Amino Acids

Question 1

What are amino acids used for ?

3

Answer 1

1) energy
2) makes proteins
3) makes molecules ie: urea ( carrier of waste nitrogen )

Question 2

The carbon backbone in the amino acids can be converted to ——
(4)

Answer 2

• Glucogenic : degraded to pyruvate ->Krebs -> can be stored as glucose
• ketogenic: degraded to ACYL COA -> makes fatty acids or ketone bodies ( CAN NOT BE MADE INTO GLUCOSE )
• BOTH ( glycogenic and ketogenic ) like phenylalanine

Question 3

What happens in amino acid metabolism?
( first section )
(3)

Answer 3

1) AA is degraded into free AA group and carbon skeleton

Step 1: amino group is TRANSFERRED to alpha-ketoglutarate = glutamate! This is called TRANSAMINATION(transfer of amine group)
driven by alanine aminotransferase

Step2: OXIDATIVE DEAMINATION of glutamate and ammonia is removed (NH4+ released), water is added and then Alpha-ketoglutarate is remade
via enzyme glutamate dehydrogenase

2)Urea cycle occurs to remove the NH4+

Question 4

Outline the urea cycle! 
What does it do?
1) Orange coloured cats always ask for awesome umbrellas 
(5 steps ) 
10 marks

Answer 4

( the ammonia is converted to Urea which is easily excreted)

1) ammonium -> carbomoyl phosphate (2ATP used)
2) carbomyl phosphate + Orthinine -> Citruilline ( Pi is released )
3) Citruilline + Aspartate —>Argininosuccinate (ATP->AMP)
4) Argininosuccinate —> arginine and Fumarate
5) Arginine+water-> Urea -> blood-> URINE

Question 5

Describe the basis of phenylketonuria!
(6)
- what is the condition genetically

Answer 5

Phenylalanine is normally broken down into tyrosine via an enzyme called phenylalanine hydroxylase (PAH) (normally tyrosine can then be broken down to acetic acid and metabolised )

1) PAH is not produced due to autosomal recessive condition causing the synthesis of PAH To be disrupted
2) phenylalanine remains in blood =phenyl pyruvic acid
3) this can cross blood Brain barrier, entering the cerebrospinal fluid ( CSF)
4) phenylalanine occupies all transports protein-membrane receptors in the brain! so no tyrosine and tryptophan can join!
5) This means that no dopamine, noradrenaline or Serotonin is made ( tyrosine - dopamine and norepinephrine)
6) this leads to mental retardation!

Question 6

Outline purine metabolism
(Adenine and guanine )

De novo pathway ( 6) steps

Salvage pathway ( 2)

what diseases affect this? (2)

Answer 6

1) denovo pathway
- purine ( 2ringed structure) —> AMP->adenosine-> adenine -> xanthine ->URIC ACID

2) savage pathway ( recycle)
HGPRT ENZYME recycles Adenine and guanine back into AMP and GMP

3)Gout (accumulation of uric acid )
Lesch -Nyhan syndrome (no HGPRT enzyme, rare X linked recessive )

Question 7

What can happen if u have increased levels of URIC acid ?!

What happens if enzyme HGPRT isn’t produced ?

(6)

Answer 7

1) hyperuricemia ( too much URIC acid in blood stream)
2) GOUT - urate Crystal ( URIC acid has low water solubility , hence stones are formed in the kidney ) deposition -> arthritis -> powerful inflammatory response

3)when HGPRT enzyme is not working = lesch-Nyah syndrome = rare X-linked recessive
1-symptoms are GOUT / neurological symptoms
2-There will be a loss of purine nucleotides from salvage pathway !