Cell signaling by oxygen: Reactive Oxygen

Question 1

Does high pO2 or low pO2 cause damage?

Answer 1

Both cause damage

Question 2

Which free radicals cause the most damage

Answer 2

hydroxyl radical

nitrite radical

Question 3

What are reactive oxygen species?

Answer 3

Oxygen-containing molecules that oxidize substrates

Question 4

What are free radicals?

Answer 4

Molecule that contains an unpaired electron

Question 5

What is the fenton reaction?

Answer 5

2 H2O2 atoms react with Iron to create water, a peroxide radical and a hydroxyl radical

2 H2O2 -Fe2+–> H2O + HOO* + *OH

Question 6

Name 2 free radical precursors

Answer 6

Hydrogen peroxide (H2O2)
hypochlorite anion (OCl-)

Question 7

Describe the superoxide-nitric oxide reaction

Answer 7

H+ + O2* + NO* –> H+ + ONOO* –> *OH + *NO2

Question 8

What reaction produces hypochlorite anion from hydrogen peroxide?

Answer 8

myeloperoxidase reaction

Question 9

Name the 6 reactions that can generate free radicals

Answer 9

Fenton reaction
Haber-Weiss reaction
Superoxide-nitric oxide reaction
Myeloperoxidase reaction
Hypochlorite-iron reaction
Hypochlorite-superoxide reaction

Question 10

What is the free radical chain reaction?

Answer 10

A free radical donates its electron to a substrate (R2)

r2 becomes a free radical

Question 11

What causes the free radical chain reaction to speed up or slow down?

Answer 11

Speeds up when highly reactive radicals are formed

Slows down when unreactive molecules are formed

Question 12

What is usually the R1 in the free radical chain reaction? What is the resulting R2?

Answer 12

R1 is usually a macromolecule (lipid, protein)

R2 is usually an aggressive free radical (*OH or *NO2)

Question 13

What is the result of oxidation or nitration?

Answer 13

Alters function similar to phosphorylation

Question 14

What are the 5 sources of reactive oxygen species?

Answer 14

Ionizing radiation (X-ray, radon, cosmis rays)

Metal catalysts (Fe2+)

ROS reactions

Metabolism (ubiquinon)

Enzymatic catalysts (NADPH oxidases, macrophages)

Question 15

What is the mitochondrial ubiquinon cycle?

Answer 15

Mitochondria generate superoxide as a by-product of electron transport by ubiquinon cycle to the electron transport chain

Question 16

What causes the most damage during reperfusion after ischemia?

Answer 16

Reactive oxygen species burst occurs between ischemia and reperfusion

Question 17

What produces the ROS burst after ischemia?

Answer 17

Mitochondria

Question 18

What can the ROS burst after ischemia lead to?

Answer 18

Apoptosis & necrosis

Question 19

What is an example of an ischemia?

Answer 19

Heart attack
stroke
gut torsion

Question 20

What occurs to ATP, cytosolic pH and mitochondrial potential during ischemia?

What about cytosolic Na+ and Ca2+?

Answer 20

ATP, pH, and mitochondrial potential go down

Na+ and Ca2+ increase

Question 21

Describe the production of ROS by neutrophils

Answer 21

Neutrohpil binds with NADPH oxidase (NOX)

NOX associates with RAC to produce a superoxide radical (*O2)

*O2 forms hydrogen peroxide spontaneously or by using enzyme superoxide dismutase (SOD)

Neutrophil binds myeloperoxidase vesicles

MPO makes hypochlorite from H2O2 and Cl-

• O2 reacts with OCl- to form *OH
• O2 and *OH kill bacteria

Question 22

What other pathway can nitric oxide take aside from cell signaling?

Why is this reaction important?

Answer 22

• NO + *O2 –> *NO2

* NO2 is highly reactive and capable of substance nitration

Question 23

Name some of the damaging features of oxidation or nitration caused by ROS

Answer 23

Damage to lipid membranes
Failing enzymes
Failing cell function
Altered DNA expression
Failure to repair DNA

Question 24

What are the 2 defense cycles against ROS?

Answer 24

Superoxide dismutase and catalase

GLutathione cycle

Question 25

Describe the superoxide dismutase & catalase defense cycle

Answer 25

2 *O2 --SOD--> H2O2 2 H2O2 --catalase--> O2 + H2O

Question 26

Describe the glutathione cycle

Answer 26

H2O2 + 2 GSH --> GSSG + 2 H2O 2 NADPH + GSSG --> 2 NADP+ + 2 GSH

Question 27

What is GSH?

Answer 27

Reduced glutathione

Question 28

What is GSSG?

Answer 28

Oxidized glutathione

Question 29

What are the 2 enzmes associated with the glutathione defense cycle?

Answer 29

glutathione peroxidase | glutathione reductase

Question 30

How can the control of iron defend against ROS?

Answer 30

Iron is bound to transferrin and stored in ferritin No fenton reaction

Question 31

How can antioxidants combat ROS damage?

Answer 31

Ascrobic acid is radicalized by a free radical 2 *Asc --> dehydro-ascorbate (DH-Asc) + Asc

Question 32

Name 5 antioxidants

Answer 32

``` Ascorbic acid, Uric acid Vitamin E Vitamin A Beta-carotene ```

Question 33

What receptors are responsible for oxygen sensing?

Answer 33

Peripheral receptors Carotid bodies Aortic bodies

Question 34

How do peripheral sensors control oxygen?

Answer 34

Send afferent signals to brain to increase respiration

Question 35

What cranial nerve do carotid bodies send signals to?

Answer 35

Cranial nerve 9

Question 36

Describe the depolarization of a glomus cell in the carotid body

Answer 36

Cell membrane heme closes K+ channels in response to low blood pO2 low blood pO2 initiates AMP kinase to create AMP which acts to keep K+ channels closed NADPH oxidase produces *O2 to keep K+ channels closed Depolarization Depolarization opens Ca2+ voltage-gated channels Ca2+ influx initiates release of neurotransmitters acetylcholine and dopamine neurotransmitters activate afferent dendrites of CN IX

Question 37

What are the 3 sensors in the glomus cell that react to low pO2?

Answer 37

Cell membrane heme protein production of AMP via AMP-kinase Superoxide production by NADPH-oxidase

Question 38

What is HIF-1?

Answer 38

During hypoxia, Hypoxia inducible factor upregulates expression of genes that enable cells to cope or to ensure hypoxia returns to normoxia

Question 39

Describe HIF-1 during normoxia

Answer 39

prolyl-hydroxylases hydroxylate HIF-1alpha Hydroxylated HIF-1alpha is ubiquinated

Question 40

Describe HIF-1 during hypoxia

Answer 40

In absence of O2, HIF-1alpha moves to nucleus and binds with subunit HIF-1beta and transcription factors p300/CBP Transcription of lactate dehydrogenase, GLUT1, EPO, VEGF