Chapter 17: Cytoskeleton Flashcards
What are intermediate filaments?
Rope like fiber (proteins) that enable cells to withstand mechanical stress that occur when cells are stretch
Where are intermediate filaments found?
- Desmosomes (cell-cell junction)
- Nuclear Lamina (meshwork of intermediate filament within the nucleus)
What makes intermediate filaments so strong?
They are like ropes that twist together to provide tensile strength
What generates the rope like structure in intermediate filaments?
- Coil Coil dimer: two alpha helixes winding around each other
- Staggered antiparallel tetramer of two coiled-coil dimers: Two coil-coil dimer coming together in an antiparallel fashion
- Lateral association of 8 tetramer
- Addition of 8 tetramer to growing filaments
How does intermediate filament strengthen cells against mechanical stress?
by distributing the effects of locally applied forces, thereby keeping cells and their membranes from tearing in response to mechanical shear.
What is the nuclear envelope supported by?
Nuclear lamina: meshwork of intermediate fillaments
What are lamins?
Type of intermediate filament protein that makes up the nuclear lamina
Why are lamin phosphorylation so crucial?
They weakened the interaction between filaments, causing the lamina to fall apart for cell division
What were to happen if there is a defect in lamin?
progeria—rare disorders that cause affected individuals to age prematurely.
What are microtubules?
polymers of tubulin that form part of the cytoskeleton
What are the functions of microtubules?
They create a system of track within the cell by
- Transporting and positioning organelles within the cell
- Guide intracellular transport of cytosolic macromolecules
- Assemble into the mitotic spindle during cell division
- Form cilia and flagella
How are microtubules structured?
- α-tubulin and β-tubulin are bound tightly to form a heterodimer
- Tubulin dimer stack together to form protofilaments
- 13 protofilaments form one microtubulin
- Protofilaments come together forming a hollow cylindrical structure
What does it mean for microtubules to have structural polarity?
α-tubulin exposed atone end and β-tubulin at the other
Why is it crucial that microtubules have structural polarity?
Structural polarity allows for directional intracellular transport
Where do microtubules come from?
The centrosome
What is the centrosome’s structure?
Matrix of protein surrounding a pair of centrioles
How does nucleation come from the centrosome?
The centrosome has nucleating site ( γ tubulin ring complex) which serves as a starting point for the growth of one microtubules.
The αβ-tubulin dimer adds to the + end of the growing microtubules
Why do cells need nucleation site?
This allows the cell to control which microtubules to grow from where and how
What does it mean for microtubules to be dynamic instability?
microtubules can switch back and forth between polymerization and depolymerization, growing and shrinking ONLY on their + end
Why is dynamic instability crucial to microtubules?
Allows it to undergo rapid remodeling to carry their function
When does dynamic instability stop for microtubules?
When its plus end is stabilized by attachment to another protein/structure. Thus Microtubules stabilize when
attached to capping proteins
What is dynamic instability driven by?
GTP hydrolysis
What side of the microtubules does dynamic instability affect?
only + end
How does GTP hydrolysis dictate microtubules assembly and dissembly?
Assembly: GTP addition proceeds faster than GTP hydrolysis, forming a GTP cap
Dissembly: GTP hydrolysis is faster than GTP addition
