Redox Biology I

Question 1

Which reaction do oxidoreductases catalyse?

Answer 1

Net transfer of electronsto or from a substrate

Question 2

What kinds of enzymes are classes as oxidoreductases?

Answer 2

• Dehydrogenases
• Oxidases
• Reductases

Question 3

How are reactive oxygen species formed?

Answer 3

By slippage in the ETC

Question 4

What are the major sites for ROS production?

Answer 4

• Complex 1
• Complex 2
• Complex at FMN and quionine binding sites

Question 5

What non-respiratory enzymes can also produce ROS?

Answer 5

eNOS and xanthine oxidase

Question 6

How can ROS be produced in an inorganic way?

Answer 6

• Ionising radiation
• Environmental stress

Question 7

What are ROS particularly damaging to?

Answer 7

• Fe-S clusters
• DNA

Question 8

Why are ROS damaging to DNA?

Answer 8

They can cause unwanted disulfide bond formation

Question 9

What electronic state does oxygen have?

Answer 9

Triplet ground state

Question 10

What is interesting about the z electrons in oxygen?

Answer 10

They are unpaired with the same spin

Question 11

Why is OH· so bad?

Answer 11

It can react with anything

Question 12

Give examples of enzymes which shield us from ROS

Answer 12

• Superoxide dismutase
• Catalase

Question 13

What reaction does superoxide dismutase catalyse?

Answer 13

2O₂ + 2H⁺ → O₂ + H₂O

Question 14

What are the 3 forms of superoxide dismutase?

Answer 14

• MnSOD
• CuZnSOD
• NiSOD

Question 15

What is the superoxide dismutase reaction 2nd order with respect to?

Answer 15

Superoxide

Question 16

What reaction does catalase catalyse?

Answer 16

2H₂O₂ → 2H₂O +O₂

Question 17

What is the major small molecule anti-oxidant?

Answer 17

Glutathione

Question 18

What 3 amino acids make up glutathione?

Answer 18

Glutamate, cysteine, glycine

Question 19

Which form of glutathione is linked by a disulfide bond?

Answer 19

oxidised GSSG

Question 20

Which enzyme maintains cellular glutathione?

Answer 20

Glutathione reductase

Question 21

What induces glutathione reductase?

Answer 21

Oxidative stress

Question 22

What does glutathione reductase use to reduce the disulfide bond of GSSG?

Answer 22

NADPH

Question 23

What cofactor does glutathione reductase rely on?

Answer 23

FAD

Question 24

What reaction does glutathione reductase catalyse?

Answer 24

2GSSG + NADPH +H⁺ → 2GSH + 2NADP⁺

Question 25

What do glutathione peroxidases protect against?

Answer 25

Damage by H₂O₂

Question 26

What is unusual about glutathione peroxidases?

Answer 26

It contains selenocysteine

Question 27

What reaction does glutathione peroxidase catalyse?

Answer 27

2GSH + H₂O₂ → GSSG + 2H₂O

Question 28

What do the Grx family of enzymes do?

Answer 28

• Help to maintain cellular redox balance by reducing or oxidising bonds in other proteins

Question 29

Which enzyme is involved in protection of damage from lipid hydroperoxidases?

Answer 29

GPx4

Question 30

Which vitamins are maintained in their active state by glutathione?

Answer 30

• Vitamin C
• Vitamin E
• Vitamin A

Question 31

Why are carotenoids useful in plants?

Answer 31

They help protect plants from oxidative damage to photosystems

Question 32

What is beta-carotene susceptible to reaction with?

Answer 32

Single oxgen

Question 33

How do plant-based carotenoids protect photosystems?

Answer 33

Dissipation of excitation as heat

Question 34

What is the role of vitamin C in radical protection?

Answer 34

It acts as a radical scavenger which can also initiate free radical chain reactions