16 MHR • Unit 1 Metabolic Processes
These functional groups are hydrophilic. Except
for the phosphate group, they are polar and so
they increase the solubility in water of the organic
molecules to which they are attached. Each
functional group also has capabilities to change
the chemical properties of the organic molecules to
which it bonds. For example, if a hydrogen atom in
ethane is replaced by a sulfhydryl group, the result
is ethanethiol, also known as ethyl mercaptan.
While ethanethiol in small amounts stabilizes
protein structures, it is also a dangerous neurotoxin
and respiratory toxin.Each functional group has a specific role in
cell metabolism. Phosphates are essential to the
metabolic processes of photosynthesis and cellular
respiration. For example, the transfer of a phosphate
group from ATP (adenosine triphosphate) begins
the very important process of glycolysis — the first
step in cellular respiration. You will discover more
about this process in Chapter 3.
While amino and phosphate groups contribute to
energy transactions in the cell, the sulfhydryl (–SH)
group is essential to protein stabilization. Amino
acids with –SH groups form bonds called disulfide
bridges (S–S bonds) that help protein molecules to
take on and maintain a specific shape.Functional
group Formula Name of compound Structural examplehydroxylcarbonylcarboxylaminosulfhydrylphosphatealcoholsaldehydesketonescarboxylic acidsaminesthiolsorganic phosphatesOH C
H
H C
H
HH
OH
SH
C
H
H
H
C
H
O
C
H
H
H
C
OH
O
C
H
H
H
N
H
H
C
H
H C
O
H
C
H
H
H
C
O
C
H
O
C
OH
O
N
H
H
H
H
H
+N
C
O
O−
PO
O
O−
O−
C
H
H C
H
HH
C
H
H
C
H
H
SH
C
C
H
H C
H
PO
O
OH
HO
O
O−
O−
(non-ionized) (ionized)(non-ionized) (ionized)ethanolacetaldehyde (ethanal)acetoneacetic acidmethylaminebutanethiol3-phosphoglyceric acid Figure 1.13Functional groups of
organic compounds