What is a protein?
How is the protein content of a feed determined?
Forages contain from 2% to 30% crude protein (CP).
Seeds and grains can have up to 35% CP.
Meals can have up to 50% CP.
Animals contain about 16% CP.
What are true proteins?
Where do amino acids come from?
How many amino acids are there?
How many are required (indispensable) in the diet?
What is the basic structure of amino acids?
What is a peptide bond?
How are peptide bonds formed?
What is the difference between L-form and D-form
Classification and Structure:
Proteins can be separated or classified in a number of ways:
Based on solubility and composition.
Globular protein- soluble in water or dilute acid or dilute base or in alcohol..
Albumins- soluble in water
Globulins- soluble in dilute neutral solutions of salts of bases and acids
Glutelins- soluble in dilute acids or bases
Prolamines- soluble in 70 to 80% ethanol
Histones- soluble in water
Protamines- soluble in water
Fibrous protein- insoluble in water and resistant to digestive enzymes
Collagens- can be converted to gelatin
Elastins- similar to collagen but cannot be converted to gelatin
Keratins- insoluble in water, resistant to digestive
enzymes and contain up to 15% cystine
Conjugated protein- proteins that contain compounds of a non protein nature
Lipoprotein- proteins complexed with lipids
Glycoprotein- proteins complexed with carbohydrates
Based on type of amino acids.
Essential or indispensable amino acids- Ones that
are required in the diet. Why?
Arginine, Histidine, Isoleucine, Leucine, Lysine,
Methionine, Phenylalanine, Threonine, Tryptophane and Valine
PVT MAT HILL or PHILL MT VAT
Nonessential or dispensable amino acids- ones not
required in the diet. Why?
Alanine, Aspartic acid, Citrulline, Cystine, Glutamic
acid, Glycine, Hydroxyproline, Proline, Serine and Tyrosine.
Based on chemical structure of amino acids.
Functions of Proteins and Amino Acids:
Metabolically Active Peptides and Polypeptides
Conversion of dietary protein to tissue
dietary protein -
amino acids in lumen
amino acids in blood
intact protein synthesis
Digestibility of Proteins
Metabolic fecal nitrogen
Absorption of amino acids
(one system for neutral a.a. and one system for basic a.a.)
Can be competition for sites
high amounts of leucine in diet may increase isoleucine
Fate of absorbed amino acids
tissue protein synthesis
synthesis of enzymes, hormones and peptides
deamination or transamination and used for energy
Synthesis and degradation of protein
Synthesis controlled by DNA through RNA
ribosomal RNA - part of structure of ribosome
transfer RNA - carries specific amino acids
messenger RNA - determines sequence to ribosome
SEE figure 9.5
Deamination and Transamination
Deaminations - removal of amino group
Transamination - transfer of amino group
Urea cycle vs. uric acid
Protein and Amino Acid requirements and Deficiencies:
Ruminants vs. Simple Stomached Animals
negative N balance
reduced feed efficiency
reduced serum protein
reduced milk production
Complementarity of feeds to supply amino acids
See figure 9.9
Nonprotein nitrogen (NPN)
What is it used for?
What is bypass protein?
Amino Acid Antagonism, Toxicity and Imbalance:
Antagonism - growth depression that
can be overcome by supplementation with an a.a. structurally similar
Toxicity - adverse affect cannot be overcome by
Imbalance - can be modified by supplementation
Excess Protein Intake
Measures of Nutritive Value of Proteins:
Biological value - the percentage of N absorbed
from the GI tract that is available for production
Net Protein Utilization - measures efficiency of growth by comparing body N compared to feeding protein free diet