Page 41 - Anatomy and Physiology of Farm Animals, 8th Edition

26 / Anatomy and Physiology of Farm Animals

is neither a protein nor an amino acid. These include serving as membrane receptors
for hormones and drugs, contributing to
Rather, it is called a prosthetic group. The
VetBooks.ir conjugated proteins and examples of each the transport of water and particles into
and out of cells, acting as membrane‐bound
are as follows:
enzymes, and serving as markers to permit
1. Glycoproteins: a carbohydrate prosthetic the immune system to recognize cells as
group, includes mucopolysaccharides and normal or abnormal body components.
oligosaccharides (in connective tissue Differences in the sequence of the amino
and salivary mucus)
2. Lipoproteins: prosthetic group is lipid acids of the polypeptide chains of proteins
(in blood plasma and egg yolk) often occur between species. For example,
3. Nucleoproteins: nucleic acid prosthetic the serum albumin in the blood plasma
group (in cell nuclei, chromosomes, and of horses is different from that in the
viruses) plasma of cattle and sheep. In cattle, the
4. Chromoproteins: proteins with a protein hormone insulin is slightly
colored substance as their prosthetic different from that in swine. Such variable
group (hemoglobin, cytochromes) proteins may still function in a different
5. Metalloproteins: contain iron, zinc, or species, though usually at levels below
copper (blood transferrin, ferritin, car­ that of the naturally occurring form of
bonic anhydrase) the molecule.
6. Phosphoproteins: phosphate prosthetic
group (casein in milk, vitellin in eggs)
Lipids
Most proteins can be classified as
structural proteins or as reactive proteins. Lipids (fatty substances) consist primarily
Structural proteins include the following of carbon, hydrogen, and oxygen, but
fibrous proteins: collagens, which are the some also contain minor amounts of phos­
major proteins of connective tissue and phorus, nitrogen, and sulfur. Most lipids
which represent about 30% of the total are nonpolar molecules and thus are insol­
protein content of the animal body; elastins, uble in water. The four primary chemical
which are present in elastic tissues such as types of lipids in animals are fatty acids,
the ligamentum nuchae, the abdominal triglycerides or triacylglycerols, phospho­
tunic, and some arteries; and keratins, lipids, and steroids.
which are the proteins of wool, hair, horns, Fatty acids are chains of covalently
and hoofs. Reactive proteins include bound carbon atoms with hydrogens
enzymes, protein hormones, and histones attached (Fig. 2‐3). If each carbon atom has
that are associated with nucleic acids in the four single covalent bonds, the fatty acid is
nucleus of cells, and contractile proteins saturated. If any carbon atom has fewer
in muscle (actin and myosin). Many varie­ than four single bonds, the fatty acid is
ties of proteins are found in blood plasma. unsaturated. A polyunsaturated fatty acid
Functions of plasma proteins include the has multiple carbon atoms with fewer than
transport of substances such as hormones four single bonds. Animal tissues tend to
and lipids in the blood, contributing to the have higher amounts of saturated fatty
process of blood coagulation, and creating acids than do vegetable oils.
an effective osmotic pressure difference Prostaglandins and leukotrienes,
between the plasma and interstitial fluid. derived from fatty acids, are produced
Plasma proteins also include antibodies, by a variety of cells throughout the body.
which are produced by certain blood cells In many cases, these serve as local
and are part of an overall immune response. messengers that permit one cell to affect
All cell membranes contain proteins, the function of another nearby. Both
and like plasma proteins, the proteins in prostaglandins and leukotrienes are local
cell membranes have a variety of functions. messengers in the process of inflammation,