L29 - Nitrogen Metabolsim 2 Flashcards

1
Q

What is transamination?

A

The process by which -NH2 is transferred from an amino acid to a keto-acid to form a new amino acid

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2
Q

What amino acid does ammonia assimilation change nitrogen into?

A

Glutamate

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3
Q

What are 2 kinds of enzyme that catalyse transamination called?

A

Transaminases and Aminotransferase

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4
Q

What compound acts as a coenzyme to transfer the -NH2 group?

A

Pyridoxal Phosphate (PP)

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5
Q

What does transamination allow?

A

allows plants and some micro-organisms

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6
Q

When glutamate reacts with keto-acids with the R groups following, which amino acid does it create?

a) -CH3 (Pyruvate)
b) -CH2OH (3-phosphoglycerate)
c) -CH2COOH (oxaloacetate)

A

a) Alanine
b) Serine
c) Aspartate

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7
Q

What is the source of keto-acids for amino acid synthesis?

A

Intermediates of carbohydrate and lipid metabolism

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8
Q

If some enzymes that are necessary to make some of the AAs where are they gained from? What are these called?

A

Those amino acids have to be supplied in the diet or growth medium

They are called essential or indispensable AAs

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9
Q

Name the essential amino acids for humans for each category:

a) Basic AAs
b) Branch chain AAs
c) Aromatic AAs
d) Others

A

a) Arginine, Lysine, Histidine
b) Leucine, Isoleucine, Valine
c) Tyrosine, Tryptophan, Phenylalanine
d) Methionine, Threonine

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10
Q

Can excess amino acids taken in in the diet be stored for later?

A

No - they are degraded

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11
Q

Name and describe the 2 stages of AA degradation

A

1) Deamination
- opposite of transamination
- NH2 group is transferred from the AA to 2-oxo-glutarate to form glutamate

2) Oxidative deamination
- reverse of ammonia assimilation
- the NH2 group of glutamate is removed by glutamate dehydrogenase

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12
Q

The keto acids formed during deamination feed into the central metabolic pathways. What happens to each:

a) glycogenic keto acids
b) ketogenic keto acids

A

a) they can be used as a substrate for glucose synthesis

b) they can be used to synthesise ketone bodies

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13
Q

The NH3 formed by oxidative deamination is potentially toxic to animals, what do most to do get rid of it? How are birds, most reptiles and fish different?

A

Convert it to urea, as then it can be excreted through the kidneys as urine.

Birds and most reptiles excrete uric acid
Fish excrete ammonia

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14
Q

Where does the first part of the process of getting rid of NH3 take place?

A

In mitochondria and requires 2ATP

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15
Q

What enzyme is needed for the first step of getting rid of NH3 and what does it convert into what?

A

Carbamoyl phosphate synthetase

Converts:
bicarbonate + ammonia —> carbamoyl phosphate
requiring 2ATP

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16
Q

What is Ornithine?

A

It is an AA, but it isn’t present in proteins

17
Q

Describe how Ornithine reacts with carbamoyl phosphate

A

Ornithine + carbamoyl phosphate —> Citrulline + Pi

Uses the enzyme - ornithine transcarbamolayse

18
Q

What happens to citrulline once it has been made in the mitochondria?

A

It moved out of the mitochondria where the rest of the cycle takes place

19
Q

Citrulline has to be changed back to ornithine and urea must be produced. Describe how this happens

A
  • Aspartate joins the citrulline using ATP
  • Produces argininosuccinate
  • Argininosuccinate then splits into fumerate and arginine
    fumerate goes into TCA cycle
    Arginine is the hydrolysed by arginase:

Arginine + H2O —> Urea + Ornithine

20
Q

When urea is excreted, how can it be broken down by micro-organisms?

A

Urea + H2O —> CO2 + 2NH3 (ammonia)

Enzyme = urease