Nitrogen Metabolism

Question 1

where does the body get a source of N from?
how do we store XS N?

what does this ^^ mean with regards to ensuring we have enough N in our bodies?

Answer 1

Nitrogen intake: only from diet - gives us amino groups.

Nitrogen storage: cannot store excess nitrogen or amino acids. Excess amino acids/nitrogenis excreted. muscles arent a store !

SO: we need nitrogen intake to be equal or more than output - maintain the nitrogen balance.

Question 2

how many amino acid?

what are essential amino acids?

what are non-essentil amino acids?

what are condentially essential amino acids?

Answer 2

20 amino acids

• essential - need from diet eg phenylalanine.
• non-essential - can be synthesised. Eg. Alanine.
• conditionally essential - when you need to take in additional AA to the amount that can be synthesised eg. Arginine. (i.e during growth spurt, might need topping up from diet)

Question 3

why do we need a.a.s? (6)

Answer 3

 Protein synthesis

 ATP production - from glucose or ketone bodies

 DNA - purines and pyrimidines

 Neurotransmitters (either a.a. or products of a.a)

 intermediates in metabolic cycles

 Building blocks for other chemicals, or themselves signalling molecules:
- Tyrosine -> dopamine
- Tryptophan -> serotonin
- Arginine -> nitric oxide
- Histidine -> histamine
- Glycine/glutamate/aspartate used as NT directly.
(dont need to know!)

Question 4

what is transamination?
how does it occur?
where does it occur mostly?
what is the enyzme used for it?

Answer 4

transamination: transfer of an amino group. new amino acids can be made by using the carbon skeleton of other amino acids and transferreing a new side chain on it

mechanism:

• keto acid / group (a.a but instead of the NH2, is replaced by C double bonded O) swaps with the amine of another amino acid
• requires an intermediary: pyridoxal phosphate (from vitamin B6)

location: liver

Enzyme: tranaminase

Question 5

what is pyridoxal phosphate a derivative from?

Answer 5

pyridoxal phosphate derived from B6

Question 6

what are glucogenic and ketogenic amino acids?

e.g.s?

Answer 6

• *glutogenic: c**an be converted to glucose by gluconeogenesis or enter the TCA
• can either be transaminated to oxaloacetate or pyruvate (or other intermediates that will form oxaloacetate):
• e.g. alanine or glutamate

ketogenic: can be converted to ketone bodies, these can feed into the TCA cycle, mostly via A-CoA or acetoacetyl-CoA.

Question 7

what is the excretory form of surplus nitrogen?

Answer 7

urea !

Question 8

how is ammonia produced?

how is ammonia excreted from body ? why is it excreted?

Answer 8

• occurs as a reult of amino acids underoing deamination reactions (reactions where you lose amine groups): when amino acids are converted to other molecules, but there arent other molecules to pick up with NH4+ (which is toxic).
• remove the NH4+ via the urea cycle:

Question 10

which is the most abundant amino acid in the body?

a) glycine
b) serine
c) glutamine
d) cysteine

Answer 10

which is the most abundant amino acid in the body?

a) glycine
b) serine
c) glutamine
d) cysteine

Question 11

the conversion of the glutamine (a.a) to glutmate and then a-ketoglutarate generates WHAT?

why might this conversion occur?

why is lots of NH4+ produced?

Answer 11

a-keto glutarateglutamateglutamine: generates free ammonia (as NH4+)

• a-ketoglutarate is needed for TCA cycle for energy.
• Glutamine has 2 amino groups, glutmate has 1, a-keto glutarate has 0 - so each step removes/adds an amino group so the metabolism of glutamine releases a lot of ammonium.

us

Question 12

what is glutamine used for? (4)

Answer 12

 Source of fuel during fasting - especially in muscles and immune cells.

 Used for gluconeogenesis, esp. in kidney.

 Produces ammonia, which can act as buffer for unwanted protons.

 Glutamine has anti-inflammatory properties in the gut.

Overall: fuel, building block, needed for metabolites: a-ketoglutarate and glutamate.

Question 13

what are sources of ammonia from the body? (5)

Answer 13

o Microflora in gut
o Deamination of amino acid
o Breakdown of DNA/RNA
o Metabolism of AA
o Ketogenesis/gluconeogenesis from AAs releases ammonia.

Question 14

where does urea cycle occur?

Answer 14

in the liver

Question 15

MoA of urea cycle:

a) what is the rate determining step?
b) what are the two amino groups required? for it
c) what is the key regulating enzyme?

Answer 15

Rate controlling step:

o HCO3- + NH4+ –> carbamoyl phosphate (via enzyme carbamoyl phosphate synthase 1)
o Requires 2 ATP.
o Controlled allosterically by glutamate metabolite: N-acetyl glutamate - this is formed in an excess of glutamate, so drives urea cycle.

b) the two amino groups required from: aspartate (1) & ammonia (1)

essentially is a shuttle reaction of NH4 into from aspartate and ammonia into urea

a) the two amino groups required?

Question 16

what happens if u get defects in urea formation?

symptoms?

Answer 16

• get a reduction of urea & therefore urine
• therefore, you get a build up of NH3 which is toxic, especially to neurons: neurological defects

- symptoms:
 Vomiting
 Nausea
 Neurological disorders
 Lethargy
 Coma
 Death.

Question 17

what are the two types of defects of urea formation?

how do u treat?

Answer 17

Type 1: generally neonatal

 Autosomal recessive defect in carbamoyl phosphate synthase 1of the cycle:

 This stops the conversion of NH4 -> carbamoyl phosphate and posistive feedback/acceleration of urea cycle.

 Can cause cerebral oedema + coma -> death.

Type 2: generally slightly post-natal

 X-linked disorder with ornithine transcarbamoylase

 Cerebral oedema, coma & death.

• *treatment:**
• low protein diet
• ammonia scavangers