chapter 2

Electronegativity

the power to attract electrons to itself

reversible reaction

the products can revert to the original reactants. A reversible reaction is indicated by two half‐arrows pointing in opposite directions:

inorganic compounds

usually lack carbon and are structurally simple.

polypeptide

(10-2000 or more amino acids).

carboxyl

-COOH

amino

-NH2

phospahte

-P04

saturated fats

A fat that mainly consists of saturated fatty acids. ex:lard

hydrogen bonds and how they contribute to the properties of water and structure of macromolecules.

A hydrogen bond forms when a hydrogen atom with a partial positive charge (δ+) attracts the partial negative charge (δ−) of neighboring electronegative atoms, most often larger oxygen or nitrogen atoms. The hydrogen bonds that link neighboring water molecules give water considerable cohesion, the tendency of like particles to stay together. The cohesion of water molecules creates a very high surface tension, a measure of the difficulty of stretching or breaking the surface of a liquid. At the boundary between water and air, water's surface tension is very high because the water molecules are much more attracted to one another than they are attracted to molecules in the air. This is readily seen when a spider walks on water or a leaf floats on water. The influence of water's surface tension on the body can be seen in the way it increases the work required for breathing. A thin film of watery fluid coats the air sacs of the lungs. So, each inhalation must have enough force to overcome the opposing effect of surface tension as the air sacs stretch and enlarge when taking in air. Even though single hydrogen bonds are weak, very large molecules may contain thousands of these bonds. Acting collectively, hydrogen bonds provide considerable strength and stability and help determine the three‐dimensional shape of large molecules. As you will see later in this chapter, a large molecule's shape determines how it functions.

solvent

A liquid substance capable of dissolving other substances

acids

A solution that has more H+ than OH− is an acidic solution and has a pH below 7

bases

A solution that has more OH− than H+.has a pH above 7.

solute

A substance that is dissolved in a solution.

hydroxyl (R-O-H)

Alcohols contain an — OH group, which is polar and hydrophilic due to its electronegative O atom. Molecules with many — OH groups dissolve easily in water.

the law of conservation of energy

Although energy can be neither created nor destroyed, it may be converted from one form to another

amino

Amines have an — NH 2 group, which can act as a base and pick up a hydrogen ion, giving the amino group a positive charge. At the pH of body fluids, most amino groups have a charge of 1+. All amino acids have an amino group at one end.

Explain why and how an atom can lose or gain electrons, and what the resulting balance between numbers of electrons and protons produces, as with sodium and chlorine.

As you have already learned, when atoms lose or gain one or more valence electrons, ions are formed. Positively and negatively charged ions are attracted to one another—opposites attract. The force of attraction that holds together ions with opposite charges is an ionic bond. Consider sodium and chlorine atoms, the components of common table salt. Sodium has one valence electron (Figure 2.4a). If sodium loses this electron, it is left with the eight electrons in its second shell, which becomes the valence shell. As a result, however, the total number of protons (11) exceeds the number of electrons (10). Thus, the sodium atom has become a cation (KAT‐ī‐on), or positively charged ion

how activation energy is required to produce a chemical reaction and concentration and temperature influence the rate of reaction.

Because particles of matter such as atoms, ions, and molecules have kinetic energy, they are continuously moving and colliding with one another. A sufficiently forceful collision can disrupt the movement of valence electrons, causing an existing chemical bond to break or a new one to form. The collision energy needed to break the chemical bonds of the reactants is called the activation energy of the reaction (Figure 2.8). This initial energy "investment" is needed to start a reaction. The reactants must absorb enough energy for their chemical bonds to become unstable and their valence electrons to form new combinations. Then, as new bonds form, energy is released to the surroundings.Both the concentration of particles and the temperature influence the chance that a collision will occur and cause a chemical reaction. Concentration. The more particles of matter present in a confined space, the greater the chance that they will collide (think of people crowding into a subway car at rush hour). The concentration of particles increases when more are added to a given space or when the pressure on the space increases, which forces the particles closer together so that they collide more often. Temperature. As temperature rises, particles of matter move about more rapidly. Thus, the higher the temperature of matter, the more forcefully particles will collide, and the greater the chance that a collision will produce a reaction.

carboxyl group

COOH. Carboxylic acids contain a carboxyl group at the end of the carbon skeleton. All amino acids have a — COOH group at one end. The negatively charged form predominates at the pH of body cells and is hydrophilic.

properties of carbon

Carbon has several properties that make it particularly useful to living organisms. For one thing, it can form bonds with one to thousands of other carbon atoms to produce large molecules that can have many different shapes. Due to this property of carbon, the body can build many different organic compounds, each of which has a unique structure and function. Moreover, the large size of most carbon‐containing molecules and the fact that some do not dissolve easily in water make them useful materials for building body structures.

nucleic acids

DNA and RNA. dna- forms the inherited genetic material inside each human cell. rna-relays instructions from the genes to guide each cell's synthesis of proteins from amino acids.

the four nitrogenous bases

DNA contains four different nitrogenous bases, which contain atoms of C, H, O, and N. In DNA the four nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). Adenine and guanine are larger, double‐ring bases called purines (PŪR‐ēnz); thymine and cytosine are smaller, single‐ring bases called pyrimidines (pī‐RIM‐i‐dēnz). The nucleotides are named according to the base that is present. For instance, a nucleotide containing thymine is called a thymine nucleotide, one containing adenine is called an adenine nucleotide, and so on. three components might be arranged in DNA. Their insights into data gathered by others led them to construct a model so elegant and simple that the scientific world immediately knew it was correct! In the Watson-Crick double helix model, DNA resembles a spiral ladder (Figure 2.25). Two strands of alternating phosphate groups and deoxyribose sugars form the uprights of the ladder. Paired bases, held together by hydrogen bonds, form the rungs. Because adenine always pairs with thymine, and cytosine always pairs with guanine, if you know the sequence of bases in one strand of DNA, you can predict the sequence on the complementary (second) strand. Each time DNA is copied, as when living cells divide to increase their number, the two strands unwind. Each strand serves as the template or mold on which to construct a new second strand. Any change that occurs in the base sequence of a DNA strand is called a mutation. Some mutations can result in the death of a cell, cause cancer, or produce genetic defects in future generations.

catabolic chemical reactions

Decomposition reactions split up large molecules into smaller atoms, ions, or molecules

Describe each component of an atom in terms of its relative position, charge, and mass.

Dozens of different subatomic particles compose individual atoms. However, only three types of subatomic particles are important for understanding the chemical reactions in the human body: protons, neutrons, and electrons (Figure 2.1). The dense central core of an atom is its nucleus. Within the nucleus are positively charged protons (p+) and uncharged (neutral) neutrons (n0). The tiny, negatively charged electrons (e−) move about in a large space surrounding the nucleus. They do not follow a fixed path or orbit but instead form a negatively charged "cloud" that envelops the nucleus (Figure 2.1a).

how atoms and molecules release or store energy in processes known as chemical reactions

Each chemical reaction involves energy changes. Energy (en‐ = in; ‐ergy = work) is the capacity to do work. Two principal forms of energy are potential energy, energy stored by matter due to its position, and kinetic energy, the energy associated with matter in motion. For example, the energy stored in water behind a dam or in a person poised to jump down some steps is potential energy. When the gates of the dam are opened or the person jumps, potential energy is converted into kinetic energy. Chemical energy is a form of potential energy that is stored in the bonds of compounds and molecules. The total amount of energy present at the beginning and end of a chemical reaction is the same. Although energy can be neither created nor destroyed, it may be converted from one form to another. This principle is known as the law of conservation of energy. For example, some of the chemical energy in the foods we eat is eventually converted into various forms of kinetic energy, such as mechanical energy used to walk and talk. Conversion of energy from one form to another generally releases heat, some of which is used to maintain normal body temperature.

amino acid structure

Each of the 20 different amino acids has a hydrogen (H) atom and three important functional groups attached to a central carbon atom.

how enzymes are named and their properties

Enzyme names end in -ase and are often named after the substrate. For example, the enzyme that catalyzes the hydrolysis of sucrose is sucrase .1.) Enzymes are highly specific. Each particular enzyme binds only to specific substrates. 2.) ENZYMES ARE EFFICIENT Under optimal conditions, enzymes can catalyze reactions at rates that are from 100 million to 10 billion times. 3.) Enzymes are subject to a variety of cellular controls. Their rate of synthesis and their concentration at any given time are under the control of a cell's genes.

the general operation of enzymes

Enzymes lower the activation energy of a chemical reaction by decreasing the "randomness" of the collisions between molecules. They also help bring the substrates together in the proper orientation so that the reaction can occur. Figure 2.23a depicts how an enzyme works: 1The substrates make contact with the active site on the surface of the enzyme molecule, forming a temporary intermediate compound called the enzyme-substrate complex. In this reaction the two substrate molecules are sucrose (a disaccharide) and water. 2The substrate molecules are transformed by the rearrangement of existing atoms, the breakdown of the substrate molecule, or the combination of several substrate molecules into the products of the reaction. Here the products are two monosaccharides: glucose and fructose. 3After the reaction is completed and the reaction products move away from the enzyme, the unchanged enzyme is free to attach to other substrate molecules.

ester

Esters predominate in dietary fats and oils and also occur in our body as triglycerides. Aspirin is an ester of salicylic acid, a pain‐relieving molecule found in the bark of the willow tree.

buffers

Even though strong acids and bases are continually taken into and formed by the body, the pH of fluids inside and outside cells remains almost constant. One important reason is the presence of buffer systems, which function to convert strong acids or bases into weak acids or bases. Strong acids (or bases) ionize easily and contribute many H+ (or OH−) to a solution. Therefore, they can change pH drastically, which can disrupt the body's metabolism. Weak acids (or bases) do not ionize as much and contribute fewer H+ (or OH−). Hence, they have less effect on the pH. The chemical compounds that can convert strong acids or bases into weak ones are called buffers

Carbonyl

Ketones contain a carbonyl group within the carbon skeleton. The carbonyl group is polar and hydrophilic due to its electronegative O atom. Aldehydes have a carbonyl group at the end of the carbon skeleton.

simple sugar

Simple sugars are called monosaccharides, made up of single sugar molecules. Examples of these are glucose, fructose, and galactose.

phosphate

Phosphates contain a phosphate group ( — PO 2 − 4 ) , which is very hydrophilic due to the dual negative charges. An important example is adenosine triphosphate (ATP), which transfers chemical energy between organic molecules during chemical reactions.

valence shell electrons

The likelihood that an atom will form a chemical bond with another atom depends on the number of electrons in its outermost shell, also called the valence shell. An atom with a valence shell holding eight electrons is chemically stable, which means it is unlikely to form chemical bonds with other atoms. Neon, for example, has eight electrons in its valence shell, and for this reason it does not bond easily with other atoms. The valence shell of hydrogen and helium is the first electron shell, which holds a maximum of two electrons. Because helium has two valence electrons, it too is stable and seldom bonds with other atoms. Hydrogen, on the other hand, has only one valence electron (see Figure 2.2), so it binds readily with other atoms.

Explain how mass number is related to radioisotopes and atomic weight

The mass number of an atom is the sum of its protons and neutrons. Because sodium has 11 protons and 12 neutrons, its mass number is 23 (Figure 2.2). Although all atoms of one element have the same number of protons, they may have different numbers of neutrons and thus different mass numbers. Isotopes are atoms of an element that have different numbers of neutrons and therefore different mass numbers. In a sample of oxygen, for example, most atoms have 8 neutrons, and a few have 9 or 10, but all have 8 protons and 8 electrons. Most isotopes are stable, which means that their nuclear structure does not change over time. The stable isotopes of oxygen are designated 16O, 17O, and 18O (or O‐16, O‐17, and O‐18). As you already may have determined, the numbers indicate the mass number of each isotope. As you will discover shortly, the number of electrons of an atom determines its chemical properties. Although the isotopes of an element have different numbers of neutrons, they have identical chemical properties because they have the same number of electrons. The standard unit for measuring the mass of atoms and their subatomic particles is a dalton, also known as an atomic mass unit (amu). A neutron has a mass of 1.008 daltons, and a proton has a mass of 1.007 daltons. The mass of an electron, at 0.0005 dalton, is almost 2000 times smaller than the mass of a neutron or proton. The atomic mass (also called the atomic weight) of an element is the average mass of all its naturally occurring isotopes. Typically, the atomic mass of an element is close to the mass number of its most abundant isotope.

Sulfhydryl R-S-H

Thiols have an — SH group, which is polar and hydrophilic due to its electronegative S atom. Certain amino acids (for example, cysteine) contain — SH groups, which help stabilize the shape of proteins.

pH homeostasis

To ensure homeostasis, intracellular and extracellular fluids must contain almost balanced quantities of acids and bases. The more hydrogen ions (H+) dissolved in a solution, the more acidic the solution; the more hydroxide ions (OH−), the more basic (alkaline) the solution. The chemical reactions that take place in the body are very sensitive to even small changes in the acidity or alkalinity of the body fluids in which they occur. Any departure from the narrow limits of normal H+ and OH− concentrations greatly disrupts body functions.

chemical elements of the human body

Twenty‐six different chemical elements normally are present in your body. Just four elements, called the major elements, constitute about 96% of the body's mass: oxygen, carbon, hydrogen, and nitrogen. Eight others, the lesser elements, contribute about 3.6% to the body's mass: calcium, phosphorus (P), potassium (K), sulfur (S), sodium, chlorine (Cl), magnesium (Mg), and iron (Fe; ferrum = iron). An additional 14 elements—the trace elements—are present in tiny amounts. Together, they account for the remaining body mass, about 0.4%. Several trace elements have important functions in the body. For example, iodine is needed to make thyroid hormones. The functions of some trace elements are unknown. Table 2.1 lists the main chemical elements of the human body.

anabolic chemical reactions

When two or more atoms, ions, or molecules combine to form new and larger molecules, the processes are called synthesis reactions.

water

Water is the most important and abundant inorganic compound in all living systems. Although you might be able to survive for weeks without food, without water you would die in a matter of days. Nearly all the body's chemical reactions occur in a watery medium. Water has many properties that make it such an indispensable compound for life. We have already mentioned the most important property of water, its polarity—the uneven sharing of valence electrons that confers a partial negative charge near the one oxygen atom and two partial positive charges near the two hydrogen atoms in a water molecule (see Figure 2.5e). This property makes water an excellent solvent for other ionic or polar substances, gives water molecules cohesion (the tendency to stick together), and allows water to resist temperature changes. Water as a Solvent In medieval times people searched in vain for a "universal solvent," a substance that would dissolve all other materials. They found nothing that worked as well as water. Although it is the most versatile solvent known, water is not the universal solvent sought by medieval alchemists.

covalent bond

When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them. Atoms form a covalently bonded molecule by sharing one, two, or three pairs of valence electrons

molecules

When two or more atoms share electrons, the resulting combination

how atoms bond together to from molecules

When two or more atoms share electrons, the resulting combination is called a molecule (MOL‐e‐kūl). A molecular formula indicates the elements and the number of atoms of each element that make up a molecule. A molecule may consist of two atoms of the same kind, such as an oxygen molecule (Figure 2.3a). The molecular formula for a molecule of oxygen is O2. The subscript 2 indicates that the molecule contains two atoms of oxygen. Two or more different kinds of atoms may also form a molecule, as in a water molecule (H2O). In H2O one atom of oxygen shares electrons with two atoms of hydrogen.

mixtures

a combination of elements or compounds that are physically blended together but not bound by chemical bonds

chemical energy

a form of potential energy that is stored in the bonds of compounds and molecule

polymer

a large molecule formed by the covalent bonding of many identical or similar small building‐block molecules called monomers

disaccharides

a molecule formed from the combination of two monosaccharides by dehydration synthesis

compounds

a substance that contains atoms of two or more different elements

endergonic reactions

absorb more energy than they release.

organic compounds

always contain carbon, usually contain hydrogen, and always have covalent bonds

free radicals

an atom or group of atoms with an unpaired electron in the outermost shell.

ions

an atom that has a positive or negative charge because it has unequal numbers of protons and electrons.

matter

anything that occupies space and has mass

proteins

are large molecules that contain carbon, hydrogen, oxygen, and nitrogen. Structural Form structural framework of various parts of body. Examples: collagen in bone and other connective tissues; keratin in skin, hair, and fingernails. Regulatory-Function as hormones that regulate various physiological processes; control growth and development; as neurotransmitters, mediate responses of nervous system. Examples: the hormone insulin (regulates blood glucose level); the neurotransmitter known as substance P (mediates sensation of pain in nervous system). Contractile- Allow shortening of muscle cells, which produces movement. Examples: myosin; actin. Immunological- Aid responses that protect body against foreign substances and invading pathogens. Examples: antibodies; interleukins. Transport Carry vital substances throughout body. Example: hemoglobin (transports most oxygen and some carbon dioxide in blood). Catalytic-Act as enzymes that regulate biochemical reactions. Examples: salivary amylase; sucrase; ATPase.

eicosanoid

are lipids derived from a 20‐carbon fatty acid called arachidonic acid. The two principal subclasses of eicosanoids are the prostaglandins (pros′‐ta‐GLAN‐dins) and the leukotrienes (loo′‐kō‐TRĪ‐ēnz). Prostaglandins have a wide variety of functions. They modify responses to hormones, contribute to the inflammatory response (Chapter 22), prevent stomach ulcers, dilate (enlarge) airways to the lungs, regulate body temperature, and influence formation of blood clots, to name just a few. Leukotrienes participate in allergic and inflammatory responses.

methyl

ch3

catalysts

chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur (Figure 2.9). The most important catalysts in the body are enzymes, which we will discuss later in this chapter.

the properties of triglycerides

consists of two types of building blocks: a single glycerol molecule and three fatty acid molecules. A three‐carbon glycerol molecule forms the backbone.

monosaccharides

contain from three to seven carbon atoms

monosatrated fats

contain triglycerides that mostly consist of monounsaturated fatty acids. ex: olive oil

polyunsaturated fats

contain triglycerides that mostly consist of polyunsaturated fatty acids. ex: Corn oil

polysaccharides

contains tens or hundreds of monosaccharides joined through dehydration synthesis reactions

hydrolysis synthesis

decomposition reactions break down large nutrient molecules into smaller molecules by the addition of water molecules

structure of steriods

differs considerably from that of the triglycerides. Steroids have four rings of carbon atoms

colloids

differs from a solution mainly because of the size of its particles. The solute particles in a colloid are large enough to scatter light, just as water droplets in fog scatter light from a car's headlight beams

potential energy

energy stored by matter due to its position

how a disaccharide is formed

formed from the combination of two monosaccharides by dehydration synthesis (

Structure of a phospholipid

have a glycerol backbone and two fatty acid chains attached to the first two carbons.

solutions

homogeneous mixture of two or more substances.

ph

hydrogen ion concentration

the difference between nonpolar and polar covalent bonds

in a nonpolar covalent bond the two atoms share the electrons equally, but polar bondsis when two atoms share their electrons unequal.

the role of cholesterol

is needed for cell membrane structure

the role of glycogen in the body

made entirely of glucose monomers linked to one another in branching chains (Figure 2.16). A limited amount of carbohydrates is stored as glycogen in the liver and skeletal muscles. Starches are polysaccharides formed from glucose by plants. They are found in foods such as pasta and potatoes and are the major carbohydrates in the diet. Like disaccharides, polysaccharides such as glycogen and starches can be broken down into monosaccharides through hydrolysis reactions. For example, when the blood glucose level falls, liver cells break down glycogen into glucose and release it into the blood, making it available to body cells, which break it down to synthesize ATP

the chemical makeup and properties of lipids

make up 18-25% of body mass in lean adults. Like carbohydrates, lipids contain carbon, hydrogen, and oxygen. Unlike carbohydrates, they do not have a 2:1 ratio of hydrogen to oxygen. The proportion of electronegative oxygen atoms in lipids is usually smaller than in carbohydrates, so there are fewer polar covalent bonds. As a result, most lipids are insoluble in polar solvents such as water; they are hydrophobic. Because they are hydrophobic, only the smallest lipids (some fatty acids) can dissolve in watery blood plasma.

chemical reactions

occurs when new bonds form or old bonds break between atoms

four levels of structural organization

primary- the unique sequence of amino acids that are linked by covalent peptide bonds to form a polypeptide chain. secondary- structure of a protein is the repeated twisting or folding of neighboring amino acids in the polypeptide chain (Figure 2.22b). Two common secondary structures are alpha helixes (clockwise spirals) and beta pleated sheets. The secondary structure of a protein is stabilized by hydrogen bonds, which form at regular intervals along the polypeptide backbone. tertiary- the three‐dimensional shape of a polypeptide chain. Quaternary- In those proteins that contain more than one polypeptide chain (not all of them do), the arrangement of the individual polypeptide chains relative to one another.

exergonic reactions

release more energy than they absorb

ATP

the "energy currency" of living systems (Figure 2.26). ATP transfers the energy liberated in exergonic catabolic reactions to power cellular activities that require energy (endergonic reactions). structure- consists of three phosphate groups attached to adenosine, a unit composed of adenine and the five‐carbon sugar ribose.

mass

the amount of matter in any object, which does not change.

energy

the capacity to do work

kinetic energy

the energy associated with matter in motion

the law of conservation of mass

the mass of the system must remain constant over time

suspensions

the suspended material may mix with the liquid or suspending medium for some time, but eventually it will settle out. Blood is an example of a suspension.

exchange reactions

they consist of both synthesis and decomposition reactions

describe what happens to most ionic molecules when put into water.

they dissolve

triple covalent bond

two atoms share three pairs of electrons, as in a molecule of nitrogen (Figure 2.5c). Notice in the structural formulas for covalently bonded molecules in Figure 2.5 that the number of lines between the chemical symbols for two atoms indicates whether the bond is a single (—), double , or triple covalent bond.

salts

when dissolved in water, dissociates into cations and anions, neither of which is H+ or OH−

single covalent bonds

when two atoms share one electron pair. For example, a molecule of hydrogen forms when two hydrogen atoms share their single valence electrons (Figure 2.5a), which allows both atoms to have a full valence shell at least part of the time.

double covalent bond

when two atoms share two pairs of electrons, as happens in an oxygen molecule

dehydration synthesis

when two smaller molecules join to form a larger molecule. a water molecule is one of the products formed