Oxygen toxicity

Question 1

Explain oxygen’s reactivity?

Answer 1

Favour reduction single electron
2 unpaired electrons
Highly reactive

Question 2

Explain reactive oxygen species (ROS)?

Answer 2

Highly reactive oxygen containing compounds Free radicals- single unpaired electron in orbital
OR
Compounds readily converted to oxygen free radicals in cell
Compounds contribute to ageing, homeostasis and some cancers.

Question 3

What do ROS cause?

Answer 3

Ageing
Homeostasis
Cancers

Question 4

Name 3 exogenous sources of ROS?

Answer 4

UV radiation
Tobacco
Drugs

Question 5

Name 2 endogenous sources of ROS?

Answer 5

NADPH
Electron transport chain

Question 6

What is the most potent ROS?

Answer 6

Hydroxyl radical

Question 7

Formation of radicals

Answer 7

Oxygen reduced by single electron form superoxide
Superoxide further reduced form hydrogen peroxide
Hydrogen peroxide reduces produce hydroxyl free radical
Further reduced produce water

Question 8

Is hydrogen peroxide a radical, soluble?

Answer 8

Not radical but is ROS
Easily converted hydroxyl radical (OH-)
Lipid soluble- cause damage away site of formation

Question 9

What catalyses the formation of hydroxyl radical from hydrogen peroxide?

Answer 9

Fe2+, Cu2+

Question 10

What processes changes hydrogen peroxide into hydroxyl radical?

Answer 10

Fenton reaction- iron dependent
Donate single electron

Haber Weiss also forms hydroxyl radical

Question 11

Write Fenton reaction?

Answer 11

Question 12

Write Haber-Weiss equation?

Answer 12

Question 13

Write Haber-Weiss cycle?

Answer 13

4 Reactions combine to produce OH. and consume H2O2

Question 14

What is the most potent ROS?

Answer 14

Hydroxyl radical
Initiator chain reactions form lipid peroxides

Question 15

Why is hydroxyl radical dangerous?

Answer 15

Lipid soluble- cause damage away from site formation and damage lipid barriers

Question 16

What is a respiratory burst?

Answer 16

Immune system defense against bacteria
Sudden release ROS by immune cells during phagocytosis (neutro, macro, monocytes)

Question 17

What is the process of respiratory burst?

Answer 17

Immune cells use NADPH oxidase to reduce oxygen to superoxide
Superoxide released
Superoxide further reduced hydrogen peroxide
Reduced again to hydroxyl radical- generate ROS

Neutrophils and monocytes use myeloperoxidase combine H202 with Cl- produces hypochlorite
H202+Cl- forms H20 + Cl-

Question 18

What is function of hypochlorite?

Answer 18

Damage bacterial cell membranes
Destroy bacteria

Question 19

What occurs if absence of NADPH oxidase?

Answer 19

Prevent formation ROS
Cause chronic granulomatous disease
Build up of pathogens in phagocytes
Can engulf not kill
Lead skin infections

Question 20

How is the body protected against oxygen toxicity?

Answer 20

Antioxidant enzymes
Antioxidant vitamins
Cellular compartmentalisation

Question 21

How do antioxidant enzymes protect body?

Answer 21

Superoxide dismutase
Convert superoxide to hydrogen peroxide (non-toxic) and oxygen

Catalase
Catalyses conversion hydrogen peroxide to water and oxygen
Protect white blood cells against own resp burst

Glutathione Peroxidase
Catalyses reduction hydrogen peroxide to water and disulphide

Question 22

What enzyme protects white blood cell against own respiratory burst?

Answer 22

Catalase

Question 23

How do antioxidant vitamins protect the body?

Answer 23

Vit E- found liver
- free radical scavenger
- protect against lipid peroxidation
- terminate free radical propagation in
membranes

Vit C- ascorbic acid
- react with superoxide and hydroxyl
radical
- regenerates reduced vit E

Question 24

How does cellular compartmentalisation protect the body?

Answer 24

Resp burst only in phagosomes
Harmful chemicals can’t exit and damage healthy tissue

Question 25

What do free radicals damage? and result?

Answer 25

Proteins, lipids, carbohydrates, nucleic acid
Membranes of: cell, nuc, mito, ER

Cell membrane damage- increased permeability membrane- influx Ca, H20, Na
Changes electrical gradient- cell function

Damage DNA- strand break and mutations

Question 26

What are diseases associated with free radical damage?

Answer 26

Emphysema
Parkinson’s
Diabetes
Acute renal failure