Lipids
and
Their
Structures

Definition:
Organic
molecule
of
biological
origin
that
is
insoluble
in
water
 and soluble
in
nonpolar
solvents.

Solubility
Explained:
Lipids
do
have
both
nonpolar
and
polar
regions;
 however, the
majority
of
the
molecule
is
nonpolar
(due
to
large
nonpolar
 tails). Since
"like
dissolves
like",
lipids
are
soluble
in
nonpolar
solvents.

There
are
eight
general
categories
of
lipids,
but
I
will
only
go
into
seven

(fatty
acids,
waxes,
triacylglycerides,
phospholipids,
prostaglandins,
steroids,
 and lipophilic
vitamins)


Fatty
Acids
(Function:
Precursor
to
other
lipids.)

Structure:
Carboxylic
acid
and
long,
unbranched
hydrocarbon
chain


• Most
have
an
even
number
of
carbons


• Most
common:
12‐20
carbons

• May
or
may
not
have
pi
bonds
in
the
chain
(saturated‐
no
C=C
and
unsaturated‐

1+
C=C)


• Saturated
fatty
acids
are
not
too
fancy,
don't
over
complicate
them.
Check
out
 these examples
to
see
the
extremely
small
differences
between
them.


• Within
unsaturated
fatty
acids
are
divided
into
monounsaturated
fatty
acids
(one

C=C
bond)
and
polyunsaturated
fatty
acids
(more
than
one
C=C
bond)


• Unsaturated
fatty
acid
structures
are
a
little
more
complicated,
but
you
can
see
a
 pattern in
the
important
structure
(besides
arachidonic
acid).
Try
and
familiarize
 yourself with
the
pattern.


Waxes
(Function:
Water
barrier)

Structure:
Esters
with
long
hydrocarbon
chains
on
both
sides
of
the
ester
(with
the
=O
in
 the middle)


• Derived
from
a
fatty
acid
and
a
long‐chain
alcohol


Triacylglycerides
(Function:
Energy
Storage)

Structure:
Fatty
acid
triester
of
glycerol


• They
are
call
fats
if
solid
at
room
temperature
and
oils
in
they
are
liquids

• The
structure
is
easy
to
remember
if
you
just
think
in
steps:
 o remove
the
alcohols
from
the
glycerol
 o remove
the
hydrogen
(of
the
carboxylic
acid)
from
each
fatty
acid

 o bond
the
oxygen
with
now
three
lone
pairs
on
it
to
one
of
the
three
 outside carbons.
 o Now
you
have
a
triaclyglyceride.


Phospholipids
(Function:
Cell
membrane)

Structure:
Glycerol
esterified
with

two
fatty
acids
and
one
phosphate
group


• Phospholipid
structure
is
very
easy
to
grasp
if
one
has
already
grasped
the
 structure of
a
triacylglyceride.
I
would
recommend
making
sure
you
grasp
that


first
before
you
try
to
grasp
phospholipids
because
it
makes
it
much
simpler
to
 comprehend. • A
sign
that
it
is
a
phospholipid
is
the
fatty
acids
are
usually
palmitic,
stearic,
 and/or oleic
acid.
This
isn't
always
the
case,
but
it
can
help
you
determine
if
it
is
a
 phospholipid. • To
get
the
structure
of
a
phospholipid:
 o take
the
structure
of
a
triacylglyceride


 o remove
one
fatty
acid
 o replace
it
with
a
phosphate
 o Now
you
have
a
phospholipid


Prostaglandins
(Function:
Regulators
and
signal
molecules)

Structure:

A
prostanoic
acid
skeleton


• For
structure
all
you
should
know
is
the
structure
of
a
prostanoic
acid
and
that
 the name
changes
based
on
the
number
of
OH,
C=O,
and
C=C
groups.

• This
tutorial
is
focused
on
structure,
but
for
prostaglandins
there
are
a
lot
of
 functions that
are
important
and
I
recommend
you
know
them.


Steroid
(Function:
Each
steroid
has
a
variety
of
functions)

Structure:
A
ring
system
of
three
adjacent
cyclohexanes
and
a
cyclopentane.


• This
ring
system
is
approximately
flat
while
the
other
components
are
not
limited
 to being
flat
or
not.

• To
understand
the
structure
of
steroid,
one
must
look
at
the
steps
of
steroid
 biosynthesis. Specifically
we
are
going
to
observe
the
process
of
changing
acetyl

CoA
to
chlosterol.


Lipophilic
Vitamins
(Functions:
Broad
range
of
functions)

Structure:
Broad
range
of
structures

• There
are
a
broad
range
of
structures
for
lipophilic
vitamins,
but
we
only
go
into
 three vitamins:
Vitamin
E,
Vitamin
C,
and
Vitamin
A.

• Just
familiarize
yourself
with
these
structures.

• There
really
isn't
a
trick
to
these
structures
so
just
do
a
lot
of
practice
problems
 involving these
and
you
will
get
the
hang
of
it.


• Vitamin
E
protects
against
radicals


• Vitamin
C
is
a
antioxidant


Vitamin
A
(retinol)


• Vitamin
A
is
essential
to
vision


Works
Cited:

Hardinger,
Steven.
Chemistry
14C:
Organic
Molecular
Structures
and




Interactions:
Lecture
Supplements.
Plymouth,
MI:
Hayden‐McNeil
Pub.,
2008.


Print.



Hardinger,
Steven.
Organic
Chemistry
at
UCLA.
N.p.,
n.d.
Web.
9
June
2012.



All
images
from
lecture
supplement