Vitamin B12 and Folate Metabolism

Question 1

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

Answer 1

B12, Folate

Question 2

Provides Methylation for the conversion of homocysteine to ________

Answer 2

Methionine

Question 3

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

Answer 3

Deoxythymidine Monophosphate (dTMP)

Question 4

What is the average dietary intake of B12

Answer 4

20

Question 5

What is the average dietary intake of folate

Answer 5

250

Question 6

What is the major food source of Vitamin B12

Answer 6

Animal Produce only

Question 7

What are the major food sources of Folate

Answer 7

Liver, Vegetables

Question 8

How long is the normal body store for Vitamin B12

Answer 8

Several years

Question 9

What long is the normal body store for folate

Answer 9

A few months

Question 10

What is the mode of absorption for Vitamin B12

Answer 10

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

Question 11

What is the mode of absorption for folate

Answer 11

Converted to Tetrahydrofolate and absorbed in the duodenum and jejeunum

Question 12

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

Answer 12

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

Question 13

Folate and B12 is necessary for synthesis of ________

Answer 13

DNA

Question 14

B12 deficiency causes Folate to be trapped in _______ form

Answer 14

Methyl Form

Question 15

Tue or False, RNA synthesis is unaffected

Answer 15

True

Question 16

The resultant deficiency in what substance affects DNA synthesis

Answer 16

Methylene FH4

Question 17

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

Answer 17

Large red cells with nuclear retention and a flimsy membrane

Question 18

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

Answer 18

Megaloblastic Anaemia

Question 19

Where does B12 absorption occur

Answer 19

Illeum

Question 20

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

Answer 20

R protein, gastric and duodenal enzymes, intrinsic factor

Question 21

What cells synthesize and and secrete IF

Answer 21

Gastric Parietal Cells

Question 22

What is the MW of the glycoprotein IF

Answer 22

45,ooo

Question 23

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

Answer 23

Calcium ions and a neutral pH

Question 24

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

Answer 24

6 hours

Question 25

What are the two mechanisms of Cobalamin absorption

Answer 25

Passive Absorption and Active Absorption

Question 26

Which mechanism of Cobalamin transport is insufficient

Answer 26

Passive Absorption

Question 27

Where does the passive absorption of Cobalamin occur

Answer 27

Buccal, duodenal and ileal mucosa

Question 28

True or False, passive absorption is Slow

Answer 28

False it is rapid

Question 29

What is the Mode of Administration for Vitamin B12

Answer 29

Oral

Question 30

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

Answer 30

True

Question 31

What substance mediates oral doses of Cobalamin

Answer 31

Gastric IF

Question 32

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

Answer 32

Stomach, Duodenum and jejunum

Question 33

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

Answer 33

Haptocorrins

Question 34

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

Answer 34

Pancreatic trypsin, Intrinsic Factor

Question 35

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

Answer 35

Hydrochloric Acid

Question 36

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

Answer 36

Cubulin

Question 37

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

Answer 37

Endocytosed , IF

Question 38

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

Answer 38

Transcobalamines

Question 39

What is the name of the 3 Transcobalaminese

Answer 39

TCI-TCII-TCIII

Question 40

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

Answer 40

TCII

Question 41

Where does the TCII- B12 complex bind

Answer 41

Developing blood cells in the bone marrow

Question 42

The Transcobalamines I and II are what type of globulins

Answer 42

Alpha

Question 43

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

Answer 43

Granulocytes

Question 44

What is another name for Transcobalamines and where are they found

Answer 44

R binders in gastric juices

Question 45

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

Answer 45

TCI and TCIII

Question 46

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

Answer 46

True

Question 47

Where are Folates absorbed maximally

Answer 47

Upper Jejunum

Question 48

Folate Polyglutamate must be digested to form __________ before Absorption

Answer 48

Monoglutamate

Question 49

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

Answer 49

N-5- methyltetrahydrofolate

Question 50

True or False, Folate functions as single carbon donor acceptor

Answer 50

True

Question 51

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

Answer 51

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

Question 52

What is the cause of Pernicious Anaemia

Answer 52

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

Question 53

What abnormalities cause Pernicious Anaemia

Answer 53

Gastric cell Atrophy, Achlorhydria

Question 54

What is the most common age group for Pernicious Anaemia

Answer 54

Women over 50 years

Question 55

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

Answer 55

True

Question 56

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

Answer 56

True

Question 57

What are the causes of Vitamin B12 Deficiency

Answer 57

Inadequate dietary intake Intestinal Malabsorption Failure of utilization of Vitamin B12

Question 58

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

Answer 58

methylmalonic acid and homocysteine

Question 59

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

Answer 59

True

Question 60

What does Anaesthetic Nitrous Oxide do in the body

Answer 60

Inactivated Vitamin B12 coenzymes and induces megaloblastic changes and mild neuropathy

Question 61

What causes Folic Acid deficiency

Answer 61

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

Question 62

What causes a failure of folate metabolism

Answer 62

Enzyme deficiencies associated with megaloblastic changes and mental retardation