Vitamins Flashcards
What is a vitamin?
What are these?
Act as coenzymes or cofactors in enzyme catalysed reactions
Any non-protein substance required by a protein for a biological activity
What are the 2 classes of vitamins?
Water soluble
Fat soluble
What are the 9 water soluble vitamins?
B1 B2 B6 B12 C Choline Folates Niacin Pantothenic acid
What are the 4 fat soluble vitamins?
A
D
E
K
What is vitamin B1 also known as?
Where is it found?
Thiamine
> liver
fresh veg
husk of cereal grains e.g. rice
What is the name of the disease caused by vitamin B1 deficiency?
Where is this prevalent?
Beriberi
Communities that don’t eat husk of cereal grain
What is the active component in B1/thiamine?
What is this required by?
Thiamine pyrophosphate OR diphosphate
Pyruvate dehydrogenase
What is pyruvate dehydrogenase used for?
Give the word equation
Converting Pyruvate (from glycolysis) into Acetyl CoA
Pyruvate + CoASH + NAD+
–> Acetyl CoA + CO2 + NADH
Where does Acetyl CoA go?
Where is this ATP required most?
To the TCA/ Kreb’s cycle
to produce ATP
Muscles
Nerves
What is thiamine generally required as?
A cofactor in oxidative decarboxylation reactions
e.g. important in ATP production
What are the features of pyruvate dehydrogenase?
> located in mitochondria
links glycolysis & citric acid cycle
multi-enzyme complex w/ 3 subunits
What are the 3 subunits of pyruvate dehydrogenase?
> Pyruvate dehydrogenase
> Dihydrolipoyl transacetylase
> Dihydrolipoyl dehydrogenase
What is the cofactor for pyruvate dehydrogenase?
Thiamine pyrophosphate
What is the cofactor for Dihydrolipoyl transacetylase?
Lipoate
Coenzyme A
What is the cofactor for Dihydrolipoyl dehydrogenase?
FAD
NAD+
What does NAD stand for?
Nicotinamide adenine dinucleotide
Which tissues are most affected by Beriberi?
Those w/ high ATP demand
- muscle & nerve
What are the 2 types of beriberi?
What are the different symptoms?
Wet
- oedema & heart enlargement
(eventual heart failure)
Dry
- neuropathies
What is neuropathies?
Any disease affecting peripheral nerves causing weakness & numbness
What is Wernicke’s encephalopathy?
Any disease affecting the brain
What are the 3 characteristics of Wernicke’s encephalopathy?
> nystagmus = rapid eye movements side to side OR up & down > ophthalmoplegia = paralysis of eye muscles > ataxia = unsteady gait/shaky movements
Who can get beriberi?
> alcoholics (w/ poor diet)
> communities subsisting on polished rice
What are the 5 common symptoms of beriberi?
> parasthesia = pins & needles > enlarged heart > wrist & foot drop > muscle weakness & atrophy > digestive disturbances
What causes an enlarged heart in those with beriberi?
Decrease in ATP
–> reduction in blood vessel size
–> vasodilation
= reduced blood pressure & resistance in vessels
–> heart has to pump harder to get blood around vascular tubes
= heart gets bigger
What are the sources of niacin?
Liver
Legumes
Lean meats
Cereals
What does Niacin form part of?
When is this involved in gluconeogenesis?
NAD
Lactate + NAD+ –> Pyruvate + NADH
(via lactate dehydrogenase)
What is the deficiency in niacin known as?
Pellagra
Where is pellagra endemic?
Remote areas
- green veg, fruit & animal protein are difficult to obtain
How was pellagra reduced in Egypt?
Replacing maize w/ wheat
in maize nicotinic acid is bound tightly
How was pellagra reduced in Mexico?
Washing maize w/ limewater
converts bound nicotinic acid –> free nicotinic acid
What is nixtamalisation?
Washing maize w/ limewater
What are the 4 Ds that pellagra is categorised by?
Dermatitis
Diarrhoea
Dementia
Death
What is dermatitis?
An inflammatory condition of the skin cause by an outside agent
What is dermatitis caused by?
A decrease in production of urocanic acid
- produced in body & acts as sunblock
What are the different locations for dermatitis?
Face = butterfly rash Hands = gauntlet Feet = boot Between anus & urethra = perineal lesions
What is B12 also known as?
Cobalamin
contains cobalt
What are the sources of B12?
NOT plants
Fish
Meat
Poultry
What does B12 absorption require?
GIF = gastric intrinsic factor
- a glycoprotein
- produced by parietal cells of stomach (also produce acid)
- mw = 50Kda
Why are B12 deficiencies so rare?
Body only requires v low concs
How does B12 bind to GIF?
As a complex (tetramer)
- 2 molecules of GIF bind to 2 molecules of B12
What does stomach acid do to food?
Helps to release nutrients via hydrolysis
How is B12 absorbed?
GIF-B12 complex binds to brush border of absorptive cells in the intestine
–> binds to transcobalamin + is transported to 2 main tissues:
bone marrow
nerves
What can cause B12 deficiencies?
Barrett’s metaplasia
Describe what happens in Barrett’s metaplasia
Acid reflux --> acid moves up into oesophagus from stomach = damages oesophagus --> cells replaced by intestinal cells = predisposes to cancer
What is the treatment of Barrett’s metaplasia?
How can this cause a B12 deficiency?
Achlorhydria = drug that reduces acid production
Reduced GIF production
What are the 2 main symptoms of B12 deficiencies?
Megaloblastic anaemia (Pernicious anaemia is the type of anaemia caused by B12 deficiency)
Neurological disorders e.g. paraesthesia
What is megaloblastic anaemia?
What are the symptoms?
V large red blood cells + decrease in the number of those cells
Pallor
Fatigue
Breathlessness
How is pernicious anaemia different to megaloblastic?
What is it associated with?
Can’t be treated w/ iron supplements
Chronic diseases that cause diarrhoea
e.g. tropical sprue, cholera, celiac
= prevents B12 absorption
What is Vitamin A also known as?
What is it found in?
When is it important?
Retinoic acid
Carrots
In pregnancy - for brain formation
Vit A is a teratogen. What is this?
Give examples
An agent or factor which causes malformation of an embryo
e.g. thalidomide, alcohol
What was thalidomide used to treat?
How did it affect newborn babies?
Morning sickness + sleeping trouble
Abnormal limb development
- usually absence of upper limb = phocomelia
What can alcohol cause when drank by pregnant women?
Foetal alcohol syndrome
= growth + mental retardation
What are the physical defects due to foetal alcohol syndrome?
> flat bridge of nose
epicanthal folds
flat philtre
rail road ears
What is vitamin A important for?
Visual pigments
- especially rhodopsin
(needed for low-level light)
Why is the anaemia in cobalamin deficiency referred to as megaloblastic anaemia?
There’re abnormally large numbers of megaloblasts in the blood
What are megaloblasts?
Large, nucleated immature progenitors
What are progenitors?
Cells that have a tendency to differentiate into a specific type of cell
What are the anaemia + neurological symptoms of B12 deficiency due to?
The lack of methionine
an amino acid
Why do megaloblasts accumulate in the blood on the anaemic?
DNA synthesis + protein synthesis are required to convert megaloblasts –> erythrocytes
Cobalamin is a cofactor of methionine synthase which is involved in DNA + protein synthesis
Not enough Cobalamin –> not enough DNA + protein for cell differentiation
How do erythrocytes form from bone marrow?
Bone marrow
- > stem cells
- > megaloblasts
- > erythroblasts
- > erythrocytes
What are the 2 main forms of vitamin A?
Retinol
- can be converted into retinoic acid
- found in liver & eggs
Retinal (provitamin A)
- can be converted in to retinol
- found in carrots & spinach
