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Biochemistry > Unit 3 - VI. Amino Acid and Protein Metabolism > Flashcards

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
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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
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3
Q

Conditionally indispensable amino acids

A
  • arginine must be supplied by the diet under certain pathophysiological conditions (infants, children, disease states)
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4
Q

Complete proteins

A
  • derive from animal sources (meat, eggs ..)

- contain all essential amino acids

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5
Q

Incomplete proteins

A
  • derive from plant sources (fruits, vegetables, etc.)

- tend to be deficient in one or more essential amino acid

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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)
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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
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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
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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)
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10
Q

Carboxypeptidase

A
  • enzyme activated by trypsin
  • found in the intestines
  • zymogen = procarboxypeptidase
  • exopeptidase
  • preference: attacks free carboxylic acid group end
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11
Q

Aminopeptidase

A
  • enzymes located in luminal membrane of small intestine epithelial cells
  • exopeptidase
  • preference: works from amino end
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12
Q

Dipeptidase

A
  • enzyme located on luminal membrane of small intestine epithelial cells
  • final digestive process = hydrolyzes peptide bonds between dipeptide molecules
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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.)
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14
Q

Fate of Amino Acid once in enterocytes

A
  1. intestinal use of A.A. = synthesis of: digestive enzymes, hormones, apolipoproteins, urea, creatinine
  2. transport to portal circulation from basolateral membrane via diffusion or sodium independent or dependent transport
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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
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16
Q
  1. Transamination
A
  • converts A.A. to either alanine or glutamate by transferring the alpha amine group with an alpha-keto group
17
Q

AST

  • tissue sources
  • diagnostic significance
A
  • Aspartate Aminotransferase
  • Tissue Sources: cardiac, liver, skeletal muscle, kidney, pancreas, RBC (no very specific)
  • diagnostic significance: measured in conjunction with other enzymes can help in diagnosis of: AMI (not current), heptocellular disorders, skeletal muscle disease, hepatitis, and cirrhosis
18
Q

ALT

A
  • Alanine Aminotransferase
  • tissue source: mainly liver (very specific)
  • diagnostic significance: heptocellular disorders, hepatic obstructive disorders, acute inflammatory conditions of liver
19
Q
  1. Deamination

- fate of its product

A
  • the removal of the amine group from glutamate (the only a.a in mammalian tissue to undergo deamination)
  • it is removed as ammonium ion
  • occurs primarily in liver and kidney mitochondria
  • Products: 2-Oxoglutarate + NADH + H + NH4
  • Fate if ammonium ion = urea via the urea cycle and then excreted
20
Q
  1. The urea cycle
A
  • starts in the mitochondrion and moves into the cytosol
  • it is the major nitrogenous excretory pathway to make urea for exiting the body via urine
  • one nitrogen atom comes from ammonium ion product of deamination, the other comes from the nitrogen in aspartate, and the carbon atom is from carbon dioxide = urea
  • ornithine is an amino acid that humans do not have a codon for but is regenerated in the urea cycle
21
Q

Carbamyl Phosphate Synthetase I Deficiency

A
  • this deficiency is an autosomal recessive inborn error of metabolism
  • this enzyme is important at the start of the urea cycle
  • results in nitrogen not going into urea cycle enough
  • Lab tests: high plasma ammonia, low plasma urea, and low plasma citrulline and argninine.
22
Q
  1. Fate of alpha-keto acids
A
  • alpha-keto acids are formed during the transamination of amino acids which can be further degraded to one of 7 products:
    1. alpha - ketoglutarate
    2. fumarate
    3. oxaloacetate
    4. pyruvate
    5. succinyl CoA
    6. acetoacetyl CoA
    7. acetyl CoA
  • The first five are glucogenic = means they can be converted to glucose via gluconeogenesis
  • The last two are ketogenic = means they can give rise to ketone bodies
23
Q

Regulation of protein metabolism

A
  • anabolic hormones
  • catabolic hormones
  • cytokines
24
Q

Anabolic hormones

A
  • uses energy
    1. Growth hormone = increases in children, especially during growth spurt
    2. Insulin = phosphorylates initiation factor eIF2 -> delivers initiator methionyl-tRNA to ribosomal subunit = stimulates protein synthesis
    3. Testosterone = promotes protein synthesis, esp. in muscles
25
Q

Catabolic hormones

A
  • break down to release energy
    1. Cortiol and Glucagon = stress hormones that are elevated in blood stream during infection or after injury. They increase protein degradation, promote conversion of a.a. into glucose via GNG, and inhibit muscle protein synthesis
26
Q

Cytokines

A
  • peptides produced by macrophages in response to injury/inflammation
  • increase protein catabolism
27
Q

Fed state

A
  • food intake leads to increase protein synthesis in liver and decrease protein degradation.
28
Q

Brief fasting (between meals)

A
  • increase protein degradation

- amino acids from muscles used to maintain protein synthesis

29
Q

Starvation

A
  • increase degradation of muscle protein
  • insulin decrease leads to adaptation where lipolysis is increased and liver synthesizes ketone bodies from the fatty acids to provide energy to brain
  • adaptation decreases protein degradation
30
Q

Malnutrition

A
  • decrease in protein synthesis of certain proteins (ex: antibodies) to direct synthesis of more essential protein = decrease resistance to infection
31
Q

Injury and disease

A
  • increase in protein degradation due to insulin blocking adaptation

Biochemistry (14 decks)

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