The Chemistry of Living Things Chapter 2: The Chemistry of Living Things OBJECTIVES Define/describe an atom and its subatomic particles Describe differences between atoms, isotopes, and ions Understand how and why atoms form molecules Know the attributes of water Understand what is pH and what is a buffer Describe the four organic molecules and their function

All Matter Consists of Elements Chemistry: the study of matter Matter Anything that has mass and occupies space Composed of elements Elements Cannot be broken down to a simpler form Periodic table of elements—lists all known elements

Atoms—Smallest Functional Units of an Element Atoms consist of Nucleus (central core) Protons positive charge have mass Neutrons no charge Shells (surrounding nucleus) Electrons negative charge no discernable mass

Hydrogen Oxygen Sodium Electron Proton 1 proton Shell 1 electron Figure 2.3 Electron Proton Hydrogen 1 proton 1 electron Shell Neutron Oxygen 8 protons 8 neutrons 8 electrons in 2 shells Nucleus Figure 2.3 The structure of atoms. Sodium 11 protons 11 neutrons 11 electrons in 3 shells 4

More About Atoms Atomic symbol: one or two letters Atomic number Na: sodium O: oxygen Atomic number Number of protons, always the same number for any atom of a particular element Atomic mass Roughly equal to number of protons plus neutrons In an electrically neutral atom Number of protons  number of electrons

Isotopes Have a Different Number of Neutrons Isotopes are atoms of the same element that have a different number of neutrons They will have a different atomic mass Unstable isotopes are called radioisotopes: they give off: Energy in the form of radiation, particles Some radioisotopes have scientific and medical uses Diagnostic imaging Cancer treatment Power supply for implants such as cardiac pacemakers

Energy Fuels Life’s Activities Energy: the capacity to do work Potential energy: stored energy Kinetic energy: energy in motion, doing work Potential energy can be transformed into kinetic energy

Kinetic energy is energy in motion. Figure 2.4 Potential energy is locked up in the chemical bonds of energy-storage molecules in Greg Louganis’ tissues. Figure 2.4 Energy. Kinetic energy is energy in motion. 8

Energy Fuels Life’s Activities Electrons have potential energy Each shell corresponds to a specific level of potential energy Shells that are farther from the nucleus contain electrons with more potential energy Atoms are most stable when their outermost shell is full Atoms will interact with other atoms to fill their outermost shells (rule of eight)

Chemical Bonds Link Atoms to Form Molecules Chemical bonds: attractive forces holding atoms together Kinds of chemical bonds Covalent bonds Ionic bonds Hydrogen bonds

Covalent Bonds Involve Sharing Electrons Covalent bonds form when atoms share electrons Very strong bonds Nonpolar covalent bonds: electrons are shared equally H2 O2 Polar covalent bonds: electrons are NOT shared equally H2O: The oxygen has a stronger pull on the shared electrons than the hydrogen does

Structural representation Figure 2.5 Structural formula with covalent bond Written formula Structural representation Hydrogen (H2) H H Single covalent bond Oxygen (O2) O O Double covalent bond Figure 2.5 Covalent bonds. Water (H2O) O H Two single covalent bonds H 12

Ionic Bonds Occur Between Oppositely Charged Ions Ion: an electrically charged atom or molecule Positively charged ion: forms if an atom or molecule loses electrons Negatively charged ion: forms if an atom or molecule gains electrons Ionic bond: attractive force between oppositely charged ions Example: NaCl

Loss of electron: positive charge Gain of electron: negative charge Figure 2.6 Loss of electron: positive charge Gain of electron: negative charge + –  Na Cl Na Cl Sodium atom (Na) Figure 2.6 Ionic bonds. Chlorine atom (Cl) Sodium ion (Na+) Chlorine ion (Cl–) Sodium chloride molecule (NaCl) 14

Hydrogen Bonds Form between Polar Molecules Weak hydrogen bonds form between oppositely charged regions of polar molecules Example: weak forces between polar water molecules In DNA proteins

Table 2.1 Table 2.1 Summary of the three types of chemical bonds. 16

Atoms Combine to Form Molecules When atoms gain, lose, or share they stay close together, held by attractions called chemical bonds When is a covalent bond formed? When is an ionic bond formed? What is a hydrogen bond? H H2O + – O © 2011 Pearson Education, Inc.

Living Organisms Contain Only Certain Elements Over 100 different elements 99% of body weight consists of 6 elements Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus

Life Depends on Water Key properties of water: Water is an excellent solvent Water is liquid at body temperature Water can absorb and hold heat energy Evaporation of water uses up heat energy Water participates in essential chemical reactions

Water Is the Biological Solvent Solvent: liquid in which other substances dissolve Solute: any dissolved substance Hydrophilic: polar molecules that are attracted to water and interact easily with water Hydrophobic: nonpolar neutral molecules that do not interact with or dissolve in water

Water Is a Liquid at Body Temperature Water serves an important transport function in the blood, which is 90% water Water is the main constituent of: Intracellular spaces Extracellular spaces 60% of body weight is water

Water Helps Regulate Body Temperature Water absorbs and holds a large amount of heat energy with only a modest increase in temperature Prevents rapid changes in body temperature Evaporative cooling enables body to lose excess heat quickly

Water Participates In Chemical Reactions Synthesis of carbohydrates, proteins, and lipids produces water molecules Breakdown of carbohydrates, proteins and lipids consumes water molecules

The Importance of Hydrogen Ions Acids Donate hydrogen ions (H) Increase hydrogen ion concentration in solutions Bases Accept hydrogen ions Decrease hydrogen ion concentration in solutions pH Scale A measure of hydrogen ion concentration

The pH Scale Expresses Hydrogen Ion Concentration Measure of hydrogen ion concentration in solution Ranges from 0 to 14 Acids: pH  7 Neutral: pH  7 Basic: pH  7

Concentrated nitric acid Figure 2.10 Drain opener Bleach Ammonia cleanser More alkaline Soapy water Baking soda Neutral pH Human blood, tears Saliva, urine Figure 2.10 The pH scale. Black coffee Tomatoes More acidic Vinegar, cola Lemon juice Hydrochloric acid Concentrated nitric acid 26

Buffers Minimize Changes in pH Minimize pH change Help maintain stable pH in body fluids Carbonic acid and bicarbonate act as one of the body’s most important buffer pairs HCO3 + H H2CO3 (reversible reaction) If blood is too acidic: HCO3 + H H2CO3 If blood is too alkaline: H2CO3 HCO3  H

The Organic Molecules of Life - What are organic molecules? Contain carbon forms 4 covalent bonds The backbone of biological molecules Some are called macromolecules Built by dehydration synthesis reactions Broken down by hydrolysis reaction 4 major groups of macromolecules:

Carbohydrates: Used for Energy and Structural Support General formula: Cn(H20)n Monosaccharides: simple sugars Glucose Fructose Galactose Ribose Deoxyribose Disaccharides: two monosaccharides linked together Sucrose: glucose  fructose Maltose: glucose  glucose Lactose: glucose  galactose

Polysaccharides Store Energy Polysaccharides: thousands of monosaccharides joined in linear and/or branched chains Starch: made in plants; stores energy Glycogen: made in animals; stores energy Cellulose: indigestible polysaccharide made in plants for structural support

Lipids: Insoluble in Water Three important classes of lipids Triglycerides: energy storage molecules Phospholipids: primary component of cell membranes Steroids: carbon-based ring structures

Stored in adipose tissue as energy-storage molecules Triglycerides: Stored in adipose tissue as energy-storage molecules Composed of glycerol and three fatty acids Fatty acids may be saturated or unsaturated (in oils) Steroids: Composed of four carbon rings Examples: Cholesterol, hormones e.g. estrogen, testosterone Phospholipids: primary component of cell membranes

Proteins: Complex Structures Constructed of Amino Acids Long chains (polymers) of subunits called amino acids Amino acids are joined by peptide bonds, which are produced by dehydration synthesis reactions Polypeptide: a polymer of 3–100 amino acids Protein: a polypeptide longer than 100 amino acids that has a complex structure and function

Enzymes Facilitate Biochemical Reactions Are proteins Function as biological catalysts Speed up chemical reactions Are not altered or consumed by the reaction Without enzymes, many biochemical reactions would not proceed quickly enough to sustain life

Enzyme Reactants Product Reactants approach enzyme Reactants Figure 2.22 Enzyme Reactants Product Reactants approach enzyme Reactants bind to enzyme Enzyme changes shape Products are released Figure 2.22 Enzymes facilitate chemical reactions. 35

Nucleic Acids Store Genetic Information Nucleic acids are long chains containing subunits known as nucleotides Two types of nucleic acids DNA: deoxyribonucleic acid RNA: ribonucleic acid DNA contains the instructions for producing RNA RNA contains the instructions for producing proteins Proteins direct most of life processes DNA  RNA  Proteins

Nucleic Acids Store Genetic Information Nucleotides: building blocks (monomers) of nucleic acids Each nucleotide contains 5 carbon sugar Phosphate group Nitrogenous base Adenine Guanine Cytosine Thymine in DNA & Uracil in RNA

Nucleic Acids Store Genetic Information Structure of DNA (deoxyribonucleic acid) Double–stranded Nucleotides contain Deoxyribose (sugar) Nitrogenous bases Adenine Guanine Cytosine Thymine Complementary base pairing: Adenine - Thymine Guanine - Cytosine

Base pair Phosphate Sugar Nucleotide Figure 2.24 Figure 2.24 The double helical structure of DNA. T P P A T P P G C P 39

Nucleic Acids Store Genetic Information Structure of RNA (ribonucleic acid) Single–stranded Nucleotides contain Ribose (sugar) Nitrogenous bases Adenine Guanine Cytosine Uracil

Phosphate Ribose Uracil Figure 2.25 P C P A P Figure 2.25 The structure of RNA. G P Uracil (U) P 41

ATP Carries Energy Structure and function of adenosine triphosphate (ATP) Universal energy source Bonds between phosphate groups contain potential energy Breaking the bonds releases energy ATP  ADP  P  energy

The breakdown and synthesis of ATP. Figure 2.26 Hydrolysis of ATP produces useful energy for the cell Adenosine H2O Adenine (A) Triphosphate Adenosine P P P Adenosine P P P (ATP) (ADP) Energy for ATP synthesis comes from food or body stores of glycogen or fat H2O Figure 2.26 Adenosine triphosphate (ATP). Ribose The structure of ATP. The breakdown and synthesis of ATP. The breakdown (hydrolysis) of ATP yields energy for the cell. The reaction is reversible, meaning that ATP may be resynthesized using energy from other sources. 43