Chapter 2 - The Chemical Level of Organization Flashcards
Identify the 4 major chemical elements and the 8 minor chemical elements of the human 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).
An additional 14 elements - the trace elements - are present in tiny amounts.
Describe the structures of atoms, ions, molecules, free radicals, and compounds.
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. 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. Even though their exact positions cannot be predicted, specific groups of electrons are most likely to move about within certain regions around the nucleus. These regions, called electron shells, may be depicted as simple circles around the nucleus. The first electron shell (nearest the nucleus) never holds more than 2 electrons. The second shell holds a maximum of 8 electrons, and the third shell can hold up to 18 electrons. The number of electrons in an atom of an element always equals the number of protons. Thus, each atom is electrically neutral; its total charge is zero.
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. Although the isotopes of an element have different numbers of neutrons, they have identical chemical properties because they have the same number of electrons. Certain isotopes called radioactive isotopes (radioisotopes) are unstable; their nuclei decay (spontaneously change) into a stable configuration. As they decay, these atoms emit radiation - either subatomic particles or packets of energy - and in the process often transform into a different element. The half-life of an isotope is the time required for half of the radioactive atoms in a sample of that isotope to decay into a more stable form.
If an atom either gives up or gains electrons, it becomes an ion. An ion is an atom that has a positive or negative charge because it has unequal numbers of protons and electrons. When two or more atoms share electrons, the resulting combination is called a molecule. A molecule may consist of two atoms of the same kind, such as an oxygen molecule, O2, or of two or more different kinds of atoms. as in a water molecule, H2O.
A compound is a substance that contains atoms of two or more different elements. Most of the atoms in the body are joined into compounds. Water (H2O) and sodium chloride (NaCl), common table salt, are compounds. However, a molecule of oxygen (O2) is not a compound because it consists of atoms of only one element.
A free radical is an atom or group of atoms with an unpaired electron in the outermost shell. Having an unpaired electron makes a free radical unstable, highly reactive, and destructive to nearby molecules. Free radicals become stable by either giving up their unpaired electron to, or taking on an electron from, another molecule. In so doing, free radicals may break apart important body molecules.
Describe how valence electrons form chemical bonds.
The forces that hold together the atoms of a molecule or a compound are chemical bonds. 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. 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, so it binds readily with other atoms. The atoms of most biologically important elements do not have eight electrons in their valence shells. Under the right conditions, two or more atoms can interact in ways that produce a chemically stable arrangement of eight valence electrons for each atom. This chemical principle, called the octet rule, helps explain why atoms interact in predictable ways. One atom is more likely to interact with another atom if doing so will leave both with eight valence electrons. For this to happen, an atom either empties its partially filled valence shell, fills it with donated electrons, or shares electrons with other atoms. The way that valence electrons are distributed determines what kind of chemical bond results.
Distinguish among ionic, covalent, and hydrogen bonds.
As you have already learned, when atoms lose or gain one or more valence electrons, ions are formed. A cation is a positively charged ion (it has lost a valence electron and has less electrons than protons), and an anion is a negatively charged ion (it has gained a valence electron and has more electrons than protons). 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. An ionic compound that breaks apart into positive and negative ions in solution is called an electrolyte. Most ions in the body are dissolved in body fluids as electrolytes, so named because their solutions can conduct an electric current.
When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them. For example, a molecule of hydrogen forms when two hydrogen atoms share their single valence electrons, which allows both atoms to have a full valence shell at least part of the time. Atoms form a covalently bonded molecule by sharing one, two, or three pairs of valence electrons and forming a single, double, or triple covalent bond. The larger the number of electron pairs shared between two atoms, the stronger the covalent bond. In some covalent bonds, two atoms share the electrons equally - one atom does not attract the shared electrons more strongly than the other atom. This type of bond is a nonpolar covalent bond. The bonds between two identical atoms are always nonpolar covalent bonds. In a polar covalent bond, the sharing of electrons between two atoms is unequal - the nucleus of one atom attracts the shared electrons more strongly than the nucleus of the other atom. When polar covalent bonds form, the resulting molecule has a partial negative charge near the atom that attracts electrons more strongly. This atom has greater electronegativity, the power to attract electrons to itself. At least one other atom in the molecule then will have a partial positive charge. A very important example of a polar covalent bond in living systems is the bond between oxygen and hydrogen in a molecule of water.
The polar covalent bonds that form between hydrogen atoms and other atoms can give rise to a third type of chemical bond, a hydrogen bond. 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. Thus, hydrogen bonds result from attraction of oppositely charged parts of molecules rather than from sharing of electrons as in covalent bonds, or the loss or gain of electrons as in ionic bonds. Hydrogen bonds are weak compared to ionic and covalent bonds. Thus, they cannot bind atoms into molecules. However, hydrogen bonds do establish important links between molecules or between different parts of a large molecule, such as a protein or nucleic acid.
Define a chemical reaction.
A chemical reaction occurs when new bonds form or old bonds break between atoms. Chemical reactions are the foundation of all life processes, and as we have seen, the interactions of valence electrons are the basis of all chemical reactions. Consider how hydrogen and oxygen molecules react to form water molecules. The starting substances - two H2 and one O2 - are known as the reactants. The ending substances - two molecules of H2O - are the products. The term metabolism refers to all the chemical reactions occurring in the body.
Describe the various forms of energy.
Energy 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. 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.
Compare exergonic and endergonic chemical reactions.
A chemical reaction may either release energy or absorb energy. Exergonic reactions release more energy than they absorb. By contrast, endergonic reactions absorb more energy than they release.
Explain the role of activation energy and catalysts in chemical reactions.
The collision energy needed to break the chemical bonds of the reactants is called the activation energy of the reaction. This is the initial energy “investment” needed to start a reaction.
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. Temperature: As temperature rises, particles of matter move about more rapidly and will collide more forcefully.
Catalysts are chemical compounds that speed up chemical reactions by lowering the activation energy needed for a reaction to occur. They are especially important in bodily processes because the high concentrations and high temperatures needed for many chemical reactions to occur frequently are not conducive to life.
Describe synthesis, decomposition, exchange, reversible, and oxidation-reduction reactions.
When two or more atoms, ions, or molecules combine to form new and larger molecules, the processes are called synthesis reactions. All of the synthesis reactions that occur in your body are collectively referred to as anabolism. Overall, anabolic reactions are usually endergonic because they absorb more energy than they release.
Decomposition reactions split up large molecules into smaller atoms, ions, or molecules. The decomposition reactions that occur in your body are collectively referred to as catabolism. Overall, catabolic reactions are usually exergonic because they release more energy than they absorb.
Many reactions in the body are exchange reactions; they consist of both synthesis and decomposition reactions.
Some chemical reactions proceed in only one direction, from reactants to products. Other chemical reactions may be reversible. In a reversible reaction, the products can revert to the original reactants.
Oxidation refers to the loss of electrons; in the process the oxidized substance releases energy. Reduction refers to the gain of electrons; in the process the reduced substance gains energy. Oxidation–reduction reactions are always parallel; when one substance is oxidized, another is reduced at the same time.
Describe inorganic compounds and organic compounds and the properties of water and those of inorganic acids, bases, and salts.
Inorganic compounds usually lack carbon and are structurally simple. They include water and many salts, acids, and bases.
Organic compounds always contain carbon, usually contain hydrogen, and always have covalent bonds.
Water is the most important and abundant inorganic compound in all living systems. Nearly all the body’s chemical reactions occur in a watery medium. Water is the most versatile solvent known. In a solution, a substance called the solvent dissolves another substance called the solute. The versatility of water as a solvent for ionized or polar substances is due to its polar covalent bonds and its bent shape, which allows each water molecule to interact with several neighboring ions or molecules. Solutes that are charged or contain polar covalent bonds are hydrophilic, which means they dissolve easily in water. Molecules that contain mainly nonpolar covalent bonds, by contrast, are hydrophobic.
Water serves as the medium for most chemical reactions in the body and participates as a reactant or product in certain reactions. During digestion, for example, decomposition reactions break down large nutrient molecules into smaller molecules by the addition of water molecules. This type of reaction is called hydrolysis. By contrast, when two smaller molecules join to form a larger molecule in a dehydration synthesis reaction, a water molecule is one of the products formed.
In comparison to most substances, water can absorb or release a relatively large amount of heat with only a modest change in its own temperature. For this reason, water is said to have a high heat capacity. Water also has a high heat of evaporation.
Water is a major component of mucus and other lubricating fluids throughout the body. Lubrication is especially necessary in the chest (pleural and pericardial cavities) and abdomen (peritoneal cavity), where internal organs touch and slide over one another. It is also needed at joints, where bones, ligaments, and tendons rub against one another. Inside the gastrointestinal tract, mucus and other watery secretions moisten foods, which aids their smooth passage through the digestive system.
In summary, water is highly effective solvent and lubricant, has unique thermal properties, and is necessary for countless chemical reactions.
When inorganic acids, bases, or salts dissolve in water, they dissociate, that is, they separate into ions and become surrounded by water molecules. An acid is a substance that dissociates into one or more hydrogen ions (H+) and one or more anions. Because H+ is a single proton with one positive charge, an acid is also referred to as a proton donor. A base, by contrast, removes H+ from a solution and is therefore a proton acceptor. Many bases dissociate into one or more hydroxide ions (OH−) and one or more cations. A salt, when dissolved in water, dissociates into cations and anions, neither of which is H+ or OH-. Acids and bases react with one another to form salts.
Distinguish among solutions, colloids, and suspensions.
A mixture is a combination of elements or compounds that are physically blended together but not bound by chemical bonds. For example, the air you are breathing is a mixture of gases that includes nitrogen, oxygen, argon, and carbon dioxide. Three common liquid mixtures are solutions, colloids, and suspensions.
Once mixed together, solutes in a solution remain evenly dispersed among the solvent molecules. Because solute particles in a solution are too small to scatter light, a solution looks transparent.
A colloid differs from a solution mainly because of the size of its particles. The solute particles in a colloid are large enough to scatter light. For this reason, colloids usually appear translucent or opaque.
The solutes in both solutions and colloids do not settle out and accumulate on the bottom of the container. In a suspension, by contrast, the suspended material may mix with the liquid or suspending medium for some time, but eventually it will settle out.
Define pH and explain the role of buffer systems in 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. A solution’s acidity or alkalinity is expressed on the pH scale, which extends from 0 to 14. The midpoint of the pH scale is 7, where the concentrations of H+ and OH− are equal. A substance with a pH of 7, such as pure water, is neutral. A solution that has more H+ than OH− is an acidic solution and has a pH below 7. A solution that has more OH− than H+ is a basic (alkaline) solution and has a pH above 7.
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. The chemical compounds that can convert strong acids or bases into weak ones are called buffers. They do so by removing or adding protons (H+).
Define the term functional group as it relates to organic molecules.
The chain of carbon atoms in an organic molecule is called the carbon skeleton. Many of the carbons are bonded to hydrogen atoms, yielding a hydrocarbon. Also attached to the carbon skeleton are distinctive functional groups, other atoms or molecules bound to the hydrocarbon skeleton. Each type of functional group has a specific arrangement of atoms that confers characteristic chemical properties on the organic molecule attached to it.
A functional group is a specific arrangement of atoms that defines the chemical behavior of organic molecules.
Distinguish between monomers and polymers.
Small organic molecules can combine into very large molecules that are called macromolecules. Macromolecules are usually polymers. A polymer is a large molecule formed by the covalent bonding of many identical or similar small building-block molecules called monomers.
Molecules that have the same molecular formula but different structures are called isomers. For example, the molecular formulas for the sugars glucose and fructose are both C6 H12 O6. The individual atoms, however, are positioned differently along the carbon skeleton, giving the sugars different chemical properties.
Identify the building blocks of carbohydrates.
Carbohydrates are a large and diverse group of organic compounds that include sugars, glycogen, starches, and cellulose. Carbon, hydrogen, and oxygen are the elements found in carbohydrates. The ratio of hydrogen to oxygen atoms is usually 2:1, the same as in water. Although there are exceptions, carbohydrates generally contain one water molecule for each carbon atom. The three major groups of carbohydrates, based on their sizes, are monosaccharides, disaccharides, and polysaccharides.
Monosaccharides and disaccharides are known as simple sugars. The monomers of carbohydrates, monosaccharides, contain from three to seven carbon atoms. A disaccharide is a molecule formed from the combination of two monosaccharides by dehydration synthesis. For example, molecules of the monosaccharides glucose and fructose combine to form a molecule of the disaccharide sucrose (table sugar). (Glucose and fructose are isomers.) Disaccharides can also be split into smaller, simpler molecules by hydrolysis.
The third major group of carbohydrates is the polysaccharides. Each polysaccharide molecule contains tens or hundreds of monosaccharides joined through dehydration synthesis reactions. Unlike simple sugars, polysaccharides usually are insoluble in water and do not taste sweet. The main polysaccharide in the human body is glycogen, which is made entirely of glucose monomers linked to one another in branching chains. 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. Cellulose is a polysaccharide
formed from glucose by plants that cannot be digested by humans but does provide bulk to help eliminate feces.
Describe the functions of carbohydrates.
In humans and animals, carbohydrates function mainly as a source of chemical energy for generating ATP needed to drive metabolic reactions. Only a few carbohydrates are used for
building structural units. One example is deoxyribose, a type of sugar that is a building block of deoxyribonucleic acid (DNA), the molecule that carries inherited genetic information.
Identify the different types of lipids.
A second important group of organic compounds is lipids. The diverse lipid family includes fatty acids, triglycerides (fats and oils), phospholipids (lipids that contain phosphorus), steroids (lipids that contain rings of carbon atoms), eicosanoids (20-carbon lipids), and a variety of other substances, including fat-soluble vitamins (vitamins A, D, E, and K) and lipoproteins.
Among the simplest lipids are fatty acids, which consist of a carboxyl group and a hydrocarbon chain. Fatty acids can be either saturated or unsaturated. A saturated fatty acid contains only single covalent bonds between the carbon atoms of the hydrocarbon chain. An unsaturated fatty acid contains one or more double covalent bonds between the carbon atoms of the hydrocarbon chain.
The most plentiful lipids in your body and in your diet are the triglycerides. A triglyceride consists of two types of building blocks: a single glycerol molecule and three fatty acid molecules. A three-carbon glycerol molecule forms the backbone of a triglyceride. A fat is a triglyceride that is solid at room temperature. An oil is a triglyceride that is liquid at room temperature. The fatty acids of an oil can be either monounsaturated or polyunsaturated. Monounsaturated fats contain triglycerides that mostly consist of monounsaturated fatty acids. Olive oil, peanut oil, canola oil, most nuts, and avocados are rich in triglycerides with monounsaturated fatty acids. Polyunsaturated fats contain triglycerides that mostly consist of polyunsaturated fatty acids.
Like triglycerides, phospholipids have a glycerol back-bone and two fatty acid chains attached to the first two carbons. In the third position, however, a phosphate group (PO43−) links a small, charged group that usually contains nitrogen (N) to the backbone.
The structure of steroids differs considerably from that of the triglycerides. Steroids have four rings of carbon atoms. Body cells synthesize other steroids from cholesterol, which has a large nonpolar region consisting of the four rings and a hydrocarbon tail. In the body, the commonly encountered steroids, such as cholesterol, estrogens, testosterone, cortisol, bile salts, and vitamin D, are known as sterols because they also have at least one hydroxyl (alcohol) group (OH).
Eicosanoids are lipids derived from a 20-carbon fatty acid called arachidonic acid. The two principal subclasses of eicosanoids are the prostaglandins and the leukotrienes.
Other lipids include fat-soluble vitamins such as beta-carotenes, vitamins D, E, and K; and lipoproteins.
Discuss the types and functions of lipids.
The fatty acids are used to synthesize triglycerides and phospholipids. Fatty acids can also be catabolized to generate adenosine triphosphate (ATP).
Triglycerides are the body’s most highly concentrated form of chemical energy. They protect, insulate, and provide energy.
Phospholipids are important components of cell membranes.
Steroids are important in cell membrane structure, regulating sexual functions, maintaining normal blood sugar level, aiding lipid digestion and absorption, and helping bone growth.
Eicosanoids (prostaglandins and leukotrienes) modify hormone responses, contribute to inflammation, dilate airways, and regulate body temperature.
To become more soluble in blood plasma, other lipid molecules join with hydrophilic protein molecules. The resulting lipid–protein complexes are termed lipoproteins.
Identify the building blocks of proteins.
Proteins are large molecules that contain carbon, hydrogen, oxygen, and nitrogen. The monomers of proteins are amino acids. Each of the 20 different amino acids has a hydrogen (H) atom and three important functional groups attached to a central carbon atom: 1) an amino group (-NH2), (2) an acidic carboxyl group (-COOH), and (3) a side chain (R group).
The covalent bond joining each pair of amino acids is a peptide bond. When two amino acids combine, a dipeptide results. Adding another amino acid to a dipeptide produces a tripeptide. Further additions of amino acids result in the formation of a chainlike peptide (4–9 amino acids) or polypeptide (10–2000 or more amino acids). Small proteins may consist of a single polypeptide chain with as few as 50 amino acids. Larger proteins have hundreds or thousands of amino acids and may consist of two or more polypeptide chains folded together.
Describe the functional roles of proteins.
Describe the function of enzymes.
In living cells, most catalysts are protein molecules called enzymes. Some enzymes consist of two parts - a protein portion, called the apoenzyme, and a nonprotein portion, called a cofactor. Three important properties of enzymes are as follows:
Enzymes are highly specific. Each particular enzyme binds only to specific substrates - the reactant molecules on which the enzyme acts. In some cases, the part of the enzyme that catalyzes the reaction, called the active site, is thought to fit the substrate like a key fits in a lock. In other cases, the active site changes its shape to fit snugly around the substrate once the substrate enters the active site. This change in shape is known as an induced fit.
Enzymes are very efficient. Under optimal conditions, enzymes can catalyze reactions at rates that are from 100 million to 10 billion times more rapid than those of similar reactions occurring without enzymes.
Distinguish between DNA and RNA.
Nucleic acids, so named because they were first discovered in the nuclei of cells, are huge organic molecules that contain carbon, hydrogen, oxygen, nitrogen, and phosphorus. Nucleic acids are of two varieties. The first, deoxyribonucleic acid (DNA), forms the inherited genetic material inside each human cell. Ribonucleic acid (RNA), the second type of nucleic acid, relays instructions from the genes to guide each cell’s synthesis of proteins from amino acids. Cells contain three different kinds of RNA: messenger RNA, ribosomal RNA, and transfer RNA.
Describe the 3 components of a nucleotide.
A nucleic acid is a chain of repeating monomers called nucleotides. Each nucleotide of DNA consists of three parts:
A nitrogenous base: 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; thymine and cytosine are smaller, single-ring bases called pyrimidines.
A pentose sugar: A five-carbon sugar called deoxyribose attaches to each base in DNA.
A phosphate group: Phosphate groups (PO43−) alternate with pentose sugars to form the “backbone” of a DNA strand; the bases project inward from the backbone chain.
Describe the functional role of adenosine triphosphate (ATP).
Adenosine triphosphate (ATP) is the “energy currency” of living systems. When a water molecule is added to ATP, the third phosphate group is removed, and the overall reaction liberates energy. The enzyme that catalyzes the hydrolysis of ATP is called ATPase. Removal of the third phosphate group produces a molecule called adenosine diphosphate, a free phosphate group, and energy.
The energy needed to attach a phosphate group to ADP is supplied mainly by the catabolism of glucose in a process called cellular respiration. Cellular respiration has two phases, anaerobic and aerobic:
Anaerobic phase: In a series of reactions that do not require oxygen, glucose is partially broken down by a series of catabolic reactions into pyruvic acid. Each glucose molecule that is converted into a pyruvic acid molecule yields two molecules of ATP.
Aerobic phase: In the presence of oxygen, glucose is completely broken down into carbon dioxide and water. These reactions generate heat and 30 or 32 ATP molecules.
Differentiate between atomic number, mass number, and atomic mass.
The number of protons in the nucleus of an atom is an atom’s atomic number. 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. The atomic mass (also called the atomic weight) of an element is the average mass of all its naturally occurring isotopes.
