Mito Function and Tox Ox Species---------------------------------

Question 1

what are the major sources of ROS?

Answer 1

Mitochondrial electron transport chain
Ionizing radiation
Enzymes
Phagocytes 
Endoplasmic drug metabolism (Cyt P450)
Detoxification system in the liver (Cyt P450)

Question 2

Which amino acids are particularly susceptible to ROS attack?

Answer 2

Amino acids particularly susceptible are:

Pro, His, Arg, Cys, Met

Question 3

What are consequences of ROS attack on proteins?

Answer 3

Fragmentation, cross-linking, aggregation, susceptible to proteolytic digestion

Question 4

What are consequences of ROS attack on lipids?

Answer 4

Membrane damage; aldehydes produced can cross-link proteins

Question 5

What are consequences of ROS attack on DNA?

Answer 5

Strand breaks, base alteration

Question 6

A large percentage of the superoxide formed in cells occurs in the _____? how so?

Answer 6

mitochondria; Mito has DNA that is relatively unprotected compared to nuclear DNA. So one is far more likely to encounter ROS damaged DNA in mito compared to nuclear DNA

Question 7

how does oxidative stress occur?

Answer 7

When free radicals cause
More damage more 
Quickly than our cells
Can protect against or 
Repair.

Question 8

what are the types of free radical mediated cellular injury due to oxidative stress?

Answer 8

protein damage
membrane damage
DNA damage
mito damage
cell swelling
increased permeability 
massive influx of Ca2+
lipid peroxidation

Question 9

what is oxidase?

Answer 9

an enzyme that promotes the transfer of a hydrogen atom from a particular substrate to an oxygen molecule, forming water or hydrogen peroxide

Question 10

what is oxygenase?

Answer 10

any enzyme that oxidizes a substrate by transferring the oxygen from molecular oxygen O2 (as in air) to it.

Question 11

What is formed when O2 picks up a single electron?

Answer 11

ROS, rapid oxygen species and this happens when oxidases, peroxidases, and oxygenases transfer a single electron to O2 via a metal

Question 12

what is lipid peroxidation?

Answer 12

radical derived lipid oxidation results in oxidized breakdown products like a lipid peroxy radical rearranging lipid chain breaks producing malondialdehyde(marker for oxidative stress)

Question 13

Describe electron leak when the O2 picks up the electron from the CoQH?

Why is it relevant for ROS formation?

Answer 13

Normally CoQ is bound to COMPLEX I and receives both electrons there. Leaves COMPLEX I in a fully reduced form.

Statistical possibility that CoQ will dissociate after receiving only 1 electron: semi-quinone radical form.

With high O2 levels in mitochondria, likelihood of superoxide formation is high;

Electrons can be picked readily and membrane, DNA, protein damage highly likely

Question 14

how likely is mitochondrial DNA susceptible to ROS than nuclear DNA?

Answer 14

10x more susceptible

Question 15

The nuclear DNA is protected by histones, is this the case for mitochondria?

Answer 15

no, mitochondria have lack of the protective histones.

Question 16

what is there a high generation rate of from the mitochondrial ETC at the CoQ?

Answer 16

ROS generation

Question 17

what is it important to note that mito DNA is also located near the inner membrane of mitochondria where the ETC is located?

Answer 17

ROS generated from ETC does not have to travel very far to attack the DNA.

Question 18

Describe in detail the Cytochrome P450 system

Answer 18

a monoxygenase that uses molecular oxygen and splitting it in half and one oxygen ends up on substrate and another one ends up on water.

Key to reaction mechanism is formation of superoxide anion bound to the Fe3+ center. If this O2- escapes (red circle), it will be a free radical in solution.

NADPH is also used instead of NADH providing electrons

it becomes uncoupled when the O2- gets away instead of being held

Question 19

what is the effect of the induction of Cyt 450 by drugs, alcohol and chemical toxicants?example?

Answer 19

increased cell injury due to increased free radical damage because of increased work by Cyt P450; parkinson’s disease

Question 20

what is nitric oxide?

Answer 20

a radical species produced by vascular endothelium cells but for potential for damage can happen…if we are uncoupled in our endothelial cells with lots of superoxide produced at or around the membrane close to NO production and they can unite to form proxynitrite, also know as a reactive nitrogen species (strong oxidizing agent)

Question 21

what is produced when superoxide and NO come together?

Answer 21

peroxynitrite, soluble molecule and destroys everything

Question 22

free iron has potential to cause harm to the body how is it removed?

Answer 22

by binding to ferritin, protecting it from oxygen, another form, hemosiderin is same except it is larger

Question 23

what are some other cellular defense mechanisms?

Answer 23

Vitamin E and Beta carotene and protect membrane of cells against free radicals

Question 24

what is superoxide dismutase and catalase?

Answer 24

seek and destroy superoxide and H2O2

Question 25

why is superoxide dismutase important?

Answer 25

diffusion limited enzyme which has a reaction mechanism that is faster than diffusion of superoxide which means if it found itself in the dismutase active site it is unable to escape and so it converts a 2O2-(due to its electron rearrangement) into an O2 and H2O2(not as reactive as superoxide)

Question 26

why is catalase important?

Answer 26

grabs 2 H2O2 and rearrange it to produce 2 water and 2 O2s, shows up together with superoxide dismutase and they are independent of each other

Question 27

what is glutathione peroxidase and glutathione reductase?

Answer 27

it takes H2O2 along with its reduced 2 GSH to produce 2 molecules of water and oxidized glutathione to 2 GSSG which has to be re-reduced and so you have glutathione reductase that uses power of NADPH that donates its electrons to produce 2 GSH

Question 28

what are the types of superoxide dismutase?

Answer 28

Cu-Zn SOD (cytosolic)
Mn SOD (mitochondrial)
EC-SOD (extracellular