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