Carbon Skeletons Khan Flashcards
1
Q
- What is the only tissue that has all the pathways for amino acid synthesis and degradation?
A
- Liver
2
Q
- What are all 20 AA’s able be broken down into?
A
- AcetylCoA, pyruvate, 4 TCA intermediates (OAA, fumarate, succinylCoA, alphaketoglutarate)
3
Q
- What is a ketogenic AA?
A
- Can be made into AcetylCoA or acetoacetate
4
Q
- What is a glucogenic AA?
A
- Can be made into glucose
5
Q
- What are the purely ketogenic AA’s?
A
- Leucine/Lysine
6
Q
- What are the ketogenic/glucogenic AA’s?
A
- Phe/Tyr, Ile, Trp
7
Q
- Describe the pathway of glycine synthesis
A
- Pyruvate –> serine –> glycine via PLP and THF –> Gly
8
Q
- During glycine synthesis what is a methyl group transferred to that can form carbon dioxide
and ammonium ion?
A
- THF
9
Q
- By enzymatic action of an oxidase what can glycine become?
A
- Glyoxylate
10
Q
- What is the condition caused by defective transaminase in Gly metabolism?
A
- Oxaluria type I (due to less conversion of glyoxylate back to Gly and accumulation of
glyoxylate)
11
Q
- What is a clinical condition manifested by excess glyoxylate
A
- kidney stones (ppt. with calcium)
12
Q
- Degradation of what other AA other than Ser can generate Gly?
A
- Thr
13
Q
- In cysteine metabolism where does the sulfur originally come from?
A
- Met
14
Q
- Met is degraded to generate what product (via methyltransferase)
A
- Homocysteine
15
Q
- What intermediate is used in Met degradation for methyl transfer?
A
- SAM
16
Q
- What can homocysteine be then converted into?
A
- Back to Met or into cysteine via cystathionase
17
Q
- What can cysteine be degraded to?
A
- Sulfinic acid, in presence of alpha ketoglutarate it can be degraded to pyruvate (thus it
is a glucogenic AA)
18
Q
- The sulfhydryl groups of cysteine can be oxidized to form what which generate sulfated
proteoglycans
A
- PAPs
19
Q
- Can cysteine inhibit cystathione synthase via feedback inhibition?
A
- Yes
20
Q
- What does a deficiency in cystathionase lead to?
A
- Cystathionuria (benign disorder)
21
Q
- What could cause a deficiency in cystathione?
A
- Dietary deficiency of pyridoxine(Vit. B6) or Vit. B12
22
Q
- What does a deficiency in cystathionine synthase cause?
A
- Homocystinemia/Homocystinuria (accumulation of homocysteine and met in brain,
can cause loss in cognitive fx. , tall stature, CV disease, thrombi, emboli, etc.)
23
Q
- What is the treatment for homocystinuria?
A
- Low met diet, high doses of pyridoxine
24
Q
- Can our bodies synthesize aromatic rings?
A
- No (makes them essential AA’s)
25
Q
- How is tyrosine synthesized?
A
- From Phe via hydroxylation reaction using oxygen and tetrahydrobiopterin
26
Q
- T or F: Any defective step in Phe or Tyr synthesis causes severe diseases
A
- T
27
Q
- What does a deficiency in Phe hydroxylase present as?
A
- Phenylketouia (PKU), phenylpyruvate accumulates and is excreted (mental retardation, lighter skin due to impaired tyrosine synthesis)
28
Q
- What is the treatment for PKU?
A
- Diet low in Phe, rich in Tyr
29
Q
- What is the first step in degradation of tyrosine?
A
- Removal of ammonia via tyrosine aminotransferase
30
Q
- What does a defect in this step cause?
A
- Tyrosinemia II (eye, skin, lesions, neurological disorders)low tyr and low phe diet is
treatment
31
Q
- What does deficiency in homogentisate oxidase cause?
A
- Alcaptonuria (accumulation of homogentisate which causes arthritis)
32
Q
- What does a deficiency in degradation of fumarylacetoacetate cause?
A
- Tyrosinemia I (liver failure and death within 1 yr of life)
33
Q
- Where does the aromatic ring of Trp end up via degradation pathways?
A
- NAD/NADP
34
Q
- Where does the carbon skeleton of Trp end up?
A
- Ala
35
Q
- Trp to NAD requires what cofactor? What does a deficiency in this cofactor cause?
A
- PLP, pellagra like symptoms
36
Q
- What are the branched chain AA’s?
A
- Val, Ile, Leu
37
Q
- What can these AA’s generate via transamination rxn?
A
- Alphaketovalerate, alpha keto beta methylvalerate, alphaketoisocaproate
38
Q
- What are branched chain AA’s ultimately converted to?
A
- propionylCoa or Acetyl CoA
39
Q
- What is homocistinuria type 1 caused by?
A
- cystathionine synthase deficiency (high homocystine and methionine levels)
40
Q
- What is homocystinuria type 2/3 caused by?
A
- deficiency in methl‐b‐12 and methyl THF synthesis (high serum homocysteine and low
methionine levels)