Cytoskeleton Flashcards
what is cytoskeleton?
The cytoskeleton is a DYNAMIC network of protein filaments and tubules that provides structural support, shape, and organization to cells.
How are cytoskeletons formed?
Cytoskeletal proteins form polymers or fibres from smaller protein subunits, which are held together by noncovalent bonds (like hydrogen bonds, ionic interactions, and hydrophobic interactions. This allows for dynamic and reversible assembly and disassembly, which is essential for the cytoskeleton’s functions.
CILIA AND MICRVILLI
CYTOSKELTONS FOUND IN ALL LIVING CELLS
both eukaryotic and prokaryotic cell.
what are the three main components.
Microfilaments (or actin filaments)
intermediate filaments
microtubules
Microfilaments (actin filaments)
- what is it made up of ?
- what are there functions?
Microfilaments is primarily made up of actin, specifically in two forms :
G-actin: This is the monomeric form of actin. It is a single, spherical protein and can polymerise to form filaments. It can exist freely in the cytoplasm.
F-actin: This is the filamentous form of actin- it is the polymerized form of G-actin, consisting of long, helical chains of actin monomers. (Requires ATP).
Function:
G-actin: Primarily serves as a building block for the formation of filaments.
F-actin: Plays a critical role in various cellular functions, including providing structural support, enabling cell movement, and participating in muscle contraction.
Intermediate Filaments.
There are four major types, each composed of different proteins that provide structural support and mechanical strength. Common types include:
Keratins: Found in epithelial cells, providing strength and resilience.
Vimentin: Found in mesenchymal cells, providing support to the cytoskeleton.
Neurofilaments: Found in neurons, contributing to the structural integrity of axons.
Lamins: Located in the nuclear lamina, providing support to the nuclear envelope.
Microtubules
what are they made up of?
what is its function?
α-tubulin and β-tubulin: These two subunits combine to form dimers, which then polymerize into hollow tubes called microtubules.
Microtubules are essential for maintaining cell shape, facilitating intracellular transport, and segregating chromosomes during cell division.
Organisation of Actin filaments link with function.
- Localised at the cell cortex (specialised layer beneath the plasma membrane) = helps define the shape of the cell and provides a framework for other proteins involved in signaling and cell adhesion.
- Support of the plasma membrane
Structural Support: Actin filaments reinforce the plasma membrane, helping to maintain cell integrity and resist deformation.
By anchoring to the membrane, actin contributes to cell shape, allowing it to adapt to various stresses.
provide forces to move:
Actin filaments generate the forces necessary for cell movement. This is particularly evident in processes such as:
Crawling: Actin polymerization at the leading edge pushes the plasma membrane forward.
Muscle Contraction: Myosin motor proteins interact with actin filaments to produce force for muscle contraction.
Cytokinesis: During cell division, actin forms a contractile ring that pinches the cell into two daughter cells.
Organisation of intermediate filament link to function.
Extension Across the Cell Cytoplasm:
Intermediate filaments extend throughout the cytoplasm, providing a continuous network that helps anchor organelles in place (stability), enabling cells to maintain their shape and resist deformation.
Rope-like Structures
The rope-like structure allows them to withstand tensile forces and mechanical stress. This flexibility and strength make them ideal for providing structural integrity, especially in tissues that experience stretching or pressure, such as epithelial tissues and muscle.
Intermediate filaments play a crucial role providing structural support and mechanical strength. They help protect cells from damage caused by mechanical stress and support cellular functions, such as during cell division, where they help stabilize the nuclear envelope and ensure proper segregation of chromosomes.
organisation of microtubules link to function.
initiation at the Microtubule-Organizing Center (MTOC):
Microtubules typically originate from the MTOC (like the centrosome). This organization ensures proper spatial orientation and distribution of microtubules throughout the cell.
Polarized Throughout the Cell:
Microtubules have inherent polarity, ( (+) end and a (−) end). This polarization is crucial for the directional transport of organelles and vesicles.
Motorway System for Intracellular Transport (all parts of the cell body):
The organized network of microtubules acts as a “motorway” system that facilitates rapid and efficient transport within the cell. This organization allows for the movement of cargo, such as organelles, proteins, and vesicles, along the microtubules, ensuring proper cellular function and organization.
what do causes specific changes in the assembly of cytoskeletons.
due to the interaction with other proteins.
what are molecular motors?
are specialised proteins that convert chemical energy from ATP into mechanical work, enabling the movement of cellular components (intracellular transport) and the entire cell itself (cellular movement).
Types of molecular motors.
- Name
- Direction of movement
- Function
Kinesins
Direction of Movement: Typically move toward the plus (+) end of microtubules.
Functions: intracellular/chromosome/axons
- intracellular Transport organelles and vesicles
- Facilitate the movement of chromosomes during cell division.
- transporting materials along axons.
Dyneins:
Direction of Movement: Move toward the minus (−) end of microtubules.
Functions: cellualr/cilia/position
- Transport cellular cargo, including organelles and vesicles.
- Involved in the movement of cilia and flagella.
- positioning organelles wwithin the cell.
Myosins:
Direction of Movement: Move along actin filaments, usually toward the plus end.
Functions:
muscle/motility/intracellular
- Drive muscle contraction by pulling on actin filaments.
- Enable cell motility through processes like amoeboid movement and cytokinesis.
- helps in intracellular transport(within the cell) of vesicles and organelles
Function of Cytoskeleton 1
Cell movement and motility:
The cytoskeleton enables cells to move by facilitating processes like amoeboid movement, muscle contraction, and the movement of cilia and flagella.
Function of cytoskeleton 2
Determination and Maintenance of Cell Shape and Polarity:
The cytoskeleton provides structural support= maintain cell shape= withstand mechanical stress. It also plays a role in establishing cellular polarity, which is important for functions like cell signaling and division.
Function of cytoskeleton 3
intracellular Transport and Localization:
The cytoskeleton serves as a framework for the transport of organelles, vesicles, proteins, and nucleic acids within the cell. Molecular motors (like kinesins and dyneins) move along microtubules and actin filaments, ensuring that cellular components are correctly localized.
Function of cytoskeleton 4
Dynamic Response to Signals:
The cytoskeleton is highly dynamic, capable of rapid reorganization in response to both extracellular signals (like growth factors) and intracellular cues (like changes in cell metabolism). This adaptability allows cells to respond to their environment and internal needs effectively. Additionally, the cytoskeleton acts as an anchorage for enzymes and components involved in cell signaling pathways.
Maintain the shape and provide support to the cell
Holds a variety of cellular organelles in place
Assists in vacuole formation
Enables internal and overall cell mobility
For instance, transportation of vesicles in and out of a cell, chromosomal movement during meiosis and mitosis, and migration of organelle
Communicates signals between cells
Forms cellular protrusions such as cilia and flagella in some cells
Be able to identify different components on a cytoskeleton from images.
SUMMARY OF MICROTUBULES
- structure
- diameter
- monomers
- functions
Hollow tube with a wall consisting of 13 protofilaments.
outer =25nm
inner=15nm
alpha tubulin and beta tubulin
- cell motility
- cytoplasmic organisation and maintenance of cell shape
- chromosome movement
- disposition and movement of organelles
SUMMARY OF INTERMEDIATE FILAMENTS
- structure
- diameter
- monomers
- functions
Eight protofilaments joined end to end with staggered overlaps.
8-12nm
several proteins
- structural support
- maintenance of cell shape
-formation of nuclear lamina and scaffolding - strengthening of nerve axons (NF proteins)
- Keeping muscle fibres in register(desmin)
SUMMARY OF MICROTFILAMENTS
- structure
- diameter
- monomers
- functions
two intertwined chains of F-actin
7nm
G-actin
- Muscle contraction
- Amoeboid movement
- cell locomotion (movement)
- cytoplasmic streaming
- cell division
- maintenance of cell shape.
Which one of the following statements
is INCORRECT
1) Microfilaments are made of actin
2) Actin polymerisation is induced by 100mM KCl
3) Actin monomers contain a molecule of ATP that is hydrolysed on polymerisation
4) Actin microfilaments run from the cell nucleus to the periphery of the cell
5) Microvilli are supported by microfilaments
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