Lecture 3: Oxidants and Antioxidants

Flashcards covering key concepts related to the biology of ageing, focusing on oxidants, antioxidants, and their effects.

What does ROS stand for?

Reactive Oxygen Species

What does RNS stand for?

Reactive Nitrogen Species

Name three major types of ROS.

Superoxide anion (O₂⁻), hydrogen peroxide (H₂O₂), hydroxyl radical (•OH)

Name two major types of RNS.

Nitric oxide (NO•), peroxynitrite (ONOO⁻)

How do ROS and RNS differ in reactivity?

•OH and ONOO⁻ are highly reactive and damaging; H₂O₂ and NO• are less reactive and can act as signalling molecules.

What are endogenous sources of ROS/RNS?

Mitochondrial respiration, peroxisomal reactions, NADPH oxidases, cytochrome P450 enzymes, inflammation.

What are exogenous sources of ROS/RNS?

UV radiation, ionizing radiation, pollution, smoking, certain drugs and toxins.

What are the two main types of antioxidant systems?

Enzymatic and non-enzymatic antioxidants.

Name three key enzymatic antioxidants.

Superoxide dismutase (SOD), catalase, glutathione peroxidase.

How does superoxide dismutase (SOD) work?

Converts superoxide (O₂⁻) into hydrogen peroxide (H₂O₂).

How does catalase work?

Converts hydrogen peroxide (H₂O₂) into water and oxygen.

How does glutathione peroxidase work?

Reduces H₂O₂ and lipid peroxides using glutathione.

Name three non-enzymatic antioxidants.

Vitamin C, vitamin E, glutathione (GSH).

How do non-enzymatic antioxidants work?

They donate electrons to neutralize ROS/RNS without becoming reactive themselves.

What is redox balance?

The equilibrium between oxidants (ROS/RNS) and antioxidants in cells.

What is the role of ROS in normal cell signalling?

Low levels of ROS regulate processes like gene expression, cell proliferation, and immune response.

What happens when ROS levels exceed antioxidant capacity?

Oxidative stress occurs, leading to damage of lipids, proteins, and DNA.

How do ROS damage lipids?

Through lipid peroxidation, leading to membrane instability.

How do ROS damage proteins?

By oxidizing amino acids, causing misfolding or loss of function.

How do ROS damage DNA?

By causing strand breaks, base modifications, and mutations.

What is the oxidative stress theory of ageing?

Ageing results from accumulated oxidative damage to biomolecules over time.

What evidence supports oxidative stress in ageing?

Increased oxidative damage markers in aged tissues, age-related decline in antioxidant defences, lifespan extension in some antioxidant-overexpressing model organisms.

What evidence challenges the oxidative stress theory?

Antioxidant supplementation has limited effects on lifespan; some long-lived species have high ROS levels but are resistant to oxidative damage.

How might oxidative damage interact with other ageing mechanisms?

It may exacerbate telomere shortening, mitochondrial dysfunction, and inflammation.

Is ROS always bad in ageing?

No, low/moderate ROS can promote stress resistance and longevity via hormesis (adaptive stress response).