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Fundamentals Of The Living Cell > Protein breakdown and urea formation > Flashcards

Protein breakdown and urea formation Flashcards

1
Q

What is positive nitrogen balance?

A

Too much nitrogen input

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2
Q

What is negative nitrogen balance?

A

To little nitrogen input

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3
Q

What are the two parts of the metabolism of amino acids?

A

The carbon skeleton

Nitrogen

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4
Q

What happens to amino acids?

A

They aren’t stored, they’re used or broken down

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5
Q

what is the carbon skeleton from the metabolism from amino acids used for?

A

Used for:
Energy metabolism
Biosynthetic pathways

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6
Q

Why has nitrogen got to be removed?

A

Nitrogen is so toxic so has to be removed safely

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7
Q

How is nitrogen removed in mammals?

A

In mammals, nitrogen converted to the non-toxic neutral compound urea and excreted in the urine

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8
Q

What is the enzyme involved in the first step in the transfer of amino acid nitrogen to urea (transamination)?

A

Enzyme involved in transaminase

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9
Q

What happens in transamination?

A

Nitrogen group of amino acid A transferred to keto acid B give to second amino acid B and Keto acid A

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10
Q

Why are keto acid important in transamination?

A

Keto acids are important metabolic intermediates

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11
Q

Examples of transaminase

A

Alanine and Aspartate

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12
Q

What does alanine form when catalysed with alpha ketoglutarate?

A

Alanine catalyses α-ketoglutarate to give pyruvate and glutamate

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13
Q

What does aspartate form when catalysed with alpha ketoglutarate?

A

Aspartate catalyses α-ketoglutarate to give oxaloacetate and glutamate

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14
Q

What are high levels of alanine and aspartate indicative of?

A

High levels of alanine and aspartate in the blood are indicative of liver damage

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15
Q

What does transamination reaction require?

A

Whole reaction requires pyridoxal phosphate derived from vitamin B6

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16
Q

In the second step of transfer of amino acid nitrogen to urea(oxidative deamintation), what is glutamate converted into and by what?

A

Glutamate can be converted to α-ketoglutarate by glutamate dehydrogenase

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17
Q

What type of reaction is the conversion of glutamate to alpha ketoglutarate and what is used?

A

Fully reversible and can either use NAD or NADP

18
Q

What else is formed in oxidative deamination, other than alpha ketoglutarate?

A

Ammonia is also formed and is the substrate to the urea cycle

19
Q

How is glutamine synthesised and why is it needed?

A

○ Elimination of free ammonia:
§ Glutamate gains nitrogen from ammonia
§ ATP and glutamine synthase involved
Glutamine main transporter of nitrogen as it is readily soluble

20
Q

In step 3 of the transfer of amino acid nitrogen to urea(urea formation), what is the means of this step?

A

Means of excreting nitrogen

21
Q

Where are the enzymes present for urea formation and where are they not?

A

Present in liver but not muscle

22
Q

Where does urea formation occur?

A

Takes place in mitochondria and cytoplasm

23
Q

What are the substrates involved in urea formation?

A

Substrates are bicarbonate, aspartate and ammonium ions(released from either glutamine or glutamate)

24
Q

How many amnio groups are used in the formation of urea and where do they come from?

A

○ Formation of urea uses two amino groups

One from glutamate and one from aspartate

25
Q

How does the urea cycle interact with the tricarboxylic acid cycle?

A
  • Ammonia first reacts to form carbamoyl phosphate
    • Combines with ornithine to give citrulline
    • Citrulline breaks down to give arginine which under the influence of arginase gives urea
    • Fumarate converted to malate and then oxaloacetate
26
Q

What is formed when oxaloacetate further reacts with an amino acid?

A

Oxaloacetate Can be used to react with further amino acid to give a keto acid and asparate

27
Q

What is used for energy in muscles during prolonged exercise or starvation?

A

In prolonged exercise or starvation, branched amino acids are used for energy

28
Q

What enzymes are not present in muscles?

A

Enzyme of the urea cycle not present

29
Q

What are the two routes of transport to transport nitrogen to liver from muscle?

A

○ Alanine
§ Nitrogen transferred to alanine via glutamate and pyruvate
○ Glutamine
Glutamate is made into glutamine

30
Q

What are the steps involved in the glucose alanine cycle?

A

• Break down of protein
• Transamination to form alanine
• Alanine reacts to form glutamate and pyruvate
Glutamate synthesises urea

31
Q

What happens to the carbon skeleton formed in the glucose alanine cycle?

A

• Carbon skeleton that is formed is converted to pyruvate

32
Q

What is the fate of the carbon skeleton

A

Will form α-keto acids. Some of the backbone of other amino acids can also feed into different components of the TCA cycle

33
Q

What amino acids are the only ones which cannot inter-convert into alpha keto acids?

A

lysine and threonine

34
Q

What is normal metabolism after a meal for a healthy individual in terms of insulin and glucagon levels?

A

High insulin

Low glucagon

35
Q

In normal metabolism after a meal, what happens to most amino acids?

A

Most amino acids from a protein meal used for protein synthesis in peripheral tissues such as skeletal muscle

36
Q

In normal metabolism after a meal, what happens to excess amino acids?

A

Excess amino acids used as sources of energy and nitrogen derived from their oxidation is incorporated into urea in the liver and excreted

37
Q

In normal metabolism during starvation, what are the insulun a glucagon levels like?

A

Insulin is low

Glucagon is high

38
Q

In normal individual during short term starvation, where is the net flow of amino acids and production of what is increased?

A

§ Net flow of amino acids from muscle to liver

Increased production of glucose and urea

39
Q

In normal individual during long term starvation, what happens to tissue proteins?

A

Tissue protein is spared because ketone bodies replace glucose as major energy fuel for the brain

40
Q

What is the nitrogen balance in untreated diabetes and why?

A

Negative nitrogen balance due to decreased protein synthesis or increased protein breakdown

41
Q

When is negative nitrogen balance seen?

A

Seen in conditions like chronic infections, late stage cancer or trauma

42
Q

What are some of the effects in negative nitrogen balance mediated by?

A

Some of these effects are mediated by cytokines

Fundamentals Of The Living Cell (31 decks)

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