Lecture 8 - Free radicals

Question 1

Oxygen is essential to life but

Answer 1

can be toxic

Question 2

How is oxygen essential and toxic?

Answer 2

Essential:

1. ) oxidation reactions
2. ) Generation of ATP (ox phos)
3. ) Detoxification reactions
4. ) Biosynthetic reactions

Toxic:

1. ) When oxygen accepts single electrons it is transformed into highly reactive oxygen radicals that damage:
   - cellular lipds
   - Proteins
   - DNA

Question 3

Oxygen is a biradical and so it can form?

Answer 3

1. ) O2- superoxide
2. ) H2O2 Hydrogen peroxide
3. ) OH Hydroxyl radical

Question 4

What is ROS

Answer 4

Reactive o2 species:
Its generation is a natural everyday process . It is formed as an accidental product of enzymatic and non enzymatic reactions. It is also formed during the inflammatory process as a deliberate part of teh process.

Question 5

What can increase the formation of toxic oxygen containing compounds?

Answer 5

UV radiation and pollutants in the air.

Question 6

What are the major sources of ROS in the cell?

Answer 6

1. ) CoQ generates superoxide in ETC
2. ) oxidases, oxygenases, and peroxidases
3. ) ionising radiation

Question 7

What do ROS do?

Answer 7

They react with lipids, proteins, carbs and DNA to exrtract electrons.

Question 8

How many diseases are shown to be due to free radical damage?

Answer 8

over 100 have shown evidence of it, either as the primary cause or by enhancing complications

Question 9

What does ROS do?

Answer 9

Superoxide and hydroxyl radical initiate lipid peroxidation in the cellular, mitochondrial, nuclear and ER membranes.

This increases permeability and so there is an influc of Ca2+ which causes further mitochondrial damage.

The cysteine sulfhydryl groups and other AA residues on proteins are oxidised and degraded.

Nuclear and mitochondria DNA can be oxidized resulting in strand breaks and other damage

RNOS has a similar effect.

Question 10

What is the membrane attack in ROS?

Answer 10

Chain reactions to form lipid radicals and lipid peroxides in membranes

There is membrane lipid damage which leads to loss of structural integrity of membrane. This disruption of mitochondria membrane may augment free radical damage.

What are the overall issues:
Peroxidation of lipids dammage lipid moelcular structure
The aldehydes formed can cross link proteins

Question 11

What is the biomarker for free radical damage?

Answer 11

Malondialdehyde appears in blood and urine

Question 12

What AA can be sesceptible to hydroxyl damage attack and oxidative damage?

Answer 12

Proline, histidine, arginine, cysteine and methionine.

Consequence - protein may fragment and residues cross link with other residues

Question 13

What disease has evidence of protein damage?

Answer 13

cataracts - proteins in the lens of the eye exhibit ROS damage which contain methionine and sulphoxide residues and trytophan degredation products.

Question 14

What are lipofuscin granules?

Answer 14

liver spots - heterogenous mix of cross linked polymerized lipids and proteins formed by reactions between AA residues and lipid perroxidation products such as malondialdehyde.

Question 15

What DNA damage takes place because of oxygen derived free radicals?

Answer 15

non specific bonding of Fe2+ to DNA facilitates localised production of the hydroxyl radical which can cause base alterations.
It can also attack the deoxyribose backbone and cause the strands to break
DNA repair mechanisms exist or avoided by apoptosis.

Question 16

What is the difference between the damage ROS can do on mmitochondrial vs nuclear DNA?

Answer 16

Nuclear DNA has histones which protects it from damage by radicals wheras mitochondrial DNA lacks histones and its DNA is proximal to the cellular membrane.

Question 17

Where are most radical species formed?

Answer 17

coenzyme q which is found in the mitochondria

Question 18

Functions of NO?

Answer 18

1. ) neurotransmitter

2. ) As a hormone that causes vasodilation

Question 19

How many electrons does NO have and what does it bind to?

Answer 19

one electron and binds to other compounds with one electron like Fe3+

Question 20

How is RNOS formed?

Answer 20

NO combines with O2 or superoxide to form additional reactive and toxic species that contains both - RNOS

Question 21

What is RNOS involved in?

Answer 21

1. ) neurodegenerative diseases like parkinsons

2. ) in chronic inflammatory diseases like rheumatoid arthiritis

Question 22

What are the toxic effects of NO?

Answer 22

By combining to Fe containing compounds that also have one electron, the major sites of destruction are Fe-S centres, Fe-Heme proteins

Question 23

Consequences of the formation of RNOS?

Answer 23

1. ) Inhibition of enzymes
2. ) Mitochondrial lip peroxidation
3. ) Inhibition of ETC and energy depletion
4. ) SS or DS breaks in DNA
5. ) Modification of bases in DNA

Question 24

What is the formation of free radicals during phagocytosis?

Answer 24

NADPH Oxidase: Transfers electrons from NADPH to O2 to form superoxide which is effective agaiinst bacterial infection.

Myeloperoxidase and hypochlorous acid - bacteria lose membrane transport and ability to synthesize ATP or ETC damage.

Part of the human antimicrobial defence system.

Question 25

What are the antioxidant scavenging enzymes?

Answer 25

Superoxide dismutase
Catalase
Glutathione peroxidase
Glutathion reductase

Question 26

What are the non enzymatic antioxidants?

Answer 26

VItamin: E, C, cartenoids (precursor of vitamin A) and dietary antioxidants like flavonoids (red wine, green tea and chocolate).

Question 27

What are the endogenous antioxidants?

Answer 27

Uric acid - degredation product of purines

Melatonin - receptor functions but also a free radical scavenger

Question 28

ALS?

Answer 28

both environment and genetic disease where it is caused by mutations in superoxide leading to a difficulty in disposing of superoxide radicals, leading to cell damage caused by excessive ROS.