Anatomy and Physiology

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UNIT 1
Chapters 3: The Chemical Basis of Life and Biomolecules

BASIC CHEMISTRY

  • Elements and compounds (Figure 2-1)
  • Matter: anything that has mass and occupies space
  • Element: simple form of matter; a substance that cannot be broken down into two or more different substances
  • 26 elements are present in the human body
  • Includes 11 major elements, four of which (carbon, oxygen, hydrogen, and nitrogen) make up 96% of the human body (Figure 2-2)
  • 15 trace elements make up less than 2% of body weight
  • Compound: atoms of two or more elements joined to form chemical combinations

BASIC CHEMISTRY: ATOMS

  • Atoms (Figure 2-3)

  • Atomic structure: atoms contain several different kinds of subatomic particles; the most important are:
  • Protons: positively charged subatomic particles found in the nucleus
  • Neutrons: neutral subatomic particles found in the nucleus
  • Electrons: negatively charged subatomic particles found in the electron cloud (Figure 2-4)

BASIC CHEMISTRY: ATOMS (cont.)

  • Atomic number and atomic weight
  • Atomic number (Table 2-1)
  • Number of protons in an atom’s nucleus
  • Atomic number is critically important; identifies the kind of element
  • Atomic weight
  • Mass of a single atom
  • Equal to the number of protons plus the number of neutrons in the nucleus
  • Energy levels (Figures 2-5 and 2-6)
  • Total number of electrons in an atom equals the number of protons in the nucleus (in a stable atom)
  • Electrons form a “cloud” around the nucleus

BASIC CHEMISTRY: ATOMS (cont.)

BASIC CHEMISTRY: ATOMS (cont.)

  • Isotopes (Figure 2-7)
  • Isotopes of an element contain the same number of protons but different numbers of neutrons
  • Isotopes have the same atomic number and therefore the same basic chemical properties as any other atom of the same element, but they have a different atomic weight

BASIC CHEMISTRY: CHEMICAL BONDS

  • Attractions between atoms: chemical bonds

  • Chemical bonds: two types unite atoms into molecules
  • Ionic, or electrovalent, bond: formed by transfer of electrons.

  • Covalent bond: formed by sharing electron pairs between atoms (Figure 2-9)

BASIC CHEMISTRY: CHEMICAL BONDS (cont.)

  • Hydrogen bond (Figures 2-10 and 2-11)
  • Much weaker than ionic or covalent bonds
  • Results from unequal charge distribution on molecules

BASIC CHEMISTRY: CHEMICAL BONDS (cont.)

  • Chemical reactions
  • Involve the formation or breaking of chemical bonds
  • Basic types of chemical reactions are involved in physiology:
  • Synthesis reaction: combination of two or more substances to form a more complex substance; formation of new chemical bonds: A + B  AB
  • Decomposition reaction: breakdown of a substance into two or more simpler substances; breaking of chemical bonds: AB  A + B
  • Exchange reaction: decomposition of two substances and, in exchange, synthesis of two new compounds from them: AB + CD  AD + CB
  • Reversible reactions: occur in both directions


METABOLISM

  • Metabolism: all the chemical reactions that occur in body cells (Figure 2-12)
  • Catabolism
  • Chemical reactions that break down complex compounds into simpler ones and release energy; hydrolysis is a common catabolic reaction
  • The end products of catabolism are carbon dioxide, water, and other waste products
  • More than half the energy released is transferred to adenosine triphosphate, which is then used to perform cellular work (Figure 2-33)

METABOLISM (cont.)

  • Anabolism
  • Chemical reactions that join simple molecules together to form more complex molecules.

ORGANIC AND INORGANIC COMPOUNDS

  • Inorganic compounds: few have carbon atoms and none have C–C or C–H bonds
  • Organic molecules
  • Have at least one carbon atom and at least one C–C or C–H bond in each molecule
  • Often have functional groups attached to the carbon-containing core of the molecule (Figure 2-13)

INORGANIC MOLECULES

  • Water
  • The body’s most abundant and important compound
  • Properties of water (Table 2-2)
  • Polarity: allows water to act as an effective solvent; ionizes substances in solution (Figure 2-10)
  • The solvent allows transportation of essential materials throughout the body (Figure 2-14)
  • High specific heat: water can lose and gain large amounts of heat with little change in its own temperature; enables the body to maintain a relatively constant temperature
  • High heat of vaporization: water requires the absorption of significant amounts of heat to change it from a liquid to a gas; allows the body to dissipate excess heat

INORGANIC MOLECULES (cont.)

  • Oxygen and carbon dioxide: closely related to cellular respiration
  • Oxygen: required to complete decomposition reactions necessary for the release of energy in the body,
  • Carbon dioxide: produced as a waste product and helps maintain the appropriate acid-base balance in the body.

INORGANIC MOLECULES: ELECTROLYTES

  • Electrolytes
  • Large group of inorganic compounds that includes acids, bases, and salts.
  • Substances that dissociate in solution to form ions (resulting ions are sometimes called electrolytes)
  • Positively charged ions are cations; negatively charged ions are anions.

INORGANIC MOLECULES: ELECTROLYTES (cont.)

  • Acids and bases: common and important chemical substances that are chemical opposites
  • Acids
  • Any substance that releases a hydrogen ion (H+) when in solution; “proton donor”
  • Level of acidity depends on the number of H+ a particular acid will release
  • Bases
  • Electrolytes that dissociate to yield hydroxide ions (OH) or other electrolytes that combine with H+
  • Described as “proton acceptors”
  • pH scale: assigns a value to measures of acidity and alkalinity (Figure 2-15)
  • pH indicates the degree of acidity or alkalinity of a solution
  • pH of 7 indicates neutrality (equal amounts of H+ and OH); a pH less than 7 indicates acidity; a pH higher than 7 indicates alkalinity

INORGANIC MOLECULES: ELECTROLYTES (cont.)

  • Buffers
  • Maintain the constancy of pH
  • Minimize changes in the concentrations of H+ and OH
  • Act as a “reservoir” for hydrogen ions
  • Salts (Table 2-3)
  • Compound that results from chemical interaction of an acid and a base
  • Reaction between an acid and a base to form a salt and water is called a neutralization reaction

ORGANIC MOLECULES

  • “Organic” describes compounds that contain C–C or C–H bonds (Figure 2-16; Table 2-4)

ORGANIC MOLECULES: CARBOHYDRATES

  • Carbohydrates: organic compounds containing carbon, hydrogen, and oxygen; commonly called sugars and starches
  • Monosaccharides: simple sugars with short carbon chains; those with six carbons are hexoses (e.g., glucose); those with five are pentoses (e.g., ribose, deoxyribose) (Figure 2-17)
  • Disaccharides and polysaccharides: two (di-) or more (poly-) simple sugars bonded together through a synthesis reaction (Figure 2-18)

ORGANIC MOLECULES: LIPIDS

  • Lipids (Table 2-5)
  • Water-insoluble organic molecules that are critically important biological compounds
  • Major roles:
  • Energy source
  • Structural role
  • Integral parts of cell membranes

ORGANIC MOLECULES: LIPIDS (cont.)

  • Triglycerides or fats (Figures 2-19 and 2-20)
  • Most abundant lipids and most concentrated source of energy.
  • Building blocks of triglycerides are glycerol (the same for each fat molecule) and fatty acids (different for each fat and determine the chemical nature)
  • Types of fatty acids: saturated fatty acid (all available bonds are filled) and unsaturated fatty acid (has one or more double bonds)
  • Triglycerides are formed by dehydration synthesis

ORGANIC MOLECULES: LIPIDS (cont.)

  • Phospholipids (Figure 2-21)
  • Fat compounds similar to triglyceride.
  • One end of the phospholipid is water soluble (hydrophilic); the other end is fat soluble (hydrophobic).
  • Phospholipids can join two different chemical environments.
  • Phospholipids may form double layers called bilayers that make up cell membranes.(Figure 2-22)

ORGANIC MOLECULES: LIPIDS (cont.)

  • Steroids (Figure 2-23)
  • Main component is steroid nucleus
  • Involved in many structural and functional roles
  • Prostaglandins (Figure 2-24)
  • Commonly called tissue hormones; produced by cell membranes throughout the body
  • Effects are many and varied; however, they are released in response to a specific stimulus and are then inactivated

ORGANIC MOLECULES: PROTEINS

  • Proteins (Table 2-6)
  • Most abundant organic compounds
  • Chainlike polymers
  • Amino acids: building blocks of proteins (Figures 2-25 to 2-27)
  • Essential amino acids: eight amino acids that cannot be produced by the human body
  • Nonessential amino acids: 12 amino acids that can be produced from molecules available in the human body
  • Amino acids consist of a carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a side chain

ORGANIC MOLECULES: PROTEINS (cont.)

  • Levels of protein structure (Figure 2-28)
  • Protein molecules are highly organized and show a definite relation between structure and function
  • Protein organization is defined by four levels:
  • Primary structure: the number, kind, and sequence of amino acids that make up the polypeptide chain
  • Secondary structure: polypeptide is coiled or bent into pleated sheets stabilized by hydrogen bonds
  • Tertiary structure: a secondary structure can be further twisted and converted to a globular shape; the coils touch in many places and are “welded” by covalent and hydrogen bonds
  • Quaternary structure: highest level of organization; occurs when protein contains more than one polypeptide chain

ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES

  • Nucleic acids and related molecules
  • DNA (deoxyribonucleic acid)
  • Composed of deoxyribonucleotides: structural units consist of the pentose sugar (deoxyribose), phosphate group, and nitrogenous base (cytosine, thymine, guanine, or adenine)
  • DNA molecule consists of two long chains of deoxyribonucleotides coiled into a double-helix shape (Figure 2-31)

  • Specific sequence of more than 100 million base pairs constitutes one human DNA molecule; all DNA molecules in one individual are identical and different from those of all other individuals
  • DNA functions as the molecule of heredity

ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)

  • RNA (ribonucleic acid) (Figure 2-32; Table 2-7)
  • Composed of the pentose sugar (ribose), phosphate group, and a nitrogenous base
  • Nitrogenous bases for RNA are adenine, uracil, guanine, or cytosine (uracil replaces thymine)
  • Some RNA molecules are temporary copies of segments (genes) of the DNA code and are involved in synthesizing proteins
  • Some RNA molecules are regulatory and act as enzymes (ribozymes) or silence gene expression (RNA interference)

ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)

  • Nucleotides
  • Nucleotides have other important roles in the body
  • Adenosine triphosphate (ATP) (Figure 2-33)
  • Composed of:

Adenosine

Ribose, a pentose sugar

Adenine, a nitrogen-containing molecule

  • Three phosphate subunits

High-energy bonds present between phosphate groups

ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)

  • Adenosine triphosphate (ATP) (cont.)
  • Energy stored in ATP is used to do the body’s work
  • ATP often called the energy currency of cells
  • ATP is split into adenosine diphosphate (ADP) and an inorganic phosphate group by a special enzyme