Vitamin B12 and Folate Metabolism Flashcards Preview

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

Flashcards in Vitamin B12 and Folate Metabolism Deck (62):
1

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

B12, Folate

2

Provides Methylation for the conversion of homocysteine to ________

Methionine

3

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

Deoxythymidine Monophosphate (dTMP)

4

What is the average dietary intake of B12

20

5

What is the average dietary intake of folate

250

6

What is the major food source of Vitamin B12

Animal Produce only

7

What are the major food sources of Folate

Liver, Vegetables

8

How long is the normal body store for Vitamin B12

Several years

9

What long is the normal body store for folate

A few months

10

What is the mode of absorption for Vitamin B12

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

11

What is the mode of absorption for folate

Converted to Tetrahydrofolate and absorbed in the duodenum and jejeunum

12

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

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

13

Folate and B12 is necessary for synthesis of ________

DNA

14

B12 deficiency causes Folate to be trapped in _______ form

Methyl Form

15

Tue or False, RNA synthesis is unaffected

True

16

The resultant deficiency in what substance affects DNA synthesis

Methylene FH4

17

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

Large red cells with nuclear retention and a flimsy membrane

18

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

Megaloblastic Anaemia

19

Where does B12 absorption occur

Illeum

20

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

R protein, gastric and duodenal enzymes, intrinsic factor

21

What cells synthesize and and secrete IF

Gastric Parietal Cells

22

What is the MW of the glycoprotein IF

45,ooo

23

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

Calcium ions and a neutral pH

24

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

6 hours

25

What are the two mechanisms of Cobalamin absorption

Passive Absorption and Active Absorption

26

Which mechanism of Cobalamin transport is insufficient

Passive Absorption

27

Where does the passive absorption of Cobalamin occur

Buccal, duodenal and ileal mucosa

28

True or False, passive absorption is Slow

False it is rapid

29

What is the Mode of Administration for Vitamin B12

Oral

30

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

True

31

What substance mediates oral doses of Cobalamin

Gastric IF

32

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

Stomach, Duodenum and jejunum

33

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

Haptocorrins

34

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

Pancreatic trypsin, Intrinsic Factor

35

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

Hydrochloric Acid

36

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

Cubulin

37

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

Endocytosed , IF

38

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

Transcobalamines

39

What is the name of the 3 Transcobalaminese

TCI-TCII-TCIII

40

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

TCII

41

Where does the TCII- B12 complex bind

Developing blood cells in the bone marrow

42

The Transcobalamines I and II are what type of globulins

Alpha

43

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

Granulocytes

44

What is another name for Transcobalamines and where are they found

R binders in gastric juices

45

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

TCI and TCIII

46

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

True

47

Where are Folates absorbed maximally

Upper Jejunum

48

Folate Polyglutamate must be digested to form __________ before Absorption

Monoglutamate

49

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

N-5- methyltetrahydrofolate

50

True or False, Folate functions as single carbon donor acceptor

True

51

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

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

What is the cause of Pernicious Anaemia

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

53

What abnormalities cause Pernicious Anaemia

Gastric cell Atrophy, Achlorhydria

54

What is the most common age group for Pernicious Anaemia

Women over 50 years

55

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

True

56

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

True

57

What are the causes of Vitamin B12 Deficiency

Inadequate dietary intake
Intestinal Malabsorption
Failure of utilization of Vitamin B12

58

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

methylmalonic acid and homocysteine

59

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

True

60

What does Anaesthetic Nitrous Oxide do in the body

Inactivated Vitamin B12 coenzymes and induces megaloblastic changes and mild neuropathy

61

What causes Folic Acid deficiency

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

62

What causes a failure of folate metabolism

Enzyme deficiencies associated with megaloblastic changes and mental retardation