Chemical Basics of Life

CHApTER 2

Chemical Basics of life

OuTline Key Terms Atoms, Molecules, and Chemical Bonds Acids: Electrolytes that release hydrogen ions in water. Atomic Structure Activation energy: The amount of energy required to start a Molecules reaction. Chemical Bonds Anions: Ions with a negative charge. Types of Chemical Reactions Atomic number: A whole number representing the number Enzymes of positively charged protons in the nucleus of an atom. Acids, Bases, and the pH Scale Atomic weight: The total number of protons and neutrons in Chemical Constituents of Cells the nucleus of an atom. Inorganic Substances Atoms: The smallest complete units of an element, varying in Organic Substances size, weight, and interaction with other atoms. Summary Bases: Electrolytes that release ions that bond with Learning Goals hydrogen ions. Critical Thinking Questions Carbohydrates: Substances (including sugars) that provide Websites much of the energy required by the body’s cells, as well as Review Questions helping to build cell structures. Catalysts: Atoms or molecules that can change the rate of a OBjeCTives reaction without being consumed during the process. After studying this chapter, readers should be able to: Cations: Ions with a positive charge. 1. Describe the relationships between atoms and Chemistry: The study of the composition of matter and molecules. changes in its composition. 2. Explain chemical bonds. Compounds: Molecules made up of different bonded atoms. 3. Describe how an atomic number is determined. Decomposition: A reaction that occurs when bonds with a 4. List the major groups of inorganic chemicals reactant molecule break, forming simpler atoms, molecules, common in cells. or ions. 5. Explain acids, bases, and buffers. electrolytes: Substances that release ions in water. 6. Defi ne the characteristics of lipids and proteins. electrons: Single, negatively charged particles that revolve around the nucleus of an atom. 7. Defi ne pH. 8. Describe the functions of various types of elements: Fundamental substances that compose matter, organic chemicals in cells. such as carbon, hydrogen, and oxygen. 9. List four examples of steroid molecules. 10. Explain nucleic acids.

17 © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 18 CHApTER 2 Chemical Basics of life

Key Terms COnTinueD you understand chemistry, your understanding of Hydrogen bond: The attraction of the positive hydrogen anatomy and physiology will be improved. Chemical end of a polar molecule to the negative nitrogen or oxygen changes within cells inﬂ uence body functions and end of another polar molecule. the status of the body’s structures. Chemicals of the inorganic: Not having both carbon and hydrogen atoms. body include water, proteins, carbohydrates, lipids, ions: Atoms that either gain or lose electrons. nucleic acids, and salts, as well as foods, drinks, and isotope: One of two (or more) forms of an element having the medications. same number of protons and electrons, but different numbers matter is deﬁ ned as anything that takes up space of neutrons; they may or may not be radioactive. and has mass. Mass is a physical property that lipids: Substances that do not dissolve in water and include a variety of compounds with vital cell functions, including fats, determines an object’s weight, based on the Earth’s phospholipids, and steroids. gravitational pull. Matter includes liquids, gases, matter: Liquids, gases, and solids both inside and outside of and solids both inside and outside of the human the human body; it takes up space and has weight. body. elements are fundamental substances that molecule: The formation of two or more atoms. compose matter. Copper, iron, gold, silver, alumi- neutrons: Uncharged or “neutral” particles in the nucleus of num, carbon, hydrogen, and oxygen are all exam- an atom. ples of elements. Most living organisms need about nucleic acids: Macromolecules that carry genetic informa- 20 elements to survive. Table 2–1 lists the major tion or form structures within cells, and include DNA and RNA. and trace elements required by the human body. nucleus: The central portion of an atom that contains Atoms are tiny particles that compose elements. protons and neutrons. Atoms are the smallest complete units of an element, Organic: Having both carbon and hydrogen atoms. pH: A value by which hydrogen ion concentrations may be measured. ■ Table 2–1 elements of the Human Body Polar: A molecule that uses a covalent bond in which major elements (totaling 99.9%) Percentage in the electrons are not shared equally; this results in a shape that Body has an uneven distribution of charges. Oxygen (O) 65% Proteins: Substances made up of amino acids that are vital for many body functions, including structures and their Carbon (C) 18.5% functions, energy, and hormonal requirements. Protons: Single, positively charged particles inside the Hydrogen (H) 9.5% nucleus of an atom. Nitrogen (N) 3.2% radioisotopes: Also known as radioactive isotopes or radionuclides, they are atoms with unstable nuclei. Calcium (Ca) 1.5% steroid: Molecules with four connected rings of carbon phosphorus (p) 1% atoms, including cholesterol, estrogen, progesterone, testosterone, cortisol, and estradiol. potassium (K) 0.4% synthesis: A reaction that occurs when two or more reactants Sulfur (S) 0.3% (atoms) bond to form a more complex product or structure. Chlorine (Cl) 0.2%

Chemistry is the science that deals with the struc- Sodium (Na) 0.2%

ture of matter, and the study of the human body Magnesium (Mg) 0.1% begins with chemistry. It is essential for other sci- ences, including physiology, pathology, pharma- Trace elements (totaling 0.1%) cology, and microbiology. Life is based on atomic, Chromium (Cr) ----- molecular, and chemical interactions. Each cell of Cobalt (Co) ----- the body contains organelles made up of macromolecules. e cells then compose tissues and organs. Copper (Cu) -----

e chemical basics of life require the interactions Fluorine (F) ----- of all of these components. Iodine (I) -----

Atoms, molecules, and Iron (Fe) -----

Chemical Bonds Manganese (Mn) -----

e composition of matter and changes in its com- Zinc (Zn) ----- position are the focuses of the study of chemistry. If © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Atoms, Molecules, and Chemical Bonds 19 and vary in size, weight, and interaction with other containing the same number of protons, but diff er- atoms. e characteristics of living and nonliving ent numbers of neutrons. Isotopes may or may not objects result from the atoms that they contain, be radioactive. Radioactivity is the emission of ener- as well as how those atoms combine and interact. getic particles known as radiation, which occurs us, by forming chemical bonds, atoms can com- because of instability of the atomic nuclei. bine with other atoms that are not similar to them. e nuclei of certain isotopes (radioisotopes) spontaneously emit subatomic particles or radiation Atomic Structure in measurable amounts. e process of emitting radi- Atoms are composed of subatomic particles. Each ation is called radioactive decay. Strongly radioactive atom consists of protons, neutrons, and elec- isotopes are dangerous because their emissions can trons. Protons and neutrons are similar in size and destroy molecules, cells, and living tissue. For diag- mass; however, protons bear a positive electrical nostic procedures, weaker radioactive isotopes are charge whereas neutrons are electrically neutral used to diagnose structural and functional char- (uncharged). electrons bear a negative electrical acteristics of internal organs. Radiation is basically  charge. An atom’s mass is determined mostly by the identifi ed as one of three common forms: alpha ( ),   number of protons and neutrons in its nucleus. e beta ( ), or gamma ( ). Gamma radiation is the most mass of a larger object, such as the human body, is penetrating type, and is similar to X-ray radiation. the sum of the masses of all of its atoms. Figure 2–1 shows the components of an atom and its nucleus. CHeCK yOur KnOWleDGe Electrons orbit an atom’s nucleus at high speed, ✓ forming a spherical electron cloud. Atoms normally 1. Differentiate between atomic weight and contain equal numbers of protons and electrons. atomic number. e number of protons in an atom is known as its 2. Describe the locations of electrons, protons, atomic number. us, hydrogen (H), the simplest and neutrons. atom, has one proton, giving it the atomic number 1, while magnesium, with 12 protons, has the Molecules atomic number 12. molecule e atomic weight of an element’s atom equals e term is defi ned as any chemical struc- the number of protons and neutrons in its nucleus. ture that consists of atoms held together by covalent For example, oxygen has eight protons and eight bonds (involving the sharing of electrons between neutrons, so its atomic weight is 16. An isotope atoms). When two atoms of the same element bond, is defi ned as when an element’s atoms have nuclei they produce molecules of that element, such as hydrogen, oxygen, or nitrogen molecules.

Electron Chemical Bonds Atoms can bond with other atoms by using chemical bonds that result from interactions between their electrons. During this process, the atoms may either gain, lose, or share electrons. Chemically inactive atoms are known as inert atoms. An example of a chemical that is made up of inert atoms is helium. Atoms that either gain or lose electrons are called ions. ese atoms are electrically charged. An example of an electrically charged atom, or ion, is sodium.

Proton Ionic Bonds Ionic bonds form between ions. Ions with a positive charge () are called cations, and those with a negative charge () are called anions. Oppositely Neutron charged ions attract each other to form an ionic bond. is is a chemical bond that forms arrays FiGure 2–1 The components of an atom (indiscreet molecules) such as crystals. An example © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 20 CHApTER 2 Chemical Basics of life

Slightly negative Polar covalent δ – charge bond HH+ HH O H H Slightly positive + + δ δ charge H atom H atom H molecule 2 (a)

– – FiGure 2–2 Covalent bond δ δ

O O + + H H δ δ H H is when sodium forms an ionic bond with chloride δ + δ + to create sodium chloride (table salt). δ –

O Covalent Bonds + + δ H H δ + + Some atoms can complete their outer electron shells δ H H δ O O by sharing electrons to create a covalent bond. ey δ – δ –

do not gain or lose electrons. In a covalent bond, H H

each atom achieves a stable form. An example of a + + covalent bond is when two hydrogen atoms bond to δ δ

form a hydrogen molecule (see Figure 2–2). FiGure 2–3 Hydrogen bond If a single pair of electrons is shared, the result is a single covalent bond. If two pairs are shared, the result is a double covalent bond. Some atoms of hydrogen and the one atom of oxygen. Structural can even form triple covalent bonds. Some covalent formulas are used to signify how atoms are joined bonds do not share electrons equally, resulting in a and arranged inside molecules. Single bonds are rep- polar molecule—one that has an uneven distribu- resented by single lines, and double bonds are repre- tion of charges. Polar molecules have equal num- sented by double lines. When structural formulas are bers of protons and electrons, but one end of the represented in three-dimensional models, diff erent molecule is slightly negative while the other end is colors are used to show diff erent types of atoms. slightly positive. An example of a polar molecule is water, created by hydrogen and oxygen atoms. ✓ CHeCK yOur KnOWleDGe When the positive hydrogen end of a polar mol- 1. Distinguish between ionic bonds and cova- ecule is attracted to the negative nitrogen or oxy- lent bonds. gen end of another polar molecule, the attraction 2. Which kind of bond holds together atoms in hydrogen bond is called a (see Figure 2–3). ese a water molecule? bonds are weak at body temperature, and may change form, from water to ice and back again. Hydrogen Types of Chemical Reactions bonds are important in protein and nucleic acid structure, forming between polar regions of diff er- Four types of chemical reactions are important to ent parts of a single, large molecule. the study of physiology: synthesis reactions, decom- Molecules made up of diff erent bonded atoms position reactions, exchange reactions, and revers- are called compounds. Examples of compounds ible reactions. include water (a compound of hydrogen and oxygen), table sugar, baking soda, alcohol as used in Synthesis Reactions beverages, natural gas, and most medicinal drugs. Chemical reactions change the bonds between A molecule of a compound has specifi c types and atoms, molecules, and ions to generate new chemi- amounts of atoms. For example, water consists of cal combinations. synthesis is a reaction that occurs two hydrogen atoms and one oxygen atom. When when two or more reactants (atoms) bond to form two hydrogen atoms bind with two oxygen atoms, a more complex product or structure. e forma- they form hydrogen peroxide instead of water. tion of water from hydrogen and oxygen molecules e numbers and types of atoms in a molecule are is a synthesis reaction. Synthesis always involves represented by a molecular formula. e molecular the formation of new chemical bonds, whether the

formula for water is H2O, signifying the two atoms reactants are atoms or molecules. Synthesis requires © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Atoms, Molecules, and Chemical Bonds 21 energy, and it is important for growth and the repair cell makes an enzyme molecule to promote a specifi c of tissues. reaction. Enzymatic reactions, which are reversible, Synthesis is symbolized as follows: A  B  AB can be written as: enzyme  Decomposition Reactions A B  AB Decomposition is a reaction that occurs when bonds within a reactant molecule break, forming simpler Acids, Bases, and the pH Scale atoms, molecules, or ions. For example, a typical electrolytes meal contains molecules of sugars, proteins, and fats are substances that release ions in water. that are too large and too complex to be absorbed When they dissolve in water, the negative and posi- and used by the body. Decomposition reactions in tive ends of water molecules cause ions to separate the digestive tract break these molecules down into and interact with water molecules instead of each smaller fragments before absorption begins. other. e resulting solution contains electrically Decomposition is symbolized as follows: charged particles (ions) that will conduct electric- Acids AB  A  B ity. are electrolytes that release hydrogen ions in water. An example of an acid is hydrochloric acid, Exchange Reactions made up of hydrogen and chloride ions. Bases are electrolytes that release ions that bond with hydro- In an exchange reaction, parts of the reacting mole- gen ions. An example of a base is sodium hydrox- cules are shuffl ed around to produce new products. ide, made up of sodium, oxygen, and hydrogen ions. An example of an exchange reaction is the reac- In body fl uids, the concentrations of hydrogen and tion of an acid with a base, which forms water and hydroxide ions greatly aff ects chemical reactions. a salt. ese reactions control certain physiological func- Exchange reactions are symbolized as follows: tions such as blood pressure and breathing rates. AB  CD  AD  CB Hydrogen ion concentrations can be measured by pH Reversible Reactions a value called . e hydrogen ion concentration in body fl uids is vital. It is expressed in a type of math- A reversible reaction is one wherein the products ematical shorthand based on concentrations calcu- of the reaction can change back into the reactants lated in moles per liter (with a mole representing an they originally were. ese reactions can proceed in amount of solute in a solution). e pH of a solu- opposite directions, depending on the relative pro- tion is defi ned as the level of acidity or basicity. e portions of reactants and products, as well as how pH scale ranges from 0 to 14, with 7 being the mid- much energy is available.   point (meaning it has equal numbers of hydrogen So, if A B  AB, then AB  A B. Many impor- and hydroxide ions). Pure water has a pH of 7, and tant biological reactions are freely reversible. Such this midpoint is considered to be neutral (neither reactions can be represented as the equation: acidic nor basic). Measurements of less than 7 pH  A B  AB are considered acidic, meaning that there are more hydrogen ions than hydroxide ions. Measurements ✓ CHeCK yOur KnOWleDGe of more than 7 pH are considered basic, also known 1. Describe four kinds of chemical reactions. as alkaline, meaning that there are more hydroxide 2. What are the structural formulas for synthe- ions than hydrogen ions. sis reactions and exchange reactions? e pH of blood usually ranges from 7.35 to 7.45. Abnormal fl uctuations in pH can damage calls and tissues, change the shapes of proteins, and alter Enzymes cellular functions. Acidosis is an abnormal physi- Enzymes promote chemical reactions by lower- ological state caused by blood pH that is lower than ing the activation energy requirements. Activation 7.35. If pH falls below 7, coma may occur. Alkalosis energy is the energy that must be overcome in order results from blood pH that is higher than 7.45. If pH for a chemical reaction to occur. erefore, they rises above 7.8, it generally causes uncontrollable make chemical reactions possible. Enzymes belong and sustained skeletal muscle contractions. to a class of substances called catalysts (compounds Chemicals that resist pH changes are called buf- that accelerate chemical reactions without them- fers. ey combine with hydrogen ions when these selves being permanently changed or consumed). A ions are excessive and contribute hydrogen ions © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 22 CHApTER 2 Chemical Basics of life

Concentrated Ocean Concentrated hydrochloric Vinegar, Black water sodium hydroxide acid (HCl) wine, pickles coffee Pure water (NaOH) Lemon juice Tomato Saliva Baking Household Oven Stomach acid juice Milk Blood soda Bleach ammonia cleaner

Extremely acidic Neutral Extremely basic

pH 0 12345678910 11 12 13 14

Optimal growth Optimal growth of fungi of bacteria

FiGure 2–4 pH scale

when these ions are reduced. Figure 2–4 shows the an inorganic compound produced as a waste prod- pH values of acids and bases. uct when some metabolic processes release energy. It is exhaled via the lungs. ✓ CHeCK yOur KnOWleDGe Salts are compounds of oppositely charged ions 1. Why are enzymes needed in our cells? that are abundant in tissues in ﬂ uids. Many ions 2. What does pH measure? required by the body are supplied in salts, including sodium, chloride, calcium, magnesium, phosphate, Chemical Constituents of Cells carbonate, bicarbonate, potassium, and sulfate. Salt ions are important for transporting substances to Chemicals can basically be divided into two main and from the cells, as well as for muscle contractions groups: organic and inorganic. Organic chemicals and nerve impulse conduction. Common inorganic are those that always contain the elements car- molecules are summarized in Table 2–2. bon and hydrogen, and generally oxygen as well. inorganic chemicals are any chemicals that do not. Organic Substances Inorganic substances release ions in water and are Organic substances include carbohydrates, lipids, also called electrolytes. ough many organic sub- proteins, and nucleic acids. Many organic molecules stances also dissolve in water, they dissolve to great are made up of long chains of carbon atoms linked eﬀ ect in alcohol or ether. Organic substances that by covalent bonds. e carbon atoms usually form dissolve in water usually do not release ions and are additional covalent bonds with hydrogen or oxygen known as nonelectrolytes. atoms and, less commonly, covalent bonds with Inorganic Substances nitrogen, phosphorus, sulfur, or other elements. Inorganic substances in body cells include oxygen, ✓ CHeCK yOur KnOWleDGe carbon dioxide, compounds that are known as salts, 1. Distinguish between organic and inorganic and water. e most abundant compound in the compounds. human body is water, accounting for nearly two 2. Explain how the chemical properties of oxy- thirds of body weight. Any substance that dissolves gen and water make life possible. in water is called a solute. Because solutes dissolved in water are more likely to react with each other as Carbohydrates they break down into smaller particles, most metabolic reactions occur in water. In the blood, the Carbohydrates provide much of the energy required watery (aqueous) portion carries vital substances by the body’s cells, as well as helping to build cell such as oxygen, salts, sugars, and vitamins among structures. Carbohydrate molecules consist of car- the digestive tract, respiratory tract, and the cells. bon, hydrogen, and oxygen molecules. e carbon Oxygen enters the body through the respiratory atoms they contain join in chains that vary with the organs and is transported in the blood. e red blood type of carbohydrate. Carbohydrates with shorter cells bind and carry the largest amount of oxygen. chains are called sugars. Organelles inside the cells use oxygen for energy Simple sugars have 6 carbon atoms, 12 hydro-

release from nutrients such as glucose (sugar) to gen atoms, and 6 oxygen atoms (C6H12O6). ey drive cellular metabolic activities. Carbon dioxide is are also known as monosaccharides. Simple sugars © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Chemical Constituents of Cells 23

■ Table 2–2 inorganic substances in Cells Formula or molecule or ion Function symbol

H2O Water molecule Major component of body ﬂ uids, biochemical reactions, chemical transport, and temperature regulation

O2 Oxygen molecule Used for energy release from glucose molecules

CO2 Carbon dioxide Metabolic waste product; forms carbonic acid via reaction with water

 HCO3 Bicarbonate ions Assists in acid–base balance

CA2 Calcium ions Used in bone development, muscle contraction, and blood clotting

2 CO3 Carbonate ions Important for formation of bone tissue

Cl Chloride ions Assists in maintaining water balance

Mg2 Magnesium ions Important for formation of bone tissue and certain metabolic processes

3 pO4 phosphate ions Used in ATp, nucleic acid, and other vital substance synthesis; important for formation of bone tissue and to maintain cell membrane polarization

K potassium ions Needed for cell membrane polarization

Na Sodium ions Needed for cell membrane polarization and to maintain water balance

2 SO4 Sulfate ions Assists in cell membrane polarization

include glucose, fructose, galactose, ribose, and Lipids deoxyribose. Ribose and deoxyribose diﬀ er from lipids are not soluble in water. ey may dissolve the others in that they each contain ﬁ ve atoms of in other lipids, oils, ether, chloroform, or alcohol. carbon. Complex carbohydrates include sucrose Lipids include a variety of compounds with vital cell (table sugar) and lactose (milk sugar). Some of these functions. ese compounds include fats, phospho- carbohydrates are double sugars or disaccharides. lipids, and steroids. Fats are the most common type Other types of complex carbohydrates contain many of lipids. Like carbohydrates, fat molecules also con- simple joined sugar units, such as plant starch, and tain carbon, hydrogen, and oxygen, but they have are known as polysaccharides. Humans and other far fewer oxygen atoms than do carbohydrates. animals synthesize a polysaccharide called glycogen Fatty acids and glycerol are the building blocks of (see Figure 2–5). fat molecules. A single fat molecule consists of one

)a( )b( CH2OH )c( C O CH OH O H H 2 H H CH OH CCCC 2 OH HHHO HO O CH OH C O CH OH O 2 H H 2 H C C C C H CCCCH OH OH H OH HHHO Sucrose HO OH HO CH OH 2 CH OH CH OH C C C C 2 2 C O C O H OH HO H H H HH H H Glucose Fructose CCCC OH H OH H Monosaccharides HO O OH C C C C Glycogen H OH Maltose H OH Disaccharides Polysaccharide

FiGure 2–5 a) Monosaccharide, (b) Disaccharide, and (c) polysaccharide © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 24 CHApTER 2 Chemical Basics of life

Glycerol Fatty acid H O H H H H H H H H H H H H H H H HOC C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H H O H H H H H H H H H H H H H H H CH O C C C C C C C C C C C C C C C C H H H H H H H H H H H H H H O H H H H H H H H H H H H H H H CH O C C C C C C C C C C C C C C C C H H H H H H H H H H H H Hydrogen

FiGure 2–6 Saturated fats

Carboxyl group H O

H C OH + HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

Saturated fatty acid C H C OH Hydroxyl group

C H C OH Dehydration synthesis 3 H O H 2 Glycerol

H O

H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

C H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

O Unsaturated fatty acid C H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH CH CH H 2 CH A fat 2 CH Covalent bonds 2 CH 2 CH 2 CH 3

FiGure 2–7 Saturated vs. unsaturated fats

glycerol molecule bonded to three fatty acid mol- molecules with double bonds only are called unsat- ecules. ese fat molecules are known as triglycer- urated. Fatty acid molecules with many double- ides, a subcategory of lipids that includes fat and oil. bonded carbon atoms are called polyunsaturated. ese molecules are formed by the condensation of Similar to a fat molecule, a phospholipid con- one molecule of glycerol, which is a three-carbon sists of a glycerol portion with fatty acid chains. alcohol. Glycerol contains three fatty acid molecules. Phospholipids are structurally related to glycolip- Triglycerides contain diﬀ erent saturated and unsat- ids. Human cells can synthesize both types of lipids, urated fatty acid combinations. ose with mostly primarily from fatty acids. A phospholipid includes saturated fatty acids are called saturated fats (see a phosphate group that is soluble in water and a Figure 2-6). ose with mostly unsaturated fatty fatty acid portion that is not. Phospholipids are an acids are called unsaturated fats (see Figure 2–7). important part of cell structures. Saturated fat is deﬁ ned as containing carbon steroid molecules are large lipid molecules that atoms that are bound to as many hydrogen atoms as share a distinctive carbon framework. Steroids have possible, becoming saturated with them. Fatty acid four connected rings of carbon atoms. All steroid © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Summary 25

CH H always contain nitrogen atoms. Twenty-two diff er- 3 ent amino acids make up the proteins that exist in HCC H2 CH2 CH2 C CH3 humans and most other living organisms. Protein CH3 CH3 molecules consisting of amino acids held together CH by peptide bonds are called peptides. 3 Other types of proteins include structural proteins such as collagen, which gives strength to ligaments HO and connective tissues, and keratin, which func- (a) Cholesterol tions to prevent water loss through the skin. More active proteins include antibodies and enzymes. Cell membrane proteins may serve as receptors and OH carriers for specifi c molecules. Nucleic Acids nucleic acids are large organic molecules (macromolecules) that carry genetic information or form O structures within cells. ey are composed of car- (b) Testosterone bon, hydrogen, oxygen, nitrogen, and phosphorus. Nucleic acids store and process information at the molecular level, inside the cells. e two classes of nucleic acids are deoxyribonucleic acid (DNA) and OH CH3 ribonucleic acid (RNA). Nucleic acids are found in C C all living things, cells, and viruses. C C C CH3 e DNA in our cells determine our inherited C C C C characteristics, including hair color, eye color, and CC C blood type. DNA aff ects all aspects of body structure CC C and function. DNA molecules encode the informa- O C C tion needed to build proteins. By directing struc- (c) Structural formula of testosterone tural protein synthesis, DNA controls the shape and physical characteristics of the human body. Several forms of RNA cooperate to manufacture FiGure 2–8 Various types of steroid molecules specifi c proteins by using the information provided by DNA. Important structural diff erences distin- molecules have the same basic structure: three guish RNA from DNA. An RNA molecule consists 6-carbon rings joined to one 5-carbon ring. ey of a single chain of nucleotides. include cholesterol, estrogen, progesterone, testos- Human cells have three types of RNA: terone, cortisol, and estradiol (see Figure 2–8). 1. Messenger RNA (mRNA) 2. Transfer RNA (tRNA) Proteins 3. Ribosomal RNA (rRNA) Proteins are the most abundant organic compo- A DNA molecule consists of a pair of nucleotide nents of the human body, and in many ways the chains (see Figure 2–9). e two DNA strands twist most important. Proteins are vital for many body around each other in a double helix that resembles functions, including structures and their functions, a spiral staircase. energy, enzymatic function, defense (antibodies), and hormonal requirements. On cell surfaces, some ✓ CHeCK yOur KnOWleDGe proteins combine with carbohydrates to become 1. Distinguish between saturated and unsatrated glycoproteins. ey allow cells to respond to certain fats. molecules that bind to them. 2. Distinguish between DNA and RNA. ere are more than 200,000 types of proteins in the human body. Antibodies are proteins that detect summary and destroy foreign substances. All proteins contain carbon, hydrogen, oxygen, and nitrogen atoms, Chemistry describes the composition of substances with small quantities of sulfur also present. Proteins and how chemicals react with each other. e human © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 26 CHApTER 2 Chemical Basics of life

NH2 N C C N H— C G C O O O C C N H A T N O P O P O POCH2 O G C O– O– O– CC A H H T H H G C C C C G OH OH

Adenosine triphosphate (ATP) G C C G A T A T ATP

C DNA G G C A T A T ADP

Hydrogen Energy bond released (b) A T D D P

P A T D D P P C G D D P P G C D D

O NH2 H C H N C C N C N H— C C C O C C O H O N H N N Nitrogenous – O – O O POCH2 Nitrogenous O POCH2 base (uracil) base (adenine) O– CC O– CC H H H H Phosphate H H Phosphate H H C C C C OH H OH OH Pentose sugar (deoxyribose) Pentose sugar (ribose)

DNA adenine nucleotide RNA uracil nucleotide (a)

FiGure 2–9 Nucleic acids, DNA, a DNA nucleotide, and an RNA nucleotide are shown in (a). Adenosine triphosphate (ATp) is shown in (b).

body is made up of chemicals. Matter is composed element. Compounds that release ions when they of elements, some of which occur in a pure form. dissolve in water are known as electrolytes. Inorganic Many elements are combined with other elements. substances include water, oxygen, carbon dioxide, Elements are composed of atoms, which are the and salts. Organic substances include carbohydrates, smallest complete units of elements. Atoms of diﬀ er- lipids, proteins, and nucleic acids. ent elements have characteristic sizes, weights, and ways of interacting. An atom consists of one or more leArninG GOAls electrons surrounding a nucleus, which contains one or more protons and usually one or more neutrons. e following learning goals correspond to the Electrons are negative, protons are positive, and objectives at the beginning of this chapter: neutrons are uncharged. When atoms combine, they 1. Atoms are tiny particles that compose ele- either gain, lose, or share electrons. Atoms of the ments. A molecule is formed when two or same element may bond to form a molecule of that more atoms bond. When two atoms of the © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Review Questions 27

same element bond, they produce molecules and hormonal requirements. Nucleic acids of that element, such as hydrogen, oxygen, or carry genetic information or form structures nitrogen molecules. within cells, and include DNA and RNA. 2. Atoms can bond with other atoms by using 9. Steroid molecules include cholesterol, estro- chemical bonds that result from interactions gen, progesterone, testosterone, cortisol, and between their electrons. e atoms may estradiol. either gain, lose, or share electrons. Atoms 10. Nucleic acids are macromolecules that carry that either gain or lose electrons are called genetic information or form structures within ions. cells. ey are composed of carbon, hydrogen, 3. Each atom consists of a central nucleus and oxygen, nitrogen, and phosphorus. Nucleic one or more electrons continually mov- acids are found in all living things, cells, and ing around it. Inside the nucleus are one or viruses. more protons and neutrons. e number of protons in an atom is known as its atomic CriTiCAl THinKinG QuesTiOns number. 1. How would you explain the importance 4. e major groups of inorganic chemicals of amino acids and proteins to a per- common in cells include oxygen, carbon son whose diet is composed primarily of dioxide, salts, and water. Other inorganic carbohydrates? substances in cells include the ions of bicar- 2. Explain why the symptoms of many inher- bonate, calcium, carbonate, chloride, mag- ited diseases result from abnormal protein nesium, phosphate, potassium, sodium, and function. sulfate. 5. Acids are electrolytes that release hydrogen WeBsiTes ions in water (such as hydrochloric acid). Bases are electrolytes that release ions that http://biology.clc.uc.edu/Courses/bio104/lipids. bond with hydrogen ions (such as sodium htm hydroxide). Buﬀ ers are chemicals that resist http://hyperphysics.phy-astr.gsu.edu/hbase/ pH changes. ey combine with hydrogen chemical/bond.html ions when these ions are excessive and contribute hydrogen ions when these ions are http://users.rcn.com/jkimball.ma.ultranet/ reduced. BiologyPages/P/Proteins.html 6. Lipids are not soluble in water; they may dis- http://www.biology.arizona.edu/molecular_bio/ solve in other lipids, oils, ether, chloroform, problem_sets/nucleic_acids/nucleic_acids_1. or alcohol. Proteins are vital for many body html functions. ey can combine with carbohydrates or lipids, and always contain carbon, http://www.emc.maricopa.edu/faculty/farabee/ hydrogen, oxygen, and nitrogen atoms. BIOBK/BioBookCHEM1.html 7. e term pH is deﬁ ned as the measurement http://www.madsci.org/posts/archives/2000- of hydrogen ion concentration. e pH scale 12/975719013.Ch.r.html ranges from 0 to 14, with 7 being the midpoint (an equal number of hydrogen and http://www.nlm.nih.gov/medlineplus/ hydroxide ions) or “neutral”—neither acidic carbohydrates.html nor basic. http://www.shodor.org/unchem/basic/atom/index. 8. Organic substances in cells include carbo- html hydrates, lipids, proteins, and nucleic acids. http://www.visionlearning.com/library/module_ Carbohydrates provide much of the energy viewer.php?mid58 required by the body’s cells, as well as helping to build cell structures. Lipids are vital revieW QuesTiOns for many cell functions such as the building of the cell membrane, and include fats, 1. Which of the following represents an atomic phospholipids, and steroids. Proteins are number? vital for body structures, functions, energy, A. protons in an atom enzymatic functions, defense (antibodies), B. protons and neutrons © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION 28 CHApTER 2 Chemical Basics of life

CHApTER C. electrons in an ion C. a neutron D. neutrons in an atom a protonD. 3 2. Which of the following is an important buf- 9. e building blocks of fat molecules are: fer in body fl uids? A. fatty acids A. hydrochloric acid B. triglycerides B. sodium bicarbonate C. glycerols C. sodium chloride D. fatty acids and glycerols w aterD. waterD. 10. Nucleic acids are composed of units called: 3. A solution containing an equal number of A. fatty acids hydrogen ions and hydroxide ions is: B. nucleotides basicA. basicA. C. amino acids alkalineB. alkalineB. D. adenosines Cells acidicC. acidicC. 11. Which of the following is a true statement neutralD. neutralD. about lipids? 4. Which of the following statements about A. ey provide roughly twice the energy water is false? of carbohydrates. A. It has a relatively low heat capacity. B. ey provide roughly twice the energy B. It contains hydrogen bonds. of proteins. C. It dissolves many compounds. C. ey help to cushion delicate organs D. It is responsible for about two thirds from damage. of the mass of the human body. D. All of the above. 5. Which of the following is the most important 12. A fatty acid that contains three double cova- OuTline 9. Describe the parts of the cell cycle. high-energy compound in cells? lent bonds in its carbon chain is said to be: Structure of the Cell 10. Explain cell division and cancer. glucoseA. glucoseA. A. polyunsaturated Cell Membrane proteinB. proteinB. B. monounsaturated Cytoplasm Key Terms fructoseC. fructoseC. C. hydrogenated Nucleus Active transport: The movement of particles through D. adenosine triphosphate D. saturated Movements Through Cell Membranes membranes from regions of lower concentration to regions 6. e molecules that store and process infor- 13. Which of the following is the most important passive Cell Mechanisms of higher concentration. mation at the molecular level are the: metabolic fuel molecule in the body? Active Cell Mechanisms Cell membrane: The plasma membrane; it controls steroidsA. steroidsA. starchA. The Cell Life Cycle movement of substances into and out of the cell. B. carbohydrates proteinB. Interphase Centrioles: Barrel-shaped, hollow organelles inside a C. nucleic acids glucoseC. Cell Division and Cytoplasmic Division centrosome. lipidsD. lipidsD. sucroseD. Differentiation Centrosome: A non-membranous organelle consisting of 7. An unstable isotope that emits subatomic 14. Ions with a negative charge are called: Cell Division and Cancer two hollow centrioles. Chromatin: Loosely coiled DNA and protein fi bers that particles spontaneously is referred to as: cationsA. Summary Learning Goals condense to form chromosomes. A. a proton anionsB. Chromosomes: Structures formed from condensed DNA an atomB. an atomB. C. polyatomic ions Critical Thinking Questions Websites fi bers and protein; they are thread-like, and are contained C. a radioisotope radicalsD. Review Questions within the nucleus of the cells. D. a neutron 15. e atomic weight of an element includes Cilia: Structures that extend from the surfaces of epithelial 8. Which of the following is the smallest par- which of the following? OBjeCTives (lining) cells that move in a coordinated manner to move ticle of an element that has the properties of A. protons and neutrons in the nucleus fl uids over the cell surfaces. that element? B. protons and electrons in an atom After studying this chapter, readers should be able to: Cytology: The study of cellular structure and function. 1. Explain the parts of a cell’s structure. A. an electron C. electrons in the outer shells Cytoplasm: The gel-like material that fi lls out a cell; it 2. Describe the structure and function of the cell an atomB. an atomB. D. neutrons in the nucleus makes up most of the cell’s volume, and suspends the cell’s membrane. organelles. 3. Describe the structure and function of Cytoskeleton: The cell skeleton; cellular scaffolding cytoplasm and cytosol. contained in the cytoplasm. 4. Describe the parts of the cell nucleus and their Cytosol: The clear liquid portion of the cytoplasm. functions. endocytosis: The process of movement, via a cell 5. Describe the “powerhouses” of the cell. membrane secretion, of particles too large to enter a cell 6. Describe the processes that transport by other processes within a cell vesicle. substances across the plasma membrane. endoplasmic reticulum (er): An organelle composed 7. Compare and defi ne cilia and fl agella. of fl at sacs, long canals, and fl uid-fi lled vesicles; the ER 8. Compare passive and active cell mechanisms. transports molecules between cell parts.