Matter – anything that takes up space and has weight; composed of elements Elements – composed of chemically identical atoms as of 2002, 114 elements known, though only 92 are naturally occurring 2-3 Structure of Matter

CHNOPS Bulk elements include Carbon Hydrogen Nitrogen Oxygen Phosphorus Sulfur

Table 2.1a

Table 2.1b

Atoms Atoms – smallest particle of an element Atoms - composed of subatomic particles: protons – carry a positive charge neutrons – carry no electrical charge electrons – carry a negative charge

Nucleus central part of atom composed of protons and neutrons electrons move around the nucleus 2-4 Atomic Structure

Subatomic Particles Since the nucleus contains protons and neutrons, the nucleus contains a positive charge Generally, the number of electrons is equal to the number of protons, so there is a net neutral charge for the atom

Atomic Number number of protons in the nucleus of one atom each element has a unique atomic number equals the number of electrons in the atom Atomic Weight/Mass Number the number of protons plus the number of neutrons in one atom electrons do not contribute to the weight of the atom 2-5 Atomic Number and Mass Number

Question What is the atomic number and atomic weight for the 3 examples in the previous slide?

Isotopes atoms with the same atomic numbers but with different atomic weights atoms with the same number of protons and electrons but a different number of neutrons oxygen often forms isotopes (O 16, O 17, O 18 ) unstable isotopes are radioactive; they emit subatomic particles 2-6 Isotopes

Question What is the atomic number and atomic weight for the 3 isotope examples on the previous slide?

Molecules – particle formed when two or more atoms chemically combine 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 H 2 C 6 H 12 O 6 H 2 O 2-7 Molecules and Compounds

found in regions of space called electron shells (energy shells) each shell can hold a limited number of electrons 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 lower shells are filled first if the outermost shell is full, the atom is stable; inert 2-8 Electrons

Octet Rule Atoms tend to interact so that they have 8 electrons to fill the outer shell

Ion an atom that has gained or lost an electron(s) an electrically charged atom atoms form ions to become stable Cation a positively charged ion formed when an atom loses an electron(s) Anion a negatively charged ion formed when an atom gains an electron(s) 2-9 Ions

an attraction between a cation and an anion Ionic Bond formed when electrons are transferred from one atom to another atom 2-10 Ionic Bond

Formed when atoms share electrons 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 2-11 Covalent Bond

Structural formulas show how atoms bond and are arranged in various molecules 2-12 Structural Formulas

Polar Molecule 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 2-13 Polar Molecules

Hydrogen Bond 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 2-14 Hydrogen Bonds

Solution – a mixture of one or more substances called solutes, dispersed in a dissolving medium called a solvent Solutes – Na+ & Cl - Solvent – H 2 O

Most biological activities occur in aqueous (water-based) solutions. hydrophilic molecules – dissolve in water hydrophobic molecules – repel water amphipathic molecules -have both hydrophilic and hydrophobic properties

Chemical reactions occur when chemical bonds form or break among atoms, ions, or molecules Reactants are substances being changed by the chemical reaction Products are substances formed at the end of the chemical reaction NaCl ’ Na + + Cl - ReactantProducts 2-15 Chemical Reactions

Synthesis Reaction – chemical bonds are formed A + B ’ AB Decomposition Reaction – chemical bonds are broken AB ’ A + B Exchange Reaction – chemical bonds are broken and formed AB + CD ’ AD + CB Reversible Reaction – the products can change back to the reactants A + B AB 2-16 Types of Chemical Reactions

Electrolytes – substances that release ions in water Acids – electrolytes that release hydrogen ions in water HCl  H + + Cl - Bases – substances that release ions that can combine with hydrogen ions NaOH  Na + + OH - Salts – electrolytes formed by the reaction between an acid and a base NaCl  Na + + Cl - HCl + NaOH  H 2 O + NaCl 2-17 Acids, Bases, and Salts

pH scale - indicates the concentration of hydrogen ions in solution Neutral – pH 7; indicates equal concentrations of H + and OH - Acidic – pH less than 7; indicates a greater concentration of H + Basic or alkaline – pH greater than 7; indicates a greater concentration of OH Acid and Base Concentrations

Organic molecules contain C and H usually larger than inorganic molecules dissolve in water and organic liquids carbohydrates, proteins, lipids, and nucleic acids Inorganic molecules generally do not contain C usually smaller than organic molecules usually dissolve in water or react with water to release ions water, oxygen, carbon dioxide, and inorganic salts 2-19 Organic vs Inorganic

provide energy to cells supply materials to build cell structures water-soluble contain C, H, and O ratio of H to O close to 2:1 (C 6 H 12 O 6 ) monosaccharides – glucose, fructose disaccharides – sucrose, lactose polysaccharides – glycogen, cellulose 2-22 Organic Substances Carbohydrates

soluble in organic solvents fats (triglycerides) used primarily for energy contain C, H, and O but less O than carbohydrates (C 57 H 110 O 6 ) building blocks are 1 glycerol and 3 fatty acids per molecule saturated and unsaturated 2-24 Organic Substances Lipids

phospholipids building blocks are 1 glycerol, 2 fatty acids, and 1 phosphate per molecule hydrophilic and hydrophobic major component of cell membranes 2-25 Organic Substances Lipids

steroids connected rings of carbon component of cell membrane used to synthesize hormones cholesterol 2-26 Organic Substances Lipids

structural material energy source hormones receptors enzymes antibodies building blocks are amino acids amino acids held together with peptide bonds 2-27 Organic Substances Proteins

Four Levels of Structure 2-28 Organic Substances Proteins

constitute genes play role in protein synthesis building blocks are nucleotides DNA (deoxyribonucleic acid) – double polynucleotide RNA (ribonucleic acid) – single polynucleotide 2-29 Organic Substances Nucleic Acids

Table 2.6

Prokaryotes vs Eukaryotes