The Cytoskeleton Flashcards
What are the 3 filaments which are a part of the structure of the cytoskeleton
Actin filaments (aka micro filaments), microtubules and intermediate filaments
Describe the structure of actin filaments
They are composed of monomeric actin protein subunits assembled into a twisted, two-strand polymer.
Describe the purpose of actin filaments
They provide structural support to the plasma membrane and are important for certain types of cell motility
Describe the structure of microtubules
Composed of alpha and beta tubulin heterodimers assembled into a hollow, tubelike cylinder
Describe the function of microtubules
Provide structural support, are involved in certain types of cell motility, and help to generate cell polarity
Describe the structure and function of intermediate filaments
Formed from a family of related proteins such as keratin or lamin. The subunits assemble to create a strong, rope like polymer that (depending on the specific protein) may provide support for the nuclear membrane or for cell adhesion.
What is G actin
Globular actin
What is F actin
Filamentous actin
What is required for the assembly of G actin into F actin
ATP but it does not need to be hydrolysed for assembly (ie energy is not required for this reaction).
What is nucleation in this context?
The formation of a stable multimedia of actin monomers
Is assembly of G actin I to F actin reversible?
Yes
At which end does F actin have polarity
The ATP binding site at the end
What is treadmilling?
When the rate of subunit addition at one end equals the rate of subunit loss at the other end, so that filament length remains constant as subunit flow, or treadmill, through the filament
When does treadmilling occur in microfilaments?
When the actin subunit concentration is greater than the Cc value for the positive end but less than the Cc value for the negative end. (Ie higher than 0.12 and lower than 0.6)
What is the purpose of actin binding proteins?
Regulation of the assembly and disassembly of microfilaments
What is cofilin
An actin binding protein which enhances the loss of ADP-actin from the negative end
What does Thymosin beta4 do?
Binds to G actin to provide reserve actin when needed
What is profilin?
A protein which enhances assembly at the + end by facility exchange of GDP for GTP
What is fimbrin?
A structure microtubules can be organised into which forms cross links between microvilli
What is spectrim?
A structure microtubules can be organised into which forms part of the cell cortex which acts as a scaffold for cell structures for cells such as red blood cells
