Human Anatomy & Physiology Chapter 2: Biochemistry -The Chemical Basis of Life

Why study chemistry in an Anatomy and Physiology class? Chemical Basis of Life Why study chemistry in an Anatomy and Physiology class? - Body functions depend on cellular functions - Cellular functions result from chemical changes - Biochemistry helps to explain physiological processes

Chemical Basis of Life Matter – anything that takes up space and has mass – composed of elements Elements – atoms of the same element are identical 11 Bulk elements – required by the body in large amounts carbon, oxygen, hydrogen, and nitrogen make up 96% of the human body 15 Trace elements - required by the body in small amounts Atoms – smallest particle of an element

Table 2.1 Some Particles of Matter

Atomic Number and Atomic Mass Number of protons in an atom’s nucleus Identifies the element Atomic Mass Mass of a single atom Equal to the number of protons plus the number of neutrons in the nucleus How many protons, neutrons, and electrons does carbon have? What is the atomic mass of carbon?

Molecules and Compounds Molecule – particle formed when two or more atoms chemically combine – form a covalent bond – C6H12O6 O2 Compound – particle formed when two or more atoms of different elements chemically combine Molecular formulas – depict the elements present and the number of each atom present in the molecule H2 C6H12O6 H2O

Bonding of Atoms Bonds form when atoms combine with other atoms Electrons are shared or transferred during bonding Electrons of an atom occupy regions of space called electron shells which circle the nucleus For atoms with atomic numbers of 18 or less, the following rules apply: The first shell can hold up to 2 electrons The second shell can hold up to 8 electrons The third shell can hold up to 8 electrons

Bonding of Atoms Lower shells are filled first If the outermost shell is full, the atom is stable - - - + + + + - + + - - Hydrogen (H) Helium (He) Lithium (Li)

Bonding of Atoms: Ions Ion Cation Anion An atom that gains or loses electrons to become stable An electrically charged atom Cation A positively charged ion Formed when an atom loses electrons K+, Ca2+ 11p+ 17p+ 12n0 18n0 Anion A negatively charged ion Formed when an atom gains electrons Cl-, O2- Sodium atom (Na) Chlorine atom (Cl)

Types of Bonds Ionic Bonds – between a metal and a nonmetal An attraction between a cation and an anion Formed when electrons are transferred from one atom to another atom NaCl MgBr2 Na+ Cl– + – 11p+ 17p+ 12n0 18n0 Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride

Types of Bonds Covalent Bonds – between nonmetals H ― H Formed when atoms share electrons H2O C6H12O6 H H H2 - - - + + + + - Hydrogen atom + Hydrogen atom Hydrogen molecule Hydrogen atoms form single bonds Oxygen atoms form two bonds Nitrogen atoms form three bonds Carbon atoms form four bonds H ― H O = O N ≡ N O = C = O

Bonding of Atoms: Structural Formula Structural formulas show how atoms bond and are arranged in various molecules H H H H O O O O C O H2 O2 H2O CO2

Bonding of Atoms: Polar Molecules Covalent Polar Molecules Molecule with a slightly negative end and a slightly positive end Results when electrons are not shared equally in covalent bonds Water is an important polar molecule Slightly negative ends (a) Slightly positive ends

Hydrogen Bonds Hydrogen Bonds A weak attraction between the positive end of one polar molecule and the negative end of another polar molecule Formed between water molecules Important for protein and nucleic acid structure H H O H Hydrogen bonds O H H O H H O H H O H (b)

Chemical Reactions Chemical reactions occur when chemical bonds form or break among atoms, ions, or molecules Reactants are the starting materials of the reaction Products are substances formed at the end of the chemical reaction NaCl ’ Na+ + Cl- Reactant Products

Types of Chemical Reactions 1. Synthesis Reaction – 2 or more reactants combine to form a larger product A + B ’ AB 2. Decomposition Reaction – chemical bonds are broken to form a simpler chemical structure AB ’ A + B 3. Exchange Reaction – chemical bonds are broken and new bonds are formed AB + CD ’ AD + CB Reversible Reaction – the products can change back to the reactants A + B n AB

Acids, Bases, and Salts Electrolytes – substances that dissociate to release ions in water NaCl  Na+ + Cl- Acids – substances that dissociate to release hydrogen ions in solution HCl  H+ + Cl- Bases – substances that dissociate to release hydroxide ions (OH-) in solution NaOH  Na+ + OH- Salts – electrolytes formed by the reaction between an acid and a base HCl + NaOH  H2O + NaCl

Acid and Base Concentration pH scale - indicates the concentration of hydrogen ions in solution Neutral – pH 7; indicates equal concentrations of H+ and OH- Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8.4 Sodium biocarbonate Relative Amounts of H+ (red) and OH– (blue) Acidic 6.6 cow’s milk 7.4 Human blood H + 5.3 cabbage 4.2 tomato juice 3.0 apple juice 11.5 Household ammonia 2.0 gastric juice 10.5 milk of magnesia 8.0 Egg white 7.0 Distilled water Acidic – pH less than 7; indicates a greater concentration of H+ 6.0 corn Basic OH– pH 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 Acidic H + concentration increases Neutral OH – concentration increases Basic (alkaline) Basic or alkaline – pH greater than 7; indicates a greater concentration of OH-

Neutralization and Buffers Neutralization occurs when an acid and base react to form a salt and water in a displacement reaction. HCl + NaOH  NaCl + H2O Buffers act as acids when pH is high and bases when pH is low – keep the pH at a narrow, consistent level Carbonic acid-bicarbonate system.

Chemical Constituents of Cells Inorganic molecules Generally do not contain C and H Usually smaller than organic molecules Usually dissociate in water, forming ions Water, oxygen, carbon dioxide, and inorganic salts Organic molecules Contain C and H Usually larger than inorganic molecules Dissolve in water and organic liquids Carbohydrates, proteins, lipids, and nucleic acids

Inorganic Substances Water Most abundant compound in living material Two-thirds of the weight of an adult human Major component of all body fluids Medium for most metabolic reactions Dehydration reaction – synthesis reaction – removal of a water molecule as a bond is formed between two small molecules to form a larger molecule Hydrolysis reaction – - decomposition reaction - uses water to break the bonds of a compound

Inorganic Substances Water (cont.) Important role in transporting chemicals in the body High specific heat – absorbs and gives up heat slowly, allowing water, and therefore the body, to maintain a relatively constant temperature High heat of vaporization - takes a large amount of heat to change water from liquid to gas - used in evaporative cooling of the body

Inorganic Substances Oxygen (O2) and Carbon Dioxide (CO2) oxygen is needed by cells to carry out cellular respiration in the mitochondria Oxygen is received by respiratory system and delivered by circulatory system (RBC’s) carbon dioxide is waste gas from cellular respiration

Inorganic Substances Inorganic salts Abundant in body fluids Sources of necessary ions (Na+, Cl-, K+, Ca2+, etc.) Play important roles in metabolism

Organic Substances: Carbohydrates Provide energy to cells Supply materials to build cell structures Water-soluble Contain C, H, and O ef Ratio of H to O close to 2:1 (C6H12O6) Monosaccharides (simple sugars) – glucose, fructose, galactose, xylose, and ribose Disaccharides (double sugars) – sucrose (glucose and fructose), maltose, lactose – composed of 2 simple sugars joined together by dehydration reactions Polysaccharides (complex sugars) – glycogen, cellulose – composed of many monosaccharides chemically joined by dehydration reactions

Organic Substances Carbohydrates (a) Some glucose molecules (C6H12O6) have a straight chain of carbon atoms. (b) More commonly, glucose molecules form a ring structure. (c) This shape symbolizes the ring structure of a glucose molecule.

Organic Substances: Carbohydrates (a) Monosaccharide (b) Disaccharide O O O (c) Polysaccharide

Organic Substances: Lipids – Soluble in organic solvents; insoluble in water 4 major types – triglycerides, phospholipids, steroids, and prostaglandins Composed of C, H, O; but fewer O’s than carbohydrates - some also contain P H O H H H H H H H H H H H H H H H H C 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 H H O H H H H H H H H H H H H H H H H H

Organic Substances: Lipids Triglycerides formed from a fatty acid and glycerol (a sugar) the most plentiful source of stored energy to our bodies Two types: Saturated- contain only single bonds Unsaturated- contains one(mono) or more(poly) double bonds Short, unsaturated fats are liquids (oils) and come from plants. Long, saturated fats are solid (butter and meat fat) and come from animals. glycerol portion H H H O Fatty acid H O Fatty acid H O Fatty acid H

Organic Substances: Lipids Phospholipids Building blocks are 1 glycerol, 2 fatty acids, and 1 phosphate per molecule Hydrophilic (water soluble) and hydrophobic (water insoluble) Major component of cell membranes H H H C O Fatty acid H C O Fatty acid H C O Fatty acid Water-insoluble (hydrophobic) “tail” H C O Fatty acid O H H H H C O Fatty acid H C O P O C C N Water-soluble (hydrophilic) “head” H H H O – H H Glycerol portion Phosphate portion (a) A fat molecule (b) A phospholipid molecule (the unshaded portion may vary) (c) Schematic representation of a phospholipid molecule

Organic Substances: Lipids Steroids Four connected rings of carbon Widely distributed in the body, various functions Component of cell membrane Used to synthesize hormones Cholesterol CH CH 3 CH H 3 H 3 2 C C CH CH CH CH CH 2 2 2 H C C CH 2 2 CH CH 3 H 3 C 2 HC CH CH 2 H C C CH 2 HO C C C CH H 2 C C H H 2 (a) General structure of a steroid (b) Cholesterol

Organic Substances: Lipids Prostaglandins “tissue hormones” composed of a 20-carbon unsaturated fatty acid that contains a 5-carbon ring formed and released from cell membranes in response to a stimulus regulate the effects of hormones, influence blood pressure and secretion of digestive juices, and enhance the body immune system and inflammatory response

Organic Substances: Proteins 2 main catergories according to purpose 1. structural – form structures of the cells, tissues, and organs of the body – include keratin of skin, hair, and nails, parts of cell membrane, and tendons 2. functional - shape determines the function – allows it to fit with certain other chemicals and cause some change in the molecules – enzymes, insulin

Organic Substances: Proteins Consist of amino acids joined together by peptide bonds Sequence of amino acids is what DNA actually codes for 20 commonly occurring amino acids amino acids – each consist of an alpha carbon, an amine group, carboxyl group, hydrogen, and a side chain – the side chain (R) differentiates the amino acids

Organic Substances: Proteins

Organic Substances: Proteins Protein Structure Primary structure - linear sequence of amino acids Secondary structure – regular folds or twists in proteins – most common is alpha helix (spiral staircase) Tertiary structure – when further folding of the protein forms a globular molecule Quaternary structure – when two or more polypeptide chains go together to form a functional protein

Organic Substances: Proteins Primary structure Secondary Myoglobin Tertiary Hemoglobin, Antibodies Quaternary

Organic Substances: Proteins Dehydration reactions join amino acids together – water is removed Hydrolysis reactions separate amino acids by adding water H C H C C H H H C C H S C R H C H H C H H N C C OH H N C C OH H N C C OH H H O H H O H H O

Organic Substances: Nucleic Acids Carry genes Encode amino acid sequences of proteins Building blocks are nucleotides Make up DNA (deoxyribonucleic acid) – double polynucleotide Make up RNA (ribonucleic acid) – single polynucleotide

Organic Substances: Nucleic Acids Nucleotides are composed of: a. nitrogenous base (adenine, guanine, cytosine, thymine, uracil) b. phosphate group c. pentose sugar (ribose or deoxyribose) P B S

Organic Substances: Nucleic Acids RNA DNA Single helix Sugar – ribose Bases – adenine, cytosine, guanine, and uracil Double helix Sugar – deoxyribose Bases – adenine, cytosine, guanine, and thymine

Organic Substances: Nucleic Acids Base pairs are held together by hydrogen bonds. S P B P B B P S S S P B P B B P S S S P B P B B P S S S P B P B B P S S S P B P B B P S S S P B P B B P S S (a) (b)

Metabolism Anabolism Catabolism Dehydration synthesis reactions Joining together of simple molecules to form more complex biomolecules Water is removed Requires energy Catabolism Hydrolysis decomposition reactions Breaking apart of complex biomolecules to form simple molecules Water is added Releases energy

Organic Substances: Combined Forms ATP (adenosine triphosphate) Two extra phosphate groups are added to an adenine-containing RNA nucleotide Transfers energy from one chemical pathway to another

ATP