vitamin b12

once released in the duodenum and it exists as free cobalamin, b12 binds to and forms a complex with ___________ _____________ secreted by gastric parietal cells

intrinsic factor

b12 in vitamins/fortified foods is/is not bound to proteins

is not

what is vitamin b12 resistant to?

light, heat, oxidation

- there exists enough IF but there is not enough B12 - if there is not enough B12 then 5-Methyl THF cannot be converted to THF and homocysteine cannot be converted to methionine = neurologic probs

megablastic macrolytic anemia

abnormally large, immature RBC

megablastic macrolytic anemia

B12 serves as a cofactor in 2 distinct enzymatic processes: 2. homocysteine --------?----------> methionine - this reaction is also linked to _________ metabolism because the methyl group transferred to homocysteine is provided by the conversion of 5MTHfolate --> THfolate

methionine synthase, methylcobalamin, folate

main form of b12 in blood

methylcobalamin

milk products

methylcobalamin, hydroxocobalamin

what determines the form of cobalamin

R group

after b12 is liberated from proteins by pepsin and HCl it binds to what in saliva and gastric juices

R proteins

in the blood, b12 is bound to 1 of 3 transcobalamins: _______: circulating storage form _______: carries newly absorbed cobalamin to tissues _______: delivery from peripheral tissues to liver

TCI, TCII, TCIII

in the tissues, uptake of vitamin b12 is receptor dependent (all cells have the receptor for _______) and it enters the cell via receptor mediated endocytosis and degraded by _______________ to release b12

TCII, lysosomes

what is the active form of folate needed for nucleic acid metabolism and RBC formation?

THF

once in the duodenum, the R protein is digested by _________________ _______________ to release vitamin b12 (free cobalamin)

pancreatic enzymes

in the stomach, what 2 things release b12 from proteins

pepsin and HCl

- cannot absorb b12 - fixed by IM injections of b12

pernicious anemia

also known as fatal anemia

pernicious anemia

what is the name of the deficiency caused by a lack of intrinsic factor

pernicious anemia

only b12 from food sources are bound to ____________ and require release by pepsin and HCl

proteins

THfolate is essential for ____________ and _______________ production. therefore, a b12 deficiency leads to an accumulation of ______________ with impaired DNA synthesis

purine, pyrimidine, 5-MTHfolate

b12 also plays a critical role in the conversion of: L-methylmalonyl CoA ---> ______________ ________ - this reaction also relies on __________ to convert proprionyl CoA ---> D-methylmalonyl CoA which is a precursor for the L-methylmalonyl CoA

succinyl CoA, biotin

once inside the enterocyte, b12 is released from IF and is carried across the basolateral membrane by ______________________ ____ for transport in the blood

transcobalamin II

those at risk for vitamin b12 deficiency:

vegans, gastric anomalies, gastric bypass pts, malabsorptive disease, nitrous oxide

cobalt deficiency = ________________ _____ deficicency

vitamin b12

is vitamin b12 fairly stable?

yes

is vitamin b12 degraded a lot or just a little?

a little

B12 is "______ ________________" so when it binds to R proteins it is protected from bacterial use inside the stomach

acid sensitive

main form of b12 in liver

adenosylcobalamin

meat products

adenosylcobalamin, hydroxocobalamin

what are the 2 active forms of vitamin b12?

adenosylcobalamin, methylcobalamin

what kind of foods are sources of vitamin b12?

animal products (meat, fish, poultry, eggs, milk)

what is another name for vitamin b12?

cobalamin

the core of b12 is a corrin ring that encircles a central ____________ ion

cobalt

cobalamin is the generic term for a group of compounds called _________________

corrinoids

in the ileum, vitamin b12-IF complex binds to specific ___________ receptors on the brush border and is absorbed into the enterocyte via pinocytosis

cubam

supplements

cyanocobalamin, hydroxocobalamin

_________: contains less but its absorption is better

dairy

the B12-R complex (haptocorrins or transcobalamin I) travels from the stomach to __________________

duodenum

if b12 is lacking then __________ can become trapped as ____________________ - this causes the cell too be void of ________ - therefore a vitamin b12 deficiency can become a ________________ __________ deficiency

folate, 5-Methyl THF, THF, conditional folate

most vitamin b12 is reabsorbed in the _______ (does this by binding to ________ and is reabsorbed)

ileum, IF

____%/day is excreted in bile

0.1

how much vitamin b12 can prevent deficiency for 3-5 years

2-3 mg

how long is vitamin b12 stored in the body?

3-5 years

B12 serves as a cofactor in 2 distinct enzymatic processes: 1. L-methylmalonyl-CoA -----------?--------------> succinyl CoA

L-methylmalonyl CoA mutase, adenosylcobalamin