Unit 3 - VI. Amino Acid and Protein Metabolism Flashcards
1
Q
Indispensable/Essential amino acids
A
- 9 amino acid that we cannot synthesize so they must be supplied by the diet
2
Q
Dispensable/Nonessential amino acids
A
- 11 amino acids that can be synthesized in the body (from glucose, except tyrosine and cysteine) if an adequate amount is not present in the diet
3
Q
Conditionally indispensable amino acids
A
- arginine must be supplied by the diet under certain pathophysiological conditions (infants, children, disease states)
4
Q
Complete proteins
A
- derive from animal sources (meat, eggs ..)
- contain all essential amino acids
5
Q
Incomplete proteins
A
- derive from plant sources (fruits, vegetables, etc.)
- tend to be deficient in one or more essential amino acid
6
Q
Pepsin
A
- enzyme that begins digestion of proteins in the stomach
- endopeptidase (hydrolyzes interior peptide bonds)
- prefers peptide bonds adjacent to aromatic ring in side chain (phenylalanine and tyrosine)
7
Q
Enteropeptidase
A
- enzyme embedded in the luminal plasma membrane of intestinal epithelial cells (intestines)
- activates trypsin via hydrolysis of lysine peptide bond in trypsinogen
8
Q
Trypsin
A
- enzyme activated by eneteropeptidase
- found in the intestines
- Zymogen (inactive form) = trypsinogen
- preference: arginine and lysine (polar, basic a.a.)
- activates chymotrypsin and carboxypeptidase by clipping off peptide fragmetns from chymotrypsinogen and procarboxypeptidase
9
Q
Chymotrypsin
A
- enzyme activated by trypsin
- found in the intestines
- Zymogen = chymotrypsinogen
- endopeptidase
- preference: a.a. with aromatic ring in side chain (phenylalanine, tyrosine, and tryptophan)
10
Q
Carboxypeptidase
A
- enzyme activated by trypsin
- found in the intestines
- zymogen = procarboxypeptidase
- exopeptidase
- preference: attacks free carboxylic acid group end
11
Q
Aminopeptidase
A
- enzymes located in luminal membrane of small intestine epithelial cells
- exopeptidase
- preference: works from amino end
12
Q
Dipeptidase
A
- enzyme located on luminal membrane of small intestine epithelial cells
- final digestive process = hydrolyzes peptide bonds between dipeptide molecules
13
Q
Absorption and transport of amino acids
A
- both free a.a and small peptides can be absorbed in small intestine’s epithelial cells = enterocytes
- peptides are absorbed faster than free a.a. (and then they are broken down into free a.a.)
- majority absorbed in upper regions of small intestines
- transport via: sodium dependent/independent transport systems, carrier systems, and diffusion (nonpolar a.a.)
14
Q
Fate of Amino Acid once in enterocytes
A
- intestinal use of A.A. = synthesis of: digestive enzymes, hormones, apolipoproteins, urea, creatinine
- transport to portal circulation from basolateral membrane via diffusion or sodium independent or dependent transport
15
Q
Steps in degradation of A.A.
A
- occurs in liver cells
1. Convert A.A. to either alanine or glutamate
2. Remove amino group
3. Ammonium ion excreted in urine or synthesize urea (Urea cycle)
4. Degradation of alpha-keto acid (ketogenic/glucogenic) = ex: oxaloacetate, pyruvate