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Proteins
Proteins are a group of nitrogenous organic compounds synthesized by plants and animals.
They are essential for all life processes in animals. Proteins are highly complex biochemical
substances made up of carbon, hydrogen, oxygen and nitrogen with phosphorus and sulphur
present occasionally. On an average protein contains: 16% nitrogen, 51% carbon, 6.5-7.3%
hydrogen, 21.5- 23.5% oxygen, and sometimes 0.5-2% sulphur and 1.5% phosphorus.
These elements are combined in different proportion to form units of protein called amino
acids. More than 20 amino acids take part in the formation of protein. Out of these amino acids
arginine, valine, histidine, isoleucine, leucine, lysine, methionine, phenylanalinine, threonine and
tryptophan are not synthesised by the animal body. Hence they are to be provided in food from
outside. These 10 amino acids are called "essential amino acids". The protein part of feeding stuff
is also termed as crude protein, made up of following two components.
 True protein (TP): the actual nitrogen substance present as only protein.
 Non-protein nitrogenous (NPN) compounds: which do not contain protein but rich in
nitrogen and they serve as a source of body protein. For example, urea, amides, alkaloids
and ammonium salts present in the body of the animals.
Properties of proteins :
1- All proteins have colloidal properties; they differ in their solubility in water ranging from
insoluble keratin to albumins which are highly soluble in water.
2- All protein contains a number of free amino and carboxyl group there for they are
amphoteric and have buffering properties.
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3- All proteins denatured and denaturation can be defined as any non proteolytic
modification of unique structure of the protein, giving changes in chemical, physical or
biological properties; products of protein hydrolysis are under this agents which cause
denaturation includes heat, acids, alkalis, alcohols, urea and salts of heavy metals.
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Functions of proteins
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The protein takes part in building muscles, connective tissues and each cell of the body.
Protein is essential for the growth and development of the body.
It helps in repair of wear and tear of the tissues.
It contributes in the production of enzymes, hormones and digestive juices of the body.
It is also essential for the formation of egg and development of the fetus.
It is essential for the proper functioning of enzymes and hormones.
It is important for the growth and development of wool and hair of the animal. Its
deficiency in the body results in poor quality of wool.
Protein takes part in formation of skin, hooves and horns.
Protein is essential in formation of milk as milk contains 3.5% proteins. It is also essential
for better production of milk in the milk animals. The milk production may go down, if the
animals are not getting enough protein in their feed.
Lack of protein in the diet generally affects the utilization of easily digestible
carbohydrates.
Protein supplies energy when other energy sources are not available.
Protein deficiency
The symptoms of protein deficiency are retarded growth and body development with
impaired ability to perform the above mentioned functions. In the severe cases, the
animal may even die.
Tips to increase utilization of crude protein
1. The protein intake of a ruminant becomes available in two ways:
 through protein broken down by the microorganisms in the rumen of the cattle (degraded
protein)
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Through direct protein digestion and absorption in the small intestine (undegraded
protein).
Undegraded protein has a greater demand than degraded protein, because the high
yielding cows and young ruminants cannot meet all the protein requirements through degraded
protein.
The protein in silage and barley is highly degradable (85%) and therefore, supplies only a
small amount of undegradable protein. On the other hand some high protein concentrates e.g.
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soybean meal and fish meal contains a higher proportion of undegradeable protein. These feeds
should be used as protein supplements.
2. The amount of protein, its digestibility and the balance of essential amino acids are
important factors that must be considered while balancing rations. Animal proteins are
superior to plant proteins for poultry and pigs. The amino acid content of proteins varies
from various plant and animal sources. Thus, the deficiency of one protein source can be
improved by combining it with another. Therefore, a combination of protein feeds in a
ration is usually recommended when the person formulating the ration does not have
access to specific amino acids of feeds to be used.
3. Raw or inadequately heated soybean or kidney bean meals contain certain toxic proteins
which are harmful to pigs and poultry. It results in the enlargement of pancreas and a
reduction in the available energy of the feed. Growth is depressed as well. Ruminants are
not affected as the rumen fermentation renders these toxins ineffective.
4. Extensive heating or prolonged storage of the protein feed can impair the protein quality
and make some amino acids un- available to the animal.
Amino acids:
Are produced when proteins in are hydrolyzed by enzymes, acids or alkalines. Although
over 200 amino acids have been isolated from biological material, only 20 of these are commonly
found as components of proteins.
Amino acids are characterized by having a basic nitrogenous group, generally an amino group (NH2), and an acidic carboxy unit (- COOH). Most amino acids, occurring naturally in proteins are
of the α type, having the amino group attached to the carbon atom adjacent to the carboxyl
group, and can be represent by the general formula.
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Types of common amino acids founds in proteins:
1- Mono amino-monocarboxylic acids:
(glycine, serine, alanine, threonine, valine, leucine and isoleucine).
2- Sulpher containing amino acids:
(cysteine and methionine)
3- Mono amino-dicarboxylic acids and their amino derivatives:
(aspartic acid, glutamic acid, asparagine, glutamine)
4- Basic amino acids:
(lysine and arginine)
5- Aromatic and heterocyclic amino acids:
(phenylalanine,tyrosine,tryptophan, proline and thyroxine).
Function of amino acids:
 Building cells and repairing tissue.
 Amino acids form the building material major antibody to against invading bacteria and
viruses.
 An essential part of the enzyme and hormones.
 It builds nuclear proteins RNA (ribonucleic acid) and DNA.
 The amino acids also play an important role to carry oxygen to different parts of the
body.
 It's an essential component of muscle activity.
Classification of amino acids according to their importance food and
bioavailability:
 Essential amino acids: not synthesized by the body, and must be added in the food.
Example, Lucien and lysine
 Semi-essential amino acids: The body can synthesize, but not in sufficient quantities,
especially in the growth stage, and must be available in the food. For example, arginine
and histidine
 Non-essential amino acids: available in the body, and do not require their presence in
food. Example, glycine and proline
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Classification of proteins :
1- Simple proteins: these proteins produce only amino acids on hydrolysis they subdivided
into 2 groups fibrous and globular proteins according to shape, solubility and chemical
composition.
 Fibrous protein: which in most cases have structural roles in animal cells and tissues, are
insoluble and very resistant to animal digestive enzymes, this group includes collagen
(connective tissues), elastin (elastic tissues) keratin (wool and hair).
Functions of fibrous proteins:
 Structural proteins:
o Collagen and elastin are used in animal tendons and ligaments
o Keratin is the protein in hairs, horns and feathers
 Contractile proteins:
o Actin and myosin contract and to move muscles
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Globular proteins: are so called because their polypeptide chains are folded into compact
structure, the group include all enzymes, antigens and hormones.
Conjugated proteins: in addition of the amino acids a non-protein molecules are found
called prosthetic group.
Glycoproteins.
Lipoproteins.
Phosphoprotein.
Chromoprotein like hemoglobin.
Proteins classified by function:
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Catalytic: enzymes.
Storage: ovalbumen (in eggs), casein (in milk).
Transport: haemoglobin
Communication: hormones (eg insulin) and neurotransmitters.
Contractile : actin, myosin, dynein (in microtubules)
Protective: Immunoglobulin, fibrinogen, blood clotting factors.
Toxins: snake venom.
Structural : cell membrane proteins, keratin (hair), collagen.
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