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Questions and Answers
What occurs during the recovery stroke of ciliary movement?
What occurs during the recovery stroke of ciliary movement?
What is the structural arrangement of microtubules within cilia and flagella known as?
What is the structural arrangement of microtubules within cilia and flagella known as?
What role do dyneins play in ciliary movement?
What role do dyneins play in ciliary movement?
What happens when doublet microtubules are purified and ATP is added?
What happens when doublet microtubules are purified and ATP is added?
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What component helps convert dynein forces into bending of the axoneme?
What component helps convert dynein forces into bending of the axoneme?
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What direction do kinesins typically transport their cargo along microtubules?
What direction do kinesins typically transport their cargo along microtubules?
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Which portion of kinesin is responsible for binding to microtubules and ATP?
Which portion of kinesin is responsible for binding to microtubules and ATP?
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What is the primary function of dyneins in relation to microtubules?
What is the primary function of dyneins in relation to microtubules?
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What kind of motor proteins usually form homodimers?
What kind of motor proteins usually form homodimers?
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What characteristic do both kinesins and dyneins share?
What characteristic do both kinesins and dyneins share?
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In the assays used to study microtubule motors, which of the following aspects is NOT typically measured?
In the assays used to study microtubule motors, which of the following aspects is NOT typically measured?
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What unique condition is created in the second type of assay described?
What unique condition is created in the second type of assay described?
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What type of cargo can kinesins transport?
What type of cargo can kinesins transport?
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What is the primary direction in which most kinesin motors move?
What is the primary direction in which most kinesin motors move?
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Which kinesin family is noted for being a unique minus end directed motor?
Which kinesin family is noted for being a unique minus end directed motor?
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What triggers the conformational change in dynein's microtubule binding domain?
What triggers the conformational change in dynein's microtubule binding domain?
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How does ATP binding affect dynein's interaction with microtubules?
How does ATP binding affect dynein's interaction with microtubules?
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How are the motor domains in a homodimeric dynein coordinated during movement?
How are the motor domains in a homodimeric dynein coordinated during movement?
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What is the function of the light chains associated with most kinesin motors?
What is the function of the light chains associated with most kinesin motors?
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Which domain of dynein consists of the ATPase activity?
Which domain of dynein consists of the ATPase activity?
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What happens during the power stroke of dynein's movement?
What happens during the power stroke of dynein's movement?
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What is the primary function of the centrosome in cell biology?
What is the primary function of the centrosome in cell biology?
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What are the two main components of a centrosome?
What are the two main components of a centrosome?
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What role does γ-tubulin play in microtubule polymerization?
What role does γ-tubulin play in microtubule polymerization?
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How are microtubules described once they start to grow from the centrosome?
How are microtubules described once they start to grow from the centrosome?
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What characteristic orientation do microtubules have when growing from a centrosome?
What characteristic orientation do microtubules have when growing from a centrosome?
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What is the structure of centrioles within the centrosome?
What is the structure of centrioles within the centrosome?
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Where are the minus ends of microtubules typically located in a cell?
Where are the minus ends of microtubules typically located in a cell?
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What happens to microtubules during the process of dynamic instability?
What happens to microtubules during the process of dynamic instability?
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What is the main role of dynactin in dynein function?
What is the main role of dynactin in dynein function?
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How does dynein differ from kinesin in terms of step size?
How does dynein differ from kinesin in terms of step size?
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What occurs to dynein homodimers when they are not bound to dynactin?
What occurs to dynein homodimers when they are not bound to dynactin?
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What is the process called when kinesins transport cargo to the cilia tip?
What is the process called when kinesins transport cargo to the cilia tip?
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Which structures use IFT trains for cargo transport?
Which structures use IFT trains for cargo transport?
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How are cargos transported in a neuron?
How are cargos transported in a neuron?
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What role do microtubules play in organelle positioning within a cell?
What role do microtubules play in organelle positioning within a cell?
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What happens to dyneins during anterograde transport?
What happens to dyneins during anterograde transport?
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What structure is formed by the microtubules in cilia and flagella?
What structure is formed by the microtubules in cilia and flagella?
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How do motile cilia and flagella differ?
How do motile cilia and flagella differ?
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What role do axonemal dyneins play in cilia?
What role do axonemal dyneins play in cilia?
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Which of the following describes the motion cycle of cilia?
Which of the following describes the motion cycle of cilia?
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Which type of cilia are involved in sensory detection?
Which type of cilia are involved in sensory detection?
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What is the primary function of motile cilia in the respiratory tract?
What is the primary function of motile cilia in the respiratory tract?
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Which statement is true regarding cilia on tracheal cells?
Which statement is true regarding cilia on tracheal cells?
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What determines the directionality of movement for dynein or kinesin complexes on microtubules?
What determines the directionality of movement for dynein or kinesin complexes on microtubules?
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Study Notes
Centrosome Structure and Function
- The centrosome is the primary microtubule nucleation site in most cells.
- The centrosome is composed of two parts:
- A central pair of centrioles that are barrel-shaped organelles made of bundled triplet microtubules.
- A surrounding matrix of proteins (pericentriolar material, PCM), which is visible as an electron-dense "cloud" surrounding the centrioles.
- PCM acts as a scaffold for centrioles.
- The pericentriolar material is composed of numerous proteins and is the site of microtubule nucleation.
- Microtubules grow out from the centrosome in a radial organization.
- The plus ends of microtubules are oriented outward into the cytoplasm and the minus ends are capped.
- Microtubule polymerization from centrosomes requires y-tubulin in the pericentriolar material.
- Y-tubulin acts as a seed for new microtubule nucleation.
Microtubule Polymerization
- Tubulin polymerizes from nucleation sites on a centrosome.
- Fluorescent tubulin and GTP can be observed to grow from the centrosome.
- Microtubules exhibit dynamic instability, growing and shrinking.
- New microtubules grow from the centrosome acting as a nucleation site as it would inside a cell.
Microtubule Motors and Regulators
- Microtubule motor proteins convert ATP hydrolysis into movement along cytoskeletal filaments.
- Some motors move towards the microtubule plus end.
- Other motors move towards the microtubule minus end.
- These motors carry cargo (organelles, protein complexes, RNA) and mediate microtubule/microtubule sliding.
- Kinesins are a family of motor proteins that are usually homodimers.
- Kinesins have a head domain that binds to microtubules and ATP, and a tail domain that attaches to cargo (e.g., vesicles, organelles, mRNAs, or protein complexes).
- Kinesins walk along microtubules towards the plus end.
- Dyneins are similar to kinesins in that they walk along microtubules.
- Dyneins move towards the microtubule minus end, and are coordinated into cycles of molecular stepping movements.
- The ATP hydrolysis cycle of one kinesin motor domain regulates its binding affinity for the microtubule and positions the other motor domain.
- Repeated cycles of bending produce flagellar (or ciliary) beating.
- Microtubule motors help position organelles in a eukaryotic cell, such as the ER, Golgi, and the Golgi.
Specific Types of Microtubule Motors
- Cytoplasmic dynein is part of a larger complex, the dynein-dynactin complex
- Cytoplasmic dynein carries cargo in the cytoplasm and along IFT (intraflagellar transport).
- Axonemal dyneins move cargo in cilia and flagella exclusively.
- Axonemal dyneins are involved in flagella and ciliary function.
Cilia and Flagella
- Flagella and motile cilia are motile structures used to power cellular motility.
- Motile cilia line the epithelial tissue of the respiratory tract to sweep particulate matter out of the airways.
- Motile cilia line the oviduct to push the egg, and flagella allow sperm to swim.
- Cilia and flagella have similar internal structures.
- Flagella are long and present in 1 or 2 copies per cell.
- Cilia are much shorter and can range from ~10 - 100 copies per cell.
- The axoneme is the core structure composed of microtubules which are arranged in a 9+2 array.
- Each doublet microtubule carries two rows of axonemal dyneins.
Studying Microtubule Motility
- In vitro assays are used to gain information on motor activity.
- These assays look at the speed that a motor moves along a microtubule, how long a motor move on a microtubule before it dissociates, and the direction(plus or minus end).
- Other assays measure what size step a motor takes.
- One assay is the use of beads with a motor bound to them.
Distinct Microtubule structures
- Mitotic spindle
- Cilia and Flagella. Specific structures are present in each.
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Description
Test your knowledge on the structure and function of the centrosome. This quiz covers essential concepts such as the role of centrioles, microtubule nucleation, and the significance of the pericentriolar material. Perfect for students studying cell biology or related topics.
