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13 biochemistry > L18 - liver in metabolism - nitrogen > Flashcards

L18 - liver in metabolism - nitrogen Flashcards

1
Q

what is AA pool

A

free AAs in low concs in cells/bloodstream

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2
Q

what is protein turnover

A

proteins are continuously degraded to AA and resynthesized

they have differing half lives

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3
Q

what is average protein turnover

A

300 - 400g a day

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4
Q

can protein be stored?

A

no

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5
Q

can plants and microorganisms synthesise all AAs?

A

yes

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6
Q

what is nitrogen balance

A

N intake = N excretion

protein synthesis = protein degradation

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7
Q

what is positive nitrogen balance

A

N intake > N excretion

protein synthesis exceeds rate of breakdown

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8
Q

when can +ve nitrogen balance occur

A

normal growth
pregnancy
after serious illness (rebuilding proteins)

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9
Q

what is -ve nitrogen balance

A

N intake < N excretion

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10
Q

when can -ve nitrogen balance occur

A

starvation
during serious illness
late stage of some cancers

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11
Q

what can happen if -ve nitrogen balance is prolonged?

A

irreversible muscle wastage - death

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12
Q

what process degrades cellular proteins

A

ubiquitin

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13
Q

what process degrades exogenous proteins

A

endocytosis / phagocytosis

then fused with lysosomes

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14
Q

what hormone can increase rate of protein degradation in muscle

A

cortisol

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15
Q

what is oxidative deamination

A

removal of amino group on amino acid

and removal of 2H

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16
Q

where does oxidative deamination occur

A

liver

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17
Q

what catalyses oxidative deamination

A

glutamate dehydrogenase

18
Q

what is transamination

A

combining an AA and a keto acid causes the amino group to swap

19
Q

where does transamination occur

A

liver / muscle

20
Q

what is the only AA that can undergo oxidative deamination

A

glutamate

21
Q

how is glutamate formed before undergoing oxidative transamination

A

transamination of any AA and 2-oxo-glutarate forms glutamate

22
Q

what enzyme catalyses transamination reactions

A

aminotransferases

23
Q

what is needed in an aminotransferase to carry out its function

A

pyridoxal phosphate prosthetic group (carries amino group)

24
Q

what is reduced during oxidative phosphorylation

A

NADP

25
Q

what happens to AAs after transamination

A

become oxo acids which can be:

  1. metabolised by TCA cycle
  2. converted back to glucose (starvation)
26
Q

what oxo acids can be converted back to glucose and where

A

13 glucogenic ones

in liver

27
Q

define glucogenic

A

AAs that can be converted into glucose after degradation

28
Q

define ketogenic

A

AAs that cannot be converted to glucose after degradation

29
Q

examples of ketogenic AAs

A

leucine

lysine

30
Q

what can leucine and lysine be degraded to

A

acetyl CoA

31
Q

name some AAs considered ketogenic and glucogenic

A

phenylalanine
tyrosine
tryptophan
isoleucine

32
Q

what does it mean if an AA is considered glucogenic and ketogenic

A

part of its structure can be converted to glucose

33
Q

roles of liver in N metabolism

A
  1. removal of AA etc from blood
  2. synthesis of
    • haem
    • plasma proteins (albumin)
    • purines and pyrimidines
  3. transdeamination
  4. ornithine cycle (NH3 to urea)
34
Q

how is NH2 transported in blood and why

A

as glutamine/glutamate because its toxic

35
Q

where is urea produced

A

liver only

36
Q

how many NH2 groups can glutamine carry

A

2

37
Q

function of alanine in N excretion

A

provides NH4+ to urea cycle (after being transdeaminated to glutamate)

38
Q

function of aspartate in N excretion

A

provides 2nd NH4+ to urea

39
Q

what are the end products of N metabolism

A

urea
creatinine
uric acid
NH4+

40
Q

where does uric acid come from

A

DNA & RNA breakdown

41
Q

what is hyperammonaemia

A

impaired conversion of NH3 to urea - liver failure

13 biochemistry (16 decks)

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