The Chemistry of Life
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Transcript of The Chemistry of Life
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The Chemistry of Life
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Why are we studying chemistry?Chemistry is the foundation of Biology
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Proton Neutron Electron
Hydrogen1 proton1 electron
Oxygen8 protons8 neutrons8 electrons
+ 0 –
Everything is made of matter Matter is made of atoms
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The Structure of an ATOM
• Nucleus: makes up the mass of the atom•Protons – positive (+) charge•Neutrons – no charge
•Outside the Nucleus: makes up the volume of the atom•Electrons - negative (charge
•Orbit the nucleus in energy levels -) or orbitals•1st energy level holds ONLY 2 electrons•Most all others can hold 8
•OCTE TRULE•When the outer energy level is FULL (with 8 electrons) the atom is STABLE and non-reactive.
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More Structure
•Atomic Number – number of protons in the nucleus of the atom
•Atomic Mass – Mass of the nucleus
•Mass Number - the atomic mass rounded to a whole number
•SUM of the protons and neutrons in the atom•To find the number of neutrons:
•TAKE the mass number and subtract the number of protons (atomic number)
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The World of Elements
C
Different kinds of atoms = elementsDifferent kinds of atoms = elements
H
ON
P SNa
K
Mg
Ca
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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)
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Bonding properties
Effect of electrons electrons determine
chemical behavior of atom
depends on numberof electrons in atom’s outermost shell valence shell
How does this atom behave?How does this atom behave?
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Bonding properties
Effect of electrons chemical behavior of an atom depends on
number of electrons in its valence shell
What’s themagic number?
How does this atom behave?How does this atom behave? How does this atom behave?How does this atom behave?
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Elements & their valence shells
Elements in the same row have the same number of shellsElements in the same row have the same number of shells
Moving from left to right, each element has a sequential addition of electrons (& protons)Moving from left to right, each element has a sequential addition of electrons (& protons)
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Elements & their valence shells
Elements in the same column have the same valence & similar chemical properties
Elements in the same column have the same valence & similar chemical properties
FYI:some food chains
are built on reducing O to H2O
& some on reducing S to H2S
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–
–
–
Chemical reactivity Atoms tend to
complete a partially filled valence shell
or empty a partially filled valence shell
This tendency drives chemical reactions…This tendency drives chemical reactions…
and creates bondsand creates bonds
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Bonds in Biology Ionic Bonds
Form when atoms give or receive electrons Forms ions Cation - + charged ion Anion – negatively charged
ion
Covalent Bonds Form when atoms SHARE
one or more pairs of electrons
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Covalent bonds Why are covalent bonds strong?
two atoms share a pair of electrons both atoms holding onto the electrons very stable
Forms molecules
–
–
H2 (hydrogen gas)H2 (hydrogen gas)
H — H
H2O (water)H2O (water)
H
H
OxygenH
HO
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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
––
More isbetter!
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Nonpolar covalent bond Pair of electrons shared equally by 2 atoms
example: hydrocarbons = CxHx
methane (CH4 )
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
balanced, stable,good building block
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
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H
H
Oxygen
Polar covalent bonds Pair of electrons shared
unequally by 2 atoms example: water = H2O
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…
+
+
––
––
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Hydrogen bonding Polar water creates molecular attractions
attraction between positive H in one H2O molecule to negative O in another H2O
also can occur wherever an -OH exists in a larger molecule
Weak bond
Let’s go to the videotape!
HO
H
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Chemistry of Life
Properties of Water
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More about Water
Why are we studying water?Why are we studying water?
All life occurs in water inside & outside the cell
All life occurs in water inside & outside the cell
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Chemistry of water H2O molecules form H-bonds
with each other +H attracted to –O creates a
sticky molecule
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Elixir of Life Special properties of water
1. cohesion & adhesion surface tension, capillary action
2. good solvent many molecules dissolve in H2O 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
Ice! I could use more ice!
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1. Cohesion & Adhesion
Try that with flour…or sugar…
Cohesion H bonding between H2O molecules water is “sticky”
surface tension drinking straw
Adhesion H bonding between H2O & other substances
capillary action meniscus water climbs up
paper towel or cloth
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How does H2O get to top of trees?Transpiration is built on cohesion & adhesion
Let’s go to the videotape!
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2. Water is the solvent of life Polarity makes H2O a good solvent
polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions
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What dissolves in water? Hydrophilic
substances have attraction to H2Opolar or non-polar?
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What doesn’t dissolve in water? Hydrophobic
substances that don’t have an attraction to H2O
polar or non-polar?
fat (triglycerol)
Oh, lookhydrocarbons!
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3. The special case of ice Most (all?) substances are more dense
when they are solid, but
not water… Ice floats!
H bonds form a crystal
And this hasmade all the difference!
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Ice floats
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Why is “ice floats” important? 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 H2O cycles nutrients in autumn
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4. Specific heat H2O resists changes in temperature
high specific heat takes a lot to heat it up takes a lot to cool it down
H2O moderates temperatures on Earth
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Specific heat& climate
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5. Heat of vaporizationEvaporative cooling
Organisms rely on heat of vaporization to remove body heat
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Ionization of water & pH Water ionizes
H+ splits off from H2O, leaving OH–
if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic
pH scalehow acid or basic solution is1 7 14
H2O H+ + OH–H2O H+ + OH–
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pH Scale10–1
H+ IonConcentration
Examples of Solutions
Stomach acid, Lemon juice
1
pH100 Hydrochloric acid0
10–2 2
10–3 Vinegar, cola, beer3
10–4 Tomatoes4
10–5 Black coffee, Rainwater5
10–6 Urine, Saliva6
10–7 Pure water, Blood7
10–8 Seawater8
10–9 Baking soda9
10–10 Great Salt Lake10
10–11 Household ammonia11
10–12 Household bleach12
10–13 Oven cleaner13
10–14 Sodium hydroxide14
tenfold changein H+ ions
pH1 pH210-1 10-2
10 times less H+
pH8 pH710-8 10-7
10 times more H+
pH10 pH810-10 10-8
100 times more H+
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1001
2
3
4
5
6
7
8
9
3Amount of base added
Bufferingrange
4 52
pH
Buffers & cellular regulation pH of cells must be kept ~7
pH affects shape of molecules shape of molecules affect function pH affects cellular function
Control pH by buffers reservoir of H+
donate H+ when [H+] falls
absorb H+ when [H+] rises
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2007-2008
He’s gonnaearn a
Darwin Award!
Do one brave thing today…then run like hell!
AnyQuestions?
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Ice Fishing in Barrow, Alaska