Protein Metabolism: Oxidation and Urea Flashcards Preview

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Flashcards in Protein Metabolism: Oxidation and Urea Deck (40):
1

what are the 4 fates of dietary amino acids?

  • protein synthesis
  • energy production (CAC)
  • biosynthesis
  • urea excretion

2

what are the 3 divisions of protein oxidation?

  • normal synthesis and degradation
  • protein rich diet
  • starvation or diabetes mellitus

3

draw out the 4 fates of dietary amino acids

4

dietary protein stimulates the release of ___ from gastric mucosa in the stomach. This then stimulates the release of ___ from parietal cells, and ___ from chief cells.

  • gastrin
  • HCl
  • pepsinogen

5

what does pepsinogen/pepsin do?

  • it is a protease
  • hydrolyzes phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr) polypeptide bonds
  • **pepsinogen changes to it's active form (pepsin) in the stomach due to low pH (1.0-2.5) 

6

what does secretin do?

stimulates the release of bicarbonate from the pancreas

7

what does cholecystokinin do?

stimulates zymogen release from the pancreas

8

what are the 3 main pancreatic zymogens (proteases) released from the pancreas, and what are they precursors to?

  • trypsinogen → trypsin
  • chymotrypsinogen → chymotrypsin
  • procarboxypeptidase A and B → carboxypeptidase A and B
  • important to remember that zymogens are enzyme precursors that require a biochemical change (usually cleavage) to become active

9

where does amino group catabolism occur?

hepatocytes in the liver

10

what is the basic strategy of amino group catabolism in the liver?

separate the amine group, leave the carbon chain

11

what is the source of most amino acids?

diet

12

what are the 4 metabolically important amino acids for amino group catabolism? what do they do?

  • glutamate
  • glutamine
  • aspartate
  • alanine
  • amine group carriers; precursors and common metabolites; entry and exit molecules from the CAC

13

describe the functions of glutamate, glutamine, and alanine in amino group catabolism

14

ammonia is toxic. what are some effects of too much ammonia?

  • reduction in learning
  • reduction in movement
  • hyperacusis
  • imbalance
  • gait ataxia
  • seizures
  • loss of consciousness
  • death

15

how does ammonia prevent GABA inhibition?

  • crosses blood brain barrier and disrupts astrocyte K+ uptake
  • high extracellular K+ will prevent GABA inhibition
  • causes neuronal hyperactivity, seizures, oxidative stress, and death

16

how is ammonia toxicity controlled?

amine groups are stabilized as urea (vertebrates) or uric acid (birds and reptiles) for excretion

17

what are the 2 major amino acid catabolism reactions?

  • transaminase reactions
  • one-carbon transfers

18

describe transaminase reactions

  • transfer amine groups
  • PLP = pyroxidal phosphate
    • common coenzyme
    • carrier of amino groups

19

how is glutamate transported to the liver via glutamine transport in the blood?

  • glutamine is transported to the liver
  • glutamine is non-toxic
  • most cells have glutamine synthetase
  • common synthetic precursor

20

how it glutamine transported to the liver via the glucose-alanine cycle?

  • cycle allows proteins to function as energy sources
  • cycle occurs in anaerobic states
  • G-A cycle and Cori cycle occur simultaneously

21

how is intracellular ammonia buffered?

by converting glutamate to glutamine

22

what does the urea cycle excrete?

liver nitrogen

23

where does the urea cycle occur

hepatocytes in the liver

24

describe the 4 major steps of the urea cycle

  • forms urea, a stable amine-rich molecule that can safely excrete nitrogen
  • 4 steps, 5 structural changes
  • requires enzymes within the mitochondria and cytoplasm
  • ATP-dependent
  • ornithine is absolutely essential 

25

what are the 2 feeder molecules for the urea cycle?

carbamoyl phosphate and aspartate

26

draw out the urea cycle beginning with carbamoyl phosphate and aspartate

remember, ornithine is super important

27

describe the percentages of NH3 that enter the liver, and the percentages of urea that is excreted as urine vs. ammonia excreted in fecal matter

28

what are the 2 levels of urea cycle regulation?

allosteric N-acetylglutamate regulation

  • increased synthesis of:
    • ornithine transcarbomoylase
    • arginosuccinate synthetase
    • arginosuccinase
    • arginase
  • allosteric carbamoyl phosphate synthetase I regulation
    • responsible for production of carbamoyl phosphate

29

describe allosteric n-acetylglutamate regulation

30

describe how the citric acid cycle and urea cycle can be linked

  • dependent upon mitochondrial transporters
  • aspartate nitrogen donation is important
    • amino acid synthesis
    • urea cycle

31

what are the energy substrates produced by amino acid catabolism?

THESE ARE ALL REVERSIBLE

  • glucogenic - amino acids that can be converted to glucose
  • ketogenic - amino acids that can be converted to ketone bodies
  • transaminase and one-carbon transfer reactions
  • fuels 10-15% of cellular energy production

*don't need to know which amino acids are keto- and gluco-genic

32

name the nonessential amino acids

  • glutamate
  • aspartate
  • alanine
  • asparagine
  • serine

33

what are the conditionally essential amino acids?

  • glutamine
  • glycine
  • arginine
  • proline
  • tyrosine
  • cysteine

34

what are the essential amino acids?

  • phenylalanine
  • valine
  • threonine
  • tryptophan
  • isoleucine
  • methionine
  • histidine
  • leucine
  • lysine

35

which 6 amino acids are degraded to pyruvate?

  • tryptophan
  • alanine
  • cysteine
  • serine
  • glycine
  • threonine
  • they are degraded to pyruvate, which then feeds into the CAC or gluconeogenesis

36

which 7 amino acids are degraded to acetyl-coa?

  • tryptophan
  • lysine
  • phenylalanine
  • tyrosine
  • leucine
  • isoleucine
  • threonine
  • acetyl-coa feeds directly into the CAC

37

what are 3 important one-carbon transfer reaction cofactors?

  1. biotin
  2. s-adenosylmethionine
  3. tetrahydrofolate
  • one-carbon group donors or recipients
  • often methyl groups
  • vitamins

38

which 5 amino acids are degraded to alpha-ketoglutarate?

  • glutamate
  • glutamine
  • proline
  • arginine
  • histidine
  • alpha-ketoglutarate is part of the CAC
  • less exergonic because we don't produce an NADH from the isocitrate -> alpha-ketoglutarate
  • remember that whenever you have glutamate, you have alpha-ketoglutarate

39

which 4 amino acids are degraded to succinyl-coa?

  • methionine
  • isoleucine
  • valine
  • threonine
  • succinyl-coa is part of the CAC
  • less exergonic because we don't produce NADH from prior 2 steps in CAC

40

which 2 amino acids are degraded to oxaloacetate?

  • asparagine
  • aspartate
  • oxaloacetate is part of the CAC
  • least exergonic because it it towards the end of the CAC, so we are not producing any of the NADHs, FADH2s, or GTPs, from previous steps