CHAPTER ONE
,
1
The four lypes of organic molecules Ihat are associated with
life are carbohydrates, lipids, proteins, and nucleic acids.
In the preceding plate, carbohydrates were considered, and in
this plate, we will focus our attention on lipids. Lipids are a group
of organic molecules thaI dissolve in oils, but nol waler.
Fats are very efficient energy"slorage molecules that yield
about twice the amount of chemical energy per gram as do car"
bohydrates. Fats are important in the construdion of plmma
membranes, and they also provide physical and thermal insulc1'
tion to animals.
of
In the upper portion of the plate, we consider two
is built
o solllrated fat ond on lInsoturated fat. The
from two lypes of subunits: 0 ,"Bu',,",,?,,!
lains three otoms of carbon
numerous oXYf3en and hydrogen
atoms. The
containing the molecule should
shoded in a
pale color.
In the solurated fat, three
(8)
chemically bound to the glycerol subunit. A fally acid is a long
hydrocarbon chain, as the diagram shows. A saturated fally acid
contains its maximum number of hydrogen atoms; single bonds
are represented by straight lines in the diagram. When three sal"
ufoted fally ocids are conneded to glycerol os shown, the result
is a saturated fat, or triglyceride.
In the unsaturated fally acid, there are
mum number of hydrogen otoms in the
(e); there ore some double bonds, which ore
by two porallellines. Three unsaturated fatty acid chains bonded
to glycerol form cm unsaturated fat, or triglyceride.
Saturated and unsaturated fats are extremely important to the
metabolism of organisms. Fats are broken down into two"corbon
units, and these units are used in the Krebs cycle (discussed later}.
They undergo a series of conversions ond release their energy in
the form of ATP molecules. Fats serve as 0 supplemental energy
source when corbohydrate stores ore exhausted.
One of the key uses of phospholipids is in the formation of the
cell (plosma) membrone. The cell membrane consists of two loyers of phospholipids with ossociated proteins. We will discuss
membrones in depth in a later plate.
Phospholipids are basically made up of a glycerol molecule
(A) with 0 phosphate group (D) attoched to the first carbon at the
extreme right. This phosphate group consists of a phosphorus
atom ond four oxygen otoms, and you should use 0 light color
for ii. The
and third carbons of the glycerol molecule
fOlly ocid chains. Note thallhe folly acid on the left is a saturated
fatty
(B), while the fally acid on the right is unsaturated (C).
In
phospholipid biloyer of the cell
the
woups point toword the outside of
cell ond
fatty
choins
The phosphate end is the
a negative charge. The opposite
ond· ihis section of
molecule lacks on
chmge. In the construction of Ihe
membrane, millions of these molecules
next to one
onolher to form a structure similar to 0 picket
Molecules
entering or leoving the cell must poss through this double !oyer of
lipids, and the membrone ads as a selective borrier For the cell.
Steroids comprise (In important group of lipids that are insol"
uble in water and consist of carbon, hydrogen, and oxygen
atoms arranged in rings. Estrogen and ondrogens, the sex hormones in humons, ore steroid hormones.
One familior steroid is cholesterol. In the diagram, we show
this complex molecule that has a
(G). In humans,
cholesterol is used os a precursor to sex hormones, but an excess
of cholesterol is a problem
ilcan clog arteries ond veins,
which results in restricted blood flow. The liver synthesizes
cholesterol for the body, but the diet also provides some, and if
this inloke is high, excessive cholesterol accumu!otes.
-10-
I,
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(f)
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i- C- CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
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H-C-O- 1- C- CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3
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1-1
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0
I
H--C-O
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C- CH2CH2CH2CH2CH2CH2CH2CH=CH -CH2CH2CH2CH2CH2CH2CH2CH3
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H-C-O
-CH 2 CH=CH-CH 2 CH=CH-CH 2 CH 3
I
H
--7~-1
o
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D~ifP"o
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CH-C~
Jf':>
T
1
o
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co
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A
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C\H 2
()
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co ~~
2 ):H2
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CH
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7H2
C
\H2
/CH 2
CH
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2
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CH
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/CH 2
CH
\
1 CH
-. 2
2
Z
/CH 2
CH
,,2
/C1-1 2
CH
,,2
CH 3
CH 2 .
'cH
6J\2
/
CH
2
2
CH 2
'cH
(H 2
F
II
CH --\
CH
6J
o
o
o
o
o
o
o
2
\ 2
CH2
I
CH
,,2
/CH 2
CH
,,2
/CH 2
CH 3
- 11 -
Lipids
Glycerol Molecule ...... A
Saturated Fatty
Acid Chains ............ B
Unsaturated Fatty
Acid Chains ............ C
Phosphate Group ...
D
Pol a rEnd .............. E
Nonpolar End .......... F
Sterol Ring ............ G
J
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