Test 4: Protein Digestion/Absorption & Metabolism, AA Metabolism
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51 terms
Terms | Definitions |
|---|---|
 amino acid metabolism | AA... anabolism: proteins & N-containing compounds catabolism: • amino group → urea ⠀1. Excretion by kidney (majority) ⠀2. Excretion by intestinal tract (trace) • carbon skeleton (α-keto acid) ⠀1. Energy + CO₂ ⠀2. Glucose &/or ketone bodies ⠀3. Fatty acids |
| overlapping amino acid specificity | • There are many ATP using amino acid transporters with overlapping amino acid specificity → amino acids may compete for absorption. • If an individual amino acid is consumed in great excess, this may inhibit the absorption of other amino acids. • 76% of the AA we absorb are in SMALL PEPTIDE FORM. • 34% are absorbed as FREE AA. |
| what are the two types of a.a. transporter dependency? | Na dependent (upper case letter) Na independent (lower case letter) |
| peptide transport | 1. Peptides are transported into the intestinal cell along with H+. 2. The H+ are pumped back into the intestinal lumen in exchange for Na+. 3. A NaK-ATPase pumps Na+ out of the cell in exchange for K+ across the basolateral membrane. Peptides are cleaved to individual AA. Absorbed AA are put into the blood by facilitated diffusion & active transport. ATP dependent |
| where are most AA catabolized? | • liver • uses carbon skeleton for ATP production • gets approximately 50% of its energy from AA catabolism |
| why must the nitrogen group be removed from AA? | So AA can be used for functions other than protein or nitrogen containing compound synthesis |
| how is the nitrogen group removed? | by either deamination or transamination which yields the AA's carbon skeleton |
| transamination | • the removal of a nitrogen group. the nitrogen group IS transferred to another compound. • alanine aminotransferase (ALT) & aspartate aminotransferase (AST), most active in the body • aminotransferases use vitamin B6/PLP as a coenzyme • alanine (PLP) ↔ pyruvate; α-ketoglutarate → [ALT] glutamate • α-ketoglutarate (PLP) ↔ glumate; asparate (AST) ↔ oxaloacetate |
| deamination | the removal of a nitrogen group. the amino group is NOT transferred to another compound. threonine dehydratase, loss of water requires pyridoxal phosphate (PLP) = Vit. B6 |
| what can the amino group be used for? | urea synthesis (urea cycle) |
| urea cycle | • in liver • requires E from 4 ATP • coupled w/ TCA & ETS • tissues send nitrogen as glutamine or alanine to liver • glucagon ↑ the mRNA for urea cycle enzymes, stimulate gluconeogenic things |
| urea & TCA | 1. NH3 (from glu or gln) → carbamoyl-PO4; requires 2 ATP 2. Carbamoyl-PO4 → Citrulline 3. Citrulline → Arginino-succinate; requires 2 ATP & Asp 4.1 Arginino-succinate → Arg → (Arginase) Urea & Ornithine 4.2 Arginino-succinate → Fumarate (TCA) → Oxaloacetate → [transamination] Asp |
| hisitidine | histamine (allergy) |
| tryptophan | serotonin → melatonin NAD |
| glutamine | urea pyrmidines purines |
| asparate | nitrogen carriers urea pyrimidines purines |
| what AAs make glutathione? | glutathione, a patent antioxidant glutamate, glycine, cysteine |
| arginine | makes compounds that stimulate cells 1. polyamines 2. creatinine 3. nitric oxide glutamate & proline |
| NO (nitric oxide) | free radical, produced by immune system. functions: 1. smooth muscle cell relaxation (blood pressure) 2. kills bacteria/worms. |
| tyrosine | 1. dopamine → norepinephrine →epinephrine 2. melanin 3. thyroid hormones |
| what must be true for an amino acid to be gluconeogenic? | the carbon skeleton must yield a TCA cycle intermediate |
| what are the gluconeogenic AA? | Ala, Gly, Cys Ser, Trp, Thr, Asp, Asn, Phe, Tyr, Val, Met, Arg, His, Pro, Glu, Gln, Ile No Leu or Lys |
| glucose-alanine cycle | 1. Ala removes ammonia from the muscle 2. Ala sent to the liver 3. Ala → pyruvate 4. pyruvate → glucose 5. Glucose into blood & then into muscle as G6P Ala helps deliver amino group to liver |
| intestinal cell amino acid metabolism | • SI has first access to AA. Glu is an energy component for SI, leaves glucose for RB, brain, peripheral tissues, & anaerobic conditions. • yields oxaloacetate, citrulline (for N removal), ATP, Ala • to portal blood: Ala, Pro, citrulline Look at p. 170 |
| liver AA metabolism what are some plasma proteins? | • the liver obtains hydrophilic substances plasma proteins: 1. albumin 2. retinal-binding protein 3. blood clotting proteins 4. globulins 5. acute phase proteins 6. heat shock proteins |
| albumin | transports fatty acids (which are hydrophobic) some vitamins some minerals (bind to prevent free radical production caused by free divalent cations) |
| retinal-binding protein | • specific cell receptor, so can control which tissues & amount taken • transports vitamin A |
| globulins | • lipoproteins for HDL, VLDL, LDL • for immunoglobulin synthesis • for transferrin synthesis for iron transport (can be regulated |
| acute phase proteins | • regulate systemic inflammation • C-reactive protein (CRP): inflammation marker, binds bac for immune cell target & destruction • fibronectin: clot formation, wound healing • metallothionin: binds minerals like Fe to decrease bacterial growth bc bac use Fe for growth |
| heat shock proteins | released under stress, function not clear |
| nitrogen containing nonproteins | derived from amino acids 1. glutathione 2. carnitine 3. carnosine 4. choline 5. purine/pyrimidine bases 6. creatine |
| glutathione | antioxidant liver aa transport Cys, Gly, Glu |
| carnitine | FA transport into mitochondria Lys, Met |
| creatine | muscle energy-P a good muscle maker Arg, Gly, Met |
| choline | phospholipid → 1. phosphotidylcholine 2. sphingomyelin 3. acetylcholine Ser |
| ascorbate | functions as a reducing agent in two reactions. In both reactions for carnitine synthesis, the vitamin is needed to reduce the iron atom that has been oxidized (Fe3+) in the reaction back to its reduced (Fe2+) state |
| purines & pyrimidines | pyrimdine: Glu, Asp purine: Glu, Asp, Gly |
| phenylalanine/tyrosine metabolism | 1. melanin 2. thyroid hormones 3. acetyl-CoA 4. dopamine → norepinephrine → * epinephrine * Methylation: methionine → S-adenosyl Met (SAM) → [methyltransferase] SAH Tyr is non-essential |
| how are epinephrine, norepinephrine, & dopamine related? | Catechol Epinephrine: CH₃ Norepi: No CH₃ Dopamine: No OH or CH₃ |
| tryptophan metabolism | serotonin → melatonin NAD → * NAD+ * Glutamine → Glutamate * ATP + H₂O → [NAD Synthase] AMP + PPi NAD+ → * NADP+ * NAD Kinase & ATP → ADP |
| methionine metabolism | SAM → * homocysteine * acceptor of methyl group → [methyl transferase] methylated acceptor methylcobalamin → [methionine synthetase, CH3 transfer] cobalamin 5-methyl tetrahydrofolate (THF) → [CH3 transfer] THF products: cystenine, taurine, glutamate |
| arginine metabolism | arginine → 1. + glycine → [transamidinase, kidney] ⠀guanidoacetate → * creatine ⠀⠀* Met → SAM → [methyltransferase, liver] SAH 2. [H₂O → Urea / Arginase] Ornithine → glutamate Histidine → [decarboxylase, - CO₂] histamine |
| branch chain amino acid metabolism | leucine → [BCAA aminotransferase (PLP)] Glutamine (NH₃ removal) [glutamine synthetase] ↔ [glutaminase] Alanine (NH₃ removal) products: ammonia or ammonium, α-ketoglutarate 1. important E source for muscle 2. stimulate PRO & glycogen synthesis (muscle recovery) BCAA = Ile, Val |
| what are the breakdown components of BCAA? | • α-ketoglutarate → [BCAA transaminase] glutamate → α-ketoglutarate • α-ketoglutarate → [BCAA transaminase] glutamate → * glutamine ⠀* ATP → [glutamine synthetase] ADP + Pi • Asp → fumarate → TCA & ETS cycle |
| what are areas of BCAA/AA metabolism? | Brain: Trp → serotonin, Tyr → dopamine → norepi Muscle: BCAA (Ile & Val) Kidney: Urea; AA catabolism puts stress on kidney; Gln & Ala excrete amino group here |
| ubiquitination & protein degradation | ubqituin conjugation: marks PRO for degradation w/ ubiquitin-activating enzyme & ubiquitin-ligase complex protein degradation: tagged goes inside a PROTEASOME, peptides & AA go into general AA pool → 1. Energy 2. PRO synthesis 3. further metabolism (e.g. neurotransmitters) |
| starvation | in liver: • ketogenesis: a way to deal w/ high FA (from adipose) oxidation to meet E needs • glycogen is depleted within 1st day adipose also sends FA to muscle |
| trauma/sepsis | sepsis = systemic infection Glutamine important E source for immune cells, will stimulate their function. |
| last page? | burns, sepsis, surgery, trauma → stimulation of the CNS → 1. antidiuretic hormone → water retention 2. catecholamines → ⠀• lipolysis ⠀• (-) insulin → hyperglycemia ⠀• (+) glucagon release → hyperglycemia & proteolysis 3. adrenocorticotropin hormne (ACTH) → (+) glucocorticoid release → gluconeogenesis → hyperglycemia |
| stomach | pepsinogen → [HCl or pepsin] pepsin |
| intestine | trypsinogen → [enteropeptidase or trypsin] trypsin |
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