Nutrition: Protein Flashcards
What’s the first step in protein digestion?
mechanical breakdown
What’s the second step in protein digestion? Is it enzymatic?
Low pH denatures proteins - so it’s not enzymatic, like the rest
What’s the third step of protein digestion?
lumenal proteases digest the protein down to tripeptides, dipeptides and amino acids
True or false: the proteins need to be brokn down to individuals amino acids before the epithelial cells can take them up?
false - the intetinal epithelial cells can take up tripeptides, dipeptides and amino acids
What happens tot he tripeptides and dipeptides once they get into the epithelial cell?
they’re broken down into amino acids by intracellular peptidases
then all the amino acids are transported into the blood
Protein malnutrition is called what?
kwashiorkor
In what general form are the peptidases synthesized?
they’re synthesized as zymogens or proenzymes that must have a portion cleaved off them before they can be active
What peptidase is the first one to activate and where is it located in the GI tract?
pepinogen is hydrolyzed to pepsin under the acidic conditions in the stomach
It’s secreted by chief cells in the stomach
What are some of the other peptidases and where are they located?
trypsin, chymotrpysin, elastase, carboxypeptidases
they’re synthesized by the pancreas, but mainly work in the small intestine
What determines where a particular endopeptidase will cleave?
each one has a different substrate specificity depending on the sequence of amino acids - the side chains of the carbonyl-containing amino acids determine recognition and cleavage sites
How does protein uptake into epithelial cells differ from that of carbohydrates? How is it the same?
It differs in that there need to be multiple transporters for amino acids instead of just one GLUT transporter for carbs, since there are so many different AAs
Other than that it’s the same in the sense that it’s through facilitated diffusionin the upper GI and active diffusion in the lower GI with ATP hydrolysis driving a Na/K ATPase
What are the three general sources for the intracellular amino acid pool?
- extracellular amino acids brought in from the diet
- protein degradation within the cells
- do novo synthesis of amino acids from glycoslysis or TCA cycle intermediates
What are the three key cofactors for enzymes in amino acid metabolism?
- pyridoxal phosphate (PLP) or B6
- Tetrahydrofolate (FH4)
- Tetrahydrobiopterin (BH4)
What type of reaction uses PLP?
any reaction that grabs hold of an amino acid and does something with it - transaminations, deaminations, carbon chain transfers, etc
What symptoms will occur with a deficiency of PLP?
mostly neurological - seizures and EEG abnormalitis
also diarrhea and anemia
What type of reaction uses FH4?
reactions requiring one-carbon transfers
What symptom will occur with a deficiency of FH4 (folate)?
megaloblastic anemia
What type of reaction uses BH4?
ring hydroxylations, espcially making tyrosine from phenylalanine
What symptoms will occur with an inherited issue with BH4?
seizures and developmental delays
The balance between protein synthesis and degrataion is sensitive to what?
the general metabolic state of the cell - will lean towards synthesis in an anabolic state and degradation in a catabolic state
What is the main signaling pathway that activates protein synthesis and inhibit autophagy?
the mTORC1 complex
How does the mTORC1 complex get turned off when the cell wants to make sure to use energy instead of store it?
In low energy states, the AMP:ATP ratio will be high
AMP will then activate AMPkinase alpha, which will activate two inhibitors of mTORC1: TSC1 and TSC2
Thus, when AMP levels are high and ATP levels are low, protein synthesis is inhibited, so the cell isn’t wasting the little ATP it has on synthesis
What other biosynthetic pathway will be inhibited by an activation of AMPkinase alpha?
the ACC pathway of lipid metabolism
