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Basic Haemotology (1204) > Vitamin B12 and Folate Metabolism > Flashcards

Vitamin B12 and Folate Metabolism Flashcards

1
Q

In DNA synthesis, _______ acting as a coenzyme and ______ as a cofactors

A

B12, Folate

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2
Q

Provides Methylation for the conversion of homocysteine to ________

A

Methionine

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3
Q

Provides Methylation for the conversion of deoxyuridine monophosphate (dUMP) to __________

A

Deoxythymidine Monophosphate (dTMP)

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4
Q

What is the average dietary intake of B12

A

20

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5
Q

What is the average dietary intake of folate

A

250

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6
Q

What is the major food source of Vitamin B12

A

Animal Produce only

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7
Q

What are the major food sources of Folate

A

Liver, Vegetables

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8
Q

How long is the normal body store for Vitamin B12

A

Several years

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9
Q

What long is the normal body store for folate

A

A few months

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10
Q

What is the mode of absorption for Vitamin B12

A

It combines with the transport protein intrinsic factor secreted by gastric parietal cells - then absorbed through ileum via special receptors

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11
Q

What is the mode of absorption for folate

A

Converted to Tetrahydrofolate and absorbed in the duodenum and jejeunum

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12
Q

Vitamin B12 is required as a Coenzyme for what two metabolic reactions

A

Isomerization of L-methylmalonyl CoA to succinylcholine CoA
-Important substrate I’m Hb synthesis

Methylation of Homocysteine to Methionine
-This step is important in intracellular synthesis of folate coenzyme

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13
Q

Folate and B12 is necessary for synthesis of ________

A

DNA

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14
Q

B12 deficiency causes Folate to be trapped in _______ form

A

Methyl Form

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15
Q

Tue or False, RNA synthesis is unaffected

A

True

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16
Q

The resultant deficiency in what substance affects DNA synthesis

A

Methylene FH4

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17
Q

What type of red cell are formed due to B12 and Folate deficiency

A

Large red cells with nuclear retention and a flimsy membrane

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18
Q

What type of disease is formed due to a lack of Folate and B12

A

Megaloblastic Anaemia

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19
Q

Where does B12 absorption occur

A

Illeum

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20
Q

Vitamin B12 is liberated from ______ protein by ______ and _____ enzymes and complexes in a 1:1 ratio with the _______

A

R protein, gastric and duodenal enzymes, intrinsic factor

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21
Q

What cells synthesize and and secrete IF

A

Gastric Parietal Cells

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22
Q

What is the MW of the glycoprotein IF

A

45,ooo

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23
Q

B12 attaches to specific receptors on the ileal mucosal Cells under what conditions

A

Calcium ions and a neutral pH

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24
Q

How long does it take for B12 to be released into circulation

A

6 hours

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25
Q

What are the two mechanisms of Cobalamin absorption

A

Passive Absorption and Active Absorption

26
Q

Which mechanism of Cobalamin transport is insufficient

A

Passive Absorption

27
Q

Where does the passive absorption of Cobalamin occur

A

Buccal, duodenal and ileal mucosa

28
Q

True or False, passive absorption is Slow

A

False it is rapid

29
Q

What is the Mode of Administration for Vitamin B12

A

Oral

30
Q

True or False, the normal physiological mechanism for B12 absorption is active

A

True

31
Q

What substance mediates oral doses of Cobalamin

A

Gastric IF

32
Q

Dietary Cobalamin is released from protein complexes by enzymes in which 3 areas of the body

A

Stomach, Duodenum and jejunum

33
Q

What is the name of the protein that binds to Dietary Cobalamin

A

Haptocorrins

34
Q

In the intestines the haptocorrins are digested by the _________ enzyme and the Cobalamin is transferred to ________

A

Pancreatic trypsin, Intrinsic Factor

35
Q

The IF is produced in the _______ of the fundus and body of the stomach, it’s secretions m parallels that of _________

A

Hydrochloric Acid

36
Q

What receptor does the IF-Cobalamin complex attaches to in the ileum on the microvillus membrane of the Enterocytes

A

Cubulin

37
Q

Cubulin with its ligand IF-cobalamin complex is ________. Where it enters the ileal cell, the _______ is destroyed.

A

Endocytosed , IF

38
Q

What is the collective name for the B12 transport proteins normally present in the plasma

A

Transcobalamines

39
Q

What is the name of the 3 Transcobalaminese

A

TCI-TCII-TCIII

40
Q

What is the name of the physically active transcobalamine that is physiologically active in the 1:1 ratio with Vitamin B12

A

TCII

41
Q

Where does the TCII- B12 complex bind

A

Developing blood cells in the bone marrow

42
Q

The Transcobalamines I and II are what type of globulins

A

Alpha

43
Q

The Transcobalamines I and III are synthesized by what type of cells

A

Granulocytes

44
Q

What is another name for Transcobalamines and where are they found

A

R binders in gastric juices

45
Q

What two types of Transcobalamines do not release Vitamin B12 readily to developing tissues

A

TCI and TCIII

46
Q

True or False, the congenital abscence of TCI and TCIII will cause no physiological impairment

A

True

47
Q

Where are Folates absorbed maximally

A

Upper Jejunum

48
Q

Folate Polyglutamate must be digested to form __________ before Absorption

A

Monoglutamate

49
Q

The absorbed folate is converted into __________, then releases into the portal blood stream

A

N-5- methyltetrahydrofolate

50
Q

True or False, Folate functions as single carbon donor acceptor

A

True

51
Q

What are the 5 ways in with folate acts as a single carbon donor- acceptor

A

Synthesis of Methionine. By donation of methyl group from N-5-methyl-tetrahydrofolate and requires Vitamin B12 as a coenzyme
Pyrimidine Synthesis, which is the rate limiting step in DNA synthesis
Purine Synthesis
Conversion of serine into glycine
Histidine Catabolism

52
Q

What is the cause of Pernicious Anaemia

A

Failure of absorption of B12 due to lack of IF and autoimmune disorder

53
Q

What abnormalities cause Pernicious Anaemia

A

Gastric cell Atrophy, Achlorhydria

54
Q

What is the most common age group for Pernicious Anaemia

A

Women over 50 years

55
Q

True or False, several years of malabsorption is required for deficiency to manifest

A

True

56
Q

True or False, Subacute Combined Degeneration of the spinal cord (unsteady gait) is a resultant of Pernicious Anaemia

A

True

57
Q

What are the causes of Vitamin B12 Deficiency

A

Inadequate dietary intake
Intestinal Malabsorption
Failure of utilization of Vitamin B12

58
Q

What appears in urine when there is a failure to metabolize Vitamin B12

A

methylmalonic acid and homocysteine

59
Q

True or False, the patients that fail to metabolize Vitamin B12, are usually mentally retarded but rarely develop megaloblastic Anaemia

A

True

60
Q

What does Anaesthetic Nitrous Oxide do in the body

A

Inactivated Vitamin B12 coenzymes and induces megaloblastic changes and mild neuropathy

61
Q

What causes Folic Acid deficiency

A

Inadequate diet
intestinal malabsorption
Excessive Alcohol usage
Failure of utilization of the absorbed Vitamin B12

62
Q

What causes a failure of folate metabolism

A

Enzyme deficiencies associated with megaloblastic changes and mental retardation

Basic Haemotology (1204) (16 decks)

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