CHAPTER 2 The Chemistry of Living Things

Slide 2.1 “atom” means “can’t be cut” by Greeks 2500 years ago. Atoms, the smallest functional unit of an element, consist of: All Matter Consists of Elements Made of Atoms

Atoms are made of Protons: positive charge, in nucleus, are heavy, “p + ” Neutrons: no charge, in nucleus, are heavy, “n 0 ” Electrons: negative charge, outside nucleus “electron cloud”, very light (1/1840 of a proton or neutron), “e - ”

Charges in an Atom The + charge on a proton is equal to the - charge on an electron. Atoms are neutral (have no overall charge) Therefore, the # of protons = # electrons in an atom.

Slide 2.2 Atomic number determines the identity of the atom. It tells us the number of protons in the atom. It also tells us the number of electrons (b/c an atom is neutral in charge.) Ex: atomic number of carbon, C = 6 Question: how many protons? How many electrons? How many neutrons?

Isotopes The number of neutrons can vary from atom to atom in an element. Atoms of the same element w/different #s of neutrons are called ISOTOPES. In order to know how many neutrons in an atom you must be told. The mass number tells you how much mass the atom has. Since p + and n 0 are the heavy parts, the mass # tells you the # of p + ’s + n 0 ’s.

QUESTION: If the mass number of a carbon atom is 14, How many protons? How many electrons? How many neutrons? LET’S PRACTICE! Whiteboard Marker Paper towel

Slide 2.3. Joining atoms requires energy Energy is the capacity to do work Stored energy = potential energy Energy in motion, doing work = kinetic energy Electrons have potential energy Shells = the energy levels of electrons Orbitals describe the probable location of an electron BONDING: Atoms Combine to Form Molecules

Table 2.1 Slide 2.4 Three Types of Chemical Bonds

Written NaCl NOT Na-Cl Ionic Bonds

Elements of Living Organisms Table 2.2 Slide 2.5

Water molecules are polar (they have slight electrical charges) o The biological solvent-ex: K+ for muscle contraction o Hydrogen bonds make it expand when frozen Water is liquid at body temperature Water can absorb and hold heat energy o Water helps regulate body temperature o Has high heat of evaporation Slide 2.6 Life Depends on Water

Hydrogen bonds (dotted lines) Oxygen slightly –ve charge Hydrogen slightly +ve

Figure 2.8 Slide 2.8 Water Keeps Ions in Solution

Acids are proton (hydrogen ion) donors, bases accept hydrogen ions pH Scale = a logarithmic scale of the hydrogen ion concentration (going from a pH of 2 to 4 is a change of 2 numbers= 10 2, so pH 4 is 100 times less acidic than pH 2 Buffers: minimize pH change Carbonic acid and bicarbonate act as one of body’s most important buffer pairs Slide 2.9 The Importance of Hydrogen Ions

Figure 2.10 Slide 2.10 The pH Scale

Carbon, the building block of living things: Comprises 18% of body by weight Forms four covalent bonds Can form single or double bonds Can build micro- or macromolecules Slide 2.11 The Organic Molecules of Living Organisms

Figure 2.12 Slide 2.12 Carbon Can Bond in Many Ways

Figure 2.13 Slide 2.13 Making and Breaking Biological Macromolecules: Dehydration Synthesis and Hydrolysis

Dehydration synthesis Removes equivalent of a water molecule to link molecular units Requires energy (Process of ANABOLISM) Hydrolysis Adds the equivalent of a water molecule to break apart macromolecules Releases energy (Process of CATABOLISM) Slide 2.14 Dehydration Synthesis is the Reverse of Hydrolysis

Figure 2.14 Slide 2.15 Carbohydrates are Composed of Monosaccharides

Oligosaccharides: short chains of monosaccharides Disaccharides: sucrose, fructose, lactose Polysaccharides: thousands of monosaccarides joined in chains and branches Starch: made in plants; stores energy Glycogen: made in animals; stores energy Cellulose: undigestible polysaccharide made in plants for structural support Slide 2.16 Carbohydrates are Used for Energy and Structural Support

Triglycerides: energy storage molecules Fatty acids: saturated and unsaturated Phospholipids: cell membranes Steroids: carbon-based ring structures Cholesterol: used in making estrogen and testosterone Slide 2.17 Lipids: Insoluble in Water

Unsaturated triglyceride

Steroids (type of lipid)

Structure Primary: amino acid sequence Secondary: describes chain’s orientation in space; e.g., alpha helix, beta sheet Tertiary: describes three-dimensional shape created by disulfide and hydrogen bonds Creates polar and nonpolar areas in molecule Quarternary: describes proteins in which two or more tertiary protein chains are associated Slide 2.18 Proteins: Complex Structures Contructed of Amino Acids

Hemoglobin (4 protein strands held together)

Enzymes: are proteins function as catalysts facilitate chemical reactions The functional shape of an enzyme is dependent on: temperature of reaction medium pH ion concentration presence of inhibitors Slide 2.19 Enzyme Function

Enzyme Action

Functions Store genetic information Provide information used in making proteins Structure Nucleotides consist of a phosphate group, a sugar, and a nitrogenous base DNA structure is a double helix: two associated strands of nucleic acids RNA is a single-stranded molecule Slide 2.20 Structure and Function of Nucleic Acids

DNA: double-stranded Sugar: deoxyribose Nitrogenous bases: adenine, thymine, cytosine, guanine Pairing: adenine-thymine and cytosine-guanine RNA: single-stranded Sugar: ribose Nitrogenous bases: adenine, uracil, cytosine, guanine Pairing: adenine-uracil, cytosine-guanine Slide Structure of DNA and RNA

DNA nucleotides

RNA structure

Figure 2.25 Slide 2.22 Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc. Structure and Function of Adenosine Triphosphate (ATP)