L11: The Scaffold of the Cell Flashcards
What are the three main components of the cytoskeleton?
Actin filaments, microtubules, and intermediate filaments
What is the cytoskeleton’s role in cell structure?
It provides shape, support, and resistance to external forces to allow cell migration, division and maintenance, while also enabling dynamic changes in cell structure from environmental changes
What protein forms microtubules?
Tubulin, specifically as dimers of alpha and beta tubulin
What are the primary functions of microtubules?
Microtubules help maintain cell shape, facilitate movement (like cilia and flagella), organize chromosomes during cell division, and transport cellular cargos
What are the key features of actin filaments?
Actin filaments support cell shape, drive cell movement, and are involved in processes like cell adhesion, division, and cargo transport within the cell
What distinguishes actin filaments from microtubules in terms of filament size?
Actin filaments are much smaller, about 7 nanometers in diameter, while microtubules are approximately 25 nanometers in diameter
How does actin contribute to cell motility?
Actin polymerises at the cell membrane, creating forces that push the cell in the direction of movement
What role do intermediate filaments play in the cytoskeleton?
They provide structural stability and resistance to mechanical stress, especially in skin and nerve cells
What role do intermediate filaments play in skin cells?
Intermediate filaments composed of keratin provide structural stability to skin cells, helping them withstand external stress and protect underlying tissues
Describe the dynamic instability of microtubules
Microtubules grow by adding tubulin dimers and can rapidly disassemble, a process regulated by GTP hydrolysis on tubulin subunits
What is the significance of tubulin isoforms in different cell types?
Different tubulin isoforms allow microtubules to interact with unique proteins and fulfill specific functions in various cell types, such as neuron-specific transport functions
How does GTP hydrolysis contribute to the instability of microtubules?
GTP hydrolysis in tubulin dimers destabilises microtubules, causing them to disassemble, a process key to their dynamic restructuring
What are microtubule-associated proteins (MAPs)?
Proteins that interact with microtubules, helping stabilise them, control their organisation, and link them to other cell structures
How are microtubules organised within cells?
They radiate from the microtubule organising center (MTOC), also called the centrosome, which provides a base for rapid microtubule growth
What drugs target microtubules, and what are their uses?
- Drugs like colchicine prevent microtubule polymerisation, and Taxol stabilises microtubules.
- Both are used in research and some are used clinically, such as in cancer treatments
How does Taxol interact with microtubules, and what is its clinical relevance?
Taxol binds to microtubules, stabilizing them and preventing disassembly, which inhibits cell division. It is used in cancer treatment to target rapidly dividing cells
What is the difference between G-actin and F-actin?
- G-actin refers to globular, monomeric actin
- F-actin is filamentous, polymerised actin forming the actin filaments, arranged in a twisted chain
What are intermediate filaments made from?
A variety of proteins, such as keratin, vimentin, and lamin, depending on the cell type and its specific needs
How does the structure of intermediate filaments differ from microtubules and actin filaments?
Intermediate filaments are composed of rope-like twisted fibers without polarity, providing strength rather than dynamic motion
What is the role of ATP and GTP in actin and microtubule dynamics?
ATP is bound and hydrolysed in actin polymerisation, while GTP is bound and hydrolysed in microtubule dynamics, both providing energy for structural changes
Why is ATP hydrolysis important in actin filament dynamics?
ATP-bound G-actin can polymerise into F-actin, and subsequent ATP hydrolysis destabilises F-actin, enabling actin filament turnover
Why are intermediate filaments considered the least dynamic cytoskeletal component?
They have low turnover rates and are more stable, primarily providing mechanical support rather than facilitating movement
How does the cytoskeleton differ across cell types and organisms?
All eukaryotes have actin, tubulin, and intermediate filaments, but specific types and structures vary by cell type and function
What is the effect of actin-binding proteins on actin filaments?
They stabilise, organise, or modulate actin filaments, helping form structures like microvilli or enabling cell movement
What are protofilaments in the context of microtubules?
Protofilaments are linear chains of tubulin dimers arranged head-to-tail, which bundle into a hollow tube to form a microtubule
What is the ‘catastrophe’ event in microtubule dynamics?
Catastrophe is a rapid disassembly of a microtubule, occurring when GTP bound to tubulin dimers is hydrolysed to GDP, destabilising the structure
What is the microtubule organising center (MTOC), and why is it important?
The MTOC, or centrosome, contains pre-formed tubulin oligomers and initiates microtubule growth, serving as nucleation sites rapid microtubule assembly when needed
How do cilia and flagella use microtubules for movement?
Microtubules slide past each other in cilia and flagella to produce beating or whipping motions, driving movement
Describe the role of gamma tubulin in microtubule formation
Gamma tubulin forms a template within the MTOC that stabilises the start of microtubule growth, helping form a stable nucleation site
What cellular process do microtubules assist with during mitosis?
Microtubules form the mitotic spindle, which separates chromosomes into daughter cells during cell division
Explain the function of the mitotic spindle in cell division
The mitotic spindle, formed by microtubules, organises and separates chromosomes into daughter cells during mitosis, ensuring each cell receives a complete set of chromosomes
What is the difference between type I and type II microtubule-associated proteins (MAPs)?
Type I MAPs bind microtubules at the N-terminus, while type II MAPs bind at the C-terminus, each playing a role in stabilising or organising microtubules
How does the drug colchicine affect microtubules?
Colchicine binds to tubulin dimers, preventing their addition to microtubules, thereby inhibiting microtubule growth
What structural arrangement allows actin filaments to have plus and minus ends?
Actin monomers (G-actin) polymerise head-to-tail, creating a structural polarity with distinct plus (barbed) and minus (pointed) ends
What is the role of ATP in actin filament polymerisation?
ATP binds to G-actin monomers, which then join to form F-actin. ATP is later hydrolysed to ADP, which affects filament stability and dynamics
What are some cellular structures that rely on actin filaments?
Structures like microvilli, adhesion bands, and contractile rings in dividing cells depend on actin filaments for stability and function
Describe the term “microvilli” and the role actin plays in them
Microvilli are finger-like projections on some cell surfaces, supported by actin filaments, which increase the cell’s surface area for absorption, such as in intestinal cells
What role does phalloidin play in actin dynamics?
Phalloidin binds to F-actin, stabilising it and preventing turnover, which can be lethal to cells by halting their structural rearrangements
What are intermediate filaments primarily composed of in epithelial cells?
In epithelial cells, intermediate filaments are primarily composed of keratin, which provides resilience to mechanical stress
How are intermediate filaments structurally distinct from actin filaments and microtubules?
Intermediate filaments are rope-like structures made from various proteins, lack polarity, and do not associate with molecular motors, making them less dynamic
What is the difference in molecular motors between actin filaments and microtubules?
Actin filaments are associated with myosin motors, while microtubules interact with kinesin and dynein motors, each facilitating different types of intracellular transport
What is the significance of coiled-coil dimers in intermediate filaments?
Coiled-coil dimers provide the basic structural unit, which further assembles into a stable, rope-like filament that resists tension
How do intermediate filaments contribute to neural function?
Neurofilaments provide structural support for axons, contributing to neuron stability and function in the nervous system
What is the primary mechanical advantage of intermediate filaments in cells?
Intermediate filaments can deform under stress without breaking, making them ideal for withstanding forces and maintaining cell integrity
Why are microtubules considered important for intracellular transport?
Microtubules serve as tracks for motor proteins, enabling the transport of vesicles, organelles, and other cargoes within the cell
What are some diseases associated with defects in intermediate filaments?
Diseases like ALS (Amyotrophic Lateral Sclerosis) and certain skin blistering disorders are linked to issues with neurofilaments and keratin filaments
How do microtubules contribute to the function of neuronal cells?
In neurons, microtubules provide tracks for transporting cargos along axons and dendrites, supporting cellular communication and function
What is the role of actin in the process of phagocytosis?
Actin polymerisation helps form membrane extensions that engulf particles, allowing cells to ingest large molecules or pathogens in a process known as phagocytosis.
What are lamins, and where are they found?
Lamins are intermediate filaments found in the nucleus, providing structural support to the nuclear envelope and helping organise nuclear contents
Describe how actin-binding proteins contribute to cell movement
Actin-binding proteins regulate the polymerisation and organisation of actin filaments, enabling the cell to push its membrane forward in the direction of movement
What is the structural significance of the 13 protofilament arrangement in microtubules?
The 13-protofilament arrangement forms a stable, hollow tube that supports cellular shape and enables interactions with motor proteins for transport
What causes microtubule ‘catastrophe’ and ‘rescue’ events?
Catastrophe occurs when GTP on tubulin is hydrolyzed, leading to disassembly; rescue happens when GTP-bound tubulin is added back, stabilizing and regrowing the microtubule
What happens to actin filaments during cell division?
Actin filaments form a contractile ring during cytokinesis, pinching the cell into two daughter cells at the end of cell division
How do diseases like ALS relate to cytoskeletal components?
ALS is associated with defects in neurofilaments (intermediate filaments) that disrupt nerve cell function and lead to progressive muscle weakness
Why do cells with high mechanical stress, like skin cells, rely on intermediate filaments?
Intermediate filaments provide high tensile strength, allowing skin cells to endure mechanical stress without rupturing
