems in the regulation of blood sugar, or glucose. Insulin is a peptide hormone, and as you have learned, peptides are chains of amino acids. Therefore, insulin is in the class of biochemical compounds called proteins. Joseph is at increased risk of diabetes partly because there is a genetic component to the disease. DNA, which is a type of chemical compound called a nucleic acid, is passed down from parents to their offspring and carries the instructions for the production of proteins in units called genes. If there is a problem in a gene (or genes) that contributes to the development of a disease, such as type 2 diabetes, this can get passed down to the offspring and may raise that child’s risk of getting the disease.

    But genetics is only part of the reason why Joseph is at increased risk of diabetes. Obesity itself is a risk factor and one that can be shared in families due to shared lifestyle factors such as poor diet and lack of exercise, in addition to genetics. Consumption of too many refined carbohydrates, such as white bread and soda, also may contribute to obesity and the development of diabetes. As you probably now know, these simple carbohydrates are more easily and quickly broken down in the digestive system to glucose than larger complex carbohydrate molecules, such as those found in vegetables and whole grains. This can lead to dramatic spikes in blood sugar levels, which is particularly problematic for people with diabetes because they have trouble maintaining their blood sugar at a safe level. You can understand why Joseph’s father limits consumption of refined carbohydrates, and in fact, some scientific studies have shown that avoiding refined carbohydrates may actually help reduce the risk of getting diabetes in the first place.

    Joseph’s friend recommended eating a low fat and high carbohydrate diet to lose weight, but you can see that which type of carbohydrate — simple or complex — is an important consideration. Eating lots of white bread and rice may not help Joseph reduce his risk of diabetes! But a healthy diet that helps him lose weight may lower his risk of diabetes since obesity itself is a factor. Which specific diet will work best to help him lose weight probably depends on a variety of factors including his biology, lifestyle, and food preferences. Joseph should consult with his doctor about his diet and exercise plan so that his specific situation can be taken into account and monitored by a medical professional.

    Drinking enough water is usually good advice for everyone, especially if it replaces sugary drinks like soda. You now know that water is important for many of the chemical reactions that take place in the body.

    Finally, you probably now realize that “chemicals” do not have to be scary, toxic substances. All matter consists of chemicals, including you, water, and healthy fresh fruits and vegetables, like the ones pictured above. When people advocate “clean eating” and avoiding “chemicals” in food, they are usually referring to avoiding synthetic, or man-made, chemical additives such as preservatives. This can be a healthy way to eat because it involves eating a variety of whole, fresh, unprocessed foods. But there is no reason to be scared of chemicals in general – they are simply molecules and how they react depends on what they are, what other molecules are present, and the environmental conditions surrounding them.

    Chapter Summary

    By now, you should have a good understanding of the basics of the chemistry of life. Specifically, you have learned:

    • All matter consists of chemical substances. A chemical substance has a definite and consistent composition and may be either an element or a compound.
    • An element is a pure substance that cannot be broken down into other types of substances.
      • An atom is the smallest particle of an element that still has the properties of that element. Atoms, in turn, are composed of subatomic particles, including negative electrons, positive protons, and neutral neutrons. The number of protons in an atom determines the element it represents.
      • Atoms have equal numbers of electrons and protons so they have no charge. Ions are atoms that have lost or gained electrons so they have either a positive or negative charge. Atoms with the same number of protons but different numbers of neutrons are called isotopes.
      • There are almost 120 known elements. The majority of the elements are metals. A smaller number are nonmetals, including carbon, hydrogen, and oxygen.
    • A compound is a substance that consists of two or more elements in a unique composition. The smallest particle of a compound is called a molecule. Chemical bonds hold together the atoms of molecules. We discussed four types of bonds, polar covalent bond, hydrogen bond, non-polar covalent bond, and ionic bond.

      • In an ionic bond, an atom gives away one or more electrons to another atom.
      • In a covalent bond, two atoms share one or more electrons. The equal sharing of electrons gives rise to a non- polar covalent bond, and unequal sharing of electrons gives rise to a polar covalent bond.
      • The polar molecules make hydrogen bonds between them. A hydrogen bond is a relatively weak bond between two oppositely charged sides of two or more molecules. Water is a polar molecule.
      • A chemical bond is a force of attraction between atoms or ions. Bonds form when atoms share or transfer valence electrons.
      • Atoms form chemical bonds to achieve a full outer energy level, which is the most stable arrangement of electrons.
    • Compounds can form only in chemical reactions, and they can break down only in other chemical reactions.
    • Biochemical compounds are carbon-based compounds found in living things. They make up cells and other structures of organisms and carry out life processes. Most biochemical compounds are large molecules called polymers that consist of many repeating units of smaller molecules called monomers.
    • There are millions of different biochemical compounds, but all of them fall into four major classes: carbohydrates, lipids, proteins, and nucleic acids.
    • Carbohydrates are the most common class of biochemical compounds. They provide cells with energy, store energy, and make up organic structures such as the cell walls of plants. The basic building block of carbohydrates is the monosaccharide.
      • Sugars are short-chain carbohydrates that supply us with energy. Simple sugars, such as glucose, consist of just one monosaccharide. Some sugars, such as sucrose, or table sugar, consist of two monosaccharides and are called disaccharides. Disaccharides are formed with the condensation reaction.
      • Complex carbohydrates, or polysaccharides, consist of hundreds or even thousands of monosaccharides. They include starch, glycogen, cellulose, and chitin.
        • Starch is made by plants to store energy and is readily broken down to its component sugars during digestion.
        • Glycogen is made by animals and fungi to store energy and plays a critical part in the homeostasis of blood glucose levels in humans.
        • Cellulose is the most common biochemical compound in living things. It forms the cell walls of plants and certain algae. Humans cannot digest cellulose, but it makes up most of the crucial dietary fiber in the human diet.
        • Chitin makes up organic structures such as the cell walls of fungi and the exoskeletons of insects and other arthropods.
    • Lipids include fats and oils. They store energy, form cell membranes, and carry messages.
      • Lipid molecules consist mainly of repeating units called fatty acids. Fatty acids may be saturated or unsaturated, depending on the proportion of hydrogen atoms they contain. Animals store fat as saturated fatty acids; plants store fat as unsaturated fatty acids.
      • Types of lipids include triglycerides, phospholipids, and steroids.
        • Triglycerides contain glycerol (an alcohol) in addition to fatty acids. Humans and other animals store fat as triglycerides in fat cells.
        • Phospholipids contain phosphate and glycerol in addition to fatty acids. They are the main component of cell membranes in all living things.
        • Steroids are lipids with a four-ring structure. Some steroids, such as cholesterol, are important components of cell membranes. Many other steroids are hormones.
    • Proteins include enzymes, antibodies, and numerous other important compounds in living things. They have many functions including helping cells keep their shape, making up muscles, speeding up chemical reactions, and carrying messages and materials.
      • Proteins are made up of small monomer molecules called amino acids.
      • A peptide bond is formed between two amino acids when they come together in a condensation synthesis reaction. Long chains of amino acids form polypeptides. The sequence of amino acids in polypeptides makes up the primary structure of proteins. Secondary structure refers to configurations such as helices and sheets within polypeptide chains. Tertiary structure is a protein's overall three-dimensional shape, which controls the molecule's basic function. A quaternary structure forms if multiple protein molecules join together and function as a complex.
      • The chief characteristic that allows proteins' diverse functions is their ability to bind specifically and tightly with other molecules.
    • Nucleic acids include DNA and RNA. They encode instructions for making proteins, helping make proteins, and passing the encoded instructions from parents to offspring.
      • Nucleic acids are built of monomers called nucleotides, which bind together in long chains to form polynucleotides. DNA consists of two polynucleotides, and RNA consists of one polynucleotide.
      • Each nucleotide consists of a sugar molecule, phosphate group, and a nitrogen base. Sugars and phosphate groups of adjacent nucleotides bind together to form the "backbone" of the polynucleotide. Bonds between complementary bases hold together the two polynucleotide chains of DNA and cause it to take on its characteristic double helix shape.
      • DNA makes up genes, and the sequence of nitrogen bases in DNA makes up the genetic code for the synthesis of proteins. RNA helps synthesize proteins in cells. The genetic code in DNA is also passed from parents to offspring during reproduction, explaining how inherited characteristics are passed from one generation to the next.
    • A chemical reaction is a process that changes some chemical substances into others. A substance that starts a chemical reaction is called a reactant, and a substance that forms in a chemical reaction is called a product. During the chemical reaction, bonds break in reactants and new bonds form in products.
    • Chemical reactions can be represented by chemical equations. According to the law of conservation of mass, mass is always conserved in a chemical reaction, so a chemical equation must be balanced, with the same number of atoms of each type of element in the products as in the reactants.
    • Many chemical reactions occur all around us each day, such as iron rusting and organic matter rotting, but not all changes are chemical processes. Some changes, such as ice melting or paper being torn into smaller pieces, are physical processes that do not involve chemical reactions and the formation of new substances.
    • All chemical reactions involve energy and need activation energy to begin. Exothermic reactions release energy. Endothermic reactions absorb energy.
    • Biochemical reactions are chemical reactions that take place inside living things. The sum of all the biochemical reactions in an organism is referred to as metabolism. Metabolism includes catabolic reactions, which are exothermic reactions, and anabolic reactions, which are endothermic reactions.
    • Most biochemical reactions need a biological catalyst called an enzyme to speed up the reaction by reducing the amount of activation energy needed for the reaction to begin. Most enzymes are proteins that affect just one specific substance, called the enzyme's substrate.
    • Water is a polar molecule; therefore, water molecules make hydrogen bonds between them. Due to this property water exists as a liquid over a wide range of temperatures and dissolves many substances. These properties depend on water's polarity, which causes water molecules to "stick" together.
    • Organisms need water to dissolve many substances and for most biochemical processes, including photosynthesis and cellular respiration.
    • A solution is a mixture of two or more substances that has the same composition throughout. Many solutions consist of water and one or more dissolved substances.
    • Acidity is a measure of the hydronium ion concentration in a solution. Pure water has a very low concentration and a pH of 7, which is the point of neutrality on the pH scale. Acids have a higher hydronium ion concentration than pure water and a pH lower than 7. Bases have a lower hydronium ion concentration than pure water and a pH higher than 7.
    • Many acids and bases in living things are secreted to provide the proper pH for enzymes to work properly.

    Now that you understand the chemistry of the molecules that make up living things, in the next chapter you will learn how these molecules make up the basic unit of structure and function in living organisms — cells — and will be able to understand some of the crucial chemical reactions that occur within cells.

    Chapter Summary Review

    1. The four major classes of biochemical compounds are carbohydrates, lipids, proteins, and nucleic acids. For each of the substances below, identify which of these classes includes the substance.

    A. Enzymes

    B. Fructose

    C. DNA

    D. RNA

    E. Steroids

    2. The chemical formula for the complex carbohydrate glycogen is C24H42O21.

    a. What are the elements in glycogen?

    b. How many atoms are in one molecule of glycogen?

    c. Is glycogen an ion? Why or why not?

    d. Is glycogen a monosaccharide or polysaccharide? Besides memorizing this fact, how would you know this based on the information in the question?

    e. What is the function of glycogen in the human body?

    3. What is the difference between an ion and a polar molecule? Give an example of each in your explanation.

    4. Define monomer and polymer.

    5. For each of the following polymers, identify the name of its monomers.

    a. RNA

    b. Protein

    c. Complex carbohydrate

    6. What is the difference between a protein and a polypeptide?

    7. People with diabetes have trouble controlling the level of glucose in their bloodstream. Knowing this, why do you think it is often recommended that people with diabetes limit their consumption of carbohydrates?

    8. Identify each of the following reactions as endothermic or exothermic.

    a. Cellular respiration

    b. Photosynthesis

    c. Catabolic reactions

    d. Anabolic reactions

    9. Pepsin is an enzyme in the stomach that helps us digest protein. Answer the following questions about pepsin.

    a. What is the substrate for pepsin?

    b. How does pepsin work to speed the reaction of protein digestion?

    c. Given what you know about the structure of proteins, what do you think are some of the products of the reaction that pepsin catalyzes?

    d. The stomach is normally acidic. What do you think would happen to the activity of pepsin and the effect on protein digestion if the pH is raised significantly?

    10. What defines a neutral pH? What is the numerical value of a neutral pH?

    11. True or False. Unsaturated fatty acids have straight chains.

    12. True or False. The DNA code carries instructions for the correct sequence of nucleic acids in a protein.

    13. True or False. Phospholipids make up cell membranes.

    14. The function of proteins can include

    A. helping cells keep their shape

    B. helping to destroy foreign substances

    C. speeding up biochemical reactions

    D. all of the above

    15. Which of the following is not part of a nucleotide?

    A. a nitrogen base

    B. a cellulose molecule

    C. a sugar molecule

    D. a phosphate group

    16. The “push” needed to start a chemical reaction is the

    A. enzymatic energy

    B. endothermic energy

    C. activation energy

    D. reactant energy