Organelle structure

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Organelle structure • Nucleus • Sarco(endo)plasmic reticulum • Mitochondria • Peroxisome • Autophagosome

description

Organelle structure. 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 l = h/mv - PowerPoint PPT Presentation

Transcript of Organelle structure

Page 1: Organelle structure

Organelle structure

• Nucleus• Sarco(endo)plasmic reticulum• Mitochondria• Peroxisome• Autophagosome

Page 2: Organelle structure

Electron microscope

• Diffraction limit– Wave nature of light passing through lens– Optical: ~0.6 um, resolution ~0.2 um– Confocal, FT, nanohole arrays

• De Broglie wavelength– = h/mv– Electron: = 1.2(V- ½) nm (V: accelerating voltage)

B~/(2 NA)

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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)

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Structure

Myofibril Nucleus

Mitochondria

Artifact

Out of plane

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Eisenberg et al., 1974

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Common features

• Densely packed myofibrils• Subsarcolemmal space

– Nuclei– Mitochondria

• Intermyofibrillar I-band space– Mitochondria– SR/T-tubule triads

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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% 26%

Mitochondrial 2-5% (18% SS, 3-4% core)

1-4% (female-male)

26%

T-system 0.15-0.25%

Nuclei 0.9%

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Rattlesnake tail muscle: prominent extensive glycogen & mitochondria; relatively few myofibrilsClark & Schultz, 1980

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Nucleus

• Multiple– MND 3e4-5e4 um3/nucleus– Fiber volume 5e5-5e6 um3 (10-1000 nuclei)

• Cylindrical, ~30 um3

• Nucleolus• Cajal bodies• DNA• RNA processing

Terada et al., 2010

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RNA processing

• Nucleolus: rRNA synthesis & ribosome assy• Cajal bodies: Spliceosome assembly• Speckles: RNA splicing

Pollard & Earnshaw, 2008

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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

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Nuclear Envelope

• Dual membrane• Control nuclear import/export• Nuclear pore complex

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Nuclear membrane proteins

• Chromatin anchors– Lamin, lamin B receptor, emerin

• Transport proteins– Importin, Exportin, Ran

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Mitochondria

• Dual membrane• Oxidative ATP synthesis

– Citric acid cycle– Electron transport

chain• Separate genome

– Most Mt proteins come from nuclearDNA

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Mitochondrial syncytium

• Network, not bacterium-like

• Regulated growth– Division– Fusion

• Apoptosis

Manella, 2000

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Muscle mitochondria

• Extensive subsarcolemmal syncitia• Elongated tubules, perpendicular to fiber

– Frequently doubled around Z-disks

Ogata & Yamasaki, 1997

Subsarcolemmalmitochondria

Intermyofibrillarmitochondria

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Inner membrane

• Cristae– “Shelf-like”– Tubular network

Manella, 2008

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Oxidative ATP Synthesis

• Electron transport chain– NADH– FADH2– Ubiquinone– Cytochrome C

• Reactive oxygen

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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

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Sarcoplasmic Reticulum

• Single membrane– Lamellar, fenestrated– Terminal cisternae

• Synthesis of transmembrane and extracellular proteins

• Calcium storage

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SR T-tubule communication

• Terminal cisternae wrapT-tubule

• Communication of membrane events to SR

Ogata & Yamasaki, 1997

SEM of I-band region of a myofiber with myofibrils extracted, leaving only membrane-bounded skeletons of T-tubule (T), SR (blue), terminal cisternae (arrowheads), and mitochondria. Fiber axis is vertical.

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Triad

• Physical association between T-Tubule and SR

• “Feet”– Dihydropyridine receptor

(DHPR)– Ryanodine Receptor (RyR)

Franzini-Armstrong, 1970

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“white” vs “red” muscle

• Red: larger, more extensive mitochondria• White: (slightly) more extensive SR

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Autophagosome

• Double membrane– Small (1 um), spherical

• Self-engulfment• Recruit lysosome & degrade

Mizushima & al., 2002

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Autolysis

• Degradation of large structures• Starvation defense• Infection defense• Targeting

– Apg5/Apg12 targeting complex– LC3 microtubule associated light chain– PI3k, FOXO3

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Summary

• Specialized chemistry is constrained to isolated cellular domains

• Nucleus• Mitochondria• ER/SR• Autophagosome• Peroxisome