Reactive Oxygen Species

Question 1

What is the Fenton reaction?

Answer 1

Fe2+ H2O2 = OH + Fe3 and OH-

Question 2

What are 3 types of ROS?

Answer 2

Hydroxyl radical, superoxide, hydrogen peroxide

Question 3

Why is H2O2 a ROS?

Answer 3

It can create a hydroxyl radical and diffuse throughout the body

Question 4

What is a free radical?

Answer 4

an atom, molecule, or ion with unpaired valence electrons

Question 5

What is the most reactive RNOS?

Answer 5

Peroxynitrorous acid

Question 6

Reactive oxygen and free radicals initiate what?

Answer 6

Cell injury

Question 7

What does oxygen toxicity result from?

Answer 7

Reactive oxygen species and free radicals

Question 8

Antioxidant defenses have evolved in parallel with what?

Answer 8

Evolution of aerobic metabolism

Question 9

How are ROS generated?

Answer 9

One electron transfers

Question 10

What is the Harber-Weiss reaction?

Answer 10

O2- + h2o2 with H+ —— O2 + h2o + OH

Question 11

The OH radical is especially dangerous in which cell type? Why?

Answer 11

RBC; leads to anemia

Question 12

What is the most reactive ROS?

Answer 12

Hydroxyl radical

Question 13

How does peroxynitrous induce damage?

Answer 13

Adds nitronium ions to aromatic rings, especially aromatic aa

Question 14

What are 3 normal biological processes that generate superoxides?

Answer 14

Phase I detox (p450), ETC (CoQ), LOX and COX

Question 15

What immune system cells generate ROS?

Answer 15

Neutrophils (respiratory burst)

Question 16

Which lipids are most susceptible to oxidative damage?

Answer 16

PUFA

Question 17

What are the 4 phases of free radical damage?

Answer 17

Initiation, propagation, termination, degradation

Question 18

What are 3 types of damage free radicals can produce in cells?

Answer 18

PUFA very susceptible, amino acid residues, DNA mutation from epoxides

Question 19

What are 3 ways antioxidants reduce ROS activity?

Answer 19

Before ROS are formed, get rid of them when they are formed, repair oxidative damage

Question 20

What are the 3 antioxidant enzymes?

Answer 20

Glutathione peroxidase, superoxide dismutase, catalase

Question 21

What is the first line of defense against oxidative damage?

Answer 21

Antioxidant enzymes

Question 22

What is the second line of defense against ROS?

Answer 22

Free radical scavengers like Vit C and Vit E

Question 23

What are the substrates for GPX?

Answer 23

Selenium

Question 24

Where are GPX and selenium in the cell?

Answer 24

Cytosol and mitochondrial matrix

Question 25

What are the substrates for SOD?

Answer 25

Cu, Zn (cytosol); Mn (mitochondria)

Question 26

What are the substrates for CAT?

Answer 26

Iron and peroxisomes

Question 27

GPX acts on which ROS?

Answer 27

H2O2

Question 28

SOD acts on which ROS?

Answer 28

Superoxide

Question 29

CAT acts on which ROS?

Answer 29

H2O2

Question 30

Glutathione is a co substrate for which enzyme?

Answer 30

GPX

Question 31

How do Vit C, E, and glutathione act as antioxidants?

Answer 31

Reducing agents

Question 32

Where is vitamin E in the cell?

Answer 32

Membranes and lipoproteins (plasma membrane and lysosomes)

Question 33

Where is Vit C in the cell?

Answer 33

Cytosol and mitochondria

Question 34

Where does absorption if vitamin C occur?

Answer 34

Distal small intestine

Question 35

How is vitamin C absorbed?

Answer 35

Sodium-dependent ascorbate transporter (SVCT)

Question 36

Where is SCVT1?

Answer 36

Distal small intestine

Question 37

How do most cells acquire vitamin C?

Answer 37

Through SCVT2 and GLUT transporters

Question 38

What does ascorbate do as a primary antioxidant?

Answer 38

Neutralizes radical oxygen and nitrogen species, peroxides, and superoxides

Question 39

Why must dehydroascorbate be reduced?

Answer 39

Has a short half life, must be reduced to avoid loss as diketogulonic acid

Question 40

Regeneration of the reduced form of Vitamin C involves which reducing agents?

Answer 40

NADH or glutathione

Question 41

Regeneration of the reduced form of Vitamin C involves which enzymes?

Answer 41

NADH reductase, dehydroascorbate reductase, thioredoxin reductase

Question 42

What are 3 points to remember for why vitamin C is such an important dietary antioxidant?

Answer 42

Major water soluble antioxidant, can neutralize both oxygen and nitrogen ROS, ascorbate radical is stable

Question 43

How do vitamin E and vitamin C differ as antioxidants?

Answer 43

Vitamin C acts as a direct antioxidant while vitamin E is a stable place to put the electrons until vitamin C can remove it

Question 44

What 2 things make up vitamin E?

Answer 44

Tocopherols, tocotrienols

Question 45

What component of vitamin E is selectively extracted in the liver?

Answer 45

a-tocopherol

Question 46

Where does vitamin E accumulate?

Answer 46

Membranes and lipoproteins

Question 47

How does vitamin E function as an antioxidant?

Answer 47

Terminates membrane lipid oxidation through single electron transfers, forming a stable tocopherol species