Oxidative stress

Question 1

What is Oxidative stress

Answer 1

Oxidative stress reflects an imbalance between reactive oxygen species and a biological systems ability to detoxify them or to repair the resulting damage
More ROS than the cell can tolerate

Question 2

What are ROS?

Answer 2

ROS are damaging chemical entities, often very reactive and short lived, that react with and damage other biological molecules

Question 3

How is the cellular state of oxidative stress described?

Answer 3

Increased generation of free radicals, and ROS in excess of antioxidant defences

Question 4

Why is an increase in free radicals and ROS bad?

Answer 4

They can potentially damage macromolecules including DNA, proteins and lipids

Question 5

What are free radicals?

Answer 5

Are molecules with one or more unpaired electrons —-> highly unstable and reactive
Their types include ROS and RNS

Question 6

What are some examples of free radicals?

Answer 6

• Superoxide radical
• Hydrogen peroxide
• Hydroxyl radical
• Nitric oxide radical

Question 7

What are the sources of ROS?

Answer 7

Some are inevitable/accidental by products of chemical reactions involving oxygen

Question 8

What have cells adapted in regards to producing ROS?

Answer 8

Cells have evolved enzymes to produce ROS with specific biochemical purposes
e.g. NADPH oxidase to kill microbes

Question 9

What are the endogenous sources of ROS?

Answer 9

• Some ROS- inevitable/accidental by products (mitochondria)
• Evolved specifically to produce ROS (NADPH oxidase)

Question 10

What type of cells generate large amounts of ROS?

Answer 10

Phagocytes (Neutrophils and Macrophages)- white blood cells generating ROS to kill microbes trapped/eaten by the phagocytes

Question 11

How are ROS usually removed?

Answer 11

Inside of most cells = high concentration of passive redox buffers and active antioxidant defences which in combination use energy to remove ROS

Question 12

Why is it hard to experiment with ROS?

Answer 12

If biological molecules are removed from the cellular reducing environment, it is hard to stop them rapidly oxidising in the lab before analyzing them

Question 13

Typically, how are ROS measured?

Answer 13

Localised ROS probes with rapid kinetics can show where in cells ROS are generated

Question 14

How are free radicals produced from mitochondria?

Answer 14

If electrons leak during aerobic respiration then 0.2% of total daily oxygen consumption is converted to ROS

Question 15

What happens during phagocytosis with regards to ROS?

Answer 15

There is a large increase in oxygen uptake by neutrophils and most macrophages through activation of an NDPH-oxidase that reduces oxygen to superoxide (oxidative burst)

Question 16

What happens to the individuals with a defect in the NADPH-oxidase?

Answer 16

granulomatous disease (chronic)
Often die as a result of recurrent bacterial infection
Almost all cells have an active NADPH-oxidase complex

Question 17

What is the problem with ROS during phagocytosis?

Answer 17

ROS are secreted into the phagosome to kill bacteria. However, many ROS freely diffuse through membranes

Question 18

What cellular biomolecules do ROS damage?

Answer 18

Damaged lipids and proteins must be re-synthesised
DNA is less reactive and resistant to damage and is repaired
However, unrepaired damage can lead to mutations

Question 19

How common is oxidative DNA damage?

Answer 19

estimated at 10,000 events per cell per day
slow accumulation of mutations = aging

Question 20

How do ROS damage proteins?

Answer 20

Cysteine oxidation: a sulphur switch
The sulphur in a cysteine amino acid can be oxidised to several higher oxidation states, so cysteine can be reversibly oxidised to many forms
This changes protein function

Question 21

What is Cysteine?

Answer 21

Cysteine is a naturally occurring amino acids incorporated into most proteins
Contains a sulphur containing sidechain making it sensitive to oxidation

Question 22

What’s the difference between reversible and irreversible?

Answer 22

Reversible- regulation
Irreversible- Probably damage

Question 23

What diseases are associated with protein oxidative damage?

Answer 23

-Neurodegenerative diseases
-Muscular dystrophy
-Rheumatoid arthritis

Question 24

What are the exogenous sources of free radicals?

Answer 24

-Air pollution
-Radiation
-Cigarette smoke
-UV exposure
-Alcohol consumption
-Anticancer drugs
-Exposure to heavy metals

Question 25

What are antioxidants?

Answer 25

The first line of defence against free radical-induced cellular damage
Categorized into enzymatic and non enzymatic

Question 26

What are the non-enzymatic Antioxidants (redox buffers)?

Answer 26

Glutathione- most important intracellular defence against ROS
Vitamin E- Major lipid soluble antioxidant

Question 27

What are the enzymatic antioxidants?

Answer 27

Superoxide Dismutase- superoxide into oxygen and hydrogen peroxide
Catalase- hydrogen peroxide into water and oxygen
Glutathione Peroxidase- Hydrogen peroxide to water