Biochem: 11.4-5 Mitochondria transport systems and Regulation

Explain the reason for transporting ATP from the MT matrix to the cytosol and for transporting ADP +Pi from the cytosol to the MT matrix.
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Explain the reason for transporting ATP from the MT matrix to the cytosol and for transporting ADP +Pi from the cytosol to the MT matrix.
ATP is used in the cytosol for glycolysis, ADP and Pi is needed in the matrix for
the ETC
State the function of each transporter and identify whether it is a passive or an active
transporter. And if an active transporter, identify whether it is a primary or secondary active
transporter.
-ATP/ADP translocase: secondary active transport antiporter
transports ADP into the mitochondrial matrix and ATP out of the matrix into the
IM space

Phosphate Translocase:
secondary active transport antiporter or synporter, acts like a channel
moves Pi and H+ into matrix or Pi into matrix and OH- into IM space

Malate-Aspartate Shuttle (liver cells)
Malate-alpha ketoglutarate transporter and aspartate-glutamate transporter
Both are secondary active transport antiporters
move malate into matrix, alpha ketoglutarate into IM space
move aspartate into IM space, glutamate into matrix

Glycerol-3-P shuttle (muscle cells)
passive transport channels for glycerol-3-P and dihydroxyacetone-P
List the steps or describe the mechanism for the ATP/ADP translocase.
-ADP enters the protein from the IM space in the C state
-protein changes conformation into the M state and release ADP into the matrix
-ATP enters the protein from the matrix
-another conformational change occurs back to the C state, releasing ATP to IM space
Describe the symporter activity of the phosphate translocase transporter.
-Translocates Pi and H+ ions from the IM space into the matrix (symporter)
-Can also translocate Pi into the matrix and OH- out into the IM space (antiporter)
Describe the need for the malate-aspartate and the glycerol-3-phosphate shuttles.
Need to shuttle NADH and FADH2 back into glycolysis (cytosol)
Explain the four steps in the malate-aspartate shuttle mechanism of liver cells.
-Reduction of oxaloacetate in the cytosol with NADH + H+ by cytosolic malate
dehydrogenase to form malate and NAD+
-Malate is transported into the m. matrix and oxidized by mitochondrial malate
dehydrogenase with NAD+ to form oxaloacetate and NADH + H+
-Transamination of oxaloacetate by mitochondrial aspartate aminotransferase and glutamate
to form alpha-ketoglutarate and aspartate, which is shuttled across the membrane
-Transamination of aspartate in the cytosol by systolic aspartate aminotransferase and
alpha-ketoglutarate to form oxaloacetate and glutamate
Explain the 3 steps in the glycerol-3-phosphate shuttle.
-Reduces dihydroxyacetone phosphate in the cytosol, product glycerol-3-P diffuses across
the outer m. membrane via porin channels into the IM space
-Glycerol-3-P reoxidized to form dihydroxyacetone phosphate, 2 electrons are transferred
to FAD in glycerol-3-P dehydrogenase (dihydroxy. back to cytoplasm via porin channel)
-2 electrons passed to Q, transferred one at a time to complex III via Q cycle
If given inhibitors of the ATP/ADP translocase, deduce which steps in the mechanism would be
inhibited and the impact this would have on glycolysis and CAC.
-atractyloside binds to C state and blocks ADP binding
-Bongkrekic acid binds to M state and inhibits ATP in the matrix from binding to the
translocase
Explain how the proton-motive force works in conjugation with the ATP/ADP and phosphate
translocases to keep the cell's energy needs met.
-3 protons in the IM space (from ETC) run through ATP synthase, 1 proton moves through
phosphate translocase into the matrix
-Flow of 4 electrons is required for each ATP
Explain why muscle cells use the glycerol-3-phosphate shuttle rather than the malate-aspartate
shuttle. What is different about muscle cells compared to liver cells that a different shuttle
system is required?
The gly-3-P shuttle is less complex and therefore faster, muscle requires higher rates of
energy conversion from glucose, quick energy
Compare and contrast the malate-aspartate shuttle with the glycerol-3-phosphate shuttle, in terms of the mechanism used, the number of ATP generated for each NADH oxidized, and the complexes in ETS used to transfer the electrons.-Both have channels, glycerol-3-P shuttle more like porin proteins and simpler -both oxidize 2 NADH, m-a shuttle produces 5 ATP from these while gly-3-P only produces 3 ATP from these -m-a interacts with complex I, gly-3-P interacts with complex II bypassing complex ICalculate the number of ATP generated from the complete oxidation of one glucose molecule in liver cells and in muscle cells, accounting for the differences between the cells.-32 in liver (malate-aspartate Shuttle) -30 in muscle (glycerol-3-P shuttle)If given results for electron transport experiments that added cyanide, or 2,4-dinitrophenol, or oligomycin, determine the impact on oxygen consumption and the activity of CAC.-cyanide: blocks flow of electrons through complex 4 and oxygen consumption halting ATP production due to loss of proton-motive force -2,4-DNP: can easily diffuse across the membrane and carry protons from the IM space to the matrix, acts as a chemical uncoupler body activates fatty acid degradation, increasing supply of acetyl-CoA for CAC and stimulating oxidative phosphorylation, difficulty in maintaining energy homeostasis leading to liver damage and death -oligomycin: blocks proton flow through ATP synthase complex (Binds to ATP synthase), inhibits ATP synthesis and decreased O2 consumption