16 Questions
What are the three main classes of the cytoskeleton, and what are they composed of?
The three main classes of the cytoskeleton are microfilaments (composed of actin), intermediate filaments (IFs), and microtubules (MT).
What is the role of microtubules in the cell, and how do they contribute to the organization of organelles?
Microtubules act as 'tracks' for the movement of organelles and materials, and also provide a framework for the organization of organelles.
What is the function of microfilaments in cell growth and motility?
Microfilaments are involved in the growth of axons and also form the force-generating apparatus for cell motility.
What is the structure of microtubules, and how do their components contribute to their polarity?
Microtubules are hollow tubular structures with 13 protofilaments, composed of alternating a- and b-tubulin subunits, which results in their structural and functional polarity.
What is the role of Microtubule-Associated Proteins (MAPs) in microtubule stability and assembly?
MAPs play a role in increasing microtubule stability and promoting the assembly of tubulin subunits, and many are regulated by phosphorylation.
What is the relationship between Tau protein and microtubules in the context of dementia?
Hyperphosphorylated Tau protein is incapable of binding to microtubules, and is found in neurofibrillary tangles and plaques, which is linked to various forms of dementia.
What is the role of microtubules in determining the overall shape of the cell?
Microtubules provide structural support and their arrangement determines the overall shape of the cell.
How does the association with integral membrane proteins influence the organization of microtubules?
The association with integral membrane proteins, such as cellulose synthase, influences the organization of microtubules by determining the location and orientation of cellulose microfibrils, which in turn determines plant cell shape and growth.
What are the main roles of microfilaments in a cell?
Microfilaments play roles in structural support, cellular motility, intracellular motile processes, and muscle contraction.
What is the main function of intermediate filaments in cells?
Intermediate filaments provide mechanical strength to cells, particularly those that undergo large amounts of stress, such as nerves, muscles, and epithelia.
What is the basic structure of all intermediate filaments?
The basic structure of all intermediate filaments consists of a central α-helical fibrous domain, terminal globular domains of variable size and sequence, and a nonpolar tetramer formed by the anti-parallel association of dimers.
What is the mechanism of intermediate filament growth and regulation?
Intermediate filaments grow through end-to-end association and intercalation within existing filaments, and their polymerization and depolymerization are regulated through phosphorylation.
What are the main components of cytoplasmic intermediate filaments?
Cytoplasmic intermediate filaments include proteins such as keratin, desmin, and neurofilaments, which are interconnected to other cytoskeletal filaments by plectin crossbridges.
What is the role of keratin intermediate filaments in epithelial cells?
Keratin intermediate filaments are found radiating throughout epithelial cells and often terminate on desmosomes, which are communication points between cells.
What is unique about the structure of neurofilaments?
Neurofilaments have sidearms that ensure appropriate spacing between parallel fibers, and their structure is unique due to the presence of these sidearms.
What is the function of lamins in the nuclear envelope?
Lamins form a strong, mesh-like grid on the nucleoplasmic side of the inner nuclear membrane, called the nuclear lamina, and provide mechanical support to the nucleus.
Study Notes
Microtubules
- Determine the overall shape of the cell
- Radial arrangement seen in cultured animal cells, resulting in a round, flattened shape
- Basal to apical arrangement in columnar epithelial cells
- Lengthwise arrangement along axons
- Association with integral membrane proteins influences organization
- Cellulose synthase association determines the location and orientation of cellulose microfibrils, which determines plant cell shape and manner of growth
- Organelle localization, such as the Golgi apparatus
Microfilaments
- Also known as actin filaments or F-actin
- Roles: structural support, cellular motility, intracellular motile processes, and muscle contraction
- Highly conserved, with different isoforms for specialized roles
Intermediate Filaments
- Provide mechanical strength to cells, particularly those that undergo large amounts of stress
- Found in animals, but other insoluble fibers of diverse protein sequences are found in other eukaryotes
- Chemically heterogeneous, with approximately 70 different genes in humans
- 5 classes based on cell type of expression, and biochemical, genetic, and immunologic criteria
- Structure: solid and unbranched with a 10-12 nm diameter
- Consist of a-helical central fibrous domain, homologous sequences, and terminal globular domains of variable size and sequence
Intermediate Filament Structure
- Subunits associate in groups of 8 to form a unit length
- End-to-end association to form the polymerized IF
- Growth through intercalation within existing IF
- Polymerization and depolymerization regulated through phosphorylation
- Only cytoskeletal fibers that lack polarity
Cytoplasmic Intermediate Filaments
- Include proteins such as keratin, desmin, and neurofilaments
- Interconnected to other cytoskeletal filaments by plectin crossbridges
- Examples: keratin in epithelial cells, desmin in muscle, and neurofilaments in CNS and PNS nerves
Epithelial Cells
- Intermediate filaments composed of keratin
- Found radiating throughout the cell
- Often terminate on desmosomes (communication points between cells)
Neurofilaments
- At least three different proteins (Type IV IFs)
- Unique in structure due to the presence of sidearms
- Ensure appropriate spacing between parallel fibers
- Increasing amounts of IFs as neurons mature
Lamins
- Form a strong, mesh-like grid on the nucleoplasmic side of the inner nuclear membrane
- Disassembled during prophase of mitosis and meiosis
Cytoskeletal Organization
- Divided into three classes: microfilaments (actin), intermediate filaments, and microtubules
- Noncovalently bonded protein polymers: highly dynamic
- All three classes play various roles in providing structure and support
- Microtubules act as "tracks" for the movement of organelles and materials
Test your knowledge of the cytoskeleton, including its structure, function, and the roles of microfilaments, microtubules, and intermediate filaments in providing cellular support and organization.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
