Protein Digestion And Absorption Flashcards
(26 cards)
How are proteins digested in non-ruminants?
Proteins are denatured and peptide bonds are exposed
Bonds are split apart by hydrolysis
Free amino acids are absorbed
What are endopeptidases?
Hydrolyze peptide bonds with primary structures
What are exopeptidases?
Cleave amino acids at the terminal end of molecule
What are carboxypeptidases?
Remove amino acids from the carboxyl group end
What are aminopeptidases?
Act on the terminal end of amino acid with a free amino acid
Describe the digestive process of proteins.
- Beings in stomach, chair cells secrete pepsinogen in the gastric mucosa
- A protective polypeptide exposes the active pepsin
- Proteins and polypeptides leave the stomach and travel to the small intestine
- Pancreas releases three endopeptidases in their zymogen form (trypsinogen, chymotrypsinogen, proelastase) into the small intestine and transforms into trypsin, chymotrypsin, and elastase
- The intestinal villi release aminopeptidases and carboxypeptidases for further degradation
What is pepsin?
An endopeptidase, and specifically cleaves the peptide bond between aromatic or dicarboxylic amino acids
What does trypsinogen do?
Specific for peptide bonds with basic amino acids
What does chymotrypsinogen do?
Specific for bonds involving non-charged amino acids
What does proelastase do?
Broad specificity, can digest elastin
What can inhibit pancreatic enzymes?
Raw soybeans because they contain large proteins and combine irreversibly with trypsin and chymotrypsin
When there is a deficiency of amino acids, what does the pancreas do?
Swells to produce more trypsin
What can inhibit the trypsin inhibitors?
Heat treatment
Describe the absorption process of amino acids.
- Absorbed via active transport when an amino acid attaches to a carrier protein and enter the circulatory system
- For larger proteins such as dipeptides and oligopeptides, they are hydrolyzed intracellularly
- Very large peptides that are absorbed intact stimulate antibody formation
What happens to other nitrogenous substances not digested in the small intestine?
They travel to the hindgut where amino acids are decarboxylated by microbes and produce ptomaines
This leads to the odor of feces
What are some ptomaines?
Cadaverine, putrescine, tyramine, and histamine
What factors can influence how proteins are degraded in the rumen?
Solubility and structure
What happens to amino acids if they are not used for protein synthesis?
They are deanimated and used as energy sources which produces ammonia, branched-VFAs, carbon dioxide, and methane
What is ammonia?
The nitrogenous end product of bacterial fermentation of dietary proteins and the starting point for microbial synthesis of bacterial amino acids
If ammonia is not available for protein synthesis, what will the rumen use instead?
Non-protein nitrogen such as urea, biuret, and uric acid
What are RUPs?
Rumen undegradable proteins that bypass the rumen and go to the abomasum
Describe the process of nonessential amino acid synthesis.
Amino acids are transanimated in the liver where an amino group from one amino acid is transferred to an organic acid to form a new amino acid such as vitamin B6
How does transanimation provide a link between protein and carbohydrate metabolism?
Amino acids can use their C Skelton for glucose or ketose synthesis
What us deanimation?
The removal of amino groups from amino acids to form ammonia
