24/25. Cobalamin (vitamin B12)

Question 1

Structure of vit B12:

Answer 1

Question 2

What can cobalamin be depending on the sixth substituent?

Answer 2

-Cyanocobalamin -hydroxycobalamin -chlorocobalamin

Question 3

Facts about the metabolism:

Answer 3

-Natural in bacteria flora -Found in animal liver -Absorption in ileum -Storage in liver -Excreted in urine, feces and bile (60-70% are reabsorbed) -Depend on the intrinsic factor, a glycoprotein in the fundus. It binds B12 in the lumen.

Question 4

Metabolism of B12:

Answer 4

Question 5

what is the active form?

Answer 5

-5’deoxyadenosyl cobalamin (DA-cobalamin) -Methylcobalamin

Question 6

Which reactions need DA-cobalamin?

Answer 6

Methylmalonoyl-CoA –> Succinyl-CoA (enzyme:methylmalonyl mutase) -It helps rearrange the reaction (exception in DNA synthesis) -dUMP–>dTMP

Question 7

Which reaction need methylcobalamin?

Answer 7

Homocysteine –> methionine (Enzyme:homocysteine methyltransferase, also with FH4)

Question 8

Deficiency:

Answer 8

Rare in humans - if parietal cells fail to secrete intrinsic factors, it can lead to pericious anemia (especially if you have diabetes or crohns) -Slows down DNA synthesis. -General: anemia, slow growth, decreased reproduction, nerve trouble. -Birds: egg production decrease and also reproduction.

Question 9

Where can you find it?

Answer 9

-In liver, kidney, heart, not in plants