introduction unit 8 - cytoskeleton
DESCRIPTION
INTRODUCTION Unit 8 - Cytoskeleton. 3 types of fibers make up the cytoskeleton. Microtubules interact with motor systems: dyneins and kinesins Microfilaments interact with myosins Intermediate filaments do not interact with motor proteins. Intermediate Filaments. FUNCTION : - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/1.jpg)
INTRODUCTION
Unit 8 - Cytoskeleton
![Page 2: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/2.jpg)
3 types of fibers make up the cytoskeleton
Intermediate Filaments
MicrotubulesActin
Microfilaments
- Microtubules interact with motor systems: dyneins and kinesins
- Microfilaments interact with myosins - Intermediate filaments do not interact with motor proteins
![Page 3: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/3.jpg)
Intermediate Filaments
These supportive fibers provide for mechanical reinforcement of tissues and range in diameter from 8-10 nm
FUNCTION:“provide a supporting
framework within the cell”
![Page 4: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/4.jpg)
Intermediate Filaments - STRUCTURE
Have great tensile strength!
Strengthens cells against mechanical stress!
monomer
dimer
tetramer
2 tetramers coiled together
8 tetramers twisted into a ropelike filament
10nm
![Page 5: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/5.jpg)
Types of intermediate filaments
• nuclear lamins form a meshwork that stabilizes the inner membrane of the nuclear envelope;
• keratins – junctions in epithelial cells (desmosomes) and also form hair and nails;
• neurofilaments - strengthen the long axons of neurons;
![Page 6: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/6.jpg)
What cytoskeletal element is stained green in this immunofluorescence experiment? Why?
Cell boundaries stained in blue
Intermediate filaments. They form a network that links to other cells at junctions on the plasma membrane
![Page 7: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/7.jpg)
Intermediate Filaments
• Why can you use intermediate filaments to tell whether a cancer has spread in the body?
![Page 8: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/8.jpg)
Microtubules
FUNCTION: These macromolecular assemblies are involved mainly in the movement and positioning of cell organelles.
- Minus end is attached to centrosome (or Microtubule organization Center) - Plus end is free
![Page 9: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/9.jpg)
Microtubules - STRUCTURE
Long, hollow cylinders made of 13 protofilaments and built by the assembly of dimers of alpha tubulin and beta tubulin.
Right. Electron Microscope Image of microtubules
![Page 10: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/10.jpg)
MICROTUBULES
- The growing end of the microtubule has subunits arranged with the beta-tubulin on the outside. The subunits in the microtubule all show a uniform polarity
Rapid Growth = plus end
![Page 11: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/11.jpg)
Microtubule polymerization
- microtubules keep growing with freshly added tubulin dimers and GTP
- Tubulin dimers + GTP (red) bind more tightly to one another than tubulin dimers + GDP (dark green) creating a GTP cap.
![Page 12: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/12.jpg)
Microtubule depolymerization
- the GDP-carrying subunits are less tightly bound in the polymer and readily released from the free end
- Slow microtubule growth causes the "GTP cap“ to hydrolyze GTP to GDP The GTP cap is lost
The microtubule shrinks
![Page 13: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/13.jpg)
Centrosomes
• Organized array of microtubules that radiate outward from it through the cytoplasm.
• Contains ring-shaped structures of -tubulin.– Serves as starting point for growth of new
microtubule
![Page 14: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/14.jpg)
Motor Proteins
• Dyneins– Travel towards
MINUS END
• Kinesins– Travel towards
PLUS END
KinesinsDyneins
--++
![Page 15: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/15.jpg)
Actin microfilaments
Microfilaments Interact with many types of molecules including its own class of motor proteins, the myosins
FUNCTION: support components of the cell and provide for the movement of cytoplasm and the cell surface
![Page 16: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/16.jpg)
Bundles of Actin filaments in cells
Microvilli Contractile bundles in cytoplasm
Sheet-like and finger-like protrusions from the leading edge of a moving cell
Contractile ring during cell division
Actin in RED:
![Page 17: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/17.jpg)
Actin - STRUCTURE
• Actin microfilaments are comprised of actin monomers that polymerize to form long, thin fibers. These are about 7nm in diameter.
![Page 18: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/18.jpg)
Actin Polymerization
Can occur at either end– Faster rate at
PLUS end
Triphosphate (ie ATP) hydrolyzed to diphosphate (ie ADP) soon after incorporation into actin filament.– Nucleotide hydrolysis promotes depolymerization
![Page 19: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/19.jpg)
ATP Hydrolysis
• Actin monomers in the cytosol carry ATP, which is hydrolyzed to ADP soon after assembly into growing filament.
• ADP molecules remain trapped within actin filament, until the actin monomer that carries them dissociates from filament to form a monomer again.
![Page 20: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/20.jpg)
Drug Treatments
Colchicine: Binds free tubulin and inhibits formation of microtubules by preventing polymerization
Taxol: Stabilizes microtubules by preventing depolymerization
Cytochalasin: inhibits formation of actin by preventing polymerization
Phalloidin: stabilizes actin filaments preventing depolymerization
![Page 21: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/21.jpg)
Practice Questions:
![Page 22: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/22.jpg)
Here we see Phalloidin linked to a green fluorescent dye. What cytoskeletal element is being stained green? How do you know?
Nucleus stained blue
Golgi stained red
What technique was used?
![Page 23: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/23.jpg)
What cytoskeletal element is indicated by the arrow? What are TWO other functions of this element?
![Page 24: INTRODUCTION Unit 8 - Cytoskeleton](https://reader031.vdocument.in/reader031/viewer/2022032612/56813264550346895d98fc09/html5/thumbnails/24.jpg)
NEXT TUTORIAL
MITOSIS