ANSC Exam 4 - Protein

Amino Acid Structure

-COOH group

-NH2 group

R group

central carbon

Nitrogen in Amino Acid Structure

N2 (atmospheric nitrogen is unusable) → NH3 (ammonia is usable) → urea (fertilizer)

Essential Amino Acids (EAA)

• body cannot synthesize sufficient amount for the animal

• must be absorbed from the small intestine in the required amount to optimize animal performance

• expensive and hard to find

• if we overfeed protein, it is metabolized to glucose and ketones for energy

  • NOT excreted

What are the Essential Amino Acids?

MATT HILL VP

• methionine (contains sulfur)

• arginine

• threonine

• tryptophan

• histidine

• isoleucine

• leucine

• lysine

• valine

• phenylalanine

Proteins are Chains of Amino Acids

• amino acids are connected by peptide bonds

  • broken by proteolytic enzymes

• 20 nutritially common amino acids

• all proteins contain ALL 20 amino acids (in different ratios and arrangements)

Non Essential Amino Acids (NEAA)

• synthesized by the body in sufficient amounts to meet the animal’s requirement

• metabolically very important

Ruminants and Essential Amino Acids

• ruminants do not generally require essential amino acids in their diet because ruminal microbes have the capacity to synthesize ALL amino acids

• ruminants require essential amino acids to be absorbed through the small intestine

What is Required for Microbes to Synthesize Amino Acids?

• carbon skeleton (VFA) + ammonia (NH3) (added ATP and microbial enzymes) → AA (added ATP and microbial enzymes) → MCP

• carbon skeleton (VFA) + ammonia (NH3) ← (fermentation) AA ← (fermentation) MCP

  • gain ATP

Two Types of Ruminants

• non-nursing cattle

• require essential amino acids in excess of the microbes ability to synthesize EAAs

1. high-producing dairy cows

2. implanted rapidly growing steer grazing wheat pasture

High-Producing Dairy Cows

• increased methionine

• increased milk production

• must protect methionine from microbial degredation

• could coat in lipid so methionine can arrive to the small intestine → ruminal protection

Implanted (growth implant) Rapidly Growing Steer Grazing Wheat Pasture

• supply a protein source that is ruminally undegradable → increase daily gain

Peptide Bonds

bond between two amino acids

Proteolytic Enzymes…

hydrolyze peptide bonds

Polypeptides

• =>10 amino acids

• 9+ peptide bonds

• absorbed in small intestine

Tripeptides

• 3 amino acids

• 2 peptide bonds

• absorbed in small intestine

Dipeptides

• 2 amino acids

• 1 peptide bond

• absorbed in small intestine

Amino Acid

• 1 amino acid

• 0 peptide bonds

• absorbed in small intestine

Protein Structures

• primary

• secondary

• tertiary

• quaternary

Primary Structure

• sequence of amino acids

• enzymatic hydrolysis of peptide bonds occurs in stomach and small intestine

Secondary Structure

• hydrogen bonding between amino acids

• denatured by HCl

Tertiary Structure

• clustering of hydrophobic regions

• denatured by HCl

Quaternary Structure

• interaction between polypeptides

• denatured by HCl

Nonruminant Protein Digestion

1. Denaturation

2. Hydrolysis of Peptide Bonds

3. Absorption of Amino Acids, Dipeptides, and Tripeptides

Nonruminant Denaturation

• acid (HCl) in stomach

• exposes peptide bonds for enzymatic hydrolysis

• affects the 2*,3*, and 4* structures

Nonruminant Hydrolysis of Peptide Bonds

• done by mammalian proteolytic enzymes

• occurs in stomach and small intestine

• affects primary structure

Nonruminant Absorption

• amino acids, dipeptides, tripeptides

• occurs in small intestine (enterocytes)

Mouth (nonruminant)

• decreases particle size

Stomach (nonruminant)

• HCl (acid) decreaes pH

• protein denaturing of 2*,3*,4*

• pepsinogen (+HCl/pepsin) → pepsin

Pepsinogen

• zymogen (inactive)

• site of production: stomach

• activator: HCl/pepsin

• enzyme: pepsin

• site of activity: stomach

• activity: endopeptidase

Pepsin

• enzyme

• hydrolyzes peptide bonds (1*)

• also converts pepsinogen into more pepsins

Trypsinogen

• zymogen (inactive)

• site of production: pancreas

• activator: enteropeptidase or trypsin

• enzyme: trypsin

• site of activity: small intestine

• activity: endopeptidase

Chymotrypsinogen

• zymogen (inactive)

• site of production: pancreas

• activator: trypsin

• enzyme: chymotrypsin

• site of activity: small intestine

• activity: endopeptidase

Procarboxypeptidase

• zymogen (inactive)

• site of production: pancreas

• activator: trypsin

• enzyme: carboxypeptidase A and B

• site of activity: small intestine

• activity: exopeptidase

Endopeptidase

hydrolyzes peptide bonds on the inside of the molecule

Exopeptidase

hydrolyzes peptide bonds on the outside of the molecule

Enteropeptidase

• (also called enterokinase)

• produced by the enterocyte to activate trypsinogen

• released in response to CCK and secretin

What do enterocytes release in response to enteropeptidase and brush border enzymes?

CCK and Secretin

What does the pancreas release in response to CCK and Secretin?

zymogens and buffer

What happens to zymogen production when there is excess trypsin?

• decrease in zymogen production

  • conserves amino acids and energy because zymogens are made of proteins

Brush Border Enzymes (nonruminant)

• enteropeptidase

  • activates trypsin

• aminopeptidase

  • cleaves 1 amino acid from an oligopeptide

• dipeptidylaminopeptidase

  • cleaves dipeptides from oligopeptides

• tripeptidase

  • cleaves 1 amino acid from tripeptides

When protein synthesis is greater than protein degradation…

• animal grows

• retains nitrogen

When protein synthesis is less than protein degradation…

• animal shrinks

• nitrogen loss

When protein synthesis is equal to protein degradation…

• animal is at maintenance

• no protein gain

• no nitrogen retention

Ruminally Undegradable Protein (RUP)

• microbes cannot degrade

• proteins escape microbial degradation

Ruminally Degradable Protein (RDP)

• microbes can degrade and can use to synthesize MCP

Catabolism of Amino Acids

• excess amino acids in the liver yield:

• NH3

• glucose or ketones → ATP

  • occurs when excess amino acids are absorbed from the small intestine

  • mobilizing tissue because energy requirements aren’t met

— Post Exam 4 (FINAL EXAM MATERIAL) —

…

Amino Acid Requirements

• ideal protein

  • exactly meets the animal’s requirement

• consider the following:

1. the product being produced (wool, milk, meat, etc.)

• what is the amino acid profile of the product?

2. the efficiency of amino acid deposition (<1)

3. diet being fed (are all other nutrients in excess of their requirement?)

Average Daily Gain (Nitrogen) versus Level of EAA (Lysine) Graph

• x-axis: Level of EAA (lysine)

• y-axis: average daily gain (nitrogen intake:nitrogen excreted)

• slope plateau = protein requirement

  • anything past requirement starts to slope downwards (average daily gain decreases)

• for a low genetic potential pig, the slope plateaus at a lower level of EAA

• for a high genetic potential pig, the slope plateaus at a higher level of EAA

• it is important to match the genetic potential of your animal to the genetic resources available

Low Genetic Potential Pig

• for a low genetic potential pig, the slope plateaus at a lower level of EAA

• if conditions are bad, the low genetic potential pig does better

  • because less EAAs are needed to reach requirement

High Genetic Potential Pig

• for a high genetic potential pig, the slope plateaus at a higher level of EAA

• if conditions are good, the high genetic pig does better

  • because more EAAs are needed to reach requirement

Energy Chart

Energy (calories) → f3cal energy (FE)

• gross energy (GE) = total energy content of the feed

⤷ Digestible Energy (DE) → urinary energy (nitrogen excretion) + gaseous energy (CH4)(cow>horse>pig)(SCHO>NCHO)

⤷ Metabolizable Energy (ME) → heat

⤷ Net Energy

⤷ Net Energy of Production

• energy retained in a product

  • milk, muscle, eggs, fat, bone, wool, et. (retained energy measured in stored product)

  • work (heat)

⤷ Net Energy of Maintenance

• heat (fasting heat production)

Energy Equations

ME = RE + HE

• metabolizable energy = retained energy + heat energy

ME - RE = HE

• metabolizable energy - retained energy = heat energy

ME>HE → animal weight gain

ME<HE → animal weight loss

RE=0 → ME = HE → animal is at maintenance