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FLC > Protein Breakdown & Urea Formation > Flashcards

Protein Breakdown & Urea Formation Flashcards

1
Q

Quantitatively how does growth occur?

A

Growth = Synthesis - Breakdown

We synthesise and breakdown an equal amount of protein everyday

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2
Q

How are Proteins stored?

A

They don’t have any specific store as they are either structural or functional
Excess proteins are broken down and excreted

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3
Q

How is Nitrogen transferred into Urea?

A
  1. transamination
  2. NH3 formation
  3. Urea formation
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4
Q

Give examples α-ketoacids

A
  • α-ketogluterate
  • oxaloacetate
  • pyruvate
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5
Q

What is the fate of the NH3 produced in oxidative deamination?

A

Used as the substrate for Urea Cycle

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6
Q

What is the fate of the Nitrogen released in amino acid breakdown?

A

Nitrogen is toxic so is removed safely

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7
Q

How is nitrogen transported out the body?

A

Glutamate accepts Nitrogen forming glutamine

Glutamine then is the main transporter of Nitrogen

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8
Q

How does transamination and oxidative deamination integrate to prodcue NH3?

A

Amino acids transfer their α amino group to α-ketogluterate
α-ketogluterates transfer the amino group to glutamate
glutamate dehydrogenased to produce NH3

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9
Q

Outline the reaction that occurs to produce glutamine

A

Glutamate + ATP + NH4+ Glutamine + ADP

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10
Q

What are the two major transaminases involved in Urea formation?

A

ALT - alanine

AST - aspartate

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11
Q

Why does the urea cycle only occur in the liver and not in muscles?

A

The enzymes required for the urea cycle to occur are only present in the liver and not in the muscles

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12
Q

How are the reactants reformed from the products by AST?

A

AST funnels amino groups from glutamate product to oxaloacetate to form aspartate

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13
Q

What part of the urea cycle occurs in the mitochondria?

A

HCO3- + NH4+ –> Carbamoyl phosphate
carbamoyl phosphat enters the cycle in the cytoplasm as its converted to Citruline
Transamination of oxaloacetate -> aspartate

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14
Q

What is the fate of amino acids consumed in the diet?

A

Amino acids taken up in diet and released via the break down of proteins for energy

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15
Q

How are amino acids used in muscles?

A

During prolonged exercise or starvation branched amino acids are used for energy

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16
Q

What are α-ketoacids?

A

Organic compounds containing a carboxylic acid group and a ketone group

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17
Q

Glutamine can donate Nitrogen for the biosynthesis of which molecules?

A
  • amino acids
  • nucleotides
  • amino sugars
  • NAD+
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18
Q

What is the significance of the carbon skeleton of an amino acid?

A

Carbon skeletons are involved in energy metabolism and biosynthetic pathways

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19
Q

What happens to the Nitrogen released in muscles via amino acid breakdown?

A

Urea cycle enzymes aren’t present
Two routes can be taken to excrete N to the liver
1. ALANINE
- N transferred to alanine via glutamate + pyruvate
(oxidative deamination)

  1. GLUTAMATE
    • produce glutamine to transport N
20
Q

What is the role of the transaminases in the transamination process?

A

They transfer and amino group from an amino acid to the α-ketoacid

21
Q

How is the Nitrogen balance maintained in the body?

A

Via the positive and negative protein balance

22
Q

What is the consequence of protein breakdown?

A

When proteins are broken down, NH3 ammonia is produced which is toxic

23
Q

What is the Urea cycle?

A

The urea cycle is the means of excreting toxic Nitrogen from our bodies via urine

24
Q

Outline how ammonia is transported from peripheral tissue to the liver via the Glucose alanine cycle

A
  1. Glucose transported from the liver to the muscle (or
    glycogen converted to glucose in muscle)
  2. glucose converted to pyruvate (glycolysis)
  3. pyruvate -> alanine using NH4+ from the breakdown of
    branched A.A
  4. Alanine transpirted back to liver and converted to
    (pyruvate -> glucose) or (glutamate -> urea)
25
Q

Outline the conversions carried out by ALT and AST in transamination

A

ALT: alanine + α-ketogluterate pyruvate + glutamate

AST: aspartate + α-ketogluterate oxaloacetate + glutamate

These reactions are fully reversible

26
Q

What is the positive protein balance?

A

Positive protein balance is when Input > Output

27
Q

Where are the substrates needed for the Urea cycle obtained from?

A

The urea cycle substrates are released from glutamine (O=C-(NH2)2)

28
Q

What is a negative protein balance caused by?

A
  • Wasting diseases
  • Burns
  • Trauma
  • Response to Catabolic hormones (lack of anabolic homrones) e.g. diabetes
29
Q

What are the 2 major parts of an amino acid?

A
  • Carbon skeleton

- Nitrogen

30
Q

Explain how transamination occurs

A
  1. Amino acid A reacts with α-ketoacid b
  2. Amino acid A converted to α-ketoacid A
  3. ammonia group transferred to α-ketoacid to produce
    Amino acid b
31
Q

Where does oxidative deamination occur?

A

Mitochondrial matrix

32
Q

What causes a positive protein balance?

A
  • growth
  • pregnancy
  • exercise and tissue hypertrophy
  • response to anabolic hormones
33
Q

How are amino acids metabolised?

A

Unlike carbohydrates & fats, amino acids are either used or broken down but not stored

34
Q

Where do transaminases mainly function?

A

Predominantly carry out transaminations in the liver

35
Q

Where in the hepatocytes does the urea cycle occur?

A

Occurs in the mitochondria and cytoplasm

36
Q

What happens to free NH3 that is normally produced in tissues?

A

Free ammonia generated in tissues combine with glutamate to give glutamine using glutamine synthase enzyme

37
Q

How is the transamination process regulated?

A

Transamination is regulated by transaminases (aminotransferases)

38
Q

What are the substrates required for the urea cycle?

A
  • Bicarbonate HCO3-
  • Aspartate AST
  • Ammonium Ions NH4+
39
Q

How is ammonia formed from the products of transamination?

A

Via Oxidative Deamination
Glutamate can form NH3 directly using glutamate dehydrogenase in a reversible reaction
using NAD (degradation) or NADP (synthesis)

40
Q

What is the fate of the citruline once in the cytoplasm?

A

Converted to Argininosuccinate
2 routes taken:

  1. argininosuccinate -> arginine -> urea (via arginase enzyme)
  2. argininosuccinate -> fumurate -> malate -> oxaloacetate -> aspartate
    (via transamination of A.A -> α-ketoacid)
    cycle repeats
41
Q

How much Nitrogen is present in biological compounds Urea and Proteins?

A

Urea contains 48% Nitrogen by weight
Protein contains 16% Nitrogen by weight

=> 1g Urea formed from 3g of Protein

42
Q

Despite being fully reversible, which reactions of ALT and AST are favoured by their respectable equilibrium’s?

A

ALT equilibrium favours pyruvate formation

AST equilibrium favours the generation of aspartate and α-ketogluterate

43
Q

How is Nitrogen removed from the body?

A

In mammals, Nitrogen is converted to neutral non toxic Urea compound which is then excreted in urine

44
Q

What is meant by a negative protein balance?

A

When the Nitrogen Input < Output

45
Q

How are AST and ALT used to detect liver damage?

A

High levels of AST and ALT in the blood can indicate liver damage

46
Q

Which amino acids are exempt from undergoing transamination?

A

Threonine

Lysine

47
Q

What are the products of amino acid breakdown?

A

amino acid –> α- ketoacid + NH3

FLC (34 decks)

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