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Nutritional Biochemisty > Water soluble nutrients > Flashcards

Water soluble nutrients Flashcards

0
Q

How is the majority of Ascorbate taken up?

A

by sodium ion active transport, carrier proteins and sometimes is energy dependent (leukocytes)

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1
Q

What is the name of B1?

A

Thiamin

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2
Q

What amino acid is essential for vit C metabolism?

A

Glutathione

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3
Q

What is the other name for vitamin C?

A

Ascorbic acid or Ascorbate

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4
Q

What is Vitamin C’s main function?

A

Anti-oxidant, cofactor of hydroxylating enzymes involved in synthesis of collagen, carnitine and norepinephrine.

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5
Q

What is the deficiency syndrome or symptoms of deficiency of Vit C?

A
  • Scury

- appetite, fatigue, retarded wound healing, bleeding gums, spontaneous rupture of capillaries

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6
Q

What does oxidation refer to?

A

the removal of electrons or protons

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7
Q

When is Vit C absorbed via simple diffusion?

A

when ingestion of Vit C is a higher amounts

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8
Q

Before Vit C is absorbed what need to happen?

A

it may be oxidized to form dehydroascorbate

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9
Q

How is dehydroascorbate absorbed?

A

by passive diffusion or use of glucose transporters

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10
Q

What is reduction refering to?

A

the addition of electrons or protons, sometimes back to a more stable form

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11
Q

What does GSH stand for?

A

Glutathione

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12
Q

Glutathione oxidates what, and reduces what?

A

Glutathione reduces dehydroascorbate to ascorbaate, and oxidizes ascorbate into dehydroascorbate.

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13
Q

What does GSSG stand for?

A

Oxidised Glutathione

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14
Q

What does 2GSH stand for?

A

reduced Glutathione

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15
Q

Where are the highest concentrations of Vit C found in the body?

A

in the adrenal and pituitary glands

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16
Q

What is the estimated about that the body can store of Vit C, and where?

A

In the liver and its around 1.5g.

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17
Q

A medium level of Vit C in found in what organs?

A

liver, spleen, heart, kidney, lungs, pancreas & leukocytes

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18
Q

Where is the smallest amount of Vit C found in the body?

A

muscles and red blood cells

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19
Q

What two nutrients increase the urinary loss of Vit C? (antagonists)

A

Pectin and Zinc

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20
Q

What substance is necessary to reform ascorbate from dehydroascorbate and is essential for Vit C metabolism?

A

Glutathione

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21
Q

How is Vit C influenced by intake quantities?

A

the more that is consumed the less that is absorbed. intakes of 30-180mg/day have an absorption rate of 70-90%.

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22
Q

Vitamin C is necessary to activate which enzyme responsible for energy production and collagen synthesis?

A

Hydroxylase

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23
Q

What are the sources of B1 (Thiamin)?

A

meat, legumes, whole grains, breads, cereals, yeasts, wheat germ

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24
Q

What are the two supplement forms of B1?

A

Thiamin hydrochloride

Thiamin mononitrate salts

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25
Q

What is the plant based form of B1?

A

nonphosphorylated free form

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26
Q

What are the Anti-thiamine factors?

A

1) Raw fish- contains thiaminase which catalyses the cleavage of thiamin destroying the vitamin, so cooking destroys these enzymes.
2) Polyhydroxyphenols- oxyreductive processes that inactivate thiamine
- tannic acid
- Caffeic acid

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27
Q

Only what type of Thiamin is absorbed through the intestinal wall?

A

Free Thiamin

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28
Q

What low physiological cencentrations, Thiamin aborption is…

A

active and sodium dependent.

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29
Q

When intake of Thiamin is high, absorption is predominantly by…

A

passive diffusion

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30
Q

Where is Thiamin primarily absorbed?

A

in the jejunum, can occur in the ileum with lesser amounts in the duodenum

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31
Q

What are phosphates in the intestines required to do in reference to Thiamin?

A

to break the phosphate bonds with the thiamine to produce free thiamin.

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32
Q

What does ethanol do to Thiamin?

A

blocks absorption

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33
Q

What is the deficiency syndrome for Thiamin (B1)?

A

Beriberi; loss of appetite, weight loss, cardiovascular and neurological symptoms, apathy, confusion, decreased short term memory and irritability.

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34
Q

What are the main functions of Thiamin in the body?

A
  • energy transformation (coenzyme)
  • synthesis of pentoses and NADPH (coenzyme)
  • membrane and nerve conduction
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35
Q

Where is Thiamin found at a level of 90%?

A

As Thiamin diphosphate (TDP) in red blood cells

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36
Q

Where is B1 converted to TDP?

A

In the liver

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37
Q

Where is B1 stored and by what transport does it get there?

A

Active transport into the heart, skeletal muscle, kidneys and brain

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38
Q

Name the two coenzyme forms of Thiamine?

A

TDP- Thiamin diphosphate

TPP- Thiamin pyrophosphate

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39
Q

What are the group of enzymes that are required to break the bonds of Thiamin prior to absorption?

A

Phosphates

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40
Q

What is the name given to B2?

A

Riboflavin

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41
Q

What are some of the sources of B2?

A

milk, green vegetables, eggs, meat, small amounts in legumes & grains

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42
Q

Which vitamin B may be destroyed with exposure to sunlight?

A

B2 Riboflavin

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43
Q

What are the coenzyme derivatives of B2?

A

FMN- (flavin mononucleotide)

FAD- (flavin Adenine dinucleotide)

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44
Q

What are the 3 forms of B2?

A

1) Free Riboflavin & protein-bound riboflavin
2) Coenzyme derivatives
3) Phosphorus bound riboflavin & amino acid bound FAD

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45
Q

What are some Riboflavin antagonists?

A
  • copper
  • Zinc
  • Manganese
    (chelates riboflavin & FMN iron inhibit B2)
  • Alcohol
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46
Q

Where is most B2 absorbed?

A

in the duodenum

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47
Q

What processes are used for B2 absorption?

A 
Active transport
Passive diffusion (RFT2)
Saturation dependent (amounts for 95% of absorbed
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48
Q

What are the plasma proteins that transport B2?

A
  • Albumin
  • Fibrinogen
  • Globulins (immunoglobulins)
49
Q

What compounds increase conversion of riboflavin to its flavoenzymes FMN to FAD?

A

hormones ACTH, Aldosterone & Thyroid hormones

50
Q

Where are the highest concentrations of B2 storage?

A

Liver, kidney & heart

51
Q

What does B3 stand for?

A

Niacin, Nicotinic acid, Nicotinamide

52
Q

What are sources of B3?

A

Tuna, beef, turkey, functional cereals, whole grains, legumes, halibut, chicken, pork, bread products, seeds

53
Q

What are the different forms of B3?

A

1) Active forms in animal products as NAD and NADP
2) slaughtered meat NAD & NADP hydrolyse to free floating nicotinamide
3) Plant sources: Nicotinic acid
4) Complex carbohydrates: bound covalently, called niacytin eg corn
5) bound to small peptides called niacinogens
6) Synthesised in the liver from trytophan

54
Q

Where is nicotinamide & nicotinic acid absorbed?

A

in the stomach but more readily absorbed in the small intestines

55
Q

What transport is used for the absorption of B3?

A

Concentration dependent:

  • decreased concn= sodium dependent
  • increase in concn= passive diffusion
56
Q

Where and what is Nicotinamide formed?

A

in the intestinal tract or enteroytes, NAD & NADP are converted to Nicotinamide

57
Q

In what form is B3 usually found as in the plasma?

A

nicotinamide, but nicotinic acid can be found bound to plasma protiens)

58
Q

How does B3 cross into cell membranes?

A

via simple passive diffusion

59
Q

what is the only way that B3 can get into the kidneys and red blood cells?

A

via carrier mediated transport

60
Q

What happens to excess B3 in the body?

A

Excess Niacin and tryptophan is converted to NAD which is stored in small amounts not bound to anything

61
Q

What is the other name for vitamin B5?

A

Pantothenic Acid

62
Q

What are the sources of B5?

A

wide distributed in all plant and animal products

all meats esp. liver, mushrooms, egg yolks, legumes, whole grains, Brocolli, Avocardo, Royal Jelly

63
Q

What are the forms of Pantothenic Acid?

A
  • calcium pantothenate; in supplements

- 85% found in foods are bound as a component of coenzyme A (CoA)

64
Q

By which two mechanisms do B3 get absorbed from the intestines?

A

sodium dependent carrier & mediated diffusion

65
Q

How is B5 concentration dependent?

A

increase in concn= passive diffusion

decrease in concn= sodium dependent multivitamin transporter (SMVT- shares with biotin & lipoic acid)

66
Q

What is the enzyme form of Pantothenate?

A

Coenzyme A (CoA)

67
Q

How is B5 mainly transported in circulation?

A

mostly transported via red blood cells via passive diffusion

68
Q

In cells what is B5 typically used for?

A

to synthesize and resynthesize CoA

69
Q

Where is B5 found in high concs in the body?

A

heart, liver, Adrenal glands, kidneys, brain

70
Q

What is the other name for B6?

A

Pyridoxine

71
Q

What are the 3 coenzyme forms of Pyridoxine?

A

PNP- Pyridoxine phosphate
PLP- Pyridoxal phosphate
PMP- Pyridoxamine phosphate

72
Q

What is the name of the enzyme responsible for the hydrolysis prior to absorption into the enterocytes on B6, and what nutrient is it dependent on?

A

Alkaline phosphatase which is zinc dependent

73
Q

What is the active form of B6 known as?

A

PLP - Pyridoxal phosphate

74
Q

Which vitamin is an agonist of B6?

A

B2 (Riboflavin)

75
Q

How is B6 absorbed across both the brush and basolateral boarder?

A

Passive diffusion

76
Q

What are some sources of B6?

A

Sirloin steak, chicken, salmon, whole grain, bananas, navy beans, walnuts, vegies

77
Q

What are the different forms of B6?

A

1) Pyridoxine (PN)- most soluble form found in plants
2) Pyridoxal (PL)
3) Pyridoxamine (PM)
4) Pyridoxine phosphate (PNP)
5) Pyridoxal phosphate (PLP)
6) Pyridoxamine phosphate (PMP)
7) Pyridoxamine B-glycoside - found in plants but thought that mammals cannot hydrolyse the pyridoxine component.

78
Q

Where is the majority of B6 stored?

A

muscles with 75-80% then the liver at about 5-10%

79
Q

What is the name of B12?

A

Cobalamin

80
Q

What are the sources of B12?

A
  • only found in animal products
  • produced by microorganisms
  • meat, meat product, poultry, fish, shellfish, eggs, milk, milk products
81
Q

What are the different forms of B12?

A

1) Cyanocobalamin (-CN) - active as coenzymes
2) Hydroxocobalamin (-OH) - in meat, milk, milk products
3) Aquocobalamin (-H2O)
4) Nitritocobalamin (-N02)
5) 5’-dexoyodenosylcobalamin (5’-deoxyadenosyl) - meat
6) Methylcobalamin (-CH3) - active as enzymes (milk & milk products)

82
Q

What are the forms of B12 commonly found in supplements?

A

Cyanocobalamin & Hydroxocobalamin

83
Q

In the body what is cyanocobalamin converted to?

A

aquo- & hydroxo-cobalamin

84
Q

Does B12 need to be transported and if so why & how?

A

yes it does, otherwise it will just be taken up by mucous membranes. It is transported by R proteins (Heptocorrin) & IF (intrinsic factor)

85
Q

How does B12 get transported in the blood?

A

bound to TCII

86
Q

what is the first stage of digestion for B12?

A

it is released from peptide bonds in foods by gastric enzymes pepsin & HCL

87
Q

What are R proteins, and what are they responsible for?

A

known a colalophilins or haptocorrins (HC’s) are found in saliva & gastric juices, and can bind to B12 before it is releasedd from food.

88
Q

What is Instrinsic factor (IF) and what role does it play in B12 absorption?

A

it is a glycoprotein synthesized by the gastric parietal cells, but functions in the SI to aid B12 absorption.

89
Q

In the SI proteases hydrolyse R proteins bound to B12 to free the B12. What does a pancreatic insufficiency lead to?

A

a decrease in protease causing a decrease in absorption

90
Q

Name some factors that affect absorption of B12?

A
  • IF mediated absorption reaches saturation at about 1.5-2mg/meal
  • overall absorption is about 50%
  • 1-3% may be passively absorbed at pharmacological doses of 1-2g.
  • Vit C of 500mg or more may diminish or destroy the B12 in food
  • Calcium is required for B12 absorption
91
Q

Is B12 slow to absorb and how/why?

A

yes, after the attachment of IF-B12 complex to the receptor there is a 3-4hr delay before the cobalamin appears in circulation, it peaks 8-12 hours after ingestion

92
Q

How is B12 transported?

A

By:

TCI- (Transcobalamin I) <10% From peripheral tissues in the liver

93
Q

In the blood 60-80% of B12 is in what form?

A

methylcobalamin

94
Q

in the blood B12 is in 20% of what form?

A

adenosylcobalamin

95
Q

Can B12 be stored and if so where?

A

Yes, for many years. Mainly stored in the liver as the adenosylcobalamin form.

96
Q

What is the other name of Folate?

A

Folic acid

97
Q

What are the source of Folate?

A

Mushrooms, green vegies, spinach, brussel sprouts, brocolli, asparagus, turnip greens, peanuts, legumes citrus fruits, liver

98
Q

Describe how R proteins and IF’s aid digestion of B12?

A
  • once released from food in the stomach B12 remains bound to R protein as the vitamin is emptied from the stomach into the duodenum.
  • there the R protein is hydrolyzed by pancreatic proteases, and free cobalamin is released
  • IF then binds with cobalamin once it is released from R protiens.
  • The IF-cobalamin complex then travels to the ileum where receptors of B12 (cubilins) are present.
  • the absorption of this complex is by receptor-mediated endocytosis
99
Q

Which type of foods are generally higher if folate, raw or cooked?

A

raw, as the heating process depletes it

100
Q

How many forms of folate are there?

A

150 different forms

101
Q

What three parts much be present to make up folate?

A

1) pteridine
2) PABA
3) Glutamic acid

102
Q

What are the folate forms used in supplements?

A

Pteroylmonglutamic acid or pteroylmonoglutamate (most soluble forms)

103
Q

What is the primary form found in foods?

A

pteroylmonoglutamates containing up to 9 glutamate residues.

104
Q

What mineral is a cofactor for Folate absorption?

A

Zinc

105
Q

What are conjugases and what do they do?

A
  • also known as pteroylpolyglutamate hydrolases
  • they hydrolyse polyglutamate forms of folate to monoglutamate forms necessary for absorption
  • found in bile, pancreatic enzymes and on the brush boarder of jujunal mucosa
106
Q

What are FBP’s and what are they associated with?

A

Folate binding proteins, they are associated with the active transportation across the intestinal cell

107
Q

Why is folate in milk absorbed so readily?

A

due to it already being bound to FBP’s

108
Q

Which is better absorbed, folate from food or supplement and why?

A

supplemental folate, as dietary folate contain conjuages inhibitors making 50% of dietary folate absorbed.

109
Q

How is supplemental folate absorbed?

A

passive diffusion

110
Q

What are the inhibitors of folate absorption?

A
  • Alcohol - diminishes conjugase activity
  • Zinc deficiency - also diminishes cconjugase activity
  • Conjugase inhibitors
  • Lentils
  • Legumes
  • Cabbage
  • Oranges
111
Q

How is folate transported in the liver?

A

Folates are converted to THF & derivatives 5-methyl THF, 5- or 10- formyl THF which traps folate inside cells

112
Q

How is folate transported in the blood?

A

in the form of monogluamate, almost 2 thirds of folate in the blood are bound to folate-binding proteins (FBP’s) & small amounts to albumin & alpha-2-macroglobulin

113
Q

How is folate transported in cells?

A
  • THF may be converted into polyglutamate forms to become a functional coenzyme 5-methyl THF, 5- or 10- formyl THF
114
Q

Where is folate stored mostly in the body?

A

int the cytosol & mitochondria of cells, withe the liver storing about one-half of the bodies folate

115
Q

What are some sources of Biotin?

A

liver, egg yolks, legumes, soy beans, cereals, nuts,

Biotin is also produced by the colon bacteria and absorbed in proximal and midtransverse colon.

116
Q

Tell me about Avidin

A
  • It is a glycoprotein in raw egg white which may irreversibly bind biotin in a non-covalent bond and prevent biotin absorption
  • However it is unstable with heat, therefore the ingestion of cooked egg whites does not compromise biotin absorption
117
Q

Where is Biotin mostly absorbed?

A

in the jejunum and also the ileum

118
Q

How does absorption of Biotin across the basolateral boarder occur?

A

by SMVC (sodium dependent multi-vitamin carrier) mediated but does not require sodium

119
Q

What substances can inhibit intestinal absorption of Biotin?

A

Avidin in raw egg whites and Alcohol

Nutritional Biochemisty (9 decks)

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