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08. Metabolism > 8.09 Vitamins > Flashcards

8.09 Vitamins Flashcards

1
Q

What is a vitamin?

A

An organic component that has essential biochemical functioning in the body (we cannot live without).

They are not made by the body normally (require intake in the diet)

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2
Q

What are the two broad types of vitamins?

A

Fat soluble

Water soluble

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3
Q

What are the water soluble vitamins (also give their names) [9]

A
  • Thiamin (B1)
  • Riboflavin (B2)
  • Niacin (B3)
  • Pyroxidine (B6)
  • Pantothenic acid
  • Biotin
  • Folate
  • Cobalmin (B12)
  • Ascorbic acid (C)
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4
Q

Describe the main difference in digestion and absorption between the water soluble and the fat soluble vitamins

A

Water-soluble vitamins and minerals do not undergo digestion, as they are already small enough to be absorbed.

Fat soluble vitamins are present in food and require digestion to release. They’re absorption depends on the absorption of fats through the gut

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5
Q

What are the fat soluble vitamins? [4]

A
  • Vitamin K
  • Vitamin A
  • Vitamin D
  • Vitamin E
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6
Q

Describe the digestion process of the fat soluble vitamins

A
  • Digestive processes in the stomach release vitamins from food
  • Bile produced in the liver (stored in gall bladder) mixes with chyme and aids fat and vitamin absorption
  • Digestive enzymes in the pancreas further release vitamins (especially vitamin A)
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7
Q

What part of the gut does most of the absorption of fat soluble (and the water soluble) vitamins?

A

Small intestine

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8
Q

Describe the role of microbiota as a source of vitamins

A

Small amounts of vitamin K and biotin are made by the gut bacteria in the terminal ileum and large intestine and from there they are absorbed

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9
Q

What is the main function of the water soluble vitamins (as a group)

A

They are enzyme cofactors involved in metabolism and structure (notably collagen).

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10
Q

Which of the vitamins are available over a long peroid of time from the body (ie. storage wise)

A

The fat soluble vitamins are stored in the liver and can release vitamins when required for a long time from this reserve.

Water soluble vitamins are not stored for long term use (they turn over relatively quickly). Especially thiamin (B1) which is very low in supply.

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11
Q

What is the biological role for thiamin?

A

Biological role

  • A Coenzyme in decarboxylations
  • Carbohydrate, protein and fat metabolism
  • Nerve function
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12
Q

What are the food sources for thiamin?

A

Vegemite

Wholemeal breads and fortified cereals

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13
Q

What are the three outcomes that can occur as a result of a thiamin (B1) deficiency?

A
  • Rapid depletion in starvation (stores are very low - high turnover rate)
  • Beriberi (DRY: Extreme weakness, paralysis, anaemia and wasting.
  • Wernicke-Korsakoff syndrome in alcoholics (

Through bad nutrition and alcohol metabolism destroying thiamine causing eyes to be uncoordinated (nystagmus), wide step, confusion, hypothermia, amnesia and confabulation)

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14
Q

Describe the role of thiamin in metabolism

A

All energy derived by aerobic metabolism of sugars is dependent on thiamin availability. We need it to convert pyruvate to acetyl CoA (enable glycolysis into the krebs cycle)

In particular, Thiamin is essential for the nerves which are selectively disadvantaged by deficiency.

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15
Q

What is the pathophysiology of Beriberi disease?

A

Lack of thiamine leads to a wasting away of the neural tissue because it is in high demand/sensitive to lack of energy.

Thiamine is required for the conversion of pyruvate into acetyl-coA and hence there is a deficit of energy in cells.

This leads to peripheral neuropathy characterized by symmetrical impairment of sensory, motor, and reflex functions of the extremities

Note that Wet berberi occurs when serum albumin is low (attack on the liver cells producing albumin) resulting in oedema.

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16
Q

What is the other name for Vitamin B2?

What is it important for in the body?

A

Riboflavin

  • Electron carrier (FMN, FAD)
  • Carbohydrate, protein and fat metabolism
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17
Q

What are the food sources of Vitamin B2?

A
  • Vegemite
  • milk/cheese
  • fortified cereals
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18
Q

What is a riboflavin deficiency? How common is it?

A

It is Rare (seen mainly only in chronic alcoholics)

  • Usually associated with multiple vitamin deficiencies

Tongue in riboflavin deficiency becomes markedly swollen and oedematous and to have a light magenta colour.

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19
Q

What is the specific role of riboflavin (vitamin B2) in metabolism?

A

Riboflavin is a cofactor in specific oxidation/ reduction reactions including the TCA cycle.

They accept one electron at a time to be accepted and then another accepted. They are important to the cytochromes one at a time and the electron transport chain

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20
Q

What is another name for vitamin B3?

What is the role in the body?

A

Niacin (nicotinamide, B3)

  • Coenzyme
  • Electron carrier (NADH, NADPH)
  • Carbohydrate, protein and fat metabolism
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21
Q

What are the food sources of vitamin B3 (niacin) ?

A
  • Vegemite
  • Wheat bran
  • Fortified cereals
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22
Q

Describe the biochemistry of niacin (Vitamin B3)

A

NAD+ and NADH

Obligate 2 electron acceptor, vital for the krebs cycle and the electron transport chain

Niacin is required for adequate cellular function and metabolism as an essential component in coenzyme I (oxidized form of NAD) and coenzyme II (reduced form of NADP)

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23
Q

What are deficiencies of niacin?

A
  • Alcoholics can have deficiency
  • Pellagra (dermatitis, diarrhoea, dementia, death)
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24
Q

Describe pellagra

A

Historically occured to people who were on a solely corn diet leading to tryptophan and niacin deficiency

  • NAD/NADH are able to transfer electrons in a process that captures the energy by generating high-energy phosphate bonds = ATP then provides the energy necessary for other reactions.
  • A portion of this cofactor is also converted to NADP/NADPH. Reduced NADPH is used in reactions that detoxify reactive oxygen species, that metabolize drugs in a cytochrome P450 system, and that support lipid biosynthesis.
25
Q

What is another name for vitamin B6?

What are its roles in the body?

A

= Pyridoxine

It is very important in amino acid metabolism

26
Q

What are the food sources of pyridoxine?

A
  • Vegemite
  • Nuts
  • Bananas
  • Fortified cereals
27
Q

How common is a deficiency in pyridoxine?

A

They are rare

  • Need varies with protein intake (because higher protein intake requires more amino acid breakdown)
28
Q

What reaction is pyridoxine (vitamin B6) important for?

A

Involved in amino transferase reactions

29
Q

What is the role of biotin in the body?

A
  • A cofactors important cofactor responsible for CO2
  • Glucose, fat and amino acid biosynthesis

(it does the opposite action of pyridoxine)

30
Q

What are the food sources for biotin?

A
  • Brewer’s yeast
  • Egg yolk (cooked)
  • Soybeans
31
Q

Who are at risk of biotin deficiency?

Why?

A

People who eat large amounts of raw eggs

Raw egs contain avidin which antagonizes the action of biotin - avidin makes a very strong non-covalent bone with vitamins and cannot be separated

32
Q

Describe the biochemistry of biotin

A

It acts as a carrier for carbon dioxide in the pyruvate carboxylase reaction.

It is important in the acetyl-CoA carboxylase reaction which is important for fatty acid synthesis. it catalyses the synthesis of malonyl-CoA, a building block for new fatty acids and can inhibit the beta-oxidation of fatty acids.

33
Q

What is the biological role of folate?

A

For ‘one carbon’ metabolism (of amino acids, fat, purines for DNA)

Any tissue that is rapidly producing is going to have high demand for folate

34
Q

What are food sources of folate?

A
  • Green vegetables, liver
  • Fortified cereals
35
Q

What are problems seen in folate deficiency?

A
  • common in elderly and chronic alcoholics
  • a concern for pregnant women (causes failure of replication in the growing foetuses leading to spina bifida - neural tube defect)
  • Macrocytic anemia (large RBC)
36
Q

The incidence of spina bifida has decreased in the past few years due to the introduction of folate fortification in foods. What is a potential disadvantage linked to this?

A

Many cancers have gone up in incidence (this is a possible link)

37
Q

What is the biological role of vitamin B12 and the food sources of it?

A
  • A coenzyme (containing cobalt)
  • For folate metabolism; transalkylations.

Sources:

Meat, egg yolks, cheese

38
Q

Is it possible to get adequate vitamin B12 from a vegan diet?

Why or why not?

A

No, it is impossible to get vitamin b12 from vegetables.

Vitamin B12 is selectively involved in reactions in blood cells and nerves, actions that plants do not require

39
Q

What condition appears in vitamin B12 deficiency?

A

They are rare, but a concern for vegetarians, (particularly vegans)

Leads to neurological disorders and pernicious anaemia

40
Q

What is intrinsic factor? Why is it important?

A

A glycoprotein produced by the parietal cells of the stomach.

It is necessary for the absorption of vitamin B12 in the small intestine.

It is encoded by the GIF gene.

41
Q

What are the means by which a person can become deficient in vitamin B12 (pernicious anaemia)?

A
  1. Lack in the diet
  2. Inability to absorb vitamin B12 (most commonly due to a lack of intrinsic factor)
    • Autoantibodies directed against intrinsic factor or parietal cells
    • Genetic deficiency of the GIF gene
42
Q

What is ascorbic acid?

What is its role in the body?

A

Vitamin C

Biological role

  • cofactor in collagen synthesis
  • neurotransmitter metabolism
  • iron absorption
  • antioxidant
43
Q

What are the food sources of vitamin C?

A
  • citrus fruits
  • Cabbage
44
Q

Describe the role of vitamin C in the structure collagen

A

Collagen is made up of three major amino acids:

Gly + Ala + Proline

  • The Glycines all get together in the middle
  • The prolines fan out on the outside
  • Vitamin C reduction activity helps make hydroxyl grouops on the outside (prolines) which are required for the hydrogen bonds between amino acids of collagen
45
Q

What is seen as a result of vitamin C deficiency?

A

Scurvy

Decreased collagen integrity leads to gums and teeth breakdown.

The major problem is its affect on the major arteries (collage) causing haemorrhages

46
Q

Describe the role of Vitamin A in the body

A
  • Retinal important in night vision (the responder to light in the eyes, part of rhodopsin)
  • Retinol important in epithelium growth (healthy skin and eyes) - Retinol is a growth hormone for epithelium
47
Q

What is the source of vitamin A?

Where is it stored in the body?

A

Derived from 􏰀beta-carotene

Stored in the liver

It is toxic in high amounts

48
Q

Where is vitamin D derived from?

A

Derived from cholesterol

49
Q

What are the biological roles of vitamin D?

A

Important in Ca2+ regulation (critical in allowing Ca absorption from the gut) and bone development

50
Q

What are the conditions that appear (in the young vs. adults) in vitamin D deficiency?

What are the main causes of vitamin D deficiency?

A
  • Rickets in the young.
  • Knock-knees and bow legs. Osteomalacia in the adult.

Basically due to the lack of calcium in the body and the resorption of bone to maintain calcium balance.

Causes:

  • Most lack of Vit. D is due to lack of UV
  • Others include genetic lack of hydroxylases required to activate it
51
Q

What is critical for the synthesis of vitamin D (from cholesterol)?

A

UV light

52
Q

Describe the pathway for vitamin D synthesis

A
  • UV light excites a ring to make it fall apart
  • Liver hydroxylates the structure at one region
  • The kidney hydroxylates in the other
53
Q

Kidneys normally pass around 1g Calcium per day. What is the implication of this?

A

This must be made up by vitamin-D dependent absorption from the gut.

ie. we need at least to ingest 1g of Ca a day

54
Q

What other effects does vitamin D have on the body?

What is seen if there is too much vitamin D?

A

At least 1,000 genes are affected by vitamin D and some mediate protection against infection, cancer and autoimmune diseases

Excess leads to too much hypercalcaemia leading to risk of calcification of kidney

55
Q

What is the biological role of Vitamin E?

Where is it found as a food source?

A
  • Antioxidant. It inserts in membranes and intercepts free radicals.
  • It is a signal molecule linked to inflammation and cell division (newly found functions). Suggests caution in taking vitamin E pills.

Found in high levels in seed oils

56
Q

What is the problem with taking too many antioxidants? (such as a vitamin E toxicity)

A

It may compromise DNA repair

DNA repair gene HIF-1 is activated by free radicals. The immune system uses free radicals to kill rogue cells including cancer.

57
Q

What is the importance of vitamin K in the body?

A

It is very important in blood clotting

Activated thrombin causes fibrinogen to convert to fibrin and form a blood clot. Inadequate clotting leads to haemorrhage.

prothrombin + vitamin K → gamma-carboxy-glutamate at active site

58
Q

What is the source of vitamin K?

A

Gut flora make significant vitamin K.

59
Q

Newborns do not have a gut flora? What is the implication of this in terms of vitamin K?

How is it combated?

A

Haemorrhagic disease of the newborn (sterile gut) is avoided by giving an injection to newborns. Also known as vitamin K deficiency bleeding (VKDB) of the newborn

08. Metabolism (5 decks)

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