Cell Signaling by Oxygen: Reactive Oxygen Flashcards
1
Q
O2 saturation of hemoglobin is mainly controlled by?
A
Ventilation
2
Q
p(O2) is?
A
O2 partial pressure
3
Q
p(O2) in tissues is mainly controlled by?
A
Blood flow
4
Q
p(O2) damage can be caused by?
A
Too high or low p(O2)
5
Q
Oxygen containing molecules can be?
A
Very reactive
6
Q
ROS stands for?
A
Reactive oxygen species
7
Q
ROS are?
A
Free radicals or their precursors
8
Q
What is ROS?
A
Oxygen-containing molecules that oxidize substrates (lipids, proteins, DNA, etc.) to alter their function
9
Q
What are free radicals?
A
Molecule, atom or ion containing an unpaired electron → want to find a partner (very reactive)
10
Q
4 free radicals
A
- Superoxide
- Nitric oxide
- Hydroxyl radical
- Nitrite radical
11
Q
2 very aggressive free radicals (cause most damage)
A
- Hydroxyl radical
2. Nitrite radical
12
Q
2 free radical precursors
A
- Hydrogen peroxide
2. Hypochlorite ion
13
Q
Fenton reaction
very important to know
A
2 hydrogen peroxide in presence of iron →
water + peroxide radical + hydroxyl radical
14
Q
Haber-weiss reaction
A
Hydrogen peroxide + superoxide radical →
O2 + OH- + hydroxyl radical
15
Q
Hydroxyl radical
A
●OH
16
Q
Superoxide-NO reaction
A
H+ + superoxide radical + nitric oxide →
hydroxyl radical + nitrite radical
17
Q
Hydrogen peroxide
A
H2O2
18
Q
Hypochlorite anion
A
OCl-
19
Q
Superoxide
A
O2●-
20
Q
Nitrite radical
A
●NO2
21
Q
MPO stands for?
A
Myeloperoxidase
22
Q
MPO reaction
A
Hydrogen peroxide + chloride anion →MPO→
hypochlorite anion + water
23
Q
Hypochlorite-iron reaction
A
H+ + OCl- + Fe2+ →
Fe3+ + Cl- + hydroxyl radical
24
Q
Hypochlorite-superoxide reaction
A
H+ + OCl- + superoxide radical →
O2 + Cl- + hydroxyl radical
25
Free radical chain reaction
R1● donates unpaired electron to substrate R2 → forms free radical R2●
26
Free radical chain reaction speeds up when?
Highly reactive radicals formed
27
Free radical chain reaction slows down when?
Unreactive radicals are formed
28
Free radical terminal reaction
R1● (macromolecule radical) + R2● (aggressive radical) →oxidation or nitration→ R1-R2
29
5 sources of ROS
1. Ionizing radiation
2. Metal catalysts
3. ROS reactions
4. Metabolism
5. Enzymatic catalysts
30
3 ways ionizing radiation causes ROS
1. Radon disintegration
2. X-ray
3. Cosmic rays
31
Example of metal catalyst which can cause ROS
Fe2+
32
Enzymatic catalysts which can form ROS
1. NADPH oxidases
2. Myeloperoxidase (MPO)
3. Nitric oxide synthase
33
NADPH oxidases found in?
1. Neutrophils
| 2. Macrophages
34
Myeloperoxidases found in?
Neutrophils
35
NO synthase found in?
Endothelial cells
36
Mitochondria generates superoxide as byproduct of?
Electron transport by ubiquinon-cycle (UQ)
37
What injury is mediated by free radicals?
Ischemia / reperfusion
38
What does mitochondria generate after ischemia?
ROS burst
39
NOX stands for?
NADPH-oxidase
40
Initial activation of neutrophil leads to?
Fusion of vesicles containing NOX
41
NOX associates with?
Required accessory proteins including RAC
42
What is RAC?
Small G-protein
43
Completely assembled NOX-RAC complex uses ____ to generate ___ from?
Uses NADPH to generate superoxide radical from O2
44
Superoxide radical dimutates to?
Hydrogen peroxide (spontaneous or facilitated by SOD)
45
SOD stands for?
Superoxide dismutase
46
Further activation of neutrophil leads to?
Fusion of vesicles containing MPO
47
MPO makes?
Hydrogen peroxide + chloride anion → hypochlorite
48
Hypochlorite
OCl- (bleach)
49
Superoxide radical + hypochlorite forms?
Hydroxyl radical
50
Hydroxyl radical and superoxide radical do what?
Kill bacteria
51
SOD catalyzes?
Superoxide radical → hydrogen peroxidation
52
How do ROS damage lipids?
Damage membranes → ionic gradients collapse and enzymes spill
53
How do ROS damage proteins?
1. Failing enzymes
2. Failing transporters
3. Failing cell function
4. Failing cell signaling
54
How do ROS damage DNA?
1. Altered expression
2. Failure to protect
3. Failure to repair
55
CAT stands for?
Catalase
56
GSH is?
Reduced glutathione
57
GSSG is?
Oxidized glutathione
58
CAT catalyzes?
2 hydrogen peroxide → O2 + H2O
59
SOD / CAT defense
SOD converted superoxide radical to hydrogen peroxide → CAT converts hydrogen peroxide to oxygen and water
60
Glutathione cycle
Hydrogen peroxide + 2 GSH → GSSG + 2 H2O
GSSG regenerated
61
How is GSSG regenerated?
GSSG + 2 NADPH → 2 GSH + 2 NADP+
62
What catalyzes hydrogen peroxide + 2 GSH → GSSG
Glutathione peroxidase
63
What catalyzes GSSG → 2 GSH
Glutathione reductase
64
Iron is bound to?
Transferrin
65
2 transferrins store?
2 iron atoms
66
Iron uptake into cell is guarded by?
Transferrin receptor
67
Iron is stored how?
Ferritin
68
Asc stands for?
Ascorbic acid
69
Asc cycle against free radicals
R● + Asc → Asc● + R
Asc● + Asc● → Asc + DH-Asc
70
DH-ASc stands for?
Non-toxic dehydro-ascorbate
71
1st step of Asc cycle
Asc reacts with R● and becomes free radical Asc●
72
2nd step of Asc cycle
2 Asc● combine → break down unevenly into Asc and DH-Asc
73
4 defenses against ROS
1. SOD/CAT (Superoxide dismutase / Catalase)
2. Glutathione cycle
3. Iron control
4. Antioxidants (ex: Asc)
74
2 types of oxygen sensing
1. Central sensors
| 2. Peripheral sensors
75
Central sensors are located in?
Brain
76
Peripheral sensors are located in?
1. Carotid bodies
| 2. Aortic bodies
77
Control center of oxygen sensing
Brain stem (medulla)
78
Effectors
Respiratory mm. control depth and frequency of breathing
79
Peripheral sensory cells are called?
Glomus cells
80
Glomus cells are innervated by?
CN IX afferent dendrites
81
3 sensors for p(O2)
1. Cell membrane heme-protein
2. ATP production in mitochondria maintains low AMP in cytosol
3. Superoxide radical production by cytosolic NOX
82
Heme-protein at normal p(O2)
Bound to O2, keeps K+ channels open
83
Heme-protein at low p(O2)
Empty, closes K+ channels
84
ATP production in mitochondria at normal p(O2)
Low AMP keeps AMP-kinase inactive
85
ATP production in mitochondria at low p(O2)
High AMP via AMP-kinase cause K+ channels to close
86
Superoxide radical production by cytosolic NOX at normal p(O2)
Superoxide radical oxidizes K+ channels (keeps channels open)
87
Superoxide radical production by cytosolic NOX at low p(O2)
Less superoxide radical causes K+ channels closed
88
Inhibition of K+ channels causes?
Depolarization of membrane potential
89
Depolarization of membrane potential causes?
Opens voltage-gated Ca2+ channel
90
Open voltage-gated Ca+ channel allows?
Influx of Ca2+
91
Elevation of Ca2+ initiates?
Release of neurotransmitters Ach and dopamine
92
Released neurotransmitters do what?
Activate afferent dendrites of CN IX
93
Activated CN IX activates?
Respiratory center in medulla of brainstem
94
HIF-1 stands for?
Hypoxia inducible factor
95
HIF-1 senses?
O2
96
Under hypoxia, HIF-1 does what?
Upregulates expression of genes that help cells return to normoxia
97
Examples of genes HIF-1 upregulates under hypxoia
1. Lactate DHN
2. GLUT1
3. EPO
4. VEGF
98
Lactate DHN is involved in what process?
Glycolysis
99
GLUT1 is involved in what process?
Glucose uptake
100
EPO is involved in what process?
Erythropoiesis
101
VEGF is involved in what process?
Angiogenesis (making new vessels)
102
In presence of O2, what happens to HIF-1alpha?
HIF-1alpha hydroxylated by prolyl-hydroxylases
103
What happens to hydroxylated HIF-1alpa?
Ubiquinated → marked for destruction in proteosomes
104
Under hypoxia, HIF-1alpha survives and does what?
Moves to nucleus → interacts with accessory subunit HIF-1beta and transcription factors → initiates gene transcription
105
Transcription factors involved with HIF-1
1. p300
| 2. CBP
