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Chapter 4
Biochemistry:
The Role of Functional Groups
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Testosterone
Important Functional Groups
• Six functional groups are important in the
chemistry of life
– Hydroxyl
– Carbonyl
– Carboxyl
– Amino
– Sulfhydryl
– Phosphate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C
C
OH
Carbonyl
 C=O
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
STRUCTURE
Figure 4.10
C
O
C
OH
)
The carbonyl
group consists
of a carbon
atom joined to
an oxygen atom
by a double
bond.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Carbonyl group
A ketone and an aldehyde may be structural isomers with
different properties, as is the case with many
monosaccharides.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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 from the
surrounding solution:
H+
H
N
H
+N
H
(nonionized)
H
H
(ionized)
 Ionized, with a charge
Figure 4.10
of 1+, under cellular
conditions.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
g
l
y
c
i
n
e
Sulfhydryl group
• Ability to form disulfide “bridges”; important in
stabilizing protein structure (cysteine)
AMINO
SULFHYDRYL
H
PHOSPHATE
O
SH
N
O P OH
(may be written HS- )
H
OH
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of
hydrogen; resembles a
hydroxyl group in shape.
Disulfide “bridge” between amino acids
(cysteine) often hold proteins in their specific
3D shapes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 4.10
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
Figure 4.10
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; abbreviated P . The
phosphate group (—OPO32–) is an ionized form
of a phosphoric acid group (—OPO3H2; note the
two hydrogens).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Some important functional groups of organic compounds
H
O
C
HO
C
H
H
N
H
H
Glycine
Figure 4.10
H
H
C
C
H
H
OH OH H
SH
H
C
C
C
H
H
H
O
O
P
O
O
Ethanethiol
Because it also has a carboxyl
group, glycine is both an amine
and a carboxylic acid;
compounds with both groups
are called amino acids.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycerol phosphate