Free Radical and Antioxidants

Question 1

oxygen in the ground state that has absorbed light or other sources
“excited”
- not a radical but still reactive

Answer 1

singlet oxygen

Question 2

• generated by one-electron reduction of molecular oxygen, usually involve a metal catalyst
• not very reactive

Answer 2

superoxide anion

Question 3

transfer of two electrons to oxygen

Answer 3

hydrogen peroxide

Question 4

transfer of three electrons to oxygen

Answer 4

generates hydroxyl radical and hydroxide anion

hydroxyl radical is most reactive ROS, half-life of nanoseconds

Question 5

transfer of four electrons to oxygen

Answer 5

water

Question 6

What is a by-product of ETS?

Answer 6

ROS

- instead of transferring the electron to complex III, it gets put on oxygen to make superoxide anion

Question 7

What organelle is a major source of ROS?

Answer 7

mitochondria

Question 8

NADPH/cytochrome oxdiases are a source of which ROS?

Answer 8

superoxide anion

Question 9

Xanthine oxidase is a source of which ROS?

Answer 9

2 peroxide is produces when reducing hypoxanthine and xanthine to uric acid

Question 10

Reduction of iron and copper ions are a source of which ROS?

Answer 10

can donate electron to either oxygen or peroxide:
superoxide anion (oxygen) and hydroxyl radical (peroxide)

Question 11

How does chronic alcohol metabolism stress the liver?

Answer 11

1) oxidative stress from hydrogen peroxide damages membranes and kills cells
2) DNA damage from hydroxyethyl production produces mutations and predisposes to cancer

Question 12

located in cytoplasm and mitochondria to convert superoxide into the less reactive oxygen intermediate hydrogen peroxide
- antioxidant

Answer 12

superoxide dismutase

Question 13

heme-containing enzyme that detoxifies hydrogen peroxide

- antioxidant

Answer 13

catalase

Question 14

uses the electrons from reduced glutathione to reduce hydrogen peroxide
- antioxidant

Answer 14

glutathione peroxidase

Question 15

• water-soluble electron donor to many types of free radicals
• oxidized to dehydroascorbic acid
• antioxidant

Answer 15

ascorbic acid (vitamin C)

Question 16

• lipid-soluble radical scavenger
• present in membranes where it prevents damage from free radicals as well as from lipid peroxidation
• antioxidant

Answer 16

Vitamin E (tocopherols)

Question 17

• lipid-soluble compound that functions as an electron donor for the reduction of radicals such as lipid peroxides
• “quenches” the vibrating energy from the singlet oxygen
• antioxidant

Answer 17

Vitamin A (retinol)

Question 18

• water-soluble
• metabolic antioxidant
• plant extracts: green tea, grapes, red wine, chocolate

Answer 18

Polyphenols (flavonoids)

Question 19

major metabolic antioxidant in serum

Answer 19

uric acid

Question 20

• lipid soluble metabolic antioxidant

- unconjugated form can donate electrons to radicals

Answer 20

Bilirubin

- converts back to biliverdin

Question 21

What does peroxidative breakdown of polyunsaturated fatty acids (PUFAs) affect?

Answer 21

• integrity and function of cell membrane

- most serious damage to membranes

Question 22

Summarize the process of lipid peroxidation

Answer 22

PUFA»Lipid Radical»Lipid Peroxide (unstable), reacts with itself»malondialdehyde (mutagenic, reacts with purine bases in DNA)

Question 23

What leads to large amounts of ROS in RBCs?

Answer 23

high oxygen saturation

Question 24

1) glutathione peroxidase
- destroys hydrogen and organic peroxides
2) superoxide dismutase
- destroys superoxide
3) catalase
- converts hydrogen peroxide
4) high concentrations of GSH, Vit C, Vit E
- directly react with ROS
5) methemoglobin reductase

Answer 24

how RBC control oxidative stress

Question 25

Explain how methemoglobin reductase can reduce oxidative stress in RBCs

Answer 25

- replaces electron to the iron in heme | - repairs the oxidative damage by reducing the iron and converts methemoglobin back to Hb

Question 26

Which ROS does the most damage to DNA?

Answer 26

hydroxyl radical - causes DNA double strand breaks - interferes with replication and transcription by binding to guanine bases

Question 27

What does ROS cause protein damage?

Answer 27

- causes formation of incorrect disulfide bonds | - proteins become inactive and initiate its destruction

Question 28

- free radical that acts as a powerful vasodilator - modifies proteins in signal transduction pathways - most effective through activation of guanylate cyclase

Answer 28

Nitric Oxide

Question 29

- covalently modifies lipies, DNAs, and proteins - formed from superoxide and peroxynitrate anions - very reactive

Answer 29

Peroxynitrite