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Animal nutrition lecture 5 proteins and amino acids

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Proteins and amino acids
Essential part of living organisms
Synthesized in all cells
Must come form diet unless synthesized from nonprotein N source
% required by diet decreases with age
% required increases with production and lactation
Structure
Variable in many aspects:
Chemical composition
Physical properties
Size
Shape
Solubility
Biological function
Made up of?
Protein is made up of amino acids
More than 200 aa, but 20 are most common
10 essential amino acids
carboxyl group and amino group
Primary
sequence of aa held by peptide bonds
Secondary
twists of aa into coilded structure
Alpha-helix
Beta-sheet
Tertiary
rigid structure of layers
H and disulfide bonds
Quarternary
large proteins, several tertiary linked, harder to digest complex proteins
Classification
Shape, solubility, other
Globular
Fibrous
Conjugated proteins
Globular
Albumins, globulins, glutelins, prolamines, histones, protamines
Soluble in water or dilute acid/base
Fibrous
Insoluble in water or digestive enzymes
Collagens, keratins, elastins
Conjugated proteins
Conjugated proteins
Wide array of compounds and nonprotein structure
lipoproteins
glycoproteins
Lipoproteins
Stable through electrostatic, hydrophobic and H bonds
Membrane protein in animal cells
Glycoproteins
Chondroitin sulfates (cartilage, tendon, skin)
Mucoproteins (mucous, ovalbumin)
Synthesis of protein
Chain of amino acids
Linked by peptide bonds
Elongation - add more aa to form tri or polypeptides
Feedstuff may have many proteins, but need adequate composition of amino acids
Essential vs. Non-essential AA
Essential - need in the diet
Non-essential - can by synthesized by tissues in the body
Ruminants and herbivores AA
can use non-protein N to supply amino acids.
(urea)
Cats require
taurine
Poultry require
proline
Functions of proteins
1. Structural unit in animal body
Collagen, elastin, contractions, blood, keratins
2. body metabolism
Enzymes, hormones, antibodies
3. source of energy after deamination
Examples of tissue proteins...
...
Collagen
content increases with age, contributes to toughness in meat, insoluble in water and digestive enzymes
Elastin
found with collagen, elastic, insoluble in water and digestive enzymes
Myofibrillar
proteins - in sarcoplasm
Contractile proteins
muscle contractions ,actin, tropomyosin B, myosin
Keratins
hair, wool, feathers, hooves, claws, beaks
Blood proteins
albumin and globulins
Enzymes
100s in each cell with specific function
Hormones
carried in blood, not all are proteins
Hydrolysis
Proteolytic enzymes
Efficiency determines what is absorbed(enzyme avaliability)
AA composition important
Enzymes - hydrolyze peptide bonds
stomach
pepsinogen pepsin
Small intestine
from pancreas
Trypsinogen trypsin
Chymotrypsinogen chymotrypsin
Procarboxypeptidase carboxypeptidase
Absorption
Intestinal epithelium acts as barrier
AA - active transport
Di- and Tripeptides
Whole protein
AA - active transport
Neutral, dibasic, acidic, imino
Requires energy
Specific
Di- and Tripeptides
Actively absorbed by peptide transporter (PEPT1)
Mostly in growing ruminants
Whole protein
Newborns
Engulfed by mucosal cells
(imunoglobulins from colostrum)
Post absorption of AA
1. Tissue protein synthesis
2. Synthesis of enzymes, hormones, and metabolites
3. Deamination or transamination - use C skeleton for energy
Deamination
remove amine group and then enters urea cycle. c skeleton can then be used for energy
Transamination
transfer amino group from one AA to C skeleton of keto acid
Synthesis and Degradation of Proteins
Protein synthesis requires nucleic acids
DNA - deoxyribonucleic acid
Chromosomes, genetic info
RNA - ribonucleic acid
Controlled by DNA
3 types - ribosomal, transfer, messenger
mRNA controls synthesis of proteins
DNA
phosphate-linked deoxyribose and 4 nitrogenous bases
Adenosine - Thymine
Cytosine - Guanine
Double helix structure
RNA
transfer info from DNA to protein
Ribose vs. deoxyribose
Uracil vs. thymine
Codons determine AA and thus protein
Protein Turnover
Synthesis and degradation occur at the same time
"Protein turnover"
Continuous and simultaneous
Degraded by cathepsins and calpains in muscle
Balance between the 2 determines net protein accretion
Measure by use of radioisotopes (N and C)
Precursors to endpoint
Can measure protein
Can measure this by using radio isotopes that have precursors to protein and track
Protein Turnover
Growth occurs in young and old
Regulated by polypeptides which influence protein metabolism, development and maintenance at cellular, tissue and organ level
GH and I
EGF
IGFs
NGF
PDGF
Urea Cycle
Key metabolic phenomenon in protein metabolism
Ammonia from deamination and ultimately forms urea
5 enzymes
Mitochondrial AA transporters
Urea excreted in urine.
Synthesis of AA
Three main sources in GI tract
1. diet
2. recycled
3. synthesized by microorganisms
synthesized by microorganisms
Ruminants and herbivores (horse, rabbit)
Most AA derived from microbial production
Bacteria and protozoans in rumen and lower GI tract
Synthesize AA in presence of ammonia, S, C source
Rumen Microbial Protein
Microbial crude protein (MCP) - N from:
dietary protein
nonprotein nitrogen (NPN)
Recycled N
MCP amino acids then flow through omasum, abomasum to SI
40% of nonammonia N in SI
NPN is useful from ruminal bacteria synthesis of amino acids and protein
Diet formulated to meet needs of bacteria
Rumen undegraded protein (RUP)
Quality of protein from microbial synthesis?
RUP allows protein to pass through the rumen
Digested in small intestine
Degradation of AA
Intestinal tract by microbes
Major products - ammonia, S, FA, CO2
Liver is primary organ
Also in SI
Various enzymatic reactions and pathways
N cycling in intestine
N from aa, di- and tripeptide and recycled
Endogenously produced (urea)
Urea - remove ammonia
Ammonia incorporated into AA for microbial protein
Requirements and deficiencies
Primarily for AA
Monogastric vs. ruminant
Most common nutrient deficiency
energy sources low in protein
protein supplements are expensive
Greater requirement with growth
Ratio of protein:calories is important
Protein only used for energy when:
Deficiencies
AA deficiency similar
One feedstuff will be deficient in some AA
Signs of protein deficiency
Reduced growth rate
Reduced N balance
Reduced efficiency of feed utilization
Anemia
Reduced birth weight
Measures of nutritive value of proteins
True protein = only AA
NPN (non protein N) = contains N, but not true protein
CP (crude protein) = total protein (true protein + any other N source)
%N x 6.25
Digestible protein = portion of CP that can be digested
BV (biological value) = evaluate protein source
% of N absorbed from GI tract and available for body functions