Oxidative Stress Flashcards
(25 cards)
What is oxidative stress?
Imbalance of free radicals causing damage to the body
What are free radicals?
Atoms or molecules that contain one or more unpaired electron
What are RNS?
Reactive nitrogen species
What are the RNS?
Nitric oxide - NO●
Peroxynitrite - ONOO-
What are ROS?
Reactive oxygen species
What are the ROS?
Superoxide - O2●-
Hydrogen peroxide - H2O2
Hydroxyl radical - OH●
What is the most damaging free radical?
OH●
How to ROS cause damage to DNA?
ROS reacts with base
- modified base = mispairing
ROS reacts with sugar
- strand break
How does ROS cause damage to proteins?
Fragmentation of backbone
Modify amino acids = change in protein structure
- effect disulphide bonds
What are disulphide bonds?
Bones between thiol groups on cysteine
What is the role of disulphide bonds?
Important in folding and stability of some proteins
How does ROS cause damage to lipids?
Free radical extracts hydrogen atom from lipid membrane
Lipid radical formed - can react with oxygen to form peroxyl radical
Chan reaction as peroxyl radical extracts hydrogen from nearby fatty acid
Membrane integrity fails
What are endogenous causes of oxidants?
Electron transport chain
Nitic oxide synthases
NADPH oxidases
What are exogenous causes of oxidants?
Radiation
Drugs
Toxins
How does the electron transport chain form ROS?
Electrons can escape chain and react with oxygen to form superoxide
How do nitric oxide synthases form oxidants?
Converts arginine to citrulline producing nitric oxide (NO●)
What is nitric oxide used for?
Signalling molecule
- vasodilation
- neurotransmission
What are the types of nitric oxide synthase?
iNOS - inducible nitric oxide synthase
- produces NO for phagocytes
eNOS - endothelial nitric oxide synthase
- signalling
nNOS - neuronal nitric oxide synthase
- signalling
What is a respiratory burst?
Rapid release of superoxide and H2O2 to destroy bacteria - part of defence system
What are cellular defences against oxidants?
Superoxide dismutase (SOD)
Catalase
Glutathione
Free radical scavengers
How is SOD a defence?
Converts superoxide to H2O2 and oxygen
How is catalase a defence?
Converts H2O2 to water and oxygen
What cofactors does SOD need?
Copper
Zinc
Manganese
How is glutathione a defence?
Reduced form = GSH
GSH reacts with GSH to form GSSG (glutathione peroxidase) - using a e- from ROS
GSSG reduced back to GSH (glutathione reductase) which uses electrons from NADPH
