Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Molecular and Cellular Princples of Medicine > Unit 6 - Amino Acid Degradation and the Urea Cycle > Flashcards

Unit 6 - Amino Acid Degradation and the Urea Cycle Flashcards

1
Q

what are the most abundant AA in serum? in cells?

A

serum: alanine
cells: glutamate and glutamine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

when is the AA gradient highest? (as in, what is most important for maintaining gradient?)

A

glutamate and glutamine (both are collecting sites for ammonia groups)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

in a free AA pool of 100 g, how much are glutamate and glutamine, and how much are essential?

A

50% are glutamate and glutamine

10% are essential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are essential AA? (PVT. TIM HALL)

A 
phenylalamine
valine
threonine
tryptophan
isoleucine
methionine
histidine
argininte (for growth)
lysine
leucine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what 2 AA get essential when other AA are missing?

A

cystine essential if methionine low

tyrosine essential if phenylalanine low

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is endogenous PRO associated with? how much is there?

A

skeleton and other supporting tissues, mostly collagen

-usually 6-7 kg

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is intracellular PRO like?

A

dynamic state with continual turnover

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are GI inputs to AA pool?

A

70-100 g dietary PRO

32-200 g endogenous PRO from sloshed off intestinal cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how many AA transport systems are there? what are the types? where else are there?

A

5 separate transporters, with overlapping specificity (high redundancy)

  • either Na+ or H+ symporters
  • same transporters are in the kidney
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is Hartnup’s disease? symptoms? treatment? diagnosis?

A

defect in transport system for neutral and aromatic AA from gut and renal tubules (esp. phe and trp)

  • have pellegra symptoms, so treat with niacin
  • will have high levels of neutral and aromatic AA in urine and feces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is cystinuria? symptoms? treatment? diagnosis?

A

defect in transport system for basic AA and cystine from gut and renal tubules

  • since cys is insoluble, it forms crystals to cause UTI and kidney stones
  • treat with fluids and penicillamine (makes cys soluble)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

in a 70 kg man, how much PRO is turned over a day, and how many undergo oxidative degredation?

A

400 g turnover

50 g oxidative degredation and replaced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how can protein breakdown be measured?

A

histidine residues of muscle PRO actomyosin are methylated posttranslationally
-when broken down, 3-methyl histidine is liverated and excreted into urine to be measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

when does catabolism of AA take place and what does this mean?

A

metabolic breakdown of AA to urea and CO2 is continuous drain that is reduced during starvation, but never turned fof

  • thus needs daily intake of A to replenish pools
  • -40-50 g/day
  • 12-20 g/day of N2 is excreted, mostly from urea
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

positive VS negative N2 balance

A

+ N2 losses are less than intake (growing children, recovering adults)
- N2 losses are more than intake (wasting, starvation); if prolonged, it is fatal if loss reaches 1/3rd total body PRO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what AA are plant PRO usually deficient in?

A

lysine
methionine
tryptophan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what are the 3 ways ammonia is removed?

A
  1. glutamate dehydrogenase
    - NH4+ + NADPH + H+ + a-KG glu + NADP+ + H2O
  2. glutamine synthase
    - glu + ATP + NH4 gln + ADP + Pi
  3. carbamoyl phosphate synthase I and II
    - NH4+ + CO2 + 2 ATP –> carbamoyl phosphate + 2 ADP + Pi
    - -I is in mitochondria for urea cycle
    - -II is in cytoplasm for pyrimidine nt biosynthesis (doesn’t use NH4+)
18
Q

what is the major carrier of NH4+ groups in the blood?

19
Q

what is the cofactor for all transaminations?

A

pyridoxal phosphate (vit B6)

20
Q

in what reactions does pyridoxine function as a cofactor?

A
  • transaminations (all of them)
  • decarboxylations
  • dehydrations of beta-hydroxyamino acids
  • racemizations of alpha-AA
  • removal of H2S from cysteine
21
Q

what are the free aldehyde VS aminated forms of B6?

A

pyridoxal phosphate = free aldehyde form
pyridoxamine phosphate = aminated form

these are easily interconvertable, and all transaminases have common enzyme mechanism with pyridoxal phosphate

22
Q

what 12 AA can be acted upon by pyridoxal phosphate transaminases?

A

remove alpha-AA groups

  • ala
  • arg
  • asp
  • asn
  • cys
  • ile
  • leu
  • lys
  • phe
  • tryp
  • tyr
  • val
23
Q

what AA are acted upon by asp. transaminase?

A

asp
ala
leu
tyr

24
Q

what AA can easily be made from pyruvate?

A

alanine (ala + a-KG pyruvate + glu)

  • efficient way to send 3 C back into liver to be converted into glucose, while disposing of NH4+ group (from glutamate)
  • so ala is one of most abundant AA in blood
25
what AA do most transaminases converge on?
glutamate - represents convergence of pathways and method of collecting amino groups in one AA - glu then serves as specific donor of amino groups for production of nitrogenous waste products - this is why glu is one of most abundant AA in cells
26
where is glutamate dehydrogenase located and why? cofactors? allosteric regulators?
in mitochondria (where a-KG is, and NADH is quickly used for E) - use either NADH or NADPH (normally high ratios of NADPH : NADP, and low NADH : NAD, so always cofactor available in either direction - activated by A/GDP, inhibited by A/GTP - -so lowering E charge of cell accelerates AA oxidation
27
where is glutamate mainly deaminated?
in the liver - if it needs energy, it makes NADH for e- transport - if it has E, it will make NADPH for biosynthetic reaction
28
what are AA oxidases?
both L and D occur in kidneys and liver | -enzymes use tightly bound flavins as cofactors to convert AA and water into corresponding a-keto acid and NH4+
29
what do dehydratases do? how does this work with serine? what do serine and threonine dehydratase use as cofactors?
directly deaminate - ser --> dehydrate, then hydrate --> pyruvate + NH3 - both use pyridoxal phosphate cofactor
30
what does homocysteine desulfhydrase do? what does it use as a cofactor? what happens to the product
HC + H2O --> --> H2S + NH3 + alpha-ketobutyrate - pyridoxal phosphate cofactor used to remove both NH4 + S - a-kb --> PCoA --> mmCoA --B12--> SCoA
31
why does the body convert free NH4+ to urea?
- constant excretion of NH4+ in urine would cause drastic changes in blood pH - urea is readily soluble (over 10 M) and easily excreted - -carries 2 ammonia groups - -non protonatable (10% solution pH 7.2) - -low reactivity (inert)
32
what is the stoichiometry for one turn of the urea cycle?
CO2 + NH4+ + 3 ATP + asp + 2 H2O urea + 2 ATP + 1 AMP + PPi + fumarate + 2 Pi
33
what urea cycle enzymes are in the mitochondria VS cytosol?
mitochondria: carbamoylphosphate synthetase, ornithine transcarbamoylase (steps 1 + 2) cytosol: argininosuccinate synthetase and lyase, arginase (steps 3 - 5)
34
how is urea cycle regulated? (PRO-free diet VS high-PRO diet)
PRO-free: urea excretion accounts for only 60% of total urinary nitrogen, compared to 80% of normal diet -levels of urea cycle enzymes decrease high-PRO: (also in starvation) gluconeogenesis from AA is high, so levels of urea cycle enzymes increase several fold (eventually subside if starving, b/c will use fat stores)
35
what is the most common genetic defect regarding the urea cycle?
OTC (ornithine transcarbamoylase) deficiency, b/c X-linked
36
for argininosuccinic aciduria... - sign - blood - urine - intelligence - enzyme defect
- ammonia intoxication - NH4 and argininosuccinic acid - arginosuccinic acid - normal - argininosuccinase
37
for hyperammoniemia... - sign - blood - urine - intelligence - enzyme defect
- ammonia intoxication - high NH4+ - N/A - normal intelligence - carbamoyl phosphate synthase
38
for arginiemia... - sign - blood - urine - intelligence - enzyme defect
- ammonia intoxication - high NH4 and arginine - arg, lys, orn - normal - arginase
39
for citrullinemia... - sign - blood - urine - intelligence - enzyme defect
- ammonia intoxication - high NH4+ and citrulline - citrulline - mental retardation - arginosuccinate synthetase
40
for hyper-ornithinemia... - sign - blood - urine - intelligence - enzyme defect
- ammonia intoxication - high NH4+, orotate, and ornithine - ornithine - normal - ornithine transcarbamylase
41
how is one treated if one has an inborn error of urea cycle metabolism?
low PRO diet supplemented with arginine or citrulline, since arginine becomes essential - also give sodium benzoate and sodium phenylacetate to bind up gly and gln to be excreted - ammonia levels are lowered to make more nonessential AA

Molecular and Cellular Princples of Medicine (42 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions