Page 42 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Cell / 27

Saturated fatty acid: O H H H
- - - - -
H-O-C-C-C-C-H
VetBooks.ir Polyunsaturated fatty acid: H H H -
-
-
O H H H H HHH HH H H H
- - - - - - - - - - - - - -
H-O-C-(CH ) -C C-C-C == C-C-C = C-C-C = C-(CH ) -C-H
2 3
2 4
H - H - H - H -
Figure 2-3. Saturated and polyunsaturated fatty acids. The 4‐carbon saturated fatty acid is butyric acid,
and the 20‐carbon fatty acid is arachidonic acid.

Glycerol Triglyceride
H H CH _ _ CH _ _ CH _ _ CH _ _ CH _ _ CH 3 +H O
2
2
2
2
2
_ _ _ _ _ _ 2
H C OH H C O = C CH 2 CH 2 CH 2 CH 2 CH 2
O
2
2
2
2
2
2
_
H _ C _ OH H _ C O _ C _ CH _ _ CH _ _ CH _ _ CH _ _ CH _ _ CH 3 +H O
CH
CH
CH
CH
CH
2
2
2
2
2
O =
2
2
2
2
2
_ CH _ _ CH _ _ CH _ _ CH _ _ CH _ _ CH 3 +H O
2
_
H _ C _ OH H _ C O _ = C CH 2 CH 2 CH 2 CH 2 CH 2
O
H H
Figure 2-4. Three fatty acids combined with glycerol to form a triglyceride.
and prostaglandins regulate ovarian func­ CoA within the mitochondria ultimately
tion in some species. results in the production of the high‐energy
Triglycerides consist of a glycerol mole­ compound adenosine triphosphate (ATP).
cule with three fatty acids attached (Fig. 2‐4). Details about the role of the mitochondria
Also known as neutral fats, triglycerides in the production of ATP are described
are the primary form of lipid storage in in the section on organelles later in this
adipose tissue in animals. Fatty acids must chapter.
be detached from glycerol before they can Phospholipids are similar to triglycerides
undergo further metabolism. This detach­ except that a molecule containing a phos­
ment is the function of enzymes known as phate group has replaced one of the three
lipases. Because triglycerides are not solu­ fatty acids. The replacement of the nonpolar
ble in water, most are not transported as (hydrophobic) fatty acid with a nonlipid,
individual molecules in blood plasma. For polar (hydrophilic) molecule creates a
transport, they are combined with other unique compound with two regions that
lipids and proteins into relatively large vary in water solubility. The phosphate‐
particles known as lipoproteins. In this containing region becomes water soluble
form they can be transported from site to (resembling a “head”), and the remainder of
site within the body. the phospholipid molecule is water insoluble
The glycerol and fatty acids derived (resembling a “tail”). This unique character­
from the breakdown of triglycerides are all istic is important in the role of phospholip­
sources of energy. Glycerol can serve as a ids in the structure of cell membranes. Cell
substrate for the glycolytic pathway in the membranes throughout the body primarily
cytosol. Fatty acids enter the mitochondria, consist of phospholipids.
where they are broken down into two car­ Steroids are lipids in which the carbon
bon units, which become acetyl coenzyme atoms are connected in ring structures.
A (acetyl CoA). The metabolism of acetyl Cholesterol is a steroid (Fig. 2‐5), and most