vitamin B12

Question 1

what is vit B12 also known as

Answer 1

cobalamin

Question 2

what are the forms of vit B12 in food

Answer 2

methylcabalamin &
5’-deoxyadenosylcobalamin

Question 3

vit B12 is synthesised solely by what

Answer 3

microorganisms

Cows eat grass that has microorganisms in it which goes into cow, we eat cow and so eat the microorganisms

Question 4

in humans vit B12 is involved in what

Answer 4

DNA,
fatty acid and amino acid
Metabolism

Question 5

failure of vit B12 absorption leads to what

Answer 5

pernicious Anaemia. This tends to manifest in older age groups

We have good stores of vit B12 so for this pernicious anaemia to develop symptoms can take a while

Question 6

describe B12s structure

Answer 6

Theres cobalt at centre of ring structure with variable group R

R group can be either: 5 prime - deoxyadenosyl, CH3, OH, CN

Question 7

explain how we absorb vit B12 that we eat

Answer 7

Red block is use eating something with vit B12. salivery production increases when we eat food, as it surrounds food ball lubricating it. This produces haptocorrin protein. This haptocorrin at this point in time in free. Stomach produces hydrochloric acid and peptin. Peptin breaks down protein releasing vit b12 allowing it to bind to haptocorrin.
When bound this is know as extrinsic factor. Stomach also produces an intrinsic factor that remains free from the extrinsic factor in stomach. Haptocorrin is replaced by intrinsic factor. This is the form of vit B12 that we then absorbed into epithelial cell and into blood.
Cant absorb vit b12 bound to haptocorrin or bound to nothing at all. So free vit b12 is lost
Stomach stops producing intrinsic factor in pernicious anaemia so the b12 cant be absorbed and is lost

Question 8

what is the long term store of B12

Answer 8

liver

Question 9

how much B12 do we lose and metabolise daily

Answer 9

only lose or metabolise about 0.1%

So, takes a very long time (e.g. several decades) to deplete stores and for dietary deficiency to manifest

Question 10

what is the RNI for vit B 12

Answer 10

1.5 ug/d

Question 11

what are some sources of vit B 12
and concerns over vegans diet

Answer 11

liver; Marmite and other yeast extracts; meat; (milk); (cheese)

Sources of vit b12 are animal its not associated with plant source
B12 is stored in liver so is why liver is a good source
So vegans don’t replace this daily loss as don’t eat these sources. This deficiency doesn’t manifest quickly but will eventually. So supplements are recommended but the source of the supplement may make people not want to take any

Question 12

vit B 12 is involved in what process and what does it do

Answer 12

B12 converts homocystein into methionine. So is needed for methylation reactions

If didn’t have enough then would be build up of homocysine

Question 13

explain vit B 12 deficiency

Answer 13

Anaemia – megloblastic (large cells)

hyperhomocysteinaemia

cognitive/memory deficits (due to neuropathy)

In deficiency, increased excretion
of methylmalonic acid

Same anaemia as folate anaemia so difficult to tell which one it is you have

Question 14

how can we work out if have a vit B 12 deficiency or not

Answer 14

Can measure methylmalonic acid levels is urine to work out if deficient or though a blood sample