Final Topic 22 - Eukaryotes Cytoskeleton Flashcards
Large tensile strength, main function is to help the cells withstand mechanical stress
Intermediate filaments
Called intermediate because of
their diameter
Intermediate filaments are found
throughout the cytoplasm and nucleus
Intermediate filaments form
a large network of interconnected filaments
Intermediate filaments are anchored to the plasma membrane at
cell-cell junctions called desmosomes
Intermediate filaments are also found inside the nucleus and they make up the
nuclear lamina
Intermediate filaments form strong rope-like
multi-protein assemblies
An alpha-helical monomer with a globular N-terminus and a globular C-terminus
The subunit of intermediate filaments
The intermediate filament subunit forms a
coiled-coil dimer
The dimer forms a staggered
anti-parallel tetramer
The tetramers bind together end-to-end and side-by-side to form a
twisted filament
The twisted filaments are
non-covalent interactions
Because of the anti-parallel way that the intermediate filament tetramers form, intermediate filaments lack
polarity
Four classes of intermediate filaments
- Keratins
- Vimentin and vimentin-related
- Neurofilaments
- Nuclear Lamina
In Epithelia
Keratins
In connective tissue, muscle cells, and glial cells
Vimentin
In nerve cells
Neurofilaments
In all animal cells
Nuclear Lamina
Long still hollow tubes of proteins that can rapidly assemble or disassemble
Microtubules
Microtubules extend toward the cell periphery and provide tracks for organelle and vesicle movement
Interphase cell
Microtubules make up the mitotic spindle
Dividing cell
Provides the force and movement for chromosome separation
Mitotic spindle
Microtubules are an important component of cilia and flagella, necessary for movement
Cilia and Flagella
Microtubules subunit
Tubulin Heterodimer
Alpha-tubuilin and Beta-tubulin
Tubulin Heterodimer
The tubulin heterodimer
Binds and hydrolyzes GTP
The tubulin heterodimer stacks end-to-end in a chain to make a
protofilament
13 protofilaments align next to each other and fold over to form a hollow tube
Microtubule
Microtubules have
polarity
The end with alpha-tubulin exposed
Microtubule (-) end
The end with the Beta-tubulin exposed
Microtubule (+) end
Tubulin dimers add (polymerize) to the ______ end to grow the filament
(+)
Microtubules in cells are formed by
Polymerizing from specialized organizing centers called centrosomes
Complex of proteins and y-tubulin ring complexes
Centrosomes
A special form of tubulin that acts as nucleation site for microtubule polymerization
y-tubulin ring complexes
Centrosome also contain a pair of
Centrioles
Small cylindrical array of microtubules
Centrioles
Important for stabilizing the centrosome organization
Centrioles
What structurally mimics the (+) end of a microtubule and acts as a nucleation site for polymerization from the centrosome?
y-tubulin ring complex
Microtubules grow by
Addition of the (+) end from the centrosome
Undergo dynamic instability
Microtubules
Growing and shrinking cycle
Dynamic instability
Tubulin hydrolyzes ____ shortly after addition to the _____ end
GTP
(+) end
When polymerization of GTP-tubulin is occuring rapidly, addition is
Faster than GTP hydrolysis
The end of the microtubule is comprised mostly of GTP-tubulin
The end of the microtubule is comprised mostly of GTP-tubulin
GTP-cap
When the rate of polymerization slows down and the tubulin dimers can hydrolyze GDP, this promotes
Disassembly of the microtubule
If the rate of polymerization is faster than the rate of GTP hydrolysis
The microtubule will grow (it contains a GTP-cap)
If the rate of GTP hydrolysis is faster than the rate of polymerization
The microtubule will disassemble (GTP-cap is lost)
Microtubules can be stabilized by
Attachment to proteins or cell structures that stabilize the ends
Microtubules can be both
Highly dynamic and highly stable
Binds and stabilizes microtubules
Taxol
Binds subunits and prevents polymerization
Colchicine, colcemid
Commonly used chemotherapeutic drugs
Taxol and Cochicine
Microtubules serve as
Tracks
Carry vesicles and organelles along the microtubule tracks
Motor proteins
Use ATP hydrolysis to power their movement
Motor proteins
Two main types of motor proteins
- Kinesins
2. Dyneins
Move towards the (+) end of the microtubule
Kinesins
Move towards the (-) end of the microtubule
Dyneins
Motor Protein structure
Dimers
Two Globular heads: ATPase and Microtubule binding
Motor proteins exist as
Dimers
Two globular heads of motor proteins
ATPase
Microtubule binding
Make up cilia and flagella
Microtubules
Hair-like structures that extend from the surface of eucaryotic cells
Cilia
Provide a regular “beating” movement
Cilia
Epithelia cells in the respiratory tract use these to sweep dust particles out of the lungs
Cilia
Larger structures similar to cilia that provide the force to propel bacteria and sperm
Flagella
Made up of a column of stable microtubule array
Cilia and Flagella
Microtubules are arranged in a
9+2 array
9+2 array
9 microtubule doublets
2 central singlet microtubules
Microtubule doublet
Two microtubules bound to each other
Microtubule doublets are all linked to each other through
Protein nexin
Attaches to one doublet and interacts with the adjacent doublet
Dynein
Causes the microtubules to bend
Because of the nexin links, as dynein walks towards the (-) end of the adjacent doublet, the microtubules bend
Provides the movement of the cilia and flagella
Microtubule bending
