Free Radicals 1 Flashcards by A R

What is a free radical

Any species with one or more unpaired electron in the outer orbit

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What elements are classed as free radicals

Hydrogen
Oxygen
Transition metals

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Why are free radicals important in the body

Can damage -
Nucleic acids
Nucleotides
Covalent bonds
Lipids
Membranes

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Give 3 methods that produce free radicals

Leakage from electron transport chains - Oxygen

Generated by activated phagocytes

Exogenous (external) sources of free radicals

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Give some exogenous (external) sources of free radicals

ozone
cigarette smoke
radiation
pollutants
drug administration
diet

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How can oxygen become a free radical

Oxygens pair up as covalent bonds as each O2 has 2 unpaired electrons.

The harmful effects of oxygen occur when
it is diverted from the stable O2 form to an
active state such as singlet oxygen (1 O2) and the free radical state superoxide (O-2)

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What nitrogen species is a free radical

Nitric oxide

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What electron transport chain components produce oxygen free radicals

1 and 3

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What percentage of oxygens leak from electron transport chains in the mitochondria

1-3% but some data suggests as low as 0.15%

The higher the activity/energy expenditure - the more free radicals as more active electron transport chain

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Give some cellular sites for the production of superoxide free radicals in muscle fibres

Sarcomeric proteins
Xanthine oxidase
Mitochondria - complexes 1 and 3 of electron transport chain
NADPH oxidases at the sarcolemma, sarcoplasmic reticulum and transverse tubules

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What is the Fenton reaction

The Fenton reaction describes the formation of hydroxide (OH−) and hydroxyl radical by a reaction between Iron (or any free metal e.g. copper) and hydrogen peroxide

Free metal acts as a catalyst

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Give 2 ways that free radicals are measured

Some indirect indicators of free radical production in vitro. (products of lipid peroxidation e.g ethane or DNA breaks caused by oxidation produce protein carbonyls)

The measure of antioxidant levels - particularly endogenous antioxidants.

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Why is the Fenton reaction important

Superoxide carries out the Fenton reaction. This reaction produces hydroxide (OH-) which is a very reactive free radical compared to superoxide.

This hydroxyl radical is believed to contribute oxidative damage to living cells

Usually use both to get the full picture

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Are all free radicals bad

No, have some important cell signalling roles

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Why are free radicals hard to measure

Very short half-life

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Give some endogenous (in the body) antioxidants

Glutathione peroxidase
Superoxide dismutase
Catalase
Metal-binding proteins (eg ferritin, caeruloplasmin)

What do most of these factors need - micronutrients e.g. zinc etc to work efficiently

Give some exogenous (external) antioxidants

Vitamin E (lipid-soluble)
Vitamin C (water-soluble)
Carotenoids - naturally occurring pigments synthesized by plants, algae, and photosynthetic bacteria

Give 3 mechanisms of how antioxidants work

Prevent initiation by scavenging (binds to free radicals before they can react within the body)

Binding to transition metals (stopping Fenton reaction)

Chain breaking of peroxyl radical production

What is peroxyl radical production

Happens to unsaturated fats (double bonds) when exposed to oxygen free radicals -

Peroxyl radicals are formed due to attack by molecular oxygen, which can abstract a hydrogen atom from a double bond in fatty acid side chains, producing a lipid hydroperoxide this is a chain reaction that will only stop when there is no substrate left.

How do antioxidants work chemically

Antioxidants have a similar structure through a cyclic ring. This allows them to give up a hydrogen ion to bind to the free radical to stabilise it.

The antioxidant now has an unpaired electron similar to the free radical beforehand, however, the unpaired electron can travel around that cyclic ring, making it much more stable than being unpaired as a free radical. This prevents any harm from being done.

What is important about antioxidants

They interact with each other to maintain the stability of the reactions.

e.g. - Lipoic acid cycle

What is oxidative stress

An imbalance between oxidants and antioxidants in favour of the oxidants, leading to a disruption of redox signalling and control and/or molecular damage

What causes oxidative stress, broadly speaking

Either an increase in free
radicals or a decrease
in antioxidants

What effects does exercise have on oxidative stress

Exercise is a healthy way to disturb homeostasis and increase oxidative stress (more oxygen free radicals leaking from ETC)

Found in all species so easier to study

What effects do free radicals have on muscles

Increased production of free radicals disrupt cell membranes and impair their function - can cause soreness and muscle damage after exercise.

Give 4 causes of increased free radicals in muscle

– Redistribution of blood flow - Ischemia-reperfusion injury – Immune response - increase ROS production – Disruption of calcium homeostasis - activating ROS generation -- Exercise

What is mudPIT and how is it used

Multidimensional protein idenitification technology - Uses a protein sample that is digested by tripsin into peptides. These peptides then undergo multidimensional chromatography (passing peptides through 2 difference seperation stages to seperate them more effectively than unidimentional chromatography). Directly in line with this is a tandem mass spectrometer which identifies these peptides and they are put into a peptide match database for matching and analysing

Why is mudPIT preferred over 2d electrophoresis Koller et al

A total of 1972 proteins were identified only by MudPIT, whereas 165 proteins were identified only by the 2DE approach

What can free radicals do to DNA WIDER READING - Crean 2008

Free-radical induced chain reactions can involve base pairs and result in the DNA becoming cross-linked - Guanine can be oxidized by carbonate radicals

How can free radicals lead to wrinkles WIDER READING - Pageon 2005

Via cross-linking between fat and protein molecules - Happens via glycation (attachment of sugar to protein or lipid). This causes new cross-links in the ECM of the dermins. This causes loss of elasticity and change in fibroblast shape and increase in colleganase activtiy.

What role does zanthine oxidase and NO oxidase play in superoxide WIDER READING - Jacobson et al 2015

Looking at mesenteric arteries of old and young rats - superoxide was higher in older rats and both enzymes higher in older rats and they are known to produce superoxide.

What role does superoxide have in hypertension and aging WIDER READING - hamiltion 2001

Higher superoxide in aging and hypertension and believed to impair endothelial function.

What role does Nox4 play in oxidative damage WIDER READING - Lener 2009

Nox4 codes for NADPH oxidases produce superoxide found in the human umbilical vein endothelial cells. By gene knockdown it was found that the replicative lifespine significantly increased and decreased the degree of oxidative DNA damage. Suggests Nox4 activity increases oxidative damage in umbilical vein endothelial cells and therefore leads to a loss of replication potential

What role do oxidative stress have in dry eye disease WIDER READING - Uchino 2015

Used conditional KO mice for mev-1 gene via tetracycline (causes premature aging and oxidative stress). Decreased tear production from mouse with leukocyte infiltration and fibrosis which decreased protein and aqueous secretion to the lacrimal gland.

How are mitochondria more susceptible to free radicals WIDER READING - Afanas'ev 2010

Electrons may escape from electron transport chain - electrons react with water to form superoxide or indirectly to form hydroxyl radical. These damage DNA and their mitochondria which makes these damaged areas more susceptible to ROS production starting a positive feedback loop of oxidative stress

What role does SOD1 have in ROS WIDER READING - PEREZ

SOD1 - an antioxidant enzyme protecting the cell from reactive oxygen species toxicity. Deletion of SOD1 showed - Female mice infertile due to ovarian dysfunction Accelerated loss of hind limb muscle mass with age Decreased lifespan of 30%

what are reactive oxygen species

they are not free radicals! but are highly reactive oxygen species