Session 3 Lecture 1

Question 1

What are free radicals?

Answer 1

An atom or molecule that contains one or more unpaired electrons and is capable of independent “free” existence.

Question 2

How do you denote a free radical?

Answer 2

Superscript dot

Question 3

What are the two main type of free radicals?

Answer 3

Reactive oxygen species

Reactive nitrogen species

Question 4

Describe some features of free radicals?

Answer 4

They are usually very reactive. Reaction of a radical with a molecule typically generates a second radical thereby propagating damage

Question 5

How do you get a reactive oxygen species?

Answer 5

If electron does not reach the end of the electron transport chain - superoxide is produced.

Question 6

What is most reactive and damaging free radical?

Answer 6

Hydroxyl radical

Question 7

Name some ROS?

Answer 7

Superoxide and hydroxyl radical

Question 8

What can ROS damage?

Answer 8

DNA, proteins or lipids

Question 9

What are the different ways that ROS damages DNA?

Answer 9

• ROS reacts with base

- ROS reacts with sugar

Question 10

What happens if ROS reacts with base?

Answer 10

Modified base can lead to misfiring and mutation

Question 11

What happens if ROS reacts with sugar?

Answer 11

Can cause strand break and mutation on repair

Question 12

What can ROS damage to DNA eventually lead to?

Answer 12

Cancer

Question 13

How does ROS damage proteins?

Answer 13

ROS reacts with side chain

ROS reacts with backbone

Question 14

What happens if ROS reacts with backbone of protein?

Answer 14

Causes fragmentation, protein degradation therefore change in structure so loss/gain of function

Question 15

What happens if ROS reacts with side chain of protein?

Answer 15

Modified amino acid, can cause disulfide bond to form therefore change in protein structure, loss of function or gain of function

Question 16

How can ROS lead to formation of disulfide bonds?

Answer 16

ROS takes electrons from cysteines therefore disulfide bond forms

Question 17

How does ROS damage lipids?

Answer 17

ROS reacts with polyunsaturated fatty acid in membrane lipid. Lipid radical formed and reacts with oxygen to form lipid peroxyl radical. Chain reaction. Hydrophobic environment of bilayer disrupted and membrane integrity fails.

Question 18

What is the reaction of lipid with free radicals called?

Answer 18

Lipid peroxidation

Question 19

Describe some endogenous sources of biological oxidants

Answer 19

Electron transport chain
Peroxidases
NO synthase
NADPH oxidised

Question 20

Describe some exogenous sources of biological oxidants

Answer 20

Radiation - cosmic, UV and X ray
Pollutants
Drugs - primaquine (anti-malarial)
Toxins - paraquat (herbicide)

Question 21

What are some of the body’s defences against oxidative species?

Answer 21

• Free radical scavengers
• Superoxide dismutase and catalase
• Glutathione

Question 22

How do free radical scavengers act as defence?

Answer 22

Reduce free radical damage by donating H+ and e- to free radicals in a non-enzymatic reaction

Question 23

How does superoxide dismutase act as cellular defence?

Answer 23

Converts superoxide to H2O2 and oxygen

Question 24

How does catalase act as cellular defence?

Answer 24

Converts H2O2 to water and oxygen.

Question 25

Where else is catalase used?

Answer 25

Catalase is a widespread enzyme which is important in immune cells to protect against oxidative burst