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Vitamin B12 Flashcards

(74 cards)

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1
Q

What is another name for Vitamin B12?

A

Anti-pernicious anemia vitamin

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2
Q

Who synthesizes Vitamin B12?

A

Only microorganisms

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3
Q

Is Vitamin B12 synthesized by animals or plants?

A

No

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4
Q

Which vitamin was the last to be discovered?

A

Vitamin B12

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5
Q

What is the empirical formula of cyanocobalamin?

A

C63H88CoN14O14P

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6
Q

What is the core structure of Vitamin B12?

A

Corrin ring

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7
Q

Which atom is at the center of the corrin ring?

A

Cobalt

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8
Q

What ring structure is similar to the corrin ring?

A

Tetrapyrrole ring

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9
Q

How many pyrrole units does the corrin ring have?

A

Four

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10
Q

Which pyrrole units are directly bound?

A

A and D

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11
Q

Which pyrrole units are held by methene bridges?

A

B and C

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12
Q

What groups are substituents on pyrrole rings?

A

Methyl, acetamide, propionamide

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13
Q

How many coordination states does cobalt have in B12?

A

Six

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14
Q

What is bonded below the corrin plane?

A

Dimethylbenzimidazole (DMB)

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15
Q

What does DMB contain?

A

Ribose 5-phosphate and aminoisopropanol

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16
Q

What binds with the D ring of corrin?

A

Amide group of aminoisopropanol

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17
Q

What group lies above the corrin ring?

A

Variable substituent

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18
Q

What is the substituent in cyanocobalamin?

A

Cyanide

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19
Q

What is the substituent in hydroxycobalamin?

A

Hydroxyl

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20
Q

What is the substituent in nitrocobalamin?

A

Nitrite

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21
Q

Name the two coenzyme forms of Vitamin B12.

A

Deoxyadenosylcobalamin, methylcobalamin

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22
Q

What replaces cyanide in deoxyadenosylcobalamin?

A

5� deoxyadenosine

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23
Q

What replaces cyanide in methylcobalamin?

A

Methyl group

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24
Q

In diet, how is B12 found?

A

Protein-bound

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25
How is dietary B12 released in the stomach?
By acid hydrolases
26
What is the dietary source of B12 called?
Extrinsic factor of Castle
27
What protein is secreted by the stomach for B12 absorption?
Intrinsic factor (IF)
28
What is the nature of intrinsic factor?
Glycoprotein with 8�15% carbohydrate
29
What is the molecular weight of intrinsic factor?
About 50,000
30
How many vitamin B12 molecules can IF bind?
One or two
31
Why is IF important for B12?
Protects it from bacterial use
32
Where does the B12-IF complex bind?
Ileal mucosal cell receptors
33
What ion mediates B12 entry into mucosal cells?
Ca2+
34
What is B12 converted to in mucosal cells?
Methylcobalamin
35
What transports B12 in circulation?
Transcobalamins (TC-I, TC-II)
36
Which transcobalamin carries most B12?
TC-I
37
What is the role of TC-II?
Mediates tissue uptake
38
Where is excess methylcobalamin stored?
Liver
39
What is methylcobalamin converted to in liver?
Deoxyadenosyl B12
40
How much B12 can the liver store?
4�5 mg
41
How long can liver B12 stores last?
4�6 years
42
How many mammalian enzyme reactions use B12?
Two
43
What is the first mammalian B12-dependent reaction?
Methionine synthesis from homocysteine
44
What is the coenzyme in methionine synthesis?
Methylcobalamin
45
What is liberated in methionine synthesis?
Tetrahydrofolate (THF)
46
What enzyme catalyzes methionine synthesis?
Homocysteine methyltransferase
47
What is the second mammalian B12-dependent reaction?
Isomerization of methylmalonyl CoA to succinyl CoA
48
What coenzyme is required in methylmalonyl CoA conversion?
Deoxyadenosyl cobalamin
49
Which enzyme converts methylmalonyl CoA to succinyl CoA?
Methylmalonyl CoA mutase
50
What accumulates in B12 deficiency?
Methylmalonyl CoA
51
What is methylmalonyl CoA excreted as?
Methylmalonic acid
52
What is the adult daily requirement for B12?
3 �g
53
What is the B12 requirement during pregnancy/lactation?
4 �g/day
54
What is the B12 requirement for children?
0.5�1.5 �g/day
55
What are rich sources of B12?
Liver, kidney, milk, curd, eggs, fish, pork, chicken
56
Which is a better source: curd or milk?
Curd
57
Who synthesizes Vitamin B12?
Microorganisms only
58
Is B12 found in plant foods?
No
59
How do animals get B12?
Diet or bacterial synthesis
60
What is the key disease from B12 deficiency?
Pernicious anemia
61
What are features of pernicious anemia?
Low hemoglobin, fewer RBCs, neurological symptoms
62
What causes IF absence?
Autoimmune destruction of gastric parietal cells
63
What causes hereditary B12 deficiency?
Malabsorption
64
Why do gastrectomy patients develop B12 deficiency?
Loss of intrinsic factor
65
What is a common elderly cause of B12 deficiency?
Low IF and/or gastric HCl
66
Which diet is at risk for B12 deficiency?
Strict vegetarians
67
What symptoms result from methylmalonyl CoA buildup?
Neurological degeneration
68
What are early neuro symptoms of B12 deficiency?
Paresthesia of fingers/toes
69
What are advanced neuro symptoms of B12 deficiency?
Confusion, memory loss, psychosis
70
How does methylmalonyl CoA affect myelin?
Inhibits fatty acid synthesis or creates abnormal fatty acids
71
How is B12 deficiency diagnosed?
Serum B12 levels, methylmalonic acid in urine
72
How is B12 deficiency treated?
Intramuscular B12 (100�1000 �g)
73
Can folic acid reverse B12 deficiency symptoms?
Only hematologic, not neurological
74
What is best for megaloblastic anemia treatment?
Combined B12 and folate

Biochemistry (11 decks)

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