Session 5 (2) - Byproducts of metabolism

Question 1

How are ROS’s formed?

Answer 1

Some electrons leaked from electron transport chain (1+3), prematurely reducing oxygen to super oxide radicals (O(x2)-. Oxygen molecule with unpaired electron.

Question 2

What do ROS cause damage to?

Answer 2

DNA, protein and membranes

Question 3

What enzyme catalyses formation of hydrogen peroxide and oxygen from ROS?

Answer 3

Superoxide Dismutase (SOD)

Question 4

What is the issue with hydrogen peroxide production?

Answer 4

It is in itself a Reactive Oxygen Species

Question 5

What enzyme is used to remove H2O2

Answer 5

Enzyme catalase therefore rapidly breaks it down into molecular oxygen and water.

Question 6

What do you add to H2O2 to form hydroxyl radicals? Give equation.

Answer 6

H2O2 + Fe2+ –> OH- (hydroxyl radicals)

Question 7

What is the issue with hydroxl radicals?

Answer 7

Highly reactive, damage cell membranes but cannot be elimated by enzymatic reaction.

Question 8

How are hydroxyl radicals removed?

Answer 8

NADPH provides H+ and converts to water.

Question 9

How are ROS useful in the body? What enzyme is used in reaction? What happens to cell and surrounding bacterial cells? What system is this used in?

Answer 9

Neutrophils and monocytes can rapidly produce a release of ROS, known as an oxidative burst. NADPH Oxidase is used.
Electrons from NAPH transfer across membrane.
Cell and surround bacterial cells destroyed.
Immune system.

Question 10

How can oxidizing agents be produced in the body via artificial means?

Answer 10

Primaquine (anti-malarial) and Paraquat (banned herbicide)

Ionising radiation

Question 11

What is produced from Arginine in the body? What enzyme is used, and what is it involved in?

Answer 11

NO, produced from arginine via Nitric Oxide synthase.

NO combines with O2 to produce peroxynitrite, which is involved cell damage.

Question 12

Name five cell defences against ROS other than SOD and catalase

Answer 12

NADPH, glutathione, anti-oxidant vitamins, flavenoids and minerals

Question 13

What is NADPH, and where is it produced?

Answer 13

reducing agent that is mostly produced by the pentose phosphate pathway.

Question 14

What is glutathione?

Answer 14

a tripeptide that is usually abundant in cells and acts as an important antioxidant. The thiol (-SH) group in cysteine can donate its H and therefore act as a reducing agent.

Question 15

How is oxidised glutathione converted bact to reduced form?

What enzmes catalyse the reactions?

Answer 15

NADPH

glutathione peroxidise and glutathione reductase

Question 16

Name three anti-oxidant vitamins

Answer 16

Vitamin C, Vitamin E, Vitamin A

Question 17

How is diabetes mellitus related to ROS?

Answer 17

(Type 1) B cell destruction by ROS

Question 18

How is alzheimers disease caused by ROS

Answer 18

Protein damage and misfolding by ROS

Question 19

How are the negative effects of cardiovascular disease compounded by ROS?

Answer 19

Reperfusion causes huge amounts of ROS to be produced. ROS switched on by cells when dying, encouraged by reoxygenation.

Question 20

Outline cellular defences against following 
O2- 
H2O2
OH- 
NO- 
ONOO-

Answer 20

SOD
Catalase
NADPH
Glutathione
Other antioxidants

Question 21

What is oxidative stress?

Answer 21

When ROS levels are excessive, or not enough anti-oxidants.

Question 22

What clinical condition is NADPH oxidase complicit in?

Answer 22

Atherosclerosis