mitochondria and oxidative phosphorylation

Question 1

pattern of mitochondrial genetic disorders inheritance

Answer 1

maternal

Question 2

why is succinate added in an assay for ATP synthesis

Answer 2

substrate for ATP synthesis
succinate – fumarate
FAD+ – FADH2

Question 3

why are some people’s symptoms less severe

Answer 3

heteroplasmy
have a different number of affected chromosomes
gene dosage affect
PCR used to analyse the study - densitometric analysis can reveal the percentage of mutant DNA

Question 4

why is succinate omitted to measure ATP hydrolysis

Answer 4

see rate of hydrolysis without ATP synthesis occurring

Question 5

what can be deduced about the nature of the condition

Answer 5

leucine replaced by arginine 
H+ flow into matrix is impaired 
H+ flow in hydrolysis direction fine 
result in death in the mid-teenage years
Approaches targeting native ATP6 to the mitochondria are being persued

Question 6

how is the uptake of oxygen by mt controlled

Answer 6

by components of ATP production, Pi and ADP
this is respiratory control
it allows the body to adapt oxygen consumption to energy requirements

Question 7

Describe ATP consumption

Answer 7

ATP lifecycle 1-5 mins 
recycled 300 times/day
hypoxia 
anoxia - total 
death of neuron - minute
death of muscle - hour

Question 8

cyanide and azide

Answer 8

bind high affinity to Fe3+ in cytochrome oxidase complex

block flow of electrons and ATP production

Question 9

malonate

Answer 9

resemble succinate
competitive inhibitor off succinate dehydrogenase
slow flow of electrons to ubiquinone

Question 10

rotenone

Answer 10

inhibit electron transfer from complex 1 to ubiquinone

Question 11

oligomycin

Answer 11

AB
inhibit ox phos
bind to stalk of ATP synthase

Question 12

dinitrophenol

Answer 12

proton ionophore

shuttle protein across inner mt mem

Question 13

Explain the symptoms of luft’s syndrome

Answer 13

unable to respire at maximal rate - lack of respiratory control
oligomycin doesn’t block oxygen consumption - protons enter matrix free of ATP synthase
can phosphorylate substrates efficiently
uncoupled - little effect with DNP
dissipation of energy as heat - perspiration and low weight

Question 14

describe non-shivering themogenesis

Answer 14

regulated uncoupling in brown adipose tissue in newborn and hibernating animals
hormones - release of fatty acids - activate thermogenin
uncouple

Question 15

DNP use

Answer 15

weight loss

pesticides

Question 16

mitochondria

Answer 16

double membrane (cristae)
ox phos - inner mem
TCA - matrix

Question 17

origin of mitochondria

Answer 17

endosymbiosis 
mt only arise from mt 
own genome - similar to prok 
own protein synthesis  similar to prok 
start AA is fMet (prok) not Met (euk)
AB block protein synth in mt

Question 18

mt DNA

Answer 18

circular genome 
several copies ion each cell 
transmitted by ovum 
NADH and FADH2 re-oxidised - energy released enough to make phosphanhydride bonds 
this is recovered by etc

Question 19

chemiosmotic model of ox phos

Answer 19

translocation of protons from within matrix

pumped protons back into matrix

Question 20

the etc

Answer 20

enzymes: NADH dehydrogenase complex, cytochrome b-c1 complex, cytochrome oxidase complex
carrier: ubiquinone (co-enz Q), cytochrome C
proton accept e-, H+ pump

Question 21

describe Redox

Answer 21

substance that can exist as both oxidised and reduced form - redox couple
rredox potential - ability to be oxidised/reduced
standard redox potentials E’0 measured experimentally
-ve - more reducing power
energetically favourable

Question 22

ATP synthase

Answer 22

multimeric enzyme
membrane bound part F0 and F1 - project in matrix
rotation drive transition state
conformational energy flow from catalytic subunit into the bound ADP and Pi - ATP
direction of flow alters hydrolysis/synthesis
succinate dehydrogenase communicate with ubiquinone - one less proton into membrane space - less ATP

Question 23

describe the oxygen electrode

Answer 23

measures ox conc
base of chamber Teflon membrane permeable to ox
2 electrodes pt cathode and ag anode
small voltage - ox through Teflon reduced - water pt
ag oxidised to AgCl by electrolyte
resulting current proportional to ox conc
sample of mt in chamber - effect of substances on etc