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Nutr 301 > Protein metabolism > Flashcards

Protein metabolism Flashcards

1
Q

how does AA catabolism lead to urea production

A
  • deamination produces NH3
  • liver converts NH3 to urea via urea cycle
  • urea excreted in urine
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2
Q

how does AA remodeling/catabolism link to glucose synthesis

A

gluconeogenesis to maintain blood glucose levels during fasting
- following deamination the carbon skeletons are converted to TCA intermediates (oxaloacetate/pyruvate/a-ketoglutarate) = used as precursors for gluconeogenesis in the liver
- key gluconeogenic AA contribute

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3
Q

what AAs contribute to production of a-ketoglutarate

A

Arg, His, Gln, Pro

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4
Q

what AAs contribute to production of pyruvate

A

Ser, Ala, Cys, Thr

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5
Q

how does AA remodeling/catabolism link to FA synthesis

A

AA converted into long-term fat storage while in a fed state
- following deamination the carbon skeletons are converted into Acetyl-CoA = used as precursors for lipogenesis in the liver
- key ketogenic AA contribute

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6
Q

what AAs contribute to production of Aectyl-CoA

A

Leu, Lys, Tyr, Trp, Thr, Ile

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7
Q

what mechanisms are involved in protein synthesis

A

transcription & translation

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8
Q

what mechanisms are involved in protein breakdown

A

UPS, ALP, ERAD, Ca/calpain dependent system

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9
Q

what are the major routes of nitrogen movement

A
  • ingested and endogenous proteins from dietary N + body proteins/peptides
  • free AA from digested proteins + body protein/peptide degradation
  • body proteins/peptides from free AA protein synthesis
  • urea from free AA + NH3 breakdown
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10
Q

what are the 3 major metabolic fates of AA in the body

A
  1. used for protein synthesis
  2. used as precursor for synthesis of non-proteins nitrogenous molecules
  3. catabolism with excretion of N + use of C-chains as energy substrates
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11
Q

in the liver, what pathways of AA metabolism are turned on in a fed state?

A
  • protein synthesis
  • deamination + transamination
  • conversion to energy (AAs to glucose via gluconeogenesis + to lipids via lipogenesis) for storage or use
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12
Q

in the liver, what pathways of AA metabolism are turned on in a fasted state?

A
  • gluconeogenesis
  • ketogenesis
  • urea cycle activity
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13
Q

in the liver, what pathways of AA metabolism are turned off in a fed state?

A
  • gluconeogenesis
  • ketogenesis (due to insulin increase = glucose utilization)
  • urea cycle activity (bc of positive N balance)
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14
Q

in the liver, what pathways of AA metabolism are turned off in a fasted state?

A
  • protein synthesis
  • lipogenesis
  • amino acid uptake
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15
Q

How does the TCA cycle in the liver differ in fed vs fasted state

A

fed: utilizes C from AA + other substrates to contribute to lipogenesis and protein synthesis
fasted: utilizes C from deaminated AA to produce energy/ATP and substrates for gluconeogenesis

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16
Q

what is transamination + what is it catalyzed by

A

transfer of an amino group to an a-keto acid to form a new amino acid
- catalyzed by aminotransferases (PLP dependent)

17
Q

which AA do not directly participate in transamination? which actively do?

A

do not: Lys, Thr, Pro, Trp, Arg
do: Ala, Asp, Glu, Tyr, Ser, Val, Ile, Leu

18
Q

what is the widely used acceptor of amino groups + what AA are the a-amino groups of AAs funneled through during AA catabolism

A

acceptor = a-ketoglutarate
funneled through Glu
(eg. Glu + pyruvate <–> a-ketoglutarate + alanine)

19
Q

what are ALT and AST + their function

A

catalyze transamination reaction, allow for movement of amino groups
ALT: alanine aminotransferase cytoplasmic enzyme, highest concentration in liver
AST: aspartate aminotransferase, highest concentration in heart

20
Q

what is the AST:ALT ratio for liver disease? exceptions?

A

ALT levels high due to liver more permiable = low AST:ALT ratio (<1)
exceptions: decreased serum ALT activity from low B6 (alcholoic hep/cirrhosis/early acute hep/bile duct obstruction) = high AST:ALT ration (>2)

21
Q

what is deamination + where it occurs + its purpose

A
  • liberation of free ammonia from the AA couple with oxidation
  • occurs in the mitochondria of liver/kidney
  • provides NH3 for urea synthesis + a-keto acids for various reactions
22
Q

what is the impact of a high protein diet on the urea cycle

A
  • capacity can increase
  • high rate of oxidative deamination = enzymes are highly inducible
  • long term = enzymes will be more abundant
23
Q

what is the impact of starvation on the urea cycle

A

initially = will increase activity due to breaking down AA for energy
later = lacking essential AA to make the enzymes you need to break AA down + can’t excrete urea = ammonia will build up

24
Q

what is the rate limiting step of the urea cycle

A

conversion of CO2 + NH4 to carbamoyl phosphate via carbamoyl phosphate synthetase I
- allosteric activator of carbamoyl phosphate synthetase I is NAG > Arg + Glu stimulate NAG synthesis

25
Q

how is the Urea cycle coupled to the TCA cycle

A
  • breaking down AA via TCA = energy and substrates produced
    urea cycle requires energy and substrates produced by the AA breakdown
  • oxaloacetate (from TCA) can be converted to Asp to feed into urea cycle via transamination
26
Q

what is the role of gluconeogenic AA + some examples

A

carbon skeletons convert to/make new pyruvate or CAC intermediates
- Ala, Gly, Cys, Ser, Asp, Glu, Gln, Arg, Met, Val, His, Pro

27
Q

what is the role of ketogenic AA + examples

A

carbon skeletons provide acetyl CoA for the CAC (if oxaloacetate is high enough for it to enter) –> do not produce glucose
- Lys, Leu

28
Q

what is the glucose alanine cycle?

A
  • muscle provides alanine (via transamination) to the liver
  • liver uses alanine for gluconeogenesis (easy to convert it to pyruvate)
29
Q

what are 3 ways protein structure can cause disease

A
  1. malformed protein/abnormal genes
  2. abnormal processing during synthesis
  3. inability or overdrive of protein turnover/degradation
30
Q

what are the regulation point of protein synthesis

A
  • DNA transcription*
  • RNA processing
  • mRNA stability
  • mRNA translation*
  • post-translational modifications/folding
31
Q

what is the importance of protein degradation

A
  • regulating protein abundance (ie. once enzyme use is done, we want to get rid of them)
  • eliminating abnormal proteins (ie. miscoded or damaged proteins)
32
Q

what are major protein degradation pathways

A
  • ubiquitin-proteasome system (UPS)
  • ER-associated degradation (ERAD)
  • autophagy lysosomal pathway (ALP)
  • calcium/calpain dependant system
33
Q

describe the UPS system + diseases associated with its malfunctioning

A

step 1: polyubiquitination = ubiquitins attach to substrate (abnormal/damaged protein) *requires energy
step 2: proteolysis in 26s proteasome = ubiquinated proteins are degraded
malfunction: Alzheimer’s (Ub proteolysis is blocked) + CVD (positive association with inflammatory cytokines)

34
Q

describe the ALP pathway + where does it occur

A

step 1: sequestration = membrane nucleation of substrates
step 2: fusion = lysosome fuses with phagosome
step 3: acidification & digestion = lysosome degrades contents and detaches
low activity in muscle, high activity in liver

Nutr 301 (9 decks)

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