Cytoskeleton Flashcards
What is the cytoskeleton?
A filamentous structure found throughout the cytoplasm
What is the cytoskeleton formed of?
Protein monomers which assemble into repeat structures
What 3 types of filaments are found in the cytoskeleton?
Actin
Microtubules
Intermediate filaments
What is the main property of the cytoskeleton?
It is dynamic - can assemble and disassemble rapidly to suit the cells needs
What is the function of the cytoskeleton?
To provide stability and support to the cell
What can link to the cytoskeleton?
Other cellular components
What are motor proteins?
Proteins that move organelles along filaments and filaments against each other
What is the diameter of an actin filament?
5-9nm
What are actin filaments made of?
Actin = globular protein
- Actin assembles into two stranded helical polymers
What can actin helical polymers form?
3D gels
2D networks
Bundles - by lining up
What are the functions of actin filaments?
Shape
Motility
Where are actin filaments found?
Throughout the body but mainly concentrated beneath the cortex
What is the diameter of a microtubule?
25nm
What are microtubules made of?
Tubulin = globular protein containing alpha and beta subunits
- Long and straight
What structure does tubulin form in microtubules?
Hollow tubes
How do microtubules compare to actin filaments in terms of rigidity?
More rigid
What are microtubules typically attached to?
Centrosomes at one end
What is a centrosome?
A microtubule organising centre
What does the end of the microtubule not attached to the centrosome do?
Grow and shrink
What are the functions of microtubules?
Positioning of organelles
Mitosis
Intracellular transport
What is the diameter of an intermediate filament?
10nm
What is the function of intermediate filaments?
Mechanical support
What are intermediate filaments made of?
Various intermediate filament proteins which are individually filamentous
What are dimers within intermediate filaments?
Extended alpha helical regions which are wound together
What are tetramers and how are they formed?
Soluble subunits formed by the association of dimers
What to tetramers wind to form?
Rope-like fibres
How is the cytoskeleton formed?
Monomers form end-to-end and side-to-side interactions that are non-covalent and therefore can be broken and formed easily for rapid assembly and disassembly
What does the relative strength of end-to-end and side-to-side interactions formed between monomers determine?
Mechanical strength
What is the rate of monomer addition relative to?
Monomer concentration
What happens when there is a critical concentration of monomers?
There is no net growth
What type of ends do actin filaments and microtubules have?
Fast and slow growing = + and -
What additional proteins may be associated with nucleation?
Auxiliary proteins which may act as an initiator for a new filament
What additional proteins may be associated with assembly?
Proteins which bind monomers depending on their relative concentration
What additional proteins may be associated with disassembly?
Proteins which can bind and either stabilise or destabilise filaments
What property of the cytoskeleton might toxins affect? Give two examples
Their ability to disassemble or control of actin filaments
- taxol = stabilises microtubules
- colchicine = binds free tubulin
What is myosin?
An actin based motor protein
How many myosin genes are there in a human?
40
What type of myosin makes muscles contract?
Myosin II
How are myosin long domains formed?
By the coiling of two mysoin II heavy chains
What do tail domains interact with?
Other myosin parts forming large bipolar ‘thick myosin’
What do globular myosin heads contain?
Force generating machinery
What are kinesin and dynein?
Microtubular motor proteins
Which part of kinesin and dynein interacts with the cytoskeleton?
Myosin heads
What way does kinesin move organelles?
From the - to the + end of the microtubule
What way does dynein move organelles?
From the + to the - end of the microtubule
Where in the cell is the golgi retained and what molecule is retained by?
Close to centrosomes by dynein
Where in the cell is the ER dispersed and by what molecule?
To the cell periphary by kinesin
How are vesicles moved within a cell?
Along microtubules
- From the golgi to ER by dynein
What is cell crawling and what types of cells does it occur in?
The rearrangement of actin in the cytoskeleton
- Macrophages
- Neutrophils
What are flagella and cilia and what are they composed of?
Tubular structures composed microtubules
How do flagella and cilia move?
Ciliary dynein causes microtubules to slide across one another allowing the flagella/cilia to propel the cell forward
What is found at the tip of microvilli?
Bundles of actin filaments
How do microvili move?
Myosin attached to the cell membrane moves the actin filaments causing the microvili to ‘wave’