Mitochondrial Toxicity

Question 1

physiological function of ATP

Answer 1

supplying majority of ATP!!

Question 2

Functions common to most mitochondria

Answer 2

ATP synthesis
terminal oxidationof pyruvate
beta oxidation of fatty acids
oxidation of acetyl CoA
fatty acid, protein and carbohydrate oxidations

Question 3

functions of some mitochondria

Answer 3

oxidation of branched amino chains, sulfate
nitrogen homeostatis, urea formation
activation of vit D3

Question 4

mitochondrial plasticity purpose

Answer 4

optimize energy production relative to demand

Question 5

physiological signals that could induce change

Answer 5

nutritional variations, different work loads, oxygen availability, developmental state

Question 6

example of plasticity with: nutritional value

Answer 6

urea cycle enzymes are increased by high protein diets and starvation

Question 7

example of plasticity with: different work load

Answer 7

volume density of mitonchondria in skeletal muscle change in association with aerobic activity so that ATP production and energy requirements are coordinated

Question 8

example of plasticity with: oxygen availability

Answer 8

mitochondrial enzymes decrease during chronic hypoxia

Question 9

responses to physiological signals are typically

Answer 9

reversible

Question 10

Chemiosmotic Theory

Answer 10

describes the coupling of metabolic energy in the mitochondria
says that energy transducing membranes contain a proton pump

Question 11

inner mitochondrial membrane contains

Answer 11

solute transport systems that function to allow the energy available from electron transport to be captured in the form of an electrochemical gradient which drives ATP synthesis

Question 12

chemiosmotic proton pump model

Answer 12

H+ are pumped to the cytosol (which is the postive side)

Question 13

MAIN POINT of Chemiosmotic theory

Answer 13

the primary H+ pump generates such a high gradient of H+ that it forces the secondary pump to reverse and synthesize ATP from ADP and P

Question 14

the quantitative thermodynamic measure of this H+ gradient is

Answer 14

the proton electrochemical gradient

Question 15

the proton electrochemical gradient has 2 components

Answer 15

1. concentration difference of H+ across the membrane (delta pH)
2. difference in electrical potential between the 2 aqeuous phases separated by the membrane (delta trident)

Question 16

the electrochemical gradient is typically converted into units of and is referred to as (delta p)

Answer 16

electrical potential, mV

protonmotive force

Question 17

use of protonmotive force is

Answer 17

essential for virtually every aspect of mitochondrial function

Question 18

electron transfer chain comprises a sequence of electron carriers with three separate regions where

Answer 18

redox energy can be conserved in the synthesis of ATP

Question 19

rate of respiration is controlled by

Answer 19

the demand for ATP

Question 20

coupling between respiration and ATP synthesis can be disrupted by

Answer 20

uncouplers - they abolish respiratory control and allow mitochondria to catalyze a rapid ATP hydrolysis

Question 21

oligomycin (an antibiotic) inhibits both the synthsis and

Answer 21

uncoupler-stimulated hydrolysis of ATP

Question 22

the energy from respiration can be coupled not only to the synthesis of ATP but also to

Answer 22

the accumulation of Calcium and the reduction of NAD to NADP

this can all be driven by the hydrolysis of ATP in anaerobic mitochondria

Question 23

Four Basic Postulates of Mitchell’s Chemiosmotic Theory

Answer 23

1. respiratory ETC should translocate protons
2. the ATP synthase should function as a reversible proton-translocating ATPase
3. energy-transducing membranes should have a low effective proton conductance
4. energy-transducing membranes should posses specific exchange carriers to permit metabolites to permeate and osmotic stability to be maintained in the presence of high membrane potential

Question 24

Redox reactions are not restricted to the

Answer 24

ETC

Question 25

the tendency of the redox couple to donate electrons is quantified by

Answer 25

forming an electrical cell from 2 half-cells

Question 26

the KEY POINT for mid-point potentials is

Answer 26

redox couples with more negative Em7 values are more likely to donate electrons to redox couples with more positive Em7 values

Question 27

Mitochondrial Respiratory Chains: complex I

Answer 27

NADH-UQ oxidoreductase

Question 28

Mitochondrial Respiratory Chains: complex II

Answer 28

succinate dehydrogenase

Question 29

Mitochondrial Respiratory Chains: complex III

Answer 29

bc1 complex; UQ-cyt c oxidoreductase

Question 30

Mitochondrial Respiratory Chains: complex IV

Answer 30

cytochrome c oxidase

Question 31

Ion and metabolite transport in Mitochondria

Answer 31

mitochondria require a continual interchange of metabolites and end-products with the cellular cytosol - at the same time the inner membrane must maintain a high protonmotive force for ATP synthesis

Question 32

Key Transport Processes: Monovalent cations

Answer 32

high negative membrane potential can lead to a 1000X accumulation of monovalent cations if transport occurred by a uniport mechanism - mitochondria possess a transporter that can exchange either Na or K FOR H

Question 33

Key Transport Processes: Calcium

Answer 33

there are 2 mitochondrial Ca transporters 1. membrane potential-dependent uniporter 2. Ca/2H or Ca/2Na antiporter

Question 34

perturbations in cellular Ca homeostasis may be important in many forms of chemically induced toxicity - the concentration of Ca is a critical factor in the regulation of

Answer 34

many metabolic prosses like regulation of activities of mitochondrial dehydrogenases

Question 35

six processes function in the regulation of intracellular Ca homeostasis

Answer 35

1. electroneutral Na/Ca exchange 2. Mg-dependent Ca-ATPase 2. endoplasmic reticulum: uptake by Mg-dependent Ca-ATPase 4. uptake-driven by transmembrane potential generated across inner membrane during coupled respiration 5. efflux-electroneutral Ca/H exchange 6. calcium-binding proteins (like calmodulin)

Question 36

Ca cycling is a major mechanism by which

Answer 36

toxins exert their deleterious effects in cells

Question 37

all mitochondria possess the

Answer 37

adenine nucleotide translocase, phophate carrier and pyruvate carrier

Question 38

key findings on metabolic conditions of H2O2 generation: 1. with malate + glutamate as respiratory substrates H2O2 production is

Answer 38

inhibited by rotenone

Question 39

key findings on metabolic conditions of H2O2 generation: 2. when succinate is used as respiratory substrate & electron flow is blocked by antimycin, mitochondria exhibit high rates

Answer 39

of H2O2 production

Question 40

key findings on metabolic conditions of H2O2 generation: 3. fatty acids and fatty acyl-CoA also support high rates of H2O2 production in the presence of

Answer 40

antimycin A

Question 41

mitochonrial generator of H2O2 is either a component of the respiratory chain or a chemical that is at equilibrium with is since

Answer 41

H2O2 production is maximal in HIGHLY REDUCED states | and is minimal in oxidized states like state 3

Question 42

functional consequences of mitochondrial oxidative stress

Answer 42

mitochondria contain 3 major types of redox active components: 1. electron carriers of the respiratory chain 2. protein sulfhydryl groups 3. matrix GSH

Question 43

Toxicological relevance

Answer 43

mitochondria contain a large number of critical SH groups that must be in the reduced form for appropriate enzyme activity

Question 44

Mitochondrial Permeability transition: the transition is readily reversible and occurs when

Answer 44

Ca loading is followed or preceded by addition of a second agent

Question 45

Mitochondrial Permeability transition: perturbation of a phospholipid acylation-deacylation cycle is seen as a

Answer 45

central event leading to the transition

Question 46

Mitochondrial Permeability transition: calcium ions are hypothesized to increase activity of this cycle by

Answer 46

stimulating the mitochondrial phospholipase A2

Question 47

Mitochondrial Permeability transition: the inducing agent is thought to inhibit phospholipid re-acylation as result

Answer 47

phospholipase A2 reaction products accumulate and crease membrane permeability

Question 48

Mitochondrial Permeability transition: permeability transition can occur both with and without

Answer 48

matrix swelling

Question 49

inducing agents

Answer 49

sulfhydryl reagents, peroxides, intermediary metabolites, heavy metals

Question 50

protective agents include:

Answer 50

thiols & other reductants phospholipase A2 inhibitors calcium channel blocking agents cyclosporin A

Question 51

Genome and Toxicity and Disease

Answer 51

carcinogens, mitochondrial DNA (mtDNA) is also a target

Question 52

several factors may contribute to selective adduct formation with mtDNA

Answer 52

1. mtDNA lacks histone proteins which are associated with nDNA so mtDNA may be more accessible to electrophilic metabolites of xenobiotics 2. the diverse and efficient DNA repair systems present in the nucleus are generally lacking in mitochondria 3. enzymes that bioactivate xenobiotics to reactive electrophiles are present in the mitochondria

Question 53

mitochondrial DNA repair and cell injury: mutation rate of mtDNA in mammals is reported to be 5-10X that of

Answer 53

nDNA

Question 54

mitochondrial DNA repair and cell injury: mtDNA mutations may lead to decreased

Answer 54

respiratory capacity and an increase in release of ROI's

Question 55

mitochondrial DNA repair and cell injury: the relatively small amounts of mtDNA as compared with nDNA make the

Answer 55

study of repair processes difficult

Question 56

mitochondrial genetics have several features that are unique and different from that of classical Mendelian genetics

Answer 56

1. cytoplasmic location and high copy number 2. mtDNA is maternally transmitted 3. mixed intracellular populations of mutant and normal mtDNAs segregate during both meiotic and mitotic replication 4. systemic OXPHOS defects show tissue-specific expression as a result of the different OXPHOS requirements of human tissues 5. energetic capacities decline with age- probably because accumulation of mtDNA with age 6. mtDNA has a high mutation rate partly due to lack of efficient repair systems