Micronutrients Part 2 Flashcards
What are Group 2 Micronutrients? Examples?
- Micronutrients involved in defense against oxidants.
- Selenium, Vit C, Vit E, (some metals and vit B)
How many forms of vitamin E are found? What are these structures known as? Which of these structures is the most bioactive?
- 4 tocopherols, saturated structures (alpha, beta, gamma, delta)
- 4 tocotrienols, unsaturated structures(alpha, beta, gamma, delta)
- known as vitamers
- only alpha-tocopherol has significant activity in the body
What about the structure of alpha-tocopherol makes it bioactive compared to the other vitamers?
- alpha-tocopherol is RRR, which represents the (right-sided) chiral carbon configuration of the methyl groups in the side chain (compared to other tocopherols which have varying methyl configurations around the chiral centers)
- alpha-tocopherols head group has the most methylation
- alpha-tocopherols have a saturated side chain (compared to tocotrienols)
- for both of these reasons, alpha-tocopherol can easily fit into the binding pocket of TTP (tocopherol transfer protein)
If Tocotrienols cannot fit into TTP, then what is their biological function?
- they have antioxidant activity in the LIVER only
True or false: animal meats are not considered a good source of vit E?
Ture: most of the vit E in animals is stored in the adipose tissue (fat), which humans don’t usually eat.
- vit E usually come from plants such as nuts/seeds, plant oils, avocado
How is vit E deficiency testing for in the blood?
- only based on alpha-tocopherol
- tests examine the hemolysis (breakdown of RBC) in the presence of dilute H2O2.
- if there is a significant hemolysis of RBS, there is vit E deficiency (lack of anti-oxidant present to prevent cell destruction)
Although rare, when can vitamin E deficiencies occur?
- in premature infants who are incubated in oxygen-rich environments (high oxidative stress)
- people with malabsorption disorders or have their gallbladder removed (no bile), reducing absorption of fats (vit E is fat soluble)
- rare genetic conditions that prevent the proper synthesis of TTP and thus interfere with the transportation of vit E
How is alpha-tocopherol absorbed and transported throughout the body?
- fat-soluble, therefore requires bile and is incorporated into micelles
- absorbed by the small intestine by transporters
- packaged into chylomicrons
- sent to the liver where it binds to TTP
- binding to TTP helps transfer alpha-tocopherol into VLDL, which will drop it off to extrahepatic tissue (mostly adipose tissue)
How does the formation of ROS begin in the cell?
- O2 reacts with a free election (due to mitochondrial leaking) and forms an O2 radical anion (superoxide).
- superoxide is highly reactive
What is the cell’s defense mechanism against superoxide?
- The superoxide will be reduced to hydrogen peroxide (H2O2) via SOD, by picking up an electron from metal cations (Zn2+ and Cu+)
*superoxide + (zinc or copper cation) –> H2O2 (via SOD) - H2O2 –> 2 H2O (via GSH peroxidase)
Explain why iron can promote oxidative stress
- once the body converts superoxide to H2O2, free Fe2+ can unfavorably release an electron which converts H2O2 –> OH(radical)
*H2O2 + electron –>hydroxyl radical + H2O
What is the 2nd line of defense in the event of oxidative stress (hint: proceeding the formation of PUFA peroxy radical)?
How is this process beneficial to the cell?
- PUFA peroxy radicals are less reactive and have longer life spans than hydroxy radicals
- Vitamin E (alpha-tocopherol) donates an electron to form PUFA hydroperoxide.
- This interception can prevent the continuous formation of PUFA free radicals
PUFA hydroperoxide can cause cell degradation if not converted to a safer molecule. What line of defense it used?
- FA peroxidase uses glutathione to convert PUFA hydroperoxide –> PUFA alcohol which
In what form does selenium contribute to oxidant defense?
- present as selenoproteins
- Use GSH (glutathione) as a substrate (cofactor)
Glutathione peroxidase and FA peroxidase require 2 GSH, which are oxidized to 2 GSSH.
How is GSSH then regenerated?
- NADPH + H+ donates 2 electrons back to 2 GSSH to regenerate 2 GSH.
- NADP+ is reduced via the Pentose phosphate shunt to regenerate NADPH + H+.
TRUE OR FALSE: A healthy cell will have >90% GSH.
TRUE:
- this means that the cell is not undergoing oxidative stress and/or can readily respond to it.
TRUE OR FALSE:
- ascorbic acid requires a protein transporter to circulate through the blood
FALSE:
- vit C can circulate freely
What is the role of vitamic c in collagen production?
What is the relation to iron?
- supports the conversion of prolyl-hydroxylase-Fe3+ (inactive) to prolyl-hydroxylase-Fe2+ (active form)
- this also why iron supplements are best taken with a source of vit C, as they are both involved in the post-translational modification (proline –> proline-OH)
What is the purpose of RDA for vit C? What may be the symptoms of Vit C overdose?
- maximize tissue concentration, minimize excretion in urine
- overdose may cause kidney stones and digestive issues
What are the causes and symptoms of scurvy?
- chronic vit C deficiency
SYMPTOMS: - hemorrhages (gums and skin)
-hair loss
-loose teeth
(caused by lack of collagen production)
True or false: there is strong evidence that vit C can prevent a cold
- false
-there is evidence that vit C can shorten the duration of a cold.
