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Life Substances
The Role of Carbon
AP Biology
2006-2007
Cells
 Composed of 70-95% water the rest is
made up of CARBON based
compounds

Molecules that contain CARBON are
said to be ORGANIC
 Examples: methane, carbon dioxide,
proteins
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Carbon’s Reactivity
 Carbon (C) appears in the 2nd row of the
periodic table and has 4 bonding
electrons in its valence shell.

Can form 4 bonds with other atoms
(each bond consisting of one of the
carbon’s electrons and one of the
bonding atom’s electrons)
 These bonds form a tetrahedron

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A pyramid with a spike at the top and
angles of 109°
Hydrocarbons
 Simplest organic compound
 Gets its name because it only contains

hydrogen and carbon atoms
Examples:
Methane
 Ethane
 Hexane
 Isohexane
 Cyclohexane

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Carbon Bonds
There appears to be no limit to the number of
different structures carbon can form…
Single bonding
Double
bonding
Triple bonding
Keep in mind  carbon can form 4 bonds. So, as the number
of bonds between carbon atoms increases, the number of
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hydrogen atoms decreases
Simple Hydrocarbons
 Alkanes  carbon-carbon (single bond)



Chemical formula: CnH2n+2
All enter combustion reactions with oxygen to
produce CO2 and water vapor
They are flammable!
 Alkenes  carbon = carbon (double bond)

Chemical formula: CnH2n
 Alkynes  carbon carbon=carbon (triple
bond)

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Chemical formula: CnH2n-2
Isomers
 Structures that have identical chemical
formulas but their structural formulas
are different

Different chemical properties too
 Because carbon can bond in so many
ways, a single molecule can have
different bonding configurations
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Structural Isomers
 two substances
having the same
molecular formula
but different
physical and
chemical properties
because the
arrangement of their
component atoms is
different.
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Geometric Isomers
 A chemical compound
having the same
molecular formula as
another but a different
geometric configuration,
as when atoms or
groups of atoms are
attached in different
spatial arrangements on
either side of a bond or
a ring.
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Enantiomers
 Two substances
having the same
molecular formula
but they are mirror
images of one
another.
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What type of isomer are these?
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Functional Groups
 Hydroxyl – OH

These are referred to as alcohols
 The existence of a functional group
completely changes the chemical properties
of a molecule
 Example:


Ethane (2C alkane): gas at room temp
Ethanol (2C alcohol): liquid at room temp
 Common drinking alcohol  active ingredient in
“alcoholic” beverages such as beer and wine
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CH2OH
H
O
H
OH
H
H
OH
HO
H
OH
Carbohydrates
energy
molecules
AP Biology
2006-2007
Carbohydrates
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sugar sugar sugar sugar sugar sugar sugar sugar
Carbohydrates
 Carbohydrates are composed of C, H, O
carbo - hydr - ate
General formula: CH2O
(CH2O)x
C6H12O6
 Function:
energy
 raw materials

energy storage
 structural
materials

 Monomer (building block): sugars
 ex: sugars, starches, cellulose
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Sugars
 Most names for sugars end in -ose
 Classified by number of carbons
6C = hexose (glucose)
 5C = pentose (ribose)
 3C = triose (glyceraldehyde)

CH2OH
H
O
H
OH
6H
HO
H
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OH
Glucose
H
CH2OH
OH
C
O
H
HO
H
5
OH
O
H
HO
H
Ribose
H
H
H
C
OH
C
3OH
H
Glyceraldehyde
Sugar structure
5C & 6C sugars form rings in solution
Where do
you find solutions?
In cells!
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Carbons are numbered
Numbered carbons
C 6'
5' C
O
4' C
C1'
energy stored in C-C bonds
C3'
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C2'
Simple & complex sugars
 Monosaccharides
simple 1 monomer sugars
 glucose

 Disaccharides
2 monomers
 sucrose

 Polysaccharides
large polymers
 starch

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CH2OH
H
O
H
OH
H
H
OH
HO
Glucose
H
OH
Dehydration Synthesis=
Polymerization
 Anabolic
reaction
 Produces polymer
 Monomer + Monomer  Polymer + Water
Remove H2O
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2 Monomers Bond=
Polymer
Building sugars
 Dehydration synthesis
monosaccharides
|
glucose
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|
glucose
disaccharide
|
maltose
glycosidic linkage
Building sugars
 Synthesis
monosaccharides
|
glucose
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|
fructose
Let’s go to the
videotape!
disaccharide
|
sucrose
(table sugar)
Hydrolysis
 Catabolic
reaction
 Produces monomers

Ex) Polysaccharides monosaccharides
 Polymer
+ Water  Monomer + Monomer
Add H2O
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Separate polymer into:
2 monomers
Polysaccharides
 Polymers of sugars
costs little energy to build
 easily reversible = release energy

 Function:

energy storage
 starch (plants)
 glycogen (animals)

structure = building materials
 cellulose (plants)
 chitin (arthropods & fungi)
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Linear vs. branched polysaccharides
starch
(plant)
energy
storage
What does
branching do?
glycogen
(animal)
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Let’s go to the
videotape!
Polysaccharide diversity
 Molecular structure determines function
in starch
in cellulose
isomers of glucose
 structure determines function…

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Digesting starch vs. cellulose
starch
easy to
digest
cellulose
hard to
digest
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enzyme
enzyme
Cellulose
 Most abundant organic
compound on Earth
herbivores can digest cellulose
 most carnivores cannot digest cellulose

 that’s why they
eat meat to get
their energy &
nutrients
 cellulose = roughage
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BIG DEAL!
Who can live
on this stuff?!
Cow
can digest cellulose well;
no need to eat other sugars
Gorilla
can’t digest cellulose well;
must add another sugar
source, like fruit to diet
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Helpful bacteria
 How can cows digest cellulose?

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bacteria live in their gut & help digest
cellulose-rich (grass) meals
Let’s build some
Carbohydrates!
AP Biology
2006-2007