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)
1
Q
What is the name of B1?
A
Thiamin
2
Q
What amino acid is essential for vit C metabolism?
A
Glutathione
3
Q
What is the other name for vitamin C?
A
Ascorbic acid or Ascorbate
4
Q
What is Vitamin C’s main function?
A
Anti-oxidant, cofactor of hydroxylating enzymes involved in synthesis of collagen, carnitine and norepinephrine.
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
6
Q
What does oxidation refer to?
A
the removal of electrons or protons
7
Q
When is Vit C absorbed via simple diffusion?
A
when ingestion of Vit C is a higher amounts
8
Q
Before Vit C is absorbed what need to happen?
A
it may be oxidized to form dehydroascorbate
9
Q
How is dehydroascorbate absorbed?
A
by passive diffusion or use of glucose transporters
10
Q
What is reduction refering to?
A
the addition of electrons or protons, sometimes back to a more stable form
11
Q
What does GSH stand for?
A
Glutathione
12
Q
Glutathione oxidates what, and reduces what?
A
Glutathione reduces dehydroascorbate to ascorbaate, and oxidizes ascorbate into dehydroascorbate.
13
Q
What does GSSG stand for?
A
Oxidised Glutathione
14
Q
What does 2GSH stand for?
A
reduced Glutathione
15
Q
Where are the highest concentrations of Vit C found in the body?
A
in the adrenal and pituitary glands
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.
17
Q
A medium level of Vit C in found in what organs?
A
liver, spleen, heart, kidney, lungs, pancreas & leukocytes
18
Q
Where is the smallest amount of Vit C found in the body?
A
muscles and red blood cells
19
Q
What two nutrients increase the urinary loss of Vit C? (antagonists)
A
Pectin and Zinc
20
Q
What substance is necessary to reform ascorbate from dehydroascorbate and is essential for Vit C metabolism?
A
Glutathione
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%.
22
Q
Vitamin C is necessary to activate which enzyme responsible for energy production and collagen synthesis?
A
Hydroxylase
23
Q
What are the sources of B1 (Thiamin)?
A
meat, legumes, whole grains, breads, cereals, yeasts, wheat germ
24
What are the two supplement forms of B1?
Thiamin hydrochloride
| Thiamin mononitrate salts
25
What is the plant based form of B1?
nonphosphorylated free form
26
What are the Anti-thiamine factors?
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
27
Only what type of Thiamin is absorbed through the intestinal wall?
Free Thiamin
28
What low physiological cencentrations, Thiamin aborption is...
active and sodium dependent.
29
When intake of Thiamin is high, absorption is predominantly by...
passive diffusion
30
Where is Thiamin primarily absorbed?
in the jejunum, can occur in the ileum with lesser amounts in the duodenum
31
What are phosphates in the intestines required to do in reference to Thiamin?
to break the phosphate bonds with the thiamine to produce free thiamin.
32
What does ethanol do to Thiamin?
blocks absorption
33
What is the deficiency syndrome for Thiamin (B1)?
Beriberi; loss of appetite, weight loss, cardiovascular and neurological symptoms, apathy, confusion, decreased short term memory and irritability.
34
What are the main functions of Thiamin in the body?
- energy transformation (coenzyme)
- synthesis of pentoses and NADPH (coenzyme)
- membrane and nerve conduction
35
Where is Thiamin found at a level of 90%?
As Thiamin diphosphate (TDP) in red blood cells
36
Where is B1 converted to TDP?
In the liver
37
Where is B1 stored and by what transport does it get there?
Active transport into the heart, skeletal muscle, kidneys and brain
38
Name the two coenzyme forms of Thiamine?
TDP- Thiamin diphosphate
| TPP- Thiamin pyrophosphate
39
What are the group of enzymes that are required to break the bonds of Thiamin prior to absorption?
Phosphates
40
What is the name given to B2?
Riboflavin
41
What are some of the sources of B2?
milk, green vegetables, eggs, meat, small amounts in legumes & grains
42
Which vitamin B may be destroyed with exposure to sunlight?
B2 Riboflavin
43
What are the coenzyme derivatives of B2?
FMN- (flavin mononucleotide)
| FAD- (flavin Adenine dinucleotide)
44
What are the 3 forms of B2?
1) Free Riboflavin & protein-bound riboflavin
2) Coenzyme derivatives
3) Phosphorus bound riboflavin & amino acid bound FAD
45
What are some Riboflavin antagonists?
- copper
- Zinc
- Manganese
(chelates riboflavin & FMN iron inhibit B2)
- Alcohol
46
Where is most B2 absorbed?
in the duodenum
47
What processes are used for B2 absorption?
```
Active transport
Passive diffusion (RFT2)
Saturation dependent (amounts for 95% of absorbed
```
48
What are the plasma proteins that transport B2?
- Albumin
- Fibrinogen
- Globulins (immunoglobulins)
49
What compounds increase conversion of riboflavin to its flavoenzymes FMN to FAD?
hormones ACTH, Aldosterone & Thyroid hormones
50
Where are the highest concentrations of B2 storage?
Liver, kidney & heart
51
What does B3 stand for?
Niacin, Nicotinic acid, Nicotinamide
52
What are sources of B3?
Tuna, beef, turkey, functional cereals, whole grains, legumes, halibut, chicken, pork, bread products, seeds
53
What are the different forms of B3?
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
Where is nicotinamide & nicotinic acid absorbed?
in the stomach but more readily absorbed in the small intestines
55
What transport is used for the absorption of B3?
Concentration dependent:
- decreased concn= sodium dependent
- increase in concn= passive diffusion
56
Where and what is Nicotinamide formed?
in the intestinal tract or enteroytes, NAD & NADP are converted to Nicotinamide
57
In what form is B3 usually found as in the plasma?
nicotinamide, but nicotinic acid can be found bound to plasma protiens)
58
How does B3 cross into cell membranes?
via simple passive diffusion
59
what is the only way that B3 can get into the kidneys and red blood cells?
via carrier mediated transport
60
What happens to excess B3 in the body?
Excess Niacin and tryptophan is converted to NAD which is stored in small amounts not bound to anything
61
What is the other name for vitamin B5?
Pantothenic Acid
62
What are the sources of B5?
wide distributed in all plant and animal products
| all meats esp. liver, mushrooms, egg yolks, legumes, whole grains, Brocolli, Avocardo, Royal Jelly
63
What are the forms of Pantothenic Acid?
- calcium pantothenate; in supplements
| - 85% found in foods are bound as a component of coenzyme A (CoA)
64
By which two mechanisms do B3 get absorbed from the intestines?
sodium dependent carrier & mediated diffusion
65
How is B5 concentration dependent?
increase in concn= passive diffusion
| decrease in concn= sodium dependent multivitamin transporter (SMVT- shares with biotin & lipoic acid)
66
What is the enzyme form of Pantothenate?
Coenzyme A (CoA)
67
How is B5 mainly transported in circulation?
mostly transported via red blood cells via passive diffusion
68
In cells what is B5 typically used for?
to synthesize and resynthesize CoA
69
Where is B5 found in high concs in the body?
heart, liver, Adrenal glands, kidneys, brain
70
What is the other name for B6?
Pyridoxine
71
What are the 3 coenzyme forms of Pyridoxine?
PNP- Pyridoxine phosphate
PLP- Pyridoxal phosphate
PMP- Pyridoxamine phosphate
72
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?
Alkaline phosphatase which is zinc dependent
73
What is the active form of B6 known as?
PLP - Pyridoxal phosphate
74
Which vitamin is an agonist of B6?
B2 (Riboflavin)
75
How is B6 absorbed across both the brush and basolateral boarder?
Passive diffusion
76
What are some sources of B6?
Sirloin steak, chicken, salmon, whole grain, bananas, navy beans, walnuts, vegies
77
What are the different forms of B6?
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
Where is the majority of B6 stored?
muscles with 75-80% then the liver at about 5-10%
79
What is the name of B12?
Cobalamin
80
What are the sources of B12?
- only found in animal products
- produced by microorganisms
- meat, meat product, poultry, fish, shellfish, eggs, milk, milk products
81
What are the different forms of B12?
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
What are the forms of B12 commonly found in supplements?
Cyanocobalamin & Hydroxocobalamin
83
In the body what is cyanocobalamin converted to?
aquo- & hydroxo-cobalamin
84
Does B12 need to be transported and if so why & how?
yes it does, otherwise it will just be taken up by mucous membranes. It is transported by R proteins (Heptocorrin) & IF (intrinsic factor)
85
How does B12 get transported in the blood?
bound to TCII
86
what is the first stage of digestion for B12?
it is released from peptide bonds in foods by gastric enzymes pepsin & HCL
87
What are R proteins, and what are they responsible for?
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
What is Instrinsic factor (IF) and what role does it play in B12 absorption?
it is a glycoprotein synthesized by the gastric parietal cells, but functions in the SI to aid B12 absorption.
89
In the SI proteases hydrolyse R proteins bound to B12 to free the B12. What does a pancreatic insufficiency lead to?
a decrease in protease causing a decrease in absorption
90
Name some factors that affect absorption of B12?
- 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
Is B12 slow to absorb and how/why?
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
How is B12 transported?
By:
| TCI- (Transcobalamin I) <10% From peripheral tissues in the liver
93
In the blood 60-80% of B12 is in what form?
methylcobalamin
94
in the blood B12 is in 20% of what form?
adenosylcobalamin
95
Can B12 be stored and if so where?
Yes, for many years. Mainly stored in the liver as the adenosylcobalamin form.
96
What is the other name of Folate?
Folic acid
97
What are the source of Folate?
Mushrooms, green vegies, spinach, brussel sprouts, brocolli, asparagus, turnip greens, peanuts, legumes citrus fruits, liver
98
Describe how R proteins and IF's aid digestion of B12?
- 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
Which type of foods are generally higher if folate, raw or cooked?
raw, as the heating process depletes it
100
How many forms of folate are there?
150 different forms
101
What three parts much be present to make up folate?
1) pteridine
2) PABA
3) Glutamic acid
102
What are the folate forms used in supplements?
Pteroylmonglutamic acid or pteroylmonoglutamate (most soluble forms)
103
What is the primary form found in foods?
pteroylmonoglutamates containing up to 9 glutamate residues.
104
What mineral is a cofactor for Folate absorption?
Zinc
105
What are conjugases and what do they do?
- 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
What are FBP's and what are they associated with?
Folate binding proteins, they are associated with the active transportation across the intestinal cell
107
Why is folate in milk absorbed so readily?
due to it already being bound to FBP's
108
Which is better absorbed, folate from food or supplement and why?
supplemental folate, as dietary folate contain conjuages inhibitors making 50% of dietary folate absorbed.
109
How is supplemental folate absorbed?
passive diffusion
110
What are the inhibitors of folate absorption?
- Alcohol - diminishes conjugase activity
- Zinc deficiency - also diminishes cconjugase activity
- Conjugase inhibitors
- Lentils
- Legumes
- Cabbage
- Oranges
111
How is folate transported in the liver?
Folates are converted to THF & derivatives 5-methyl THF, 5- or 10- formyl THF which traps folate inside cells
112
How is folate transported in the blood?
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
How is folate transported in cells?
- THF may be converted into polyglutamate forms to become a functional coenzyme 5-methyl THF, 5- or 10- formyl THF
114
Where is folate stored mostly in the body?
int the cytosol & mitochondria of cells, withe the liver storing about one-half of the bodies folate
115
What are some sources of Biotin?
liver, egg yolks, legumes, soy beans, cereals, nuts,
| Biotin is also produced by the colon bacteria and absorbed in proximal and midtransverse colon.
116
Tell me about Avidin
- 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
Where is Biotin mostly absorbed?
in the jejunum and also the ileum
118
How does absorption of Biotin across the basolateral boarder occur?
by SMVC (sodium dependent multi-vitamin carrier) mediated but does not require sodium
119
What substances can inhibit intestinal absorption of Biotin?
Avidin in raw egg whites and Alcohol
