Dietary Protein & Nitrogen Balance Flashcards
By what pathways are proteins degraded in cells? How do the pathways differ?
Autophagy-Lysosome Pathway - Degrades free proteins and proteins in sub-organelles, utilizes lysosomes, less selective
Ubiquitin-Proteasome Pathway - Degrades only free proteins, utilizes ubiquitination, proteasomes, and is more specific
Describe the process of protein degradation by the Autophagy-Lysosome Pathway.
This pathway degrades both free proteins and proteins in sub-organelles. An isolation membrane forms and expands to create an autophagosome around the protein/sub-organelle. The autophagosome fuses with a lysosome for degradation.
The pathway is less selective, enhanced by starvation, and inhibited by insulin and amino acids.
Describe the process of protein degradation by the Ubiquitin-Proteasome Pathway.
Free proteins are polyubiquitinated by three different enzymes. Ubiquitinated proteins are degraded by proteins and the ubiquitin is recycled.
This pathway only targets free proteins and is more specific and regulated.
In healthy adults, nitrogen loss = nitrogen intake. When may there be a positive nitrogen balance, more intake than loss?
Growth in young children, pregnancy, recovery from trauma
During negative nitrogen balance, less intake than loss, what are amino acids used for?
Amino acids are only used to make proteins and not for fuel.
What are the essential amino acids?
Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine (children), Leucine, Lysine
Pvt. Tim Hall
Where does protein degradation begin? How does this differ from carbohydrate and fat degradation?
Protein degradation begins in the stomach. Carbohydrate and fat degradation begins in the mouth
Describe the process of protein digestion, beginning with ingestion.
Proteins are ingested and moved to the stomach, where digestion begins.
Gastrin is released by G-cells in the stomach, stimulating the release of HCl from parietal cells. The acid environment denatures proteins and activates pepsinogen to pepsin to further break down proteins.
As the peptides move into the intestine, the intestine releases Cholecystokinin (CCK) to slow digestion and increase bile release, zymogen release, and feelings of satiety. Secretin is also released, targeting the pancreas to release HCO3- to neutralize the acidic environment.
The pancreas releases inactive zymogens that enter the gut. Enteropeptidase within the intestinal wall activates trypsinogen to trypsin, which creates a chain reaction activating other zymogens.
Zymogens breakdown peptides into amino acids, which can be absorbed into intestinal cells.
What hormones are involved in protein digestion? Where are they released and what are their function?
Gastrin - Released by G-cells, targetting parietal cells to release HCl
Cholecystokinin (CKK) - Released by the small intestine to decrease gastric mobility and increase bile and zymogen release
Secretin - Released by the small intestine, targeting the pancreas to secrete HCO3-
How are zymogens activated in the intestine?
Zymogens are stored in an inactive state. When they are released by the pancreas into the intestine, enteropeptidases in the intestinal wall activate trypsinogen to trypsin, which in turn activates other zymogens.
How can the body prevent the digestion of self-proteins?
Zymogens are stored in an inactive state because of the pancreatic trypsin inhibitor. Protein degradation also involved many enzymes so even if one were activated, minimal digestion would occur.
What is the function of Alpha-1-Antitrypsin?
An anti-inflammatory that inhibits elastase released by neutrophils. Deficiency leads to liver and lung disease.
How are proteins absorbed into the blood following digestion to amino acids?
Amino acids are co-transported into intestinal cells by a symporter than brings Na+ down its concentration gradient. Once inside intestinal cells, amino acids are released into the portal vein by a facilitated transporter.
True/False. All amino acids have their own symporter for absorption into intestinal cells.
False. Neutral amino acids, which makeup a majority of plasma amino acids, share the same symporter.
Both Hartnup Disorder and Kwashiorkor are the results of protein deficiency. How do these disorders differ?
Hartnup is caused by a lack of transport of neutral amino acids. Kwashiorkor is caused by insufficient protein intake in the diet.
What is homocystinuria?
A buildup of Homocysteine due to deficiencies in the methionine synthase or cystathionine synthase or low Vitamin B12 or B6.
