Chapter 5: Aerobic Respiration and the Mitochondrion
description
Transcript of Chapter 5: Aerobic Respiration and the Mitochondrion
![Page 1: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/1.jpg)
Chapter 5:
Aerobic Respiration
and the Mitochondrion
![Page 2: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/2.jpg)
Mitochondrial outer membrane
• ~50% lipid by weight• Contains many enzymes involved in diverse
activities: epinephrine oxidation, tryptophan degradation, fatty acid elongation, etc.
• Porin channel is surrounded by a barrel of β strands
• If porin channels wide open, outer membrane is freely permeable to molecules like ATP, NAD & coenzyme A
![Page 3: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/3.jpg)
Porins
• Molecules up to ~5,000 daltons to penetrate
• The intermembrane space & cytoplasm are basically continuous with respect to ATP, NAD, CoA, etc.
![Page 4: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/4.jpg)
Mitochondrial inner membrane
• Very high protein/lipid ratio
(3:1 by weight; ~1 protein/every 15 phospholipids)
• >100 different polypeptides; devoid of cholesterol• Rich in the unusual phospholipid cardiolipin• Both the presence of cardiolipin & the absence of
cholesterol are characteristic of bacterial plasma membranes
![Page 5: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/5.jpg)
Mitochondrial inner membrane
• Ca2+-ATPase
• Electron transport chain
• ATP synthase
![Page 6: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/6.jpg)
Mitochondrial matrix
• Enzymes• Ribosomes • Circular double-stranded DNAs (encode inner
membrane proteins; nuclear DNA codes for some, too)
• Humans mitochondrial DNA encodes– 13 mitochondrial polypeptides– rRNAs and 22 tRNAs that are used in protein
synthesis within the organelle
![Page 7: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/7.jpg)
The role of anaerobic and aerobic metabolism in exercise
• Muscle cells contain a store of creatine phosphate (CrP )
• CrP + ADP Cr + ATP• Human skeletal muscles consist of fast-
twitch fibers and slow-twitch fibers
![Page 8: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/8.jpg)
Fast-twitch fibers
• Contract very rapidly; 15 – 40 msec
• Nearly devoid of mitochondria
• Unable to make much ATP by aerobic respiration
![Page 9: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/9.jpg)
Slow-twitch fibers
• Contract more slowly; 40 – 100 msec
• Have large numbers of mitochondria
![Page 10: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/10.jpg)
Aerobic exercise
• Energy source– Initially by glucose stored as glycogen in
muscles– After a few minutes the muscles depend
increasingly on free fatty acids released into blood from adipose (fat) tissue
• The longer the exercise period, the greater the dependency on fatty acids
![Page 11: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/11.jpg)
Direct evidence for rotation of γ subunit relative to αβ subunits
• Prepared a genetically engineered version of working part of ATP synthase (3α, 3β & a γ [α3β3γ])
• Fixed polypeptide complex to glass coverslip by its head & attached short, fluorescently labeled actin filament to γ subunit end jutting into medium
• Add ATP & rotation seen (like propellor) • Powered by energy released as ATPs were bound
& catalyzed by β subunit catalytic sites
![Page 12: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/12.jpg)
The mechanism by which H+ movement drives c ring rotation
• Each a subunit has 2 half-channels that are physically separated (offset) from one another
• One half-channel leads from intermembrane (cytosolic) space into the middle of the a subunit; the other leads from the middle of the a subunit into the matrix
• Each proton moves from the intermembrane space through the half-channel & binds to a negatively charged Asp residue situated at the surface of the adjoining c subunit
![Page 13: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/13.jpg)
The mechanism by which H+ movement drives c ring rotation
• Binding of H+ to Asp carboxyl group generates a major conformational change in the c subunit that causes the subunit to rotate ~30° in a counterclockwise direction
• This movement of the recently protonated c subunit brings the adjoining ring subunit (protonated at an earlier step) into alignment with the second a subunit half-channel
![Page 14: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/14.jpg)
The mechanism by which H+ movement drives c ring rotation
• The Asp releases its associated proton, which diffuses into the matrix
• After proton dissociation, the c subunit then returns to its original conformation & is ready to accept another proton from the intermembrane space & repeat the cycle
![Page 15: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/15.jpg)
Peroxisomes
• Found in 1954 & called microbody• Simple membrane-bound vesicles with 0.1 - 1.0
µm diameter• Often have dense, crystalline core of an oxidative
enzyme(s) & consequently granular appearance• Multifunctional organelles containing >50
enzymes involved in diverse activities like:– Oxidation of very long chain fatty acids
(VLCFAs); whose chains typically contain 24 – 26 C
![Page 16: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/16.jpg)
Peroxisomes
• Synthesis of plasmalogens– Abnormalities in plasmalogen synthesis can
lead to severe neurological dysfunction
• Luciferase– which generates light emitted by fireflies, is
also a peroxisomal enzyme
![Page 17: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/17.jpg)
Peroxisomes
• Named peroxisomes since they are the site of synthesis & degradation of H2O2
• H2O2 is produced by a number of peroxisomal enzymes– Urate oxidase, glycolate oxidase & amino acid
oxidases that utilize molecular oxygen to oxidize their respective substrates
• Catalase (at high concentration in peroxisomes) rapidly breaks down H2O2 generated in these reactions
![Page 18: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/18.jpg)
Peroxisomes
• Form by splitting from preexisting organelles
• Import preformed proteins from cytosol
• Do similar kinds of oxidative metabolism in mitochondria– Alanine/glyoxylate aminotransferase, is seen in
the mitochondria of some mammals (cats, dogs) & peroxisomes of others (rabbits, humans)
![Page 19: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/19.jpg)
Glyoxysomes
• A specialized type of peroxisome found only in plants
• Contain some of same enzymes (catalase, fatty acid oxidase), but others as well
• Plant seedlings rely on stored fatty acids to provide energy & material to form new plant
• Glyoxylate cycle
![Page 20: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/20.jpg)
Glyoxysomes
• A primary metabolic activity in these germinating seedlings is the conversion of stored fatty acids to carbohydrate
• Stored fatty acid disassembly produces acetyl CoA & it condenses with oxaloacetate to form citrate
• Citrate is then converted to glucose by a series of glyoxylate cycle enzymes found in glyoxysomes
![Page 21: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/21.jpg)
![Page 22: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/22.jpg)
Diseases result from abnormal mitochondrial or peroxisomal function
• Muscle & nerve tissues tend to be most seriously impacted in these disorders since they have the highest demand for ATP
• Depending on protein(s) affected, conditions vary in severity from diseases that lead to death during infancy to disorders that produce seizures ( 中風驟發 ), blindness, deafness and/or strokelike episodes
• Sometimes conditions are mild & characterized by intolerance to exercise or nonmotile sperm
![Page 23: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/23.jpg)
Abnormal mitochondria
• Closer examination of mitochondria reveals large numbers of abnormal inclusions
• A number of common neurological diseases with adult onset (like Parkinson's disease) might be a consequence of degenerative changes in mitochondrial function
• The first such disease-causing mutation was reported in 1995 – The mutation occurred in gene encoding the
flavoprotein subunit of the TCA enzyme succinate dehydrogenase
![Page 24: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/24.jpg)
Mitochondrial disorder inheritance contrasts in several ways with nuclear
gene Mendelian inheritance
• Mitochondria in cells of human embryo are derived exclusively from mitochondria present in the egg at the time of conception without any contribution from the fertilizing sperm
• Mitochondrial disorders are inherited maternally• Mitochondria in cell can contain mixture of
normal (wild-type) & mutant mtDNA (heteroplasmy)
![Page 25: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/25.jpg)
mtDNA Mutation
• Nuclear DNA is protected from damage by a variety of DNA repair systems which are generally lacking in mitochondria
• mtDNA may also be subjected to high levels of mutagenic oxygen radicals
• mtDNA experiences >10 times the mutation rate of nuclear DNA
![Page 26: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/26.jpg)
Abnormal peroxisomes
• Zellweger syndrome (ZS) is a rare inherited disease characterized by a variety of neurological, visual & liver abnormalities leading to death during early infancy
• Sidney Goldfischer et al. (1973) – reported that liver & renal cells from these patients lacked peroxisomes
• Later studies showed that peroxisomes were not entirely absent from the cells of these individuals
![Page 27: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/27.jpg)
Zellweger syndrome (ZS)
• Peroxisomes were present as empty membranous ghosts (organelles lacking the enzymes normally found in peroxisomes)
• These individuals can make peroxisomal enzymes but the enzymes fail to be imported into peroxisomes & stay largely in cytosol where they are unable to carry out their normal functions
• Mutations in at least 11 different genes– Encoding proteins involved in uptake of
peroxisomal enzymes from cytosol
![Page 28: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/28.jpg)
Adrenoleukodystrophy (ALD), subject of the movie Lorenzo's Oil
• Absence of a single peroxisomal enzyme • A defect in a membrane protein that transports
very-long-chain-fatty-acids (VLCFAs) into the peroxisomes where they are normally metabolized
• In the absence of this protein, VLCFAs accumulate in brain & destroy myelin sheaths that insulate nerve cells
• Boys with the disease are typically unaffected until midchildhood, when symptoms of adrenal insufficiency & neurological dysfunction begin
![Page 29: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/29.jpg)
Adrenoleukodystrophy (ALD)
• A diet rich in certain fatty acids is able to retard the progress of the disease
• A number of ALD patients have been successfully treated by bone marrow transplantation, which provides normal cells capable of metabolizing VLCFAs
• Administration of drugs (e.g., lovastatin) that may lower VLCFA levels
• Clinical studies employing gene therapy are also being planned
![Page 30: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/30.jpg)
Chapter 8-1:
Cytoplasmic Membrane Systems:
Structure, Function, and
Membrane Trafficking
![Page 31: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/31.jpg)
Endomembrane system
• Plasma membrane, vesicles, vacuoles, ER, Golgi apparatus, nuclear membrane, lysosome– Have distinct structures & functions but
together form an endomembrane system– Dynamic, integrated network– Materials are shuttled (transport vesicles)
between the endomembrane system
![Page 32: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/32.jpg)
Transport vesicles in endomembrane system
• Transport vesicles form by budding from donor compartment
• Transport vesicles move in directed manner, often pulled by motor proteins operating on tracks formed by microtubules & microfilaments of the cytoskeleton
• When they reach their destination, they fuse with acceptor compartment
![Page 33: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/33.jpg)
Transport in endomembrane system
• Endocytic pathway
• Exocytotic pathway
– Secretory pathway
![Page 34: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/34.jpg)
Biosynthetic (secretory) pathway
• Synthesis in ER (protein) or Golgi (lipid, carbohydrate)
• Many materials made in ER (proteins) & Golgi (complex polysaccharides) fated for secretion from cell
• Two types of secretory activity– Constitutive secretion– Regulated secretion
![Page 35: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/35.jpg)
Constitutive secretion
• Synthesis & secretion into extracellular space occurs in continual, unregulated manner
• Form extracellular matrix & plasma membrane
![Page 36: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/36.jpg)
Regulated secretion
• Secretory materials stored in large, densely packed, membrane-bound secretory granules in cell periphery
• Secreted after correct stimulus – Endocrine cells release hormones – Pancreatic acinar cells release digestive
enzymes – Nerve cells release neurotransmitters
![Page 37: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/37.jpg)
Proteins targeting
• Through sorting signals located on proteins & receptors in transport vesicle walls that recognize them
• Salivary gland cell protein trafficking– Salivary mucus proteins (made in ER)
specifically targeted to secretory granules• Lysosome enzymes (also made in ER) specifically
sent to lysosome • Sorting signals are encoded in protein amino acid
sequence or in attached oligosaccharides
![Page 38: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/38.jpg)
Approaches to the study of cytomembranes
• EM micrographs give detailed view of cell cytoplasm, but little insight into functions of the structures
• Insights gained from autoradiography– Detect location of radioactively labeled
materials in cell • Insights from pulse-chase trials
![Page 39: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/39.jpg)
Pulse-chase trials
• Expose to hot amino acids briefly (pulse)
• Wash to remove excess isotope from tissue • Transferred tissue to medium with
unlabeled amino acids (chase), which lasts for varying time periods
• See wave of radioactivity moving through cell, discern pathway sequence
![Page 40: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/40.jpg)
Use of green fluorescent protein (GFP) reveals the movement of proteins within
a living cell
• GFP is small protein from certain jellyfish that emits a green fluorescent light
• GFP gene fused to DNA encoding protein to be studied
• Introduce the chimeric DNA into cells• Chimeric DNA expresses chimeric protein
(GFP fused to the protein to be studied)
![Page 41: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/41.jpg)
Use of green fluorescent protein (GFP) reveals the movement of proteins within
a living cell
• Usually, GFP stuck to end of a protein has little or no effect on its movement or function & protein under study has no effect on fluorescence of attached GFP
![Page 42: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/42.jpg)
Example: infect a mammalian cell with vesicular stomatitis virus (VSV) strain in which a viral gene
(VSVG) is fused to GFP gene
• Cell begins to make massive amounts of VSVG protein in RER
• VSVG then goes to Golgi complex & eventually to the plasma membrane of the infected cell where they are incorporated into viral envelopes
• Can see relatively synchronous wave of protein movement (green fluorescence) soon after infection
![Page 43: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/43.jpg)
Infect a mammalian cell with vesicular stomatitis virus (VSV) strain in which a viral
gene (VSVG) is fused to GFP gene
• Synchrony is enhanced by use of virus with mutant VSVG protein that cannot leave ER of infected cells grown at elevated temperature (40°C).
• The green fluorescence is restricted to the ER.
![Page 44: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/44.jpg)
• When temperature is lowered to 32°C, the fluorescent GFP-VSVG protein that had accumulated in ER moves synchronously to Golgi complex for various processing events & then to membrane
• Temperature-sensitive mutants– Permissive temperature
Mutants function normally – Restrictive temperatures
Mutants function abnormally
![Page 45: Chapter 5: Aerobic Respiration and the Mitochondrion](https://reader035.fdocument.org/reader035/viewer/2022062301/56813a42550346895da22fe5/html5/thumbnails/45.jpg)
Cell fractionation
• Homogenization
• Organelles fractionation by centrifugation