AP Biology CHAPTERS 2 & 3: THE CHEMISTRY OF LIFE

AP Biology WHY ARE WE STUDYING CHEMISTRY…AGAIN? Chemistry is the foundation of Biology

AP Biology CHEMISTRY LEADS TO… Biomolecules lead to… Cells lead to… Organisms… Populations… Communities… Ecosystems…

AP Biology Proton Neutron Electron Hydrogen 1 proton 1 electron Oxygen 8 protons 8 neutrons 8 electrons + 0 –  Everything is made of matter  Matter is made of atoms

AP Biology THE WORLD OF ELEMENTS C Different kinds of atoms = elements H ON PSNa K Mg Ca

AP Biology LIFE REQUIRES ~25 CHEMICAL ELEMENTS 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)

AP Biology Bonding…what’s up buddy? = Effect of electrons (they’re at the center of it all…har har!)  electrons determine chemical behavior of atom  depends on number of electrons in atom’s outermost shell = valence shell How does this atom behave?

AP Biology Bonding properties How does this atom behave? The most important parts of an atom interms of BIOLOGY are its…???

AP Biology Electrons!!!! WHY? Electrons are on the OUTSIDE They are the parts that BUMP INTO other atoms = the parts that REACT with and BOND to other atoms

AP Biology – – – CHEMICAL REACTIVITY DEPENDS ON BONDING! Atoms tend to:  complete a partially filled valence shell (take or share) = strong (non-metals) or  empty a partially filled valence shell (give) = weak (metals) This tendency drives chemical reactions… and creates bonds Atoms “want” 8 electrons in their outer shell!

AP Biology 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) Generally, knowing how many SHELLS an atom has Is not very useful to us (at least in ap bio)

AP Biology Why do you think the only atom other than oxygen used in food chains on planet Earth is SULFUR?

AP Biology RT Liquid or RT

AP Biology – – H 2 (hydrogen gas) Covalent bond WHAT TYPES OF BONDS SHOULD YOU KNOW FOR BIOLOGY? Weak bonds  hydrogen bonds VIDEOVIDEO  attraction between + and –  hydrophobic & hydrophilic interactions  interaction with H 2 O  van derWaals forces  disulfide bridges Strong bonds  covalent bonds  Ionic bonds Hydrogen bond H2OH2O H2OH2O

AP Biology COVALENT BONDS Why are covalent bonds strong bonds? share  two atoms share a pair of electrons  both atoms holding onto the electrons  very stable  not always equal sharing Forms molecules – – H 2 (hydrogen gas) H — H H 2 O (water) H H Oxygen H H O

AP Biology NONPOLAR COVALENT BOND Pair of electrons shared equally by 2 atoms  example: hydrocarbons = C x H x  methane (CH 4 ) balanced, stable, good building block

AP Biology H H Oxygen POLAR COVALENT BONDS = Pair of electrons shared unequally by 2 atoms example: water = H 2 O  oxygen has stronger “attraction” for the electrons than hydrogen  oxygen has higher electronegativity  + vs – poles  leads to many interesting properties of water… + + – – – –

AP Biology HYDROGEN BONDING Polar water creates external molecular attractions  between positive H in one H 2 O molecule to negative O in another  also can occur wherever an -OH exists in a larger molecule = Weak bond H O H Hydrogen bonding of water has PROFOUND importance for LIFE ON EARTH!

AP Biology KEY CONCEPTS OF CHAPTER 2 FOR AP BIO EXAM: 1.Chemical rxns are the basis of species- specific communication strategies (BIG IDEA 3) 2.Biochemistry is vital to natural selection and evolution (BIG IDEA 1) 3.Biochemistry can serve as the mechanisms by which populations interact (BIG IDEA 4)

AP Biology THE PERCENTAGES OF NATURALLY OCCURRING ELEMENTS MAKING UP THE HUMAN BODY ARE SIMILAR TO THE PERCENTAGES OF THESE ELEMENTS FOUND IN OTHER ORGANISMS. HOW COULD YOU ACCOUNT FOR THIS SIMILARITY AMONG ORGANISMS? EXPLAIN YOUR THINKING.

AP Biology

DRAW LEWIS DOT STRUCTURES FOR EACH HYPOTHETICAL MOLECULE SHOWN BELOW, USING THE CORRECT NUMBER OF VALENCE ELECTRONS FOR EACH ATOM. DETERMINE WHICH MOLECULE MAKES SENSE BECAUSE EACH ATOM HAS A COMPLETE VALENCE SHELL & EACH BOND HAS THE CORRECT NUMBER OF ELECTRONS. EXPLAIN WHAT MAKES THE OTHER MOLECULES NONSENSICAL, CONSIDERING THE NUMBER OF BONDS EACH TYPE OF ATOM CAN MAKE.

AP Biology CHEMISTRY OF LIFE PROPERTIES OF WATER: CHAPTER 3

AP Biology All life occurs in water & needs water for life processes inside & outside the cell All life occurs in water & needs water for life processes inside & outside the cell WHY ARE WE STUDYING WATER??? ITS POLARITY

AP Biology CHEMISTRY OF WATER H 2 O molecules form H-bonds with each other  +H attracted to –O (SLIGHT)  creates a sticky molecule

AP Biology REMEMBER… Covalent bonds are WITHIN the water molecule Hydrogen bonds are BETWEEN water molecules

AP Biology THE ELIXIR OF LIFE Special properties of water: 1.cohesion & adhesion  surface tension, capillary action 2.good solvent  many molecules dissolve in H 2 O  hydrophilic vs. hydrophobic 3.lower density as a solid  ice floats! 4.high specific heat  water stores heat 5.high heat of vaporization  heats & cools slowly

AP Biology 1. COHESION & 2. ADHESION Cohesion  H bonding between H 2 O molecules  water is “sticky”  surface tension  drinking straw Adhesion  H bonding between H 2 O & other substances  capillary action  meniscus  water climbs up paper towel or cloth

AP Biology TRANSPIRATION IS BUILT UPON THE CONCEPTS OF COHESION & ADHESION

AP Biology 3. WATER IS THE SOLVENT OF LIFE Polarity makes H 2 O a good solvent  polar H 2 O molecules surround + & – ions  solvents dissolve solutes creating solutions Hydration shells

AP Biology WHAT DISSOLVES IN WATER? Hydrophilic  substances have attraction to H 2 O  polar or non-polar?

AP Biology 4. WATER IS AN ORGANIZER OF NON POLAR MOLECULES Water is attracted to things that are also polar or charged in some way. Molecules that LACK polarity / charge cannot attract water…much like a magnet will not stick to plastic. However, water WILL push these non polar molecules out of the way and thus organize them as it is drawn toward other polar things WHY IS THIS IMPORTANT?

AP Biology WATER’S ABILITY TO ORGANIZE NON POLAR MOLECULES IS CRITICAL TO THE FORMATION OF CELLULAR MEMBRANES…

AP Biology WHAT DOESN’T DISSOLVE IN WATER? Hydrophobic  substances that don’t have an attraction to H 2 O  polar or non-polar? fat (triglycerol)

AP Biology SOLID WATER FLOATS?!?!...HUH?? Oceans & lakes don’t freeze solid  surface ice insulates water below  allowing life to survive the winter  if ice sank…  ponds, lakes & even oceans would freeze solid  in summer, only upper few inches would thaw  seasonal turnover of lakes  sinking cold H 2 O cycles nutrients in autumn Water is MOST dense at 4 deg. C

AP Biology 5. SPECIFIC HEAT H 2 O resists changes in temperature  specific heat HIGH OR LOW ?? H 2 O moderates temperatures on Earth & homeostasis in living things!!!

AP Biology 6. Water has a high heat of vaporization = the amount of energy it takes to cause 1g of a liquid to become a gas **It takes a lot of energy to cause water to vaporize **Why is this important? When water leaves the body, it takes a LOT of heat energy with it = Sweat cools us down! Back to homeostasis

AP Biology 7. IONIZATION OF WATER & PH Water ionizes  H + splits off from H 2 O, leaving OH –  if [H + ] = [ - OH], water is neutral  if [H + ] > [ - OH], water is acidic  if [H + ] < [ - OH], water is basic pH scale how acid or basic solution is 1  7 acidic 7  14 basic 7 neutral H 2 O  H + + OH –

AP Biology PH SCALE 10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 10 – –3 Vinegar, cola, beer 3 10 –4 Tomatoes 4 10 –5 Black coffee, Rainwater 5 10 –6 Urine, Saliva 6 10 –7 Pure water, Blood 7 10 –8 Seawater 8 10 –9 Baking soda 9 10 –10 Great Salt Lake –11 Household ammonia –12 Household bleach –13 Oven cleaner –14 Sodium hydroxide14 tenfold change in H+ ions pH1  pH  times less H + pH8  pH  times more H + pH10  pH  times more H +

AP Biology Amount of base added Buffering range 452 pH BUFFERS & CELLULAR REGULATION pH of cells must be kept ~7  affects shape of molecules shape affects function = pH affects cellular function Control pH by buffers = reservoir of H +  donate H+ when [H + ] falls  absorb H+ when [H + ] rises

AP Biology REMEMBER ALL THESE PROPERTIES EXIST BECAUSE… …Water hydrogen bonds with itself Which happens because… …Water molecules are polar Which happens because… …Oxygen is Elelctronegative