Transcript Document

Chapter 4
Carbon and the Molecular
Diversity of Life
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Organic Compounds
• All compounds discovered can be classified
into two broad categories: inorganic and
organic
• "Organic" =
• The compounds of life consist of primarily 6
elements: "CHONPS"
There are four main groups of biologically important organic
molecules: carbohydrates, proteins, lipids, and nucleic acids.
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Carbon: The backbone of Biological Molecules
• All living organisms are made up of chemicals based
mostly on the element carbon
–
“What sets the carbon atom apart is that it is shamelessly promiscuous.
It is the party animal of the atomic world, latching onto many other atoms
(including itself) and holding tight, forming molecular conga lines of
hearty robustness-the very trick of nature necessary to build proteins and
DNA.” -Bill Bryson, from “A Short History of Nearly Everything”
Figure 4.1
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Chemistry of CARBON is the chemistry of LIFE!
• Carbon forms the “backbone” (framework) of all
organic molecules, largely because of its
versatility in bonding
• C has four e- in its outermost energy level, but
needs 8 to fill it, so it readily forms covalent bonds!
fact: 98.89% of carbon is C-12
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Carbon, the basis for life
• Carbon likes to bond, with other atoms and with
itself
• single bondsethane
ethylene
• double bonds-
• triple bondsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Carbon videos
NPR: It’s All About Carbon
Episode 2: Making Carbon Bonds
Episode 3: Breaking Carbon Bonds
Episode 4: Carbon In Love
Episode 5: What Do We Do?
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Concept 4.1: Organic chemistry is the study of carbon compounds
• Organic compounds range from simple molecules to colossal ones
–
The concept of “vitalism” is the idea that organic compounds arise
only within living organisms
–
Was disproved when chemists synthesized the compounds in the
laboratory
In 1953, Stanley Miller simulated what were thought to be environmental
EXPERIMENT conditions on the lifeless, primordial Earth. As shown in this recreation,
Miller used electrical discharges (simulated lightning) to trigger reactions
in a primitive “atmosphere” of H2O, H2, NH3 (ammonia), and CH4
(methane)—some of the gases released by volcanoes.
RESULTS
A variety of organic compounds that play key roles in living cells were
synthesized in Miller’s apparatus.
Organic compounds may have been synthesized abiotically on the
CONCLUSION early Earth, setting the stage for the origin of life. (We will explore
Figure 4.2
this hypothesis in more detail in Chapter 26.)
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OTHER ELEMENTS IN ORGANIC COMPOUNDS:
•
Along with carbon and hydrogen, other elements are found in organic
compounds. The most common of these elements are nitrogen,
phosphorus, sulfur, and oxygen (the CHONPS elements).
•
Oxygen: Oxygen, as O2 makes up 21% of the earth's atmosphere and is
found in the great majority of organic compounds in living systems.
•
Nitrogen : Nitrogen is found in all proteins and nucleic acids. 79% of our
atmosphere is N2 . The bond between the two nitrogen atoms is a triple
bond and is a difficult bond to break. The only way for most organisms to
get usable nitrogen is through nitrogen fixing bacteria.
•
Phosphorus and Phosphates: Phosphorus is found in living systems
as phosphates, in ions such as HPO42- or H2PO4- . Phosphorus is
covalently bonded to four oxygen atoms. When the oxygen-phosphate
bond is broken, energy is released. Phosphorus is an important element
in nucleic acids and ATP..
•
Sulfur: Sulfur occurs in some proteins. The sulfur appears as part of
sulfhydryl groups (-SH) in the amino acid cysteine. These groups allow
parts of a proteins to bond together covalently via disulfide bridges
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Important Functional Groups
• Clusters of atoms that influence the properties of the
molecules they compose
• Six main functional groups are important in the chemistry
of life
– Hydroxyl
– Carbonyl
– Carboxyl
– Amino
– Sulfhydryl
– Phosphate
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Functional groups
–
Are the chemically reactive groups of atoms within an organic
molecule
–
Give organic molecules distinctive chemical properties
Estradiol
OH
CH3
HO
Female lion
OH
CH3
CH3
O
Figure 4.9
Male lion
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Testosterone
Hydroxyl group
• Polar, thus water-soluble; forms hydrogen
bonds
FUNCTIONAL
GROUP
HYDROXYL
Is polar as a result of the electronegative oxygen atom
drawing electrons toward itself.
 Attracts water molecules, helping dissolve organic
compounds such as sugars (see Figure 5.3).
O
O
OH
(may be written HO )
STRUCTURE In a hydroxyl group (—OH),
a hydrogen atom is bonded
to an oxygen atom, which in
turn is bonded to the carbon
skeleton of the organic
molecule. (Do not confuse
this functional group with the
hydroxide ion, OH–.)
Figure 4.10
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C
C
OH
Carbonyl
 C=O
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
STRUCTURE:
C
O
C
OH
)
The carbonyl
group consists
of a carbon
atom joined to
an oxygen atom
by a double
bond.
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Often found
in sugars
Carbonyl group
A ketone and an aldehyde may be structural isomers with
different properties, as is the case with many
monosaccharides.
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Carboxyl
• Weak acid (hydrogen donor); when it loses a
hydrogen, it becomes negatively charged
(polar)
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
C
)
STRUCTURE
Figure 4.10
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O
C
OH
When an oxygen atom is doublebonded to a carbon atom that is
also bonded to a hydroxyl group,
the entire assembly of atoms is
called a carboxyl group
(—COOH).
Carboxyl
 Has acidic properties because it is a source of
hydrogen ions.
The covalent bond
between oxygen and
hydrogen is so polar that
hydrogen ions (H+) tend
to dissociate reversibly;
for example,
H
H
C
H
Figure 4.10
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H
O
C
OH
H
C
H
O
+ H+
C
O
 In cells, found in the ionic
form, which is called a
carboxylate group.
Examples:
• Some important functional groups of organic
compounds
NAME OF
COMPOUNDS
Alcohols (their specific
names usually end in -ol)
EXAMPLE
H
H
H
C
C
H
H
Ketones if the carbonyl group is Carboxylic acids, or organic
within a carbon skeleton
acids
Aldehydes if the carbonyl group
is at the end of the carbon
skeleton
H
OH
H
C
H
C
H
H
Ethanol, the alcohol
present in alcoholic
beverages
H
O
C
H
C
OH
H
H
Acetone, the simplest ketone
H
Figure 4.10
C
O
H
H
C
C
H
H
O
C
Propanal, an aldehyde
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H
Acetic acid, which gives vinegar
its sour tatste
Some important functional groups of organic compounds
• AMINO group
• Weak base (hydrogen acceptor); when it accepts a
hydrogen, it becomes positively charged
AMINO
SULFHYDRYL
H
N
The amino group (—NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
Figure 4.10
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O
SH
(may be written HS
H
PHOSPHATE
)
O P OH
OH
Amino
• Some important functional groups of organic
compounds
 Acts as a base;
can pick up a
proton (H+) from
the surrounding
solution:
H
N
H
+N
H
(nonionized)
H
H
 Ionized, with a
charge of 1+,
under cellular
conditions.
(ionized)
Figure 4.10
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Sulfhydryl group
• Ability to form disulfide “bridges”; important in
stabilizing protein structure (ex: cysteine)
AMINO
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of H
hydrogen; resembles a N
hydroxyl group in shape.H
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SULFHYDRYL
SH
(may be written HS- )
PHOSPHATE
O
O P OH
OH
Phosphate group
•
Acid (hydrogen donor) in solution; usually negatively charged (anionic)
•
Useful in transferring energy between organic molecules (ATP)
•
Present in the backbone of DNA and RNA
AMINO
SULFHYDRYL
H
N
PHOSPHATE
O
SH
(may be written HS
H
)
O P OH
OH
In a phosphate group, a phosphorus
atom is bonded to four oxygen atoms; one
oxygen is bonded to the carbon skeleton;
two oxygens carry negative charges when
they ionize and lose their hydrogens
(protons) in solution
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Some important functional groups of organic compounds
H
O
C
HO
C
H
H
N
H
H
H
H
C
C
H
H
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OH OH H
SH
H
C
C
C
H
H
H
O
O
P
O
O