The Chemistry of Life Chapter 2

2-1 Element  Substance that cannot be broken down into simpler substances  91 occur naturally –#1-92 found naturally; except 43, 61 –#93 and above are synthetic –Only 25 needed for life  Only 4 elements make up 96% of human mass: C, H, O, N  4% are Ca, P, K, S, Na, trace elements

Atoms  Smallest particle of an element  Structure –Center is the nucleus, contains protons (+) and neutrons (0) –Electrons (-) form a cloud around the nucleus

Electron energy fields  Electrons travel around the nucleus in energy levels –1 st holds 2 electrons –2 nd holds 8 –3 rd holds 18  Atoms have equal numbers of electrons and protons (make up a neutral atom)

Isotopes  Atoms of the same element with different numbers of neutrons  Ex carbon-12 and carbon-14

Compound  Substance composed of atoms of different elements chemically combined  3 ways to combine elements –Covalent bond –Ionic bond –Hydrogen bond

Covalent bonds  Atoms share electrons equally  Bonding makes atoms more stable  Covalent bonds produce molecules –Sugar –Fat –Protein –Water

Covalent bond

Ionic bonds  Atoms combine by gaining or losing electrons in the outer energy levels  Ions-atoms that have gained or lost electrons  Attractive force between ions of opposite charges produces ionic bond  Important for biological processes –Transmission of nerve impulses –Muscle contraction

Ionic Bond

Hydrogen bonds  Bond between hydrogen of one molecule and the negative ion of another molecule  Strongest MOLECULAR bond  Important in biological molecules like protein or nucleic acids

Hydrogen bonds

Mixture  Combination of substances in which individual substances retain their own properties –Stir sand and sugar together –do not combine chemically –Do no change

Solution  A mixture in which one or more substances are distributed evenly in another substance –Kool-Aid is evenly distributed in water –Kool-Aid (solute) will dissolve –Water (solvent) does the dissolving

2-2 Importance of water  Makes up 70%-95% of most organisms  Used to transport materials in organisms

Water molecule

Water’s polarity  Covalent bonds between oxygen and hydrogen of water do not share electrons equally –Oxygen attracts electrons more strongly –Oxygen will be more negative –Hydrogen will be more positive –Creates an unequal distribution of charge or polarity –Gives water its dissolving power

Other water properties governed by hydrogen bonding  Adhesion-an attraction between molecules of different substances  Cohesion-attraction between molecules of the same substance  High specific heat-water resists changes in temperature; must absorb more heat to increase in temperature

pH  Measures amount of H+ ions in solution (the concentration of H+ determines whether a solution is acidic or basic)  Scale ranges from 0 to 14  is acidic  is basic

pH scale

Acids  Forms hydrogen ions (H+) in water  Hydrogen chloride added to water makes H+ and Cl-  As a solution this would be hydrochloric acid (HCl)

Bases  Form hydroxide ions (OH-) in water  Sodium hydroxide in water forms Na+ and OH-

Buffers  Weak acids or bases that react with strong acids or bases  Prevent sudden changes in pH

2-3 Carbon atoms  When bonded to each other can form –Straight chains –Branched chains –rings  Can also form isomers –Compounds with the same formula but different 3-D arrangement

Carbon structures

Macromolecules  Contain ten, hundreds, or thousands of carbon atoms  Used by cells for biological processes  Made by bonding small units together to make polymers

Carbohydrates  Store and release energy  Composed of C, H, and O  Single unit called monosaccharide  Largest are polysaccharides  Examples –Starch-branched chain of glucose in plants –Glycogen-highly branched chain of glucose in animals

Carbohydrates

Lipids  Contain large amounts of C, H, but less amounts of O  Called fats and oils  Insoluble in water  Used for long-term energy storage, insulation, protective coverings  Major components of membranes

Lipids

Proteins  Build structure and carry out metabolism  Made of C, H, O, N, S  Basic units are amino acids (20) –Linked by condensation reactions –Release water as waste product –Covalent bond between amino acids is called a peptide bond –Protein determined by order of acids

Proteins  Building blocks structural components of organisms  Important for –Muscle contractions –Transport of oxygen –Immunity –metabolism

Protein (peptide bond)

Proteins  Enzymes –Speeds up metabolic reactions –Help with food digestion –Synthesis of molecules –Storage and release of energy

Nucleic Acids  Stores information in code form  Units called nucleotides  Made of C, H, O, N, P arranged in 3 groups –Base –Simple sugar –Phosphate group

Nucleic Acids  DNA-deoxyribonucleic acid –Master copy of organism’s code –Forms genetic code –Contributes to physical traits  RNA-ribonucleic acid –Copy of DNA –Used for protein synthesis

Nucleic acid

2-4 Chemical reactions  In organisms are called metabolism  Break down and build molecules  Atoms are never created or destroyed, just rearranged  Reactants are on the left  Products are on the right

Chemical reaction

Energy in reactions  Some reactions release energy and are called spontaneous (exothermic)  Some require energy and must get it from another source (endothermic)  Activation energy is the energy required to get a reaction started

Chemical equilibrium  Can be seen in reactions that are reversible  Equilibrium is reached when the reaction takes place at an equal rate in both directions  So both reactants and products are made at the same time

Enzymes  Proteins that act as catalysts in reactions  Work by lowering the activation energy  So not as much energy is needed to get the product

Enzymes

Enzyme regulation  Enzymes can be controlled or affected by –pH –Temperature –Other proteins