Antioxidants

Question 1

What are the five general strategies cells use to protect themselves from ROS damage?

Answer 1

1. compartmentalization of free radical production
2. metal sequestration
3. repair processes
4. defense enzymes
5. endogenous and exogenous antioxidants

Question 2

Where do we sequester the H2O2-producing enzymes in the body?

Answer 2

peroxisomes (which have a high content of antioxidant enzymes)

Question 3

Why do we sequester the metals?

Answer 3

so they don’t undergo the fenton reaction (like Fe bound to ferritin)

Question 4

What are three major defense enzymes that will convert ROS to nontoxic products?

Answer 4

superoxide dismutase, catalase, glutathione peroxidase

Question 5

What ROS is removed by superoxide dismutase?

Answer 5

superoxide free radical

Question 6

What ROS are removed by catalase and glutathione peroxidase?

Answer 6

hydrogen peroxide and lipid peroxides

Question 7

Superoxide dismutations converts superoxide to what?

Answer 7

hydrogen peroxide and O2

Question 8

Which defense enzyme is called the “primary defense” against oxidative stress?

Answer 8

superoxide dismutase because superoxide is such a strong initiator of chain reactions

Question 9

Superoxide dismutase mutation is implicated in what disease?

Answer 9

familial ALS - about 5-10% of total ALS cases

Question 10

What catalase turn hydrogen peroxide to?

Answer 10

water and O2

Question 11

Where is catalase located in high concentrations?

Answer 11

in the peroxisomes, but also in the cytosol and microsomal cell fraction (Highest in kidney and liver where peroxisomal content is highest)

Question 12

Catalse protects immune cells from what part of the immune response?

Answer 12

the respiratory burst

Question 13

Glutathione can convert hydrogen peroxide to what and lipid peroxides to what?

Answer 13

H2O2 to water

lipid perosides to nontoxic alcohols

Question 14

Glutathione peroxidases use what heavy metal?

Answer 14

selenium (the main reason we need some selenium in our diet)

Question 15

Where in the cell is glutathione peroxidase mostly located?

Answer 15

cytosol and mitochondria

Question 16

What enzyme will convert oxidized glutathione back to the sulfhydrul form? With what cofactor? From what pathway?

Answer 16

glutathione reductase with NADPH from PPP

Question 17

WHat are antioxidants?

Answer 17

free radical scavengers that can terminate free radical chain reactions by donating electrons to ROS (usually nonenzymatically)

Question 18

Why are nonenzymatic antioxidants capable of donating hydrogen groups without become radicals themselves?

Answer 18

They have aromatic rings structures that can deal with the loss of a hydrogen atom through resonance

Question 19

What’s the most widely distributed antioxidant in nature?

Answer 19

vitamine E

Question 20

What’s the most potent form of vitamin E?

Answer 20

alpha-tocapherol

Question 21

vitamin E largely protects against what type of ROS?

Answer 21

lipid peroxidation in membranes

Question 22

Although Vitamin E deficiency is rare, how does it present when it does occur?

Answer 22

hemolytic anemia due to fragility of RBCs
imbalance
myopathy
neurologic deficits due to degeneration of neurons

Question 23

What’s ascorbic acid’s primary function in the body?

Answer 23

collagen synthesis, but also plays a role inf ree radical defense

Question 24

How does reduced ascorbate work as an antioxidant?

Answer 24

It can generate the reduced form of vitamin E by donating electrons in the redox cycle - and the vitamin E does the majority of the antioxidant work

Question 25

Is ascorbic acid water or lipid soluble?

Answer 25

water soluble - so it floats unbound in the blood and extracellular fluid so it can find the lipid bound vitamin E

Question 26

What happens in vitamin C deficiency?

Answer 26

SCURVY: impaired wound healing, bleeding ecchymoses, swollen gums, anemia, enlargment and keratosis of hair follicles, lethargy, depression

Question 27

Carotenoids are the precusors of what vitamin?

Answer 27

vitamin A

Question 28

Carotenoids and vitamin A are capable of quenching what form of oxygen?

Answer 28

singlet oxygen (has no unpaired electrons in the outer orbitals but there is one orbital that is completely empty)

Question 29

How does a vitamin A deficiency present?

Answer 29

it’s the number 1 cause of non-accidental blindness worldwide (especially night blindness)
follicular hyperkeratosis
xeropthalmia

Question 30

What’s the general struture of the flavenoids?

Answer 30

contain two spatially separate aromatic fings

Question 31

How do the flavenoids work? (4 ways)

Answer 31

1. inhibit enzymes like xanthine oxidase that are responsible for superoxide anion production
2. chelate Fe and Cu to prevent the fenton reaction
3. donate electrons to superoxide or lipid peroxy radicals
4. stabilize free radicals by complexing with them

Question 32

What antioxidant accounts for the major free-radical trapping capacity of PLASMA?

Answer 32

Uric acid (with protein thiols)
(note - it's also the highest concentration antioxidant in the blood)

Question 33

Where in the body (not specifically the plasma) is uric acid most important for ROS protection?

Answer 33

the upper airways because there aren’t many other antioxidants there

Question 34

What product from the pineal gland acts as an antioxidant?

Answer 34

melatonin