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CELL II > 🐟 Breakdown + Urea Formation > Flashcards

🐟 Breakdown + Urea Formation Flashcards

1
Q

Growth equation?

A

growth = synthesis - breakdown

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2
Q

What’s positive nitrogen balance?

A

protein/AA retained exceeds amount that’s broken down + excreted because:
-more of the AAs in the AA pool being converted into body protein + less body protein broken down or excreted

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3
Q

What’s negative nitrogen balance?

A

protein input is superseded by breakdown

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4
Q

Fate of ingested protein?

A

Broken down -> AAs to make new protein eg muscle fibres, enzymes (structural or functional)
-Proteins broken down, in nitrogen balance so breakdown = synthesis
Input is 100g a day + output 100g a day.

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5
Q

Where is nitrogen removed?

A

in liver via formation of urea

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6
Q

Causes of positive nitrogen balance?

A
  • Growth in small children
  • Pregnancy as they take in + lay down more protein
  • Exercise, tissue hypertrophy due to anabolic hormones
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7
Q

Cause of negative nitrogen balance?

A

protein deficiency

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8
Q

What’s negative N balance associated with + eg?

A

pathophysiology rather than physiology
eg wasting diseases, burns, trauma, response to catabolic hormones, or lack of anabolic ones (eg in diabetes) –> lose body protein mass

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9
Q

How protein metabolism deals with AA?

A
  • dealing with C skeleton + N

- breaking down of protein via peptidases —> constituent AAs

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10
Q

What’s C skeleton used for?

A

for energy metabolism or biosynthesis

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11
Q

Effect of N in body?

A

toxic (adverse effect on neuronal cells)

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12
Q

What happens if can’t produce urea?

A

die in infancy

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13
Q

How’s N from AA converted to urea?

A
  1. Transamination.
  2. Formation of ammonia.
  3. Formation of urea
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14
Q

What happens in transamination?

A

nitrogen part of α-amino group transferred to an α-keto acid to become a new AA (glutamate).

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15
Q

eg of α-keto acids?

A

α-ketoglutarate, pyruvate, oxaloacetate

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16
Q

Role of transaminases?

A

enzymes that transfer amino group from AA to α-keto acid

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17
Q

eg of transaminases?

A

alanine (ALT) + aspartate (AST)

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18
Q

Role of Alanine Transaminase (ALT)?

A

Alanine + α-Ketoglutarate ⇋ Pyruvate + Glutamate

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19
Q

Role of Aspartate Transaminase (AST)?

A

Aspartate + α-Ketoglutarate ⇋ Oxaloacetate (oxaloacetic acid) + Glutamate

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20
Q

Why oxidse α-ketoglutarate, pyruvate, oxaloacetate?

A
  • Make ATP in OP

- Converted to glucose (supplementing gluconeogenesis)

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21
Q

Role of Glutamate? .

A

a way the body can transport potentially toxic nitrogen

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22
Q

Where are transaminases?

A

in liver

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23
Q

What happens if high levels of AST + ALT in blood?

A

indicative of liver damage (shouldn’t be found in plasma)

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24
Q

Role of Alanine?

A

donates its α-amino group to α-ketoglutarate to give glutamate + pyruvate
reaction requires vit B6

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25
Q

What happens to glutamate?

A
  • release ammonia via glutamate dehydrogenase
  • yields back α-ketoglutarate
  • NAD used for degradation + NADPH for synthesis
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26
Q

Where does transamination occur?

A

in cytosol

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27
Q

Role of glutamate dehydrogenase

A

release ammonia from glutamate

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28
Q

Where’s glutamate dehydrogenase?

A

in the mitochondrial matrix

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29
Q

Which AA don’t undergo transamination?

A

threonine + lysine

30
Q

How’s 1g of urea formed from 3g of protein?

A

Urea contains 48% nitrogen by weight, protein contain 16%

31
Q

Why’s glutamate useful?

A

freely interchangeable with α-keto acids + ability to donate / accept ammonium ions

32
Q

Describe step 1 + 2 of urea formation?

A
  • transamination to glutamate

- oxidative deamination back to α-ketoglutarate

33
Q

Importance of converting AA into glutamate?

A

can be transported then re-converted back into something body can use for energy (or transamination again) while re-synthesising the ammonia which is fed into urea cycle

34
Q

How’s glutamine synthesised + equation?

A

glutamate formed from transamination combines with free ammonia (or NH4+) generated in tissues
Glutamate + NH4+ + ATP ⇋ Glutamine + ADP

35
Q

Role of glutamine synthase?

A

Glutamate + NH4+ + ATP ⇋ Glutamine + ADP

36
Q

Role of glutamine?

A

transports the potentially toxic N to the liver

37
Q

Where does glutamine synthesis occur?

A

in periphery

glutamine synthase widely distributed in blood vessels with a lot of protein breakdown including blood vessels of liver

38
Q

Removal of N summary?

A
  • transfer of amino groups to α-ketogluterate to form glutamate
  • glutamate oxidatively deaminized to α-ketogluterate (recycled for transamination again or used as energy source in TCA)
  • glutamate can accept more N forming glutamine
  • glutamine is main transporter of N
  • glutamine can donate nitrogen for biosynthesis of AAs, nucleotides, NAD+
39
Q

What’s the urea cycle?

A

metabolic pathway for excreting N

restricted in its distribution, being mostly in liver - not in muscle

40
Q

What does muscle produce?

A

substrates, but not enzymes

41
Q

Where does the urea cycle occur?

A

mitochondria + cytoplasm of hepatocytes

42
Q

Substrates of urea cycle?

A

bicarbonate, aspartate, ammonium ions

43
Q

Where’s ammonium ions in urea cycle from?

A

released from glutamine or glutamate produced in deamination

44
Q

Where’s bicarbonate in urea cycle from?

A

from CO2 as a byproduct of metabolising C skeleton

45
Q

Role of bicarbonate in urea cycle?

A

forms the CO2 needed

46
Q

Describe where chemical components of urea are from?

A

-2 N atoms:
donated from aspartate
from glutamine/glutamate.
-Carbon C=O from C skeleton via using CO2 that has been produced from its breakdown

47
Q

Describe how urea cycle + TCA cycle linked?

A
  • CO2 from bicarbonate reacts with NH4+ ions
  • forms carbamoyl phosphate
  • carbamoyl phosphate reacts with ornithine
  • forms citruline.
  • citruline reacts with aspartate
  • form argino-succinate.
  • argino-succinate metabolised to arginine + fumarate
  • enzyme arginase forms arginine
  • fumarate converted to malate
  • malate transported back into mitochondria
  • malate converted to oxaloacetate
  • process continues
  • starting point : aspartate
48
Q

How’s aspartate formed?

A

by transamination of α-amino acids, when reacting oxaloacetate with glutamate (an α-amino acid) in mitochondria

49
Q

How’s carbamoyl phosphate formed + where?

A

CO2 from bicarbonate + NH4+ using 2 ATP in mitochondria matrix

50
Q

How’s citruline formed?

A

carbamoyl phosphate + ornithine

51
Q

How’s argino-succinate formed?

A

citruline + aspartate

52
Q

What’s argino-succinate metabolised to + via which enzyme?

A

arginine + fumarate

via arginase

53
Q

How’s malate formed?

A

converted from fumarate

54
Q

How’s oxaloacetate formed?

A

converted from malate

55
Q

What’s oxaloacetate used for?

A
  • Gluconeogenesis (TCA Cycle)
  • Reaction with glutamate in mitochondria to form aspartate (in the transamination reaction) so recycled back into urea cycle
56
Q

Where does urea cycle occur?

A

predominantly in hepatocytes (+ kidneys)

57
Q

Why does the urea cycle occur?

A

to transform toxic by product of AA breakdown NH3, into less toxic form urea, that can be mobilised + transport to kidneys where excreted via urine

58
Q

Describe urea cycle

A
  • AA metabolism occurs
  • extra NH4+ + CO2 using 2 ATP -> carbamoyl phosphate
  • ornithine moves into matrix
  • ornithine + carbamoyl phosphate -> citrulline
  • citrulline moves to cytoplasm
  • citrulline + aspartate -> argino-succinate
  • argino-succinate metabolised -> arginine + fumarate
  • 2nd amino group that came from aspartate, ends up on the arginine.
  • C skeleton found on aspartate, ends up on fumarate (so C skeleton of the aspartate is fumarate)
  • fumarate -> malate
  • malate -> oxaloacetate
  • hydrolyse arginine using H2O (where the O comes from in urea)
  • urea is removed
  • ornithine is formed which is recycled into matrix
59
Q

Role of branched AAs + eg?

A

used for this energy

eg leucine, valine, isoleucine

60
Q

Role of branched AAs + eg?

A

used for energy

eg leucine, valine, isoleucine

61
Q

How are remaining AA dealt with?

A
  • N transferred to alanine via glutamate + pyruvate

- Circulating/intracellular glutamate made into glutamine

62
Q

What can muscle export?

A

alanine major export of muscle that is actively being broken down (due to exercise or starvation).

63
Q

Describe cycling of alanine?

A

-branched AAs taken: C skeleton used for energy production + NH4 converts pyruvate -> alanine
-alanine exported into blood + travels to liver
alanine -> glutamate via transamination (reacting with α-ketogluterate) also producing a pyruvate
-pyruvate enters gluconeogenic pathway -> glucose
-glucose transported in blood back to muscle for energy
-glutamate used with CO2 generated -> urea

64
Q

Role of the glucose-alanine cycle?

A

get rid of NH4+ from SM to transport to liver where that ammonium can be fed into the urea cycle

65
Q

Describe glucose-alanine cycle?

A
  • in SM, NH4+ formed from AA metabolism, combines with pyruvate -> alanine
  • alanine transported via bloodstream into hepatocytes
  • alanine -> pyruvate + glutamate (NH4+) via transamination with α-KG
  • NH4+ disposed into urea cycle
  • pyruvate -> glucose
  • glucose transported to SM via blood stream, so it’s recycled
  • glucose -> pyruvate in SM + reacts with NH4+
66
Q

Why’s it called glucose-alanine cycle?

A

utilize glucose to form pyruvate, which is used to attach NH4+ and form alanine

67
Q

Describe glutamine synthetize process?

A
  • uses ATP to attach NH4+ to glutamate -> glutamine.
  • glutamine can move into hepatocyte
  • broken down into glutamate, releasing NH4+
  • fed into urea cycle
68
Q

2 types of AA?

A

ketogenic AA + glucogenic AA

69
Q

What are ketogenic AAs?

A

form ketone bodies

70
Q

What are glucogenic AAs

A

used by liver to produce glucose

71
Q

Purpose of AA broken down being converted into intermedietes of TCA cycle?

A

can convert this back to glucose

CELL II (9 decks)

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