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HUNT241 > BIOC Lecture 7: Nitrogen II > Flashcards

BIOC Lecture 7: Nitrogen II Flashcards

1
Q

When does amino acid catabolism occur?

A
  • Excess protein is consumed
  • Insufficient dietary protein
  • Insufficient dietary energy
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2
Q

What happens in the situations where amino acid catabolism occurs?

A

Carbon skeletons enter the main energy pathways and amino groups are processed to urea in the liver for excretion

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3
Q

What do aminotransferase enzymes catalyse?

A

Transaminase reactions to transfer amines

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4
Q

What are aminotransferase enzymes sometimes called?

A

Transaminases

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5
Q

How do aminotransferases work?

A
  • Generate a keto acid from original AA
  • Pyridoxamine phosphate is now in N bound form
  • It then transfers N to another keto acid
  • New AA is formed
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6
Q

How do we make new AA’s?

A

An interchanging of N groups to other keto acids

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7
Q

What organ has the highest concentration of aminotransferase enzymes?

A

Liver

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8
Q

The receiving keto acid (the one that picks up the nitrogen) is generally one of what three keto acids?

A
  • α-Ketoglutarate
  • Oxaloacetate
  • Pyruvate
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9
Q

Where is Pyridoxamine phosphate derived from?

A

Vitamin B6

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10
Q

Where is Pyridoxamine phosphate found?

A

In the active center of the transaminase enzyme

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11
Q

What is the amino acid - keto acid pair for a-ketoglutarate?

A

Glutamate

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12
Q

What is the amino acid - keto acid pair for oxaloacetate?

A

Aspartate

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13
Q

What is the amino acid - keto acid pair for pyruvate?

A

Alanine

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14
Q

The deamination of most amino acids leads to the production of what?

A

Glutamate, aspartate or alanine

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15
Q

What AA is produced the most?

A

Glutamate as a-ketoglutarate is the most prominent

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16
Q

Aminotransferases are specific for the donor amino acid but mostly only accept?

A

a-ketoglutarate or oxaloacetate as the donor keto acid

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17
Q

Are aminotransferases reactions reversible?

A

Yes - dependent on concentration of substrates

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18
Q

What do aminotransferases require?

A

the co-enzyme pyridoxal-phosphate (derived from the vitamin B6) which is involved in transfer of the amino group

19
Q

What do aminotransferases allow for?

A

Generation of AA’s in short supply and safe removal of excess amino groups

20
Q

What can glutamate form?

A

Glutamine

21
Q

What is the glutamate-glutamine reaction catalysed by?

A

Glutamine synthetase (GS)

22
Q

What are glutamate and glutamine very important in?

A

Brining the nitrogen back from tissues

23
Q

Why is glutamine special?

A

Because it can carry two amine groups, therefore is very efficient in terms of transferring nitrogen

24
Q

How does the reaction of glutamate become glutamine?

A
  • Catalysed by GS
  • Fixes another ammonia group onto glutamate structure
  • Requires ATP
25
Q

When is the glutamate-glutamine reaction highly driven?

A

When there is high levels of ammonia - you don’t want free ammonia in the tissues

26
Q

What is the reaction that converts glutamine back to glutamate catalyzed by?

A

Glutaminase

27
Q

What happens in the reaction from glutamine to glutamate?

A
  • Glutamine loses an amino group
  • Release of ammonia
  • Ammonia is then used to make urea in the liver
28
Q

What is the loss of an amino group called?

A

Oxidative deamination

29
Q

What is the reaction of glutamate losing its amino group catalyzed by?

A

Glutamate dehydrogenase (GDH)

30
Q

Glutamate dehydrogenase is one of very few enzymes that can use…

A

NAD or NADP

31
Q

What ways can an amino group be removed?

A
  1. Transaminations
  2. Oxidative deamination
  3. Hydrolysis
32
Q

What is hydrolysis?

A

a molecule is split into two parts by the addition of a water molecule

33
Q

What is oxidative deamination?

A

the removal of an amino group from an amino acid, producing a keto acid and free ammonia

34
Q

Where are glutamine and alanine prominent?

A

In plasma

35
Q

How is Nitrogen transported in most tissues?

A

Most tissues in terms of nitrogen metabolism, the nitrogen for transfer to the liver will be contained in glutamate
- The glutamine synthetase reaction will occur to give you glutamine

36
Q

What happens to glutamine after it is produced in most tissues?

A

It will then go back to the liver

37
Q

What happens to glutamine in the liver?

A
  • It will undergo the glutaminase reaction which will release one ammonia group
  • Glutamate can also then undergo the glutamate dehydrogenase reaction to release its second ammonia
  • That ammonia will be used to make urea
38
Q

What is the glucose-alanine cycle?

A

a metabolic pathway that facilitates the exchange of metabolites between muscle and liver

39
Q

What does the glucose-alanine cycle allow?

A

The muscles to transfer the amino group from amino acid catabolism to the liver, where it can be safely converted into urea and excreted

40
Q

What is the main amino acid coming out of muscle?

A

Alanine

41
Q

Why does lots of alanine come out of the muscle?

A

Skeletal muscle relies a lot on glycolysis for energy, there is high levels of pyruvate being formed, therefore high levels of alanine being produced

42
Q

What happens in the muscle during the glucose-alanine cycle?

A
  • Amino acids undergo transamination to form glutamate
  • Glutamate donates its amino group to pyruvate forming alanine
  • Alanine is then transported to the liver
43
Q

What happens when alanine is transported to the liver?

A
  • Alanine undergoes transamination again to form glutamate and pyruvate.
  • Glutamate can then undergo oxidative deamination, releasing ammonia (NH₃) and regenerating α-ketoglutarate
  • ammonia is converted to urea and excreted
44
Q

What happens to the pyruvate generated by alanine in the glucose-alanine cycle?

A

used to synthesize glucose through gluconeogenesis.

HUNT241 (22 decks)

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