General Information:

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 amino acids?

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.

Aliphatic

Aromatic

Sulfur-containing

Heterocyclic

Acidic

Basic

Functions of Proteins and Amino Acids:

Tissue Proteins:

Collagen

Elastin

Myofibular Proteins

Contractile Proteins

Keratins

Blood Proteins

Enzymes

Hormones

Metabolically Active Peptides and Polypeptides

Immune Antibodies

Metabolism:

Definitions:

catabolism

anabolism

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

Active transport

(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 requirement

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

urea

uric acid

Protein and Amino Acid requirements and Deficiencies:

Ruminants vs. Simple Stomached Animals

Protein deficiency

anorexia

reduced growth

negative N balance

reduced feed efficiency

reduced serum protein

anemia

fatty livers

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:

Definitions:

Antagonism - growth depression that can be overcome by supplementation with an a.a. structurally similar to antagonist

Toxicity - adverse affect cannot be overcome by supplementation

Imbalance - can be modified by supplementation

Excess Protein Intake

Ammonia Toxicity

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