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BCH3120 > Amino Acid Deamination and the Urea Cycle > Flashcards

Amino Acid Deamination and the Urea Cycle Flashcards

1
Q

Amino acids from degraded proteins can be used to

A

1) Form new proteins
2) Form glucose during starvation
3) Be used as a source of energy

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2
Q

Before entering TCA cycle/ketogenesis, amino acids need to be altered by

A

Removal of alpha-amino group of the amino acid

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3
Q

Steps to remove alpha-amino group

A
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4
Q

T or F: amino acids can be stocked (stored)

A

False they cant

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5
Q

1st step of removing alpha-amino group

A
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6
Q

Overall scheme of converting amino acids to be used in the urea cycle

A
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7
Q

1st step: transamination

A

Exchange an amino group with a carbonyl group (=O) by amino transferase/transaminase (rxn occurs between a keto acid and amino acid)

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8
Q

Transamination process

A
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9
Q

Transaminases are bound to

A

PLP coenzyme (contains pridoxine = vitamin B6)

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10
Q

Transamination (1st stage step 1)

A

Transfer alpha-amino group of amino acid onto transminase (amino group is carried by coenzyme PLP)
-Reaction is reversible

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11
Q

Transamination (1st stage step 2)

A

Transaminase-PLP complex is converted to pyridoxamine phosphate (PMP) which role is just to hold the amino group for the next reaction

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12
Q

Transamination (2nd stage Step 1)

A

Transfer amino group from pyridoxamine phosphate (PMP) complex to alpha-ketoglutarate, forming glutamate

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13
Q

Transmaination (2nd stage step 2)

A

Once amino group us transferred from PMP to alpha-ketoglutarate, transaminase-PLP complex is formed again and the process can restart

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14
Q

4 facts summarizing Transamination

A

1) PLP-dependent transamination reactions are reversible

2) Any amino acids can be used as substrate for the first stage (forward) reaction.

3) α-ketoglutarate is the major α-keto acid substrate in the second stage (reverse) reaction.

4) This reaction happens where the protein is degraded or when proteins are ingested/digested and reach the liver

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15
Q

Transport and Oxidative Deamination

A
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16
Q

4 facts of transferring ammonia to the liver

A

1) All organs degrade amino acids and produce ammonia (NH3).
2) Ammonia accumulation has toxic consequences
3) Liver is in charge of converting ammonia into urea
4) Ammonia is transported in the blood in the form of glutamine or alanine.

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17
Q

Name 3 ways ammonia is transported to the liver

A

1) Amino acids: Ingested proteins/cellular proteins

2) Alanine: Muscle

3) Glutamine: Most tissues including muscle

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18
Q

Production of alanine in the muscle steps (Glucose-Alanine Cycle (Cahill cycle))

A

1) Transaminase reaction using pyruvate generated by glycolysis as a terminal transamination substrate and is catalyzed by alanine transaminase
2) alpha-ketoglutarate is recycled and alanine is generated
3) Alanine will be transported to the liver and converted back to pyruvate

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19
Q

Reversal of alanine and alpha-ketoglutarate reaction is

A

yielding pyruvate and glutamate

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20
Q

What is the alpha-ketoacid corresponding to alanine

A

Pyruvate

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21
Q

Glucose-Alanine Cycle (Cahill cycle) in the liver

A

NOTE this cycle is like the Cori Cycle

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22
Q

Yield of glucose alanine cycle in comparison to cori cycle

A
23
Q

Transport of ammonia to the liver using glutamine

A

1) Glutamate through transmaination is converted to glutamine by glutamine synthetase (invest 1 ATP)
2) Glutamine is carried to liver to be converted back to glutamate
3) In liver glutamine is converted into glutamate by mitochondrial glutaminase
4) Ammonia produced will enter the Urea cycle

24
Q

Oxidative deamination of glutamate in the liver

A

Glutamate dehydrogenase catalyzes the deamination which occurs in the mitochondria to produce NH4+ (ammonia) which enters the urea cycle
-Reaction is reversible
-One NADH is generated (1NADPH is used in the reverse reaction)

25
Q

After oxidative deamination of glutamate, what is the next step

A

Urea cycle

26
Q

After oxidative deamination of glutamate, what is the next step

A

Urea cycle/Krebs-Henseleit Urea cycle

27
Q

The urea cycle starts and ends with

A

Ornithine

28
Q

Ornithine

A

A carrier on which are assembled the carbon and nitrogen atoms that will constitute urea (carries urea)

29
Q

Urea Cycle Overview

A
30
Q

Urea Cycle Mitochondrial Phase

A
31
Q

Urea Cycle Mitochondrial Phase Reaction 1

A

Condensation of bixarbonate (HCO3-) with NH3 catalyzed by carbamoyl phosphate synthetase 1(CPS1)
-Requires 2 ATP

32
Q

Urea Cycle Mitochondrial Phase Reaction 2

A

Ornithine is converted to citrulline catalyzed by ornithine transcarbamylase

33
Q

Citrulline needs to move out of the mitochondrial matrix to the cytoplasm, so it uses

A

ORC1 (Ornithine Carrier 1) = bidirectional

34
Q

Ornithine carrier 1 (ORC1) transports

A

1) Ornithine
2) Lysine
3) Arginine
4) Citrulline

35
Q

Urea cycle Cystolic Phase

A
36
Q

Reaction 3 Urea cycle (cystolic phase)

A
37
Q

Where does the aspartate come from in this photo

A

Malate-aspartate shuttle (link between krebs and urea cycle)

38
Q

Reaction 4 Urea cycle (Cystolic Phase)

A

Argininosuccinase

39
Q

Reaction 5 Urea cycle (Cystolic Phase)

A

Arginase

40
Q

Krebs Bicycle

A
41
Q

Urea cycle is regulated at 2 levels

A

1)Long term regulation through rate of gene synthesis - All 4 enzymes of urea cycle and CPS1 are synthesized at higher rates under starving conditions because protein is a source of fuel and production of ammonia has increased
2)Short term regulation through allosteric control

42
Q

T or F: Nitrogen flux varies based on your diet

A

T

43
Q

2 types of short term regulation for allosteric control of urea cycle

A

1) N-acetylglutamate is an allosteric activator of carbamoyl phosphate synthetase I (CPS1) synthesized using glutamate and acetyl-CoA and is catalyzed by N-acetylglutamate synthase (requires a high concentration of glutamate)
2) Arginine is an allosteric activator of N-acetylglutamate synthase.

44
Q

regulating pathway flux by N-acetylglutamate

A

Lots of arginine means a lot of glutamate means a lot of ammonia

45
Q

Urea cycle is confined to the

A

liver

46
Q

T or F: The above raction soccur only in the mitochondria (ignore)

A

False, mitochondria and cytosol

47
Q

Ornithine transport from cytosol to mitochondria is carried out by

A

translocase

48
Q

Amino groups of urea are derived from [blanks] while the carbon atom is derived from [blank]

A

NH3 and asparate…..CO2

49
Q

T or F: Carbon skeleton products can be used in gluconeogeneis

A

True

50
Q

In a study conducted some years ago, cats were fasted overnight then given a single meal complete in all amino acids except arginine.
Within 2 hours, blood ammonia levels increased from a normal level of 18 mg/L to 140 mg/L, and the cats showed the clinical symptoms of ammonia toxicity.
A control group fed a complete amino acid diet or an amino acid diet in which arginine was replaced by ornithine showed no unusual clinical symptoms.
N.B. Cats cant synthesize arginine. They need to get it through their diet.

a) What was the role of fasting in the experiment?
b) What caused the ammonia levels to rise in the experimental group?
c) Why did the absence of arginine lead to ammonia toxicity?
d) Why can ornithine be substituted for arginine?

A

a) Want the cat to solely rely on the amino acid as a form of energy (no glycogen or glucose left so they rely only on amino acid) = lower blood glucose and catabolism of AA
b) They cant get rid of thee high levels of ammonia (cant break it down) = see image goes into c)
c) Lack of arginine slowed conversion of ammonia into urea because cats synthesize ornithine solely from arginine, so there are insufficient amounts of ornithine to feed the urea cycle
d) Ornithine can be substituted because it is an intermediate of the urea cycle

51
Q

Most amino acids can be converted to one of 7 metabolic intermediates

A
51
Q

Most amino acids can be converted to one of 7 metabolic intermediates

A
52
Q

Glucogenic AA can be converted to

A

pyruvate, α-ketoglutarate, succinyl-CoA or oxaloacetate and are therefore, glucose precursors.

53
Q

Ketogenic AA can be converted to

A

acetyl-CoA or acetoacetate to create ketone bodies (Leucine and Lysine)

BCH3120 (36 decks)

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