CHEMISTRY AND LIFE Characteristics of life is highly organized compared to inanimate objects can assimilate and use energy can respond to the environment can reproduce through use of the information encoded in DNA is composed of one or more cells Atoms invisible and indivisible cannot be further reduced through chemical reactions Atom A unit of matter the smallest unit that still retains the chemical properties of that element Sub particles protons positive neutrons neutral electrons negative cannot exist by themselves as matter First shell holds 2 electrons All other shells hold 8 The number of electrons in the outermost shell determines how reactive the atom will be Outer most shell of electrons are called valiant electrons Most of atomic weight resides in nucleus What makes the elements different from each other Atomic Number Number of protons Proton number is primarily responsible for the chemical characteristic of the atom Neutrons add weight not identity to an atom Isotope an atom with greater or fewer neutrons Carbon 14 Carbon with 8 neutrons Atoms seek stability Electrons reside in defined energy levels around nucleus Number of electrons in outermost shell determine the atom s reactivity Molecule bonded atoms Three types of chemical bonds 1 Covalent Bonds strongest of the three bond types involves a sharing of electrons between atoms Polar covalent molecules electrons are shared unequally between atoms resulting in a molecule with slightly positive and negative ends Nonpolar covalent molecules electrons are shared equally molecule has no positive or negative end 2 Ionic Bonds Ions are atoms with greater or fewer electrons An atom with a positive or a negative charge Electron transfer Ionic bond an attraction of opposites Compare covalent molecules have a fixed number of atoms ionic compounds do not Covalently bonded molecules a fixed number of atoms make up the molecule Ionic compounds no fixed number of atoms participating in the link up 3 Hydrogen bonds an attraction of opposite charges does not involve the sharing of electrons individually weak collectively strong DNA is held together by hydrogen bond Hydrophilic reacts with water are POLAR molecules Hydrophobic does not react with water are NONPOLAR molecules Water Unique characteristics less dense as a solid important because ice floats high heat capacity buffers against temperature change important to human bodies and climate control high cohesion universal solvent but cannot dissolve non polar molecules Acids and Bases Strength measured on pH scale concentration of hydrogen ions pH scale is logarithmic Acid donates hydrogen ions Base accepts hydrogen ions pH is a measure of the concentration of hydrogen ions pH power of hydrogen higher the pH the more the hydrogen ions pH scale is by the power of ten Carbon Carbon starting point for all important biological molecules can form four covalent bonds basis of hydrocarbon backbones Double bonds a type of covalent bond where two pairs of electrons are shared Biomolecules Carbohydrates Proteins Lipids fats sterols Nucleic Acids Macromolecules Macromolecules are those that are constructed on a monomer polymer concept Monomer a single molecular building block Nucleotide amino acids monosaccharide Polymer three or more monomer units bonded together Polysaccharide protein nucleic acid Water is formed when polymers are made condensation reaction water must be present to break down polymers Water is a byproduct of polymerization reactions condensation reaction and is required for breakdown of polymers Carbohydrates Three to get familiar with glucose ribose deoxyribose Glycogen how animals store energy Hexose sugars have 6 carbons Starch how plants store energy Pentose sugars have 5 carbons Cellulose a structural molecule Branching glycogen is more highly branched every 10 links than starch every 30 links Cellulose is unbranched hydrogen bonding between strands keeps water out Starch and glycogen are water soluble cellulose is not Cellulose has internal H bonding that is stronger than the H bonding between glucose and outside water water is kept out of the molecule
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