LC 42 Dr. Basel Flashcards
ROS or reactive oxygen species
describe why oxygen is both necessary and dangerous to organic organisms
Reactive oxygen specices
Highly reactive oxygen containing compounds
oxygen is a very _____ molecule that can be made to be even more ______.
reactive
The most basic reactive oxygen species is superoxide which is the _____ electron ______ of molecular oxygen
single, reduction
ROS act as _____ _____ removing electrons from other atoms
strong oxidizers
Metal center oxidation
important to enzyme function causes them to not work or work abnormally
Sulfide oxidation
Was neutral now its very negative. Certain seniors can make sulfur sulfur bonds
Nitrogen oxidatiation
result is a negative acid
carbon oxidation
results in negative acid
Radicals in the ETC
The ETC creates a highly regulated radical, Q, in its complex. It is normal for a SMALL amount of radical to be leaked. If the system is starved of oxygen and not reperfused carefully the system can run in reverse and leak super oxide radicals
Four examples of sources of ROS and intensification
1) Phagocytic Respiratory burst
2) Fe2+ and the fenton reaction
3) NO synthase
4) Ionizing radiation
Phagocytic respiratory burst
Ex. neutrophil and macrophages. NADP oxidase expressed by phagocytic cells to make super oxide, Superoxide dismutase turns that to peroxide, Myeloperoxidase turns that into hypochlorous acid (bleach) to kill engulfed bacteria
Fe2+ and the fenton reaction
Free Fe2+ causes problems in the cell (finds reactive oxygen species and activates them to be even stronger) so we want as little free Fe2+ as possible
NO synthase
uses arginine+3 NADPH –NO synthase–> nitric oxide+ super oxide–> ONOO –> NO2 and HO
Immune system can make a lot of different reactive oxygen species. If it is over stimulated what can occur?
Inflammation which can be very oxidative with the abundance of reactive oxygen species
Ionizing radition
- creates double stranded DNA breaks
- more likely to hit water before DNA
- when this happens it knocks an electron off and becomes a hydroxyl radical
- starts a radical chain reaction
- potential for a lot of damage
ROS + DNA
- oxidized DNA
- cross-linked DNA
- DNA adducts
ROS + phospholipid
- lipid peroxides
- lipid adducts
ROS + proteins
- oxidized AA
- protein dimers
- protein adducts
ROS reactions with DNA, phospholipids or proteins can all result in what?
- cell damage
- disease
- neoplasm
- aging
- cell death
Small antioxidants
Vitamin C and Vitamin E
Peptide antioxidant
glutathione
protein antioxidant
reduced thioredoxin, has two reduced cystines that it uses to donate to peroxide so it turns into water. When we use up thioredoxin we use NADPH to replace electrons and then it is reduced by Thioredoxin (uses selenium) and now it is replenished
enzymatic antioxidants
superoxide dismutase and catalase
What is found in nearly every cell that prevents the build up of ROS through enzymatic neutralization?
Superoxide dismutase and catalase
How are Superoxide dismutase and catalase used by bacteria?
they are overproduced to try to counter phagocyte use of ROS to kill them
What does superoxide do?
It reacts two super oxides
How does catalase work with superoxide dismutase?
it takes two times its products of H2O2 + O2 and turns them into water and oxygen
What happens if catalase and superoxide dismutase were mutated?
the cells die, its really not good
Peptide antioxidant
glutathione (GSH) - most important intracellular antioxidant
How is GSH used as an antioxidant?
2 GSH electrons/protons donated to hydrogen peroxide and cross links the GS molecules and produces water. This is done through the enzyme, glutathione peroxide.
GSH is made of what three AA?
glutamate, cysteine and glycine - has free SH group that reacts well with oxidants
How is GSH recycled?
cross linked GS –> add 2 NADPH –glutathione reductase (selenium important) –> produces 2GSH to be used again
What is important for recycling antioxidants?
selenium
Function of Vitamin C as an antioxidant
Vit C has conjugated double bonds OH. Radical steals proton from Vit C and now the radical is stable stopping a potential radical chain reaction. Can regenerate by handing radical off to another Vit. C fully oxidizing it.
Function of Vitamin E as an antioxidant
Vit. E bonds radical so it is now stable. The Vit. E can be regenerated by handing the radical off to a Vit. C
Central/ peripheral receptors
central and peripheral receptors are systemic level sensors to regulate O2 in the body. Peripheral sensors are able to detect O2 concentrations through glomus cells
HIF
Hypoxia -inducible factors sense low oxygen in individual cells and promote hypoxia response genes
ASK1
ASK 1 is a MAPKKK that is activated during oxidative stress conditions and promotes hyperoxia response genes
The body has 2 systemic level sensors tied to respiratory control - one for CNS, one for PNS. Where are each of these receptors located?
CNS - ventrolateral surface of the medulla
PNS - carotid and aortic bodies
What is the function of CNS receptor?
- regulation through stimulating respiration
- does not sense oxygen level
- primarily sense CO2/pH level and stimulate respiration in response
What is the function of PNS receptors?
- regulation through stimulating respiration
- responsive to pO2, pCO2 and pH –> directly O2 sensitive unlike CNS
Glomus cell and O2 sensing
- K+ channel is open with normal O2
- this keeps Ca2+ channel closed
- O2 is turned to carbon monoxide (signaling molecule for K+ channels) by heme oxygenase, this keeps K+ channel open
- O2 can also stimulate NADPH oxidase to use NADPH to make O2 into superoxide which keep K+ open
- normal metabolism also makes superoxide which keeps K+ open
- low oxygen leads to AMP build up
- this goes to AMP kinase which closes K+ channel and Ca2+ opens
What happens when Ca2+ are opened?
cell is depolarizing, Ca2+ runs into cell and allows vesicles to release neurotransmitters to stimulate axon and send message to the brain
Hypoxia inducible factors or HIF
When O2 is low - HIF are transcription factors that are induced during hypoxia to make hypoxia response genes that protect against low oxygen
Normal O2 - HIP prolyl hydroxylase oxidizes HIF to mark it for degradation so its signal is not received
Individual cells can respond to low O2 true or false?
true, using HIF
Hyperoxia and ASK1/MAPK pathway
When O2 is high - Thioredoxin is shifted towards being oxidized. It acts as a signaling molecule in this form. It doesn’t bind ASK1 allowing it to dimerize to become active (in MAPKKK pathway) and push the cell towards hyperoxia gene expression and pro-apoptotic. Under normal conditions reduced thioredoxin binds ASK1, keeping it in an inactive form
