T HE C HEMISTRY OF L IFE Chapter 2 Biology – Miller Levine

A TOMS Basic unit of matter From the Greek word atomos, which means “unable to be cut” Subatomic particles: Protons – positive charge (p + ) Neutrons – neutral, no charge (n 0 ) Electrons – negative charge (e - )

A TOMS Nucleus – contains protons & neutrons Electron cloud – area where electrons are located around the nucleus 1 st level holds 2 e- 2 nd level holds 8 e- 3 rd level holds 18 e- Atoms are neutral because p + = e -

A TOMS

E LEMENT A pure substance that consists entirely of one type of atom 92 naturally occurring elements Periodic Table of Elements: Represented by a 1 or 2 letter symbol Atomic number – # of protons Mass number – protons + neutrons Horizontal rows are called periods Vertical columns are called groups

E LEMENTS

I SOTOPES Atoms of the same element that have a different number of neutrons Radioactive isotopes – isotopes that are unstable and give off radiation Can be used in geological dating, to treat cancer, to kill bacteria in food, & as “tracers” in medical diagnosis

I SOTOPES

C HEMICAL C OMPOUNDS Compound – a substance formed by two or more different elements Always found in a fixed ratio Chemically and physically different from the elements that they include Chemical formula – shows the number of each element in a compound Ex. H 2 O

C HEMICAL B ONDS Atoms in compounds are held together by chemical bonds Valence electrons – electrons that are available to form bonds An atom is stable when its outer (valence) shell contains 8 e- (except H and He which are stable with 2 e-) 3 major types of bonds – ionic, covalent, and hydrogen

I ONIC B ONDS An ion is formed when one or more electrons are transferred from one atom to another Oppositely charged ions are attracted to each other forming an ionic bond Ex. NaCl

C OVALENT B ONDS Form when electrons are shared between atoms Molecule – when atoms are joined together by a covalent bond Ex. H 2 O

VAN DER W AALS F ORCES The random movement of electrons creates temporary areas of slightly positive and slightly negative charges When molecules come close together, these positive and negative regions form a weak attraction known as van der Waals forces

T HE W ATER M OLECULE Water is a polar molecule, where the electrons are not shared equally There is a – charge near the O and a + charge near the H Hydrogen bonds – attraction between the H of one water to the O of another Weaker than covalent or ionic

H YDROGEN B ONDS

C OHESION & A DHESION Cohesion – the attraction between molecules of the same substance Adhesion – the attraction between molecules of different substances

M IXTURES When two or more elements or compounds are physically mixed together but not chemically combined Heterogeneous mixture – the components remain distinct Suspension – a mixture of water and nondissolved materials Will settle back out over time Colloid – the particles will not settle out

M IXTURES Homogeneous mixture – uniform composition throughout Solution – a mixture in which all the components are evenly distributed Solute – the substance that is dissolved Solvent – the substance in which the solute dissolves Water is the greatest solvent

S OLUTIONS

A CIDS, B ASES, AND P H A water molecule can react to form hydrogen (H + ) and hydroxide (OH - ) ions Acid – any compound that forms H + ions in solution (pH less than 7) Base – any compound that forms OH - ions in solution (pH greater than 7)

A CIDS, B ASES, AND P H pH scale – a measurement system that indicates the concentration of H + ions in a solution (0- 14) Buffer – weak acids or bases that react with strong acids or bases to prevent sudden changes in pH

C HEMICAL R EACTIONS Process that changes one set of chemicals into another set of chemicals Fe + O 2 → Fe 2 O 3 Reactants – in front of the arrow Products – after the arrow Law of Conservation of Matter – matter can be neither created nor destroyed Equations must be balanced

E NERGY IN R EACTIONS Endergonic – reactions that require an input of energy or store energy Exergonic – reactions that release energy Activation energy – the energy needed to start a reaction

E NZYMES Some chemical reactions are too slow or have too high an activation energy Catalyst – a substance that speeds up the rate of a chemical reaction by lowering the activation energy Enzymes – proteins that are catalysts

E FFECT OF E NZYMES

E NZYME A CTION The enzyme-substrate complex Substrates – the reactants Active site – the place where the substrates bind to the enzyme When the substrates bind to the active site they form the enzyme-substrate complex Enzymes are specific to the substrate that they act upon (lock and key mechanism)

E NZYME -S UBSTRATE C OMPLEX

R EGULATION OF ENZYME ACTIVITY Can be affected by pH and temperature Most enzymes have an optimal pH and temperature Can be turned “on” or “off” Can be used over and over again