Chapter 2 The Chemistry of Life The basic composition of matter AP Biology Lecture Tamara Lookabaugh Moore High School

Unifying Themes in Biology Evolution~ biology’s core theme; differential reproductive success Emergent Properties~ hierarchy of life The Cell~ all organism’s basic structure Heritable Information~ DNA Structure & Function~ form and function Environmental Interaction~ organisms are open systems Regulation~ feedback mechanisms Unity & Diversity~ universal genetic code Scientific Inquiry~ observation; testing; repeatability Science, Technology & Society~ functions of our world

Why are we studying chemistry? Chemistry is the foundation of Biology Everything is made of matter!

Matter is made of the atoms of elements Matter (space & mass) Element; compound The atom Atomic number (# of protons); mass number (protons + neutrons) Isotopes (different # of neutrons); radioactive isotopes (nuclear decay) Energy (ability to do work); energy levels (electron states of potential energy)

Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons Examples of Elements and their atoms Proton +Neutron0Electron–

Elements essential for life About 25 elements are essential for life –Four elements make up 96% of living matter: carbon (C) hydrogen (H) oxygen (O) nitrogen (N) –Four elements make up most of remaining 4%: phosphorus (P) calcium (Ca) sulfur (S) potassium (K)

Trace Elements essential in most living things ironiron, manganese, zinc, copper, iodine, cobalt, molybdenum, selenium, chromium, silicon, fluorine, vanadium, nickel, arsenic, and tin.manganesezinccopper iodinecobaltmolybdenum seleniumchromiumsilicon fluorinevanadiumnickelarsenictin Also small amounts of Br, Sr, & Ba

Bonding properties Effect of electrons –electrons determine chemical behavior of atom –depends on number of electrons in atom’s outermost shell valence shell How does this atom behave?

Bonding properties Effect of electrons –chemical behavior of an atom depends on number of electrons in its valence shell - # bonds possible How does this atom behave?

Elements & their valence shells Elements in the same row have the same number of shells Moving from left to right, each element has a sequential addition of electrons (& protons)

Elements & their valence shells Elements in the same column have the same valence & similar chemical properties Remember some food chains were built on reducing O to H 2 O & some on reducing S to H 2 S

– – – Chemical reactivity Atoms tend to –complete a partially filled valence shell or –empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

Chemical Bonding Weak bonds –Hydrogen –Van der Waals Covalent Double covalent Nonpolar covalent Polar covalent Ionic

Strong bonds 1.covalent bonds Weak bonds 2. hydrogen bonds attraction between + and – hydrophobic & hydrophilic interactions 3. van derWaals forces 4. ionic Hydrogen bond H2OH2O H2OH2O Bonds in Biology Covalent bonding

Covalent bonds Why is this a strong bond? –two atoms share a pair of electrons –both atoms holding onto the electrons –very stable Forms molecules – – H 2 (hydrogen gas) H — H H 2 O (water) H H Oxygen H H O

Multiple covalent bonds 2 atoms can share >1 pair of electrons –double bonds 2 pairs of electrons –triple bonds 3 pairs of electrons Very strong bonds H H–C–H H – –

H H Oxygen Polar covalent bonds Pair of electrons shared unequally by 2 atoms Water = O + H –oxygen has stronger “attraction” for the electrons than hydrogen –oxygen has higher electronegativity –water is a polar molecule + vs – poles leads to many interesting properties of water… + + – – – –

Hydrogen bonding Polar water creates molecular attractions –positive H atom in one H 2 O molecule attracted to negative O in another H 2 O or a negative N –also can occur wherever an -OH exists in a larger molecule Weak bond

Ionic Bonds High electronegativity difference strips valence electrons away from another atom Electron transfer creates ions (charged atoms) Cation (positive ion); anion (negative ion) Ex: Salts (sodium chloride)

van der Waals interactions Weak interactions between molecules or parts of molecules that are brought about by localized change fluctuations Due to the fact that electrons are constantly in motion and at any given instant, ever-changing “hot spots” of negative or positive charge may develop Lysozyme protein

Chemical Reactions are constant Chemical reactions are constantly moving toward “Equilibrium” to maintain homeostasis in living things Reactants vs. Products Combustion Synthesis reactions Decomposition Displacement Acid Base reactions

Tutorial for Biochemistry /biochemistry.html