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64 Cards in this Set

  • Front
  • Back
How much is normal dietary protein intake?
100 g
What happens to dietary protein?
Degraded to AA by endo & exopeptidases in GI tract.
What degrades proteins in the stomach?
What activates Pepsinogen to Pepsin?
HCl (low pH) and Pepsin
What allows pepsinogen to be activated?
Cleavage of the N-terminus to open up the active site
2 Exopeptidases:
What they do:
Cleave N or C-terminal ends of proteins
Where do Endo/Exopeptidases function?
Intestine (lumen)
What are the 3 endopeptidases? Where activates each?
Where are they produced?
-Trypsin (enteropeptidase/itslf)
-Elastase (Trypsin)
-Chymotrypsin (Trypsin)
Made in pancreatic alpha cells
What do endopeptidases do?
Cleave internal polypeptides at specific sites.
What is Trypsin specific for?
What is in its active site?
Lys and Arg
Neg Asp for charged AAcids
What is Chymotrypsin specific for? What is in its active site?
Trp, Tyr, and Phe
Nothing; deep and empty for large bulky rings
What is Elastase specific for?
What is in its active site?
Gly and Ala
2 Valines (216/190)
How do AA's, di-, and tripeptides get into the mucosal cells from intestinal lumen?
Via specific transporters for acidic, basic, neutral, and small oligopeptides.
What happens to AA and oligopeptides in mucosal cell?
Further degraded by exopeptidases
Where do amino acids go after degradation in mucosal cells?
To bloodstream
Where does the bloodstream take amino acids?
Liver - protein synth
Other tissues - for energy
What amino acids can't be degraded by the liver? So what happens to them?
Branched chain:
Val, Leu, Ile
Go to other tissues for protein synthesis
How much body protein is degraded per day? By what?
400 g/d
-Ubiquitine-proteasome system
-Lysosomal system
What proteins is the ubiquitin-proteosome system specific for?
-Ones w/ short half lives
What is the specificity of the lysosomal system?
What is the first step in the Ubiquitin Proteasome system?
Use E1/E2/E3 to activate ubiquitin and form an isopeptide bond between it & target protein.
What does E1 do?
Adds an AMP to the c-terminal end of ubiquitin, then loses
AMP and creates a thioester bond between S and the C=O of ubiquitin
What does E2 do?
Replaces the thioester bond of E1
Why is E2 needed?
Because it is more specific - for E3.
Why is ATP needed in this process?
To have enough energy to form the thioester bond.
What is an isopeptide bond?
One between the c-terminus of one molecule, and another AA's R-group amino, not the alpha amino.
Which is most specific, E1, 2, or 3?
What does E2 recognize again?
What exactly does E3 recognize?
N-terminal Amino acids
Protein-specific sequences
(Cyclin destruction box, PEST)
What is PEST?
Pro-Glu-Ser-Thr sequence
What n-term aa's does E3 recognize? What T1/2's?
-Arg T1/2= 2min

-Met T1/2= 20 min
WWhat are the terms for the actions accomplished by E1/E2/E3?
E1 = Activation
E2 = Conjugation
E3 = Ligation
3 disorders associated w/ abnormal E3 function:
-Juvie & Early-onset Parkinson
-Angelman syndrome
-Cervical Carcinoma
What is the problem with E3 that causes Juv/Early onset Parkinson?
Defective E3 - leads to protein accumulation and aggregation
Symptoms of Angelman syndrome?
Severe neurological disorder
Absent speech
Mental retardation
What virus causes cervical carcinoma?
How does HPV cause cervical carcinoma?
It makes an E3 that ubiquinates tumor suppressor P53 - this targets the protein to proteasome for degradation
Why is HPV so important?
It is seen in 90% of cervical carcinomas
How is Polyubiquitination achieved?
By using same E2/E3 enzymes to create a Ubiquitin chain.
-Bonds btwn C-term of new Ub and Lys 48 of original Ub.
What is the next thing that happens to polyubiquitinated proteins?
Proteolysis by proteosome
What is the purpose of the Ubiquitin Proteosome Protein Degradation system?
To degrade the right proteins at the right time.
What processes are controlled by the Ubi:Proteosome system?
-Gene transcription
-Organ formation
-Circadian rythm
-Cell cycle
-Cholesterol synthesis
-Antigen processing
-Tumor suppression
Think about it; what do lysosomes do?
Degrade proteins - AND lipids, carbs, DNA, and RNA.
So where are lysosomes located?
Throughout the cell - many are active at any given time.
What is the specificity of the lysosomal system?
-Under well-nourised conditions, nonspecific.
What happens to the lysosomal system in starving and Diabetes Type 1?
It becomes more specific
What enzymes are inside lysosomes? At what pH are they active?
Acid Hydrolases - pH 5
How is the acidic environment in lysosomes achieved?
By an ATP pump that pumps protons into the lysosome.
What are the 3 mechanisms by which cells take up material for digestion in lysosomes?
1. Phagocytosis
2. Endocytosis
3. Autophagocytosis
What happen to phago, endo, and autophagosomes?
Fuse with lysosomes for degradation of the material inside.
What happens when the fused 'somes don't stay inside a membrane?
Necrosis - enzymes start to degrade extracellular material.
What happens when enzymes stay within the membrane of the 'some?
How is protein degradation different in Uncontrolled Diabetics compared to Normal?
Less intracellular protein (300) is made, so extra needs to be degraded(200) - and goes to gluconeogenesis.
How is protein degradation different in Starving People compared to Normal?
Less intracellular protein (300) is made, but no dietary intake, so only 100 needs to be degraded but it all goes to gluconeogenesis.
First step in amino acid degradation:
loss of ammonia - by loss of FREE ammonia or TRANSFER to a-ketoacid
3 sources of free ammonia:
-Amino acids
-Purine degradn
-Pyrimidine degrdn
What enzyme causes release of NH3 from amino acids?
What does an Aminotransferase do?
Transfers an NH3 from one amino acid to its conjugate a-keto acid
What is the cofactor for aminotransferases?
PLP - vitamin B6 derivative
What is the specificity of Branched Chain AA Aminotransferase?
How is PLP bound to aminotransferases?
Via the Amino group of Lys - forms a schiff base and multiple ionic bonds.
3 enzymes used to transfer extrahepatic Ammonia to the liver:
-AST (aspartate aminotransfrase)
-Glutamate Dehydrogenase
-Glutamine Synthetase
3 steps/rxns involved in transporting NH3 to liver:
1. Make Glutamate by aminotransferase reactions
2. Make Glutamate via Glutamate dehydrogenase
3. Use Glutamate to make Glutamine
Amino acid(s) predominantly transported from:
-Brain -Muscle
-Intestine -Kidney
Brain: Gln
Muscle: Ala, Gln
Intestine: Ala
Kidney: Ala, Ser, Arg