MCBL: Cytoskeleton, Part 1 Flashcards
What is the cytoskeleton?
It is the structural framework, or lattice, of the cytoplasmic matrix in eukaryotic cells.
True or false: Prokaryotes have a cytoskeleton.
False
What does the structural support role of the cytoskeleton refer to?
The cytoskeleton provides structural support that determines & maintains the shape of the cell as well as the position of the various cellular organelles.
What does the trafficking function of the cytoskeleton refer to?
The cytoskeleton is part of the machinery that is required to transport vesicles and organelles to specific sites within the cell.
It is also responsible for the invagination of the membrane during endocytosis.
It helps with the separation of chromosomes during cell division.
What does “force generating” refer to in the context of the cytoskeleton?
The cytoskeleton is responsible for the movement of cells from one place to another.
It allows fibroblasts to crawl on surfaces and it is also responsible for the construction and motions of cilia and flagella.
How does the cytoskeleton facilitate translation?
It serves as a site for anchoring mRNA and helps to facilitate mRNA translation.
How does the cytoskeleton play a role in signal transduction?
The deformation of the cytoskeleton, when it comes into contact with another cell / object, allows it to play a role in signal transduction.
What proteins are responsible for allowing the cytoskeleton to accomplish its functions?
Accessory proteins which associate with the cytoskeleton, are necessary for the controlled assembly/disassembly of the cytoskeletal filaments.
Motor proteins move filaments as well as vesicles/organelles along the cytoskeletal filaments.
What are the major functions of the cytoskeleton?
Scaffold
Cellular trafficking
Movement
Translation
Signal transduction
What does the cytoskeleton consist of?
The cytoskeleton consists of filamentous structures made of different types of proteins.
What are the elements of the cytoskeleton held together by?
All cytoskeletal filaments are composed of multiple protein subunits that are held together by non-covalent bonds.
What are protofilaments?
Protofilaments are linear arrangements of cytoskeletal monomers.
What do multiple protofilaments come together to form?
Multiple protofilaments come together to form the final cytoskeletal structure.
What are some of the key features of the individual protein subunits that make up the cytoskeleton?
Individual, small subunits
These subunits can rapidly move to regions of the cell where cytoskeletal elements are being built
The non-covalent interactions between subunits allows rapid growth/breakdown
What is an advantage of using small protein subunits to build cytoskeletal filaments?
These small subunits can move rapidly to wher ethey are needed and filaments can be rapidly broken down and rebuilt as needed.
Why are multiple protofilaments used as opposed to only one?
Multiple protofilaments provide stability to the entire cytoskeletal network.
How do cytoskeletal monomer protein s ubunits interact?
They bind end-to-end to form protofilaments as well as binding laterally, side-to-side to hold the protofilaments together.
This conformation stabilizes the filament in the middle while allowing the ends to polymerize/depolymerize.
Why is it important to have multiple protofilaments be part of a cytoskeletal network?
Multiple protofilaments impart strength and bending resistance, especially in intermediate filaments.
How many types of cytoskeletal filaments are there and what are their names?
Three:
Intermediate filaments
Microtubules
Microfilaments
What are the characteristics of intermediate filaments?
Intermediate filaments are tough, rope-like structures
Composed of several different proteins that have similar structures
About 10 nm in diameter
What are the characteristics of microtubules?
Microtubules are hollow, cylindrical structures
Make a single type of structure (a 13 protofilament tube)
Also make cilia, flagella, centriole, basal body
Composed of different proteins called tubulin (at least 3 different types)
25 nm in diameter
What are the characteristics of microfilaments?
Make a two-stranded helical fragment
Composed of actin (globular or g-actin)
Also known as actin filaments (f-actin)
5 to 7 nm in diameter
True or false: Each type of cytoskeletal filament localizes to a specific region of the cell.
True
Where do intermediate filaments loclaize within the cell?
The location of intermediate filaments is dependent upon the specific protein that makes up the intermediate filament in question
For example, vimentin associates with the inner nuclear membrane
Keratins radiate out from the plasma membrane in epithelial cells and help attach it to its neighbor
Where do microtubules localize within cells?
Microtubules form tracks throughout the cell
They also radiate out from the centrosome near the center of the cell (not always however)
Where do actin microfilaments localize within a cell?
Actin microfilaments are often found in the cell cortex around the periphery of the cell, just below the plasma membrane
They can also be found dispersed throughout the cell
What is the major role of intermediate filaments?
Their major role is to resist mechanical stress when stretched
Intermediate filament proteins have high tensile strength
Have the ability to withstand pulling without stretching/breaking due to their arrangement
These are the toughest & most durable of the cytoskeletal elements
How many genes encode intermediate filament proteins?
At least 60 different genes code for at least 60 different intermediate filament proteins
How many different classes are the intermediate filament proteins grouped into?
Six different classes based on tissue type they are found in
What is the structure of an intermediate filament protein?
They typically have a central, rod-shaped helical domain and globular domains of variable size at both their n and c terminus regions.
Which portion of the intermediate filament protein gives it its unique binding properties?
The globular regions of the N and C termini give intermediate filament proteins their unique properties.
The globular domains also serve as the binding sites between adjacent intermediate filaments.
Where are the binding sites between adjacent intermediate filaments?
There are binding sites BETWEEN adjacent intermediate filament monomers.
Non covalent interactions hold them together and depending on the type of intermediate filament, the dimers my be homo or heterodimers.
True or false: Homodimers of intermediate filaments are made of two different intermediate filament proteins.
False
True or false: Heterodimers of intermediate filament proteins are made up of two different proteins.
True
Picture showing how intermediate filaments come together.
2nd picture showing how intermediate filaments come together.
What are homodimer intermediate filaments composed of?
Homodimers are composed of the same intermediate filament protein.
They adopt a ‘coiled-coil’ conformation that shows structural polarity because the proteins line up in the same direction.
They also have a head and a tail that corresponds to the N-terminus and the C-terminus of the individual protein subunits.
True or false: The ends of the intermediate filament subunits are chemically distinct.
True