Lecture 3- Vitamin B12 Flashcards by Harriet Lynch

what food group is a rich source of vitamin B12

animal products

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why is vitamin B12 fortification very important for vegans

they do not consume animal products

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why is marmite not a very good source of vitamin B12

If you are consuming marmite you would need large amounts of it which will have bad affects of sodium

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where does vitamin B12 actually come from

bacteria

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commercial production of vitamin B12 happens how

large scale production via microbial fermentation

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commercial production of vitamin B12 predominantly uses how many strains of bacteria

three strains

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Vitamin B12 is the term used for what

the term used for all corrinoids that have biological activity of “cyancobalamin”

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what is the molecular weight if B12 like compared to other vitamins

Big molecular weight

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what is the chemical structure of vitamin B12

corrin ring (4 pyrrole rings) with a colbalt in centre and dimethylbezimidazole nucleotide

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what are three examples of corrinoids and what can be bound to the colbalt

These three are found in food
cyanocobalamin

methylcobalamin

deoxyadenosylcobalamin

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what are the active forms of B12

methylcobalamin

deoxyadenosylcobalamin

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what is the stable form of B12 and what is this used for

cyanocobalamin

most common form used for supplements

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what is cobalamin very sensitive to

very sensitive to acid

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what must happen to cobalamin and protein before it can be digested

cobalamin must be removed from protein for the body to use it

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why is the removal of cobalamin from a protein problematic

because this is done by an acid and cobalamin is very sensitive to acid

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cobalamin from the diet is bound to what

protein

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as cobalamin is swallowed what is released at the same time

haptocorrin

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what happens in the stomach to cobalamin and why is it volunerable

HCL is released and this breaks off the protein from cobalamin (vulnerable to attack by the acid)

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what will haptocorrin do and what does this mean

will bind to B12

binding to the cobalamin as soon as it released from the protein, protects it from acid attack

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what happens to cobalamin in the duodenum

proteases will split haptocorrin from the cobalamin

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why is it fine for cobalamin to be unbound in the duodenum

more alkaline space

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what does your body need in order to absorb cobalamin

transporter that will enable it to bind to a receptor

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what is the role of intrinsic factor regarding cobalamin

intrinsic factor is released from the stomach, will bind to cobalamin in the duodenum and can transport it into the ileal cell through the receptor

is B12 water soluble or water insoluble

water soluble

absorbed cobalamin is later what

later recycled after excreted in bile

what are two enzymes that are B12 dependent

methylmalonyl-CoA mutase methionine synthase

what is the role of methylmalonyl-CoA mutase enzyme

conversion of methylmalonyl CoA > succinyl CoA

what is the role of methionine synthase

transfer methyl group from 5MTHF to homocysteine, to form methionine

if you do not have enough vitamin B12, you will not have enough adenosylcobalamine (ADSB) and what does this mean

you will not have enough 1-Methylmalonyl-CoA mutase

if you have insufficient 1-Methylmalonyl-CoA mutase then what will you not be producing enough of and why is this important

succinyl-CoA = important in the citric acid cycle

if you have insufficient 1-Methylmalonyl-CoA mutase then you will have a build up of what and what will this produce more of

methylmalonyl-CoA, so more methylmalonic aicd will be produced

a build up of methylmalonyl-CoA also leads to a build up of propinoyl-CoA and what does this cause

propionic acid from gut flora odd chain fatty acids

what is the enzyme that converts a methyl group onto homocysteine to form methionine and when can this be inhibited

methionine synthase - when there is not enough B12 to support methionine synthase activity

in the methylfolate trap what will happen to the levels of 5MTHF and why

there will be higher levels, because can not go through the pathway due to methionine synthase problems

in the methylfolate trap what will happen to the levels of THF and why

there will be lower levels, the pathway is getting jammed up at 5MTHF, it can not get converted back to THF

in the methylfolate trap what will happen to the levels of 5,10-methylene THF and why

there will be lower levels, less THF so less being converted to 5,10-methylene THF

in the methylfolate trap what will happen to DNA synthesis

DNA synthesis will decrease

Q in history of viramin B12 in 1849 what were the complications described, was there treatment and was it fatal ?

clinical symptoms of pernicious (harmful in a gradual way) anaemia described - no treatment (vitamin B12 not discovered yet) - fatal

in history of viramin B12 in 1926 it was found eating what helped patients with pernicious anaemia

eating raw liver

when was vitamin B12 named

1948

what is pernicious anaemia

lack of intrinsic factor

lack of intrinsic factor is a what and what does this do

autoimmune disease = attacks parietal cells which limits or eliminates production of intrinsic factor

how is a vitamin B12 deficiency due to lack of intrinsic factor treated

treated with B12 intramuscular injection

how is B12 deficiency caused by lack of stomach acid (limited and absent) and what does this do

limited (hypochlorhydria) or absent (achlorhydria) production of HCL lessens B12 release from animal protein

lack of stomach acid related to vitamin B12 deficiency most commonly affects who

elderly

what are the two types of gastrointestinal damage that can lead to vitamin B12 deficiency

A Crohn’s disease Gastric bypass

what is crohn’s disease

a type of inflammatory bowel disease which may inflame the small intestine and reduce B12 absorption

what is gastric bypass

procedures that reduce the stomach area secreting stomach acid which can lead to reduced B12 absorption

there are 12 inherited errors of metabolism that have been identified and these affect : (4) (are they manageable)

- intestinal absorption - transport in the blood - cellular uptake - intracellular metabolism some are manageable, some are incompatible with life

what infants are particularly susceptible to vitamin B12 deficiency

breastfed infants with vegan mothers

megaloblastic anaemia has to do with vitamin B12 because of why

methylfolate trap

what is vitamin B12 neuropathy

“subacute combined degeneration of the cord” demyelination of motor neurons

what are the symptoms of vitamin B12 neuropathy

- A loss of position sense - spasms and weakness of lower limbs - cognitive changes - memory loss due to dementia - may be irreversible

what is the upper limit of vitamin B12

not possible to set no evidence of harm from several hundred times the requirement

what is the EAR and RDI of vitamin B12 in adult men and women

EAR : 2.0μg/day RDI: 2.4μg/day

what is the eating and activity guidelines around plant based milk alternatives linked to B12, vitamin D and calcium

if choosing plant based milks choose products fortified with calcium, vitamin D and vitamin B12

what products are permitted to be fortified with B12 in NZ

extracts of meat, vegetables or yeast analogues of meat legume protein containing foods