1 Carbon Metabolism

Question 1

C1 Carriers

Answer 1

Biotin, SAM, FH4

Question 2

C1 Source, Group, Reaction – Biotin

Answer 2

CO₂

Carboxyl Groups

Carboxylation Reactions

Question 3

C1 Source, Group, Reaction - SAM

Answer 3

Methionine

Methyl Groups

Methylations

Question 4

C1 Source, Group, Reaction – FH4

Answer 4

Trp, Ser, Gly

formyl methenyl, methylene, methyl

Synthesis of purines, pyrimidines and thymidine, Homocysteine –> Methionine

Question 5

The C₁ Carbons in ___ and ___ groups are in the same oxidation state

Answer 5

formyl and methenyl

Question 6

FH4 participates in how many methylation reactions?

Answer 6

One. All others use SAM.

Question 7

Biotin is cofactor for which four enzymes

Answer 7

1. Pyruvate Carboxylase
2. Acetyl CoA carboxylase
3. Propionyl CoA Carboxylase
4. (ß-methylcrotonyl CoA Carboxylase – Leucine catabolism)

Question 8

Holocarboxylases go on to partipate in what processes?

Answer 8

Protein Catabolism

FA synthesis

Gluconeogenesis

Question 9

Biotin Cycle

Answer 9

Biotin + apocarboxylases

|

(Holocarboxylase Synthase)

|

Holocarboxylases

|

Biocytin (–> Recycled)

Question 10

Biotin is recycled from ____ by ____

Answer 10

Biocytin, biotinidase

Question 11

Holocarboxylase Synthase deficiency may lead to…

Answer 11

Encephalopathic crisis (drain bamage)

Question 12

SAM Synthesis

Answer 12

Met + ATP ———(Met Adenysyl Transferase)——-> SAM

Question 13

Guanidoacetic acid methylation product

Answer 13

Creatine

Question 14

Phosphatidylethanolamine methylation product

Answer 14

Phosphatidylcholine

Question 15

rRNA and tRNA methylation product

Answer 15

methylated RNA

Question 16

Norepi methylation product

Answer 16

Epi

Question 17

Protein-bound LYS methylation product

Answer 17

Trimethyllysine

Question 18

SAM fate

Answer 18

hydrolyzed to adenosine and homocysteine

Question 19

Homocysteine fate

Answer 19

Converted to Met, or used in Cys synthesis

Question 20

FH4 reduced by what enzyme?

What cofactor is needed?

Answer 20

Dihydrofolate Reductase

NADPH

Question 21

The busines part of THF

Answer 21

N5 & N10

Question 22

Methyl, Formyl, Methylene, and Methenyl bind to THF…

Answer 22

• Methyl N5
• Formyl N10
• Methylene and Methenyl form a bridge between N5 and N10

Question 23

a.a. that THF transfers from

Answer 23

Trp, His, Gly, Ser

Question 24

Formation of N5-Methyl FH4

Answer 24

FH4 –> N¹⁰ Formyl –> N⁵, N¹⁰ Methenyl –> N⁵, N¹⁰ Methylene (+NADH) –>

N⁵Met-FH4

Question 25

Methotrexate Mechanism

Answer 25

Folate anaolg, inhibits Dihydrofolate Reductase

Question 26

5-Fluorouracil Mechanism

Answer 26

Inhibits Thymidylate Synthase | (UMP --//--\> dTMP)

Question 27

B₁₂-dependent reactions

Answer 27

1. Homocysteine --\> Methionine (Methionine Synthase) 2. Methylmalonyl CoA --\> Succinyl CoA

Question 28

B12 absorption

Answer 28

bound by haptocorrins --\> Proteases release --\> GIF binds and enters Ileum

Question 29

Explain the methyl trap

Answer 29

B12 is the only thing that can remove methyl groups from N⁵Methyl FH4 (which is needed for Regeneration of Methionine from Homocysteine). Homocysteine trapped. Low B12 = High homocysteine = Megaloblastic anemia, CNS Symptoms

Question 30

How to DDX B12 and Folate deficiencies?

Answer 30

Level of _Methylmalonyl CoA_ (will be HIGH with a B12 deficiency since it is a required cofactor)

Question 31

Causes of Homocysteinuria

Answer 31

1. Folate Deficiency 2. B12 deficiency 3. Reduced activity of _Cystathione ß Synthase_ (CBS Rxn = HC+Serine+B6--\> Cystathione)

Question 32

Betaine is a...

Answer 32

An alternate pathway for _Homocysteine---\> Methionine_

Question 33

Betaine Pathway

Answer 33

Betaine ( + Homocysteine) --\> Dimethylglycine ( + Methionine)

Question 34

Is B vitamin supplementation useful for reducing the risk of atherosclerosis? Why or why not?

Answer 34

No. No evidence despite their effect on plasma homocysteine levels.

Question 35

B12 deficiency effects? What causes this?

Answer 35

Megaloblastic anemia, Neurological symptoms (neuropathy) Neuro Sx d/t _high Methylmalonyl-CoA_, which may decrease lipid synthesis or decrease SAM.

Question 36

Megaloblast definition

Answer 36

Large erythroblast associated with B12 deficiency. _DNA synthesis is impaired_ (RNA is unaffected) becuase **dTTP** is limiting factor