Biol 1107 Chapter 2 I Metabolism sum of the chemical reactions that allow life A Chemical properties of molecules determine how they act 1 We need to know something of chemistry to understand biology B All matter is made of elements 1 Represented by a unique chemical symbol a Usually 1st or 1st and 2nd letters of the name b Sometimes use letters from Latin name i Ex O or Ni i Ex Fe 2 92 naturally occurring elements a Four elements make up 96 of organisms i O N C H b Trace elements are essential for life i Needed in very small amounts ii Most of minerals in vitamins are trace elements c Quantity elements needed in intermediate amounts 3 Elements are not changed by chemical reactions i Ca Na K etc a Ex 2H O H2O C Elements are made of atoms 1 Smallest portion of an element that retains all the properties of the element a 1 atom of C behaves exactly the same as a ton of C i Has all the same chemical and physical properties b Atoms have subcomponents i Protons positively charged particles in nucleus ii Neutrons uncharged particles found in nucleus iii Electrons negatively charged particles around nucleus 2 Number of protons determines what element it is a Called the atomic number i The periodic table is arranged by atomic number b Every atom of the same element has same atomic number c Ex every atom with exactly 1 proton is H d Ex every element with exactly 8 protons is O 3 Atomic mass is number of protons neutrons a Ex if an O atom has 8 protons and 8 neutrons its atomic mass is 16 b Ex 2 a chlorine atom has 17 protons and 18 neutrons i What is its atomic number ii What is its atomic mass c Different atoms of same element may have different atomic masses i Same number of protons different number of neutrons ii Called isotopes Ex C 12 and C 13 Each has 6 protons and either 6 or 7 neutrons iii Some isotopes are unstable radioisotopes Breakdown over time Release radiation Useful in many ways medicine science household etc D Electrons orbit around the nucleus 1 Found in layers called orbitals or shells a Different orbitals have different energy levels i Furthest from the nucleus is the valence shell ii Valence shell has the highest energy b Shells generally fill from inner to outer i ie outer shells don t start forming until inner shells are full 2 Electrons in valence shell are valence electrons a These have highest energy b First electrons involved in chemical reactions i Determines chemical properties of the atom 3 Atoms are at lowest energy most stable when valence shell is full a For H and He valence shell is full with 2e b For all other elements valence shell is full when it has 8e 4 Atoms strive to achieve lowest energy state a Can do this in three ways i Can acquire more e to fill valence shell Usually elements with mostly full shells ii Can give away e to empty out valence shell Usually elements with mostly empty shells iii Can share e with other atoms II Chemical reactions two or more chemicals interact to form new products A May result in molecules and or compounds 1 Molecule 2 or more atoms strongly combined into a stable particle a May be homogeneous ex O2 b May be heterogeneous ex CO2 2 Compounds always heterogeneous ex NaCl a May be stable or unstable B Chemical formulas describe substances 1 A molecular formula shows the number and ratio of atoms 2 A structural formula shows the arrangement of atoms a Ex H2O a Ex H O H b Obviously this contains more information C Chemical equations describe chemical reactions 1 Reactants beginning chemicals 2 Products newly created substances a Listed on left a Listed on right i Ex C6H12O6 6O2 6CO2 6H2O energy 3 Some reactions are reversible a Have a double arrow b Length of arrow shows which direction is favored i Ex CO2 H2O H2CO3 draw in other arrow D Redox reactions special type of reaction 1 Electron is transferred from one molecule to another a When e is transferred energy is transferred 2 Redox stands for reduction oxidation a Composed of two half reactions that occur simultaneously b Reduction reaction where substance gains 1 electrons i Results in a reduction of its charge c Oxidation reaction where substance loses 1 electrons d Leo Ger pneumonic device 3 Redox reactions are central to photosynthesis and cellular respiration III Atoms may be joined by chemical bonds several types A Covalent bonds strongest type 1 Electrons in the valence shell are shared between atoms a Results in a more filled shell for each 2 Can be represented by Lewis structures a O O O O draw in lines b Can be single double or triple covalent bonds i 1 2 or 3 pairs of e shared ii Ex ethane ethene ethyne acetylene 3 Covalent bonds may be polar or nonpolar a Polar bonds have unequal sharing of electrons i Electronegativity is a measure of how strongly an element pulls electrons towards it ii If 2 atoms have differing electronegativities a bond between them will be polar iii Since e spends more time around one atom results in partial charges Ex H2O b Nonpolar bonds have equal sharing of electrons i Occurs when atoms have same or very similar electronegativities ii Bonds in homogeneous molecules will be nonpolar iii Ex O2 B Ionic bonds are bonds between ions charged atoms Cations are positively charged atoms Anions are negatively charged atoms a Have the ide suffix 3 Ionic bonds results when charges on cation and anion attract each other a Ex NaCl is a compound containing an ionic bond between Na and Cl 4 Ionic bonds are weaker than covalent bonds a Usually dissociate in water C Hydrogen bonds weak attractions involving partially charged H 1 A partial positive charge exists on a H in a polar covalent bond a Because the e spends less time around it The partial positive can attract a negative charge in different molecule Draw interactions in H2O and in H2O NaCl 1 2 2 3 4 Individually very weak a Very strong when many are present IV Water is essential for life A B C Can live much longer without food than water Bulk of most organisms is water 60 70 of human mass is water Most of our metabolic reactions occur in water 1 Polar and ionic substances dissolve easily in water a Called hydrophilic 2 Nonpolar substances generally don t dissolve well in water b Ex sugars salts etc a Called hydrophobic b Ex oils D Water forms hydrogen bonds 1 2 With other H2O molecules With other substances E Water helps maintain stable temperature 1 Temperature is a measure of the amount of motion of particle present a Adding energy increases motion raising temperature b Removing energy