Transcript Organelle structure - Georgia Institute of Technology

Organelle structure
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Nucleus
Sarco(endo)plasmic reticulum
Mitochondria
Peroxisome
Autophagosome
Electron microscope
• Diffraction limit
– Wave nature of light passing through lens
– Optical: l~0.6 um, resolution ~0.2 um
– Confocal, FT, nanohole arrays
• De Broglie wavelength
B~l/(2 NA)
– l= h/mv
– Electron: l = 1.2(V- ½) nm (V: accelerating voltage)
EM imaging
• Essentially a CRT
– Vacuum
– Focus e-beam on
specimen
– Expand onto screen
• Sample prep
– Dehydrate & fix
– Heavy metal stain
(uranium)
– 90 nm slices
(Graham Colm, wikipedia)
Structure
Myofibril
Nucleus
Artifact
Mitochondria
Out of plane
Eisenberg et al., 1974
Common features
• Densely packed myofibrils
• Subsarcolemmal space
– Nuclei
– Mitochondria
• Intermyofibrillar I-band space
– Mitochondria
– SR/T-tubule triads
Fractional composition
• Stereology
– Statistical model of 3-D structure
– 2-D images & discrete sampling
Compartment
Guinnea pig
Toadfish
swimbladder
Rattlesnake tail
shaker
Myofibrils
85-90%
70-80%
32%
SR
3.5-4.5%
Mitochondrial
2-5% (18% SS, 34% core)
T-system
0.15-0.25%
Nuclei
0.9%
26%
1-4% (femalemale)
26%
Rattlesnake tail
muscle: prominent
extensive glycogen
& mitochondria;
relatively few
myofibrils
Clark & Schultz,
1980
Nucleus
• Multiple
– MND 3e4-5e4 um3/nucleus
– Fiber volume 5e5-5e6 um3 (10-1000 nuclei)
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Cylindrical, ~30 um3
Nucleolus
Cajal bodies
DNA
RNA processing
Terada et al., 2010
RNA processing
• Nucleolus: rRNA synthesis & ribosome assy
• Cajal bodies: Spliceosome assembly
• Speckles: RNA splicing
Pollard & Earnshaw, 2008
Ribosomal biogenesis
• Multiple (300+) copies of rRNA strand
– Transcribed
– Cleaved to 28S, 18S, 5.8S strands
– Ribose methylation
– Uridine isomerization to pseudouridine
• Ribosomal proteins
– Imported to nucleus
– Anneal to rRNA in nucleolus
Nuclear Envelope
• Dual membrane
• Control nuclear import/export
• Nuclear pore complex
Nuclear membrane proteins
• Chromatin anchors
– Lamin, lamin B receptor, emerin
• Transport proteins
– Importin, Exportin, Ran
Mitochondria
• Dual membrane
• Oxidative ATP synthesis
– Citric acid cycle
– Electron transport
chain
• Separate genome
– Most Mt proteins
come from nuclear
DNA
Mitochondrial syncytium
• Network, not
bacterium-like
• Regulated growth
– Division
– Fusion
• Apoptosis
Manella, 2000
Muscle mitochondria
• Extensive subsarcolemmal syncitia
• Elongated tubules, perpendicular to fiber
– Frequently doubled around Z-disks
Subsarcolemmal
mitochondria
Intermyofibrillar
mitochondria
Ogata & Yamasaki, 1997
Inner membrane
• Cristae
– “Shelf-like”
– Tubular network
Manella, 2008
Oxidative ATP Synthesis
• Electron transport chain
– NADH
– FADH2
– Ubiquinone
– Cytochrome C
• Reactive oxygen
Peroxisome
• Single membrane
• Controlled H2O2 chemistry
– Oxidases generate H2O2
– Peroxidases degrade H2O2
– Fatty acid metabolism
– Cholesterol & bile synthesis
• Peroxins (PEX) control protein composition
and biogenesis
Sarcoplasmic Reticulum
• Single membrane
– Lamellar, fenestrated
– Terminal cisternae
• Synthesis of transmembrane
and extracellular proteins
• Calcium storage
SR T-tubule communication
• Terminal cisternae wrap
T-tubule
• Communication of
membrane events to SR
SEM of I-band region of a myofiber
with myofibrils extracted, leaving only
membrane-bounded skeletons of Ttubule (T), SR (blue), terminal cisternae
(arrowheads), and mitochondria. Fiber
axis is vertical.
Ogata & Yamasaki, 1997
Triad
• Physical association between
T-Tubule and SR
• “Feet”
– Dihydropyridine receptor
(DHPR)
– Ryanodine Receptor (RyR)
Franzini-Armstrong, 1970
“white” vs “red” muscle
• Red: larger, more extensive mitochondria
• White: (slightly) more extensive SR
Autophagosome
• Double membrane
– Small (1 um), spherical
• Self-engulfment
• Recruit lysosome & degrade
Mizushima & al., 2002
Autolysis
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Degradation of large structures
Starvation defense
Infection defense
Targeting
– Apg5/Apg12 targeting complex
– LC3 microtubule associated light chain
– PI3k, FOXO3
Summary
• Specialized chemistry is constrained to
isolated cellular domains
• Nucleus
• Mitochondria
• ER/SR
• Autophagosome
• Peroxisome