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
