Bioenergetics pt 2 Flashcards
What are the three goals of ox phos?
To transfer e- from NADH and FADH2 to O2
To establish a proton gradient across the IMM and in the intermembrane space
To synthesize ATP
Describe the flow of e- during oxphos
The e- flows from the molecules with lower standard redox potential (E0’) to that with the highest redox potential (low affinity to high affinity e-)
What two factors contribute to the proton motive force (pmf) to drive ATP synthesis by complex V?
pH gradient (delta pH) and membrane potenital
How many protons are needed for the synthesis of 1 mol ATP?
3+1 H+
What inhibits ATP synthase?
oligomycin
When the transfer of e- is inhibited what occurs?
a decrease in the pumping of protons, a decrease in the proton gradient and inhibitor of ATP synthesis
What regulates Oxphos?
Presence of O2 (no oxygen, no oxphos)
ATP/ADP ratio (high decreases and low activates)
How does a high ATP/ADP ratio influence the TCA cycle and oxphos?
Inhibits ATP synthase, increases [H+] gradient, decrease e- transport and proton pumping, slows down TCA cycle, decreases glycolysis and leads to decreased [ATP]
How does a low ATP/ADP ratio influence the TCA cycle and oxphos?
Activates ATP synthase, decreases [H+] gradient, increases e- transport and proton pumping, accelerates TCA cycle, increases glycolysis and leads to increased [ATP]
Role complex I (NADH dehydrogenase) plays in oxphos
e- transfer facilitated by tightly bound FMN and Fe-S clusters
Accepts 2 e- from NADH and donates them to coenzyme Q
Pumps 4 H+ from the matrix into intermembrane space
Role complex II (succinate dehydrogenase) plays in oxphos
Protein bound to the matrix side of the IMM
e- transfer facilitated by FAD and Fe-S clusters
Transfers 2 e- from FADh2 to coenzyme Q
NO proton pumping
What role does coenzyme Q (ubquinone) play in oxphos?
Mobile - able to move freely within the lipid bilayer of the IMM
Converted to ubiquinol upon acceptance of 2 e- from complex I or II and transfers them to complex III
What role does complex III (cytochrome c reductase) play in oxphos?
e- transfer facilitated by Fe-S clusters and cytochromes b and c1 which harbor Fe-containing heme-b and c molecules
Accepts 2 e- from ubiquinol and donates them to cytochrome c
pumps 2 H+ from matrix into intermembrane space
What role does cytochrome c play in oxphos?
Also mobile
e- transfers facilitated by an iron containing heme c group
Accepts e- from complex III and donates them to complex IV
What role does complex IV (cytochrome c oxidase) play in oxphos?
e- transfer facilaited by Cu centers and cytochromes
Accepts e- from cytochrome c and transfers them to oxygen which forms water
Pumps 4 H+ into intermembrane space
What role does complex V (ATP synthase) play in oxphos?
Moves protons from inter membrane space into the matrix to obtain the energy needed to synthesize ATP from ADP and Pi
Which respiratory chain components does mtDNA encode?
13 proteins in the respiratory chain as well as 2 RNAs and 22 tRNAs
How does rotenone effect oxphos?
Inhibits NADH dehydrogenase (complex I) and prevents electron transfer to ubiquinone
How does cyanide poisoning effect oxphos?
Binds to oxidized form of iron in the heme of complex IV and prevents oxygen reduction
Mito respiration and ATP production cease which leads to cell death
Death occurs from asphyxia especially in the CNS
Cyanide vs CO action
CO is a competitive inhibitor by competing with binding of O2 whereas CN is a non-competitive inhibitor of complex IV
How does an aspirin overdose effect oxphos?
It uncouples oxphos by disrupting the H+ gradient across the IMM and causes the dissipation of energy as heat instead of ATP
What is the chemiosmosis hypothesis?
Coupling of the transfer of e- with the phosphorylation of ADP to form ATP
What occurs when uncoupling agents disrupt the H+ gradient?
Causes a H+ leakage back into the matrix, TCA cycle and e- transfer to O2 to accelerate, inhibition of ATP synthase and generation of heat instead of ATP
What are the three main ways uncouplers can achieve their effect of uncoupling oxphos and ATP synthesis?
Damaging the membrane (ex. nucleoside analogues like AZT)
Binding to and transporting protons across the membrane (ex. 2-DNP)
Serving as proton channel to allow easy passage of H+ across the inner membrane (ex. thermogenin or UCP1)
Explain thermogenesis in brown adipose
Brown adipose has more mitochondria and uses a natural uncoupler (thermogenin/UCP1) that acts a channel for protons instead of ATP synthase
Instead of making ATP, heat is generated
Brain can use NE to break down TAGs to FAs and activate UCP1 and allows heat to be generated in a cold environment
How can episodes of hypoxia such as MI or stroke affect ATP levels?
Decreases the activity of respiratory chain and the pmf
Cells depend on glycolysis causing lactate acidosis
Inhibitory protein is activated that binds to ATP synthase to prevent it from acting in reverse therefore preserving ATP levels
Which two shuttle systems does NADH use to enter the mitochondria?
Malate aspartate and glycerophosphate shuttle
Describe the malate aspartate shuttle
Operates in the heart, liver, and kidneys
Generates NADH into the mito matrix
NADH enters ETC at complex I
Describe the glycerophosphate shuttle
Operates in skeletal muscle and brain
Generates FADH2 in IMM
FADH2 joins ETC at CoQ
What is the source of mitochondrial NADH?
TCA cycle, oxidative decarboxylation of pyruvate, and from oxidation of KBs
What is the source of FADH2?
succinate dehydrogenase (complex II), glycerol phosphate shuttle and fatty acyl CoA dehydrogenase
What was the first mitochondrial disorder?
Luft’s disease
What is Luft’s disease?
Discovered by Dr. Luft by an unusual cause in a 30 y/o woman
sx: profuse perspiration, marked fluid intake but normal urine volume, daily caloric intake extremely high, stable body weight, asthenic (lack or loss of strength) with progressive weakness
Examined mitochondria from striated muscle and found uncoupling of oxphos, high levels of cytochrome c oxidase, low levels of coenzyme Q10 and high RNA in muscle homogenate (evidence of mitoprotein synthesis)
Electron microscopy revealed large accumulations of mitochondria w/ highly variable size and paracrystalline inclusions
What are the two main primary causes of mitochondrial disease?
Defect in nuclear DNA or defect in mtDNA with both affect the mitochondria since they both encode for mitochondrial proteins
What are some examples of secondary causes for mitochondrial disease?
Ischemia, repercussion, cardiovascular disease, renal failure, drugs, aging, alcohol, smoking and others
