Centrosome Structure and Function Quiz
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Questions and Answers

What occurs during the recovery stroke of ciliary movement?

  • The cilium vibrates rapidly to enhance propulsion.
  • The cilium curls back to minimize fluid disturbance. (correct)
  • The cilium remains fully extended to increase resistance.
  • The cilium extends to push fluid away from the cell.

What is the structural arrangement of microtubules within cilia and flagella known as?

  • 9+3 array
  • 9+2 array (correct)
  • 8+2 arrangement
  • 7+1 arrangement

What role do dyneins play in ciliary movement?

  • They attach the doublet microtubules to radial spokes.
  • They transport ATP to the ciliary base for energy.
  • They provide structural stability to the axoneme.
  • They facilitate the bending of the axoneme. (correct)

What happens when doublet microtubules are purified and ATP is added?

<p>They slide against each other and telescope away. (C)</p> Signup and view all the answers

What component helps convert dynein forces into bending of the axoneme?

<p>Nexins (B)</p> Signup and view all the answers

What direction do kinesins typically transport their cargo along microtubules?

<p>Towards the plus end (D)</p> Signup and view all the answers

Which portion of kinesin is responsible for binding to microtubules and ATP?

<p>The head domain (D)</p> Signup and view all the answers

What is the primary function of dyneins in relation to microtubules?

<p>They transport cargo to the minus end of microtubules. (D)</p> Signup and view all the answers

What kind of motor proteins usually form homodimers?

<p>Kinesins (D)</p> Signup and view all the answers

What characteristic do both kinesins and dyneins share?

<p>They both hydrolyze ATP for movement. (A)</p> Signup and view all the answers

In the assays used to study microtubule motors, which of the following aspects is NOT typically measured?

<p>Size of the cargo transported (A)</p> Signup and view all the answers

What unique condition is created in the second type of assay described?

<p>Microtubules are fixed to the slide (A)</p> Signup and view all the answers

What type of cargo can kinesins transport?

<p>Vesicles, organelles, mRNAs, or protein complexes (B)</p> Signup and view all the answers

What is the primary direction in which most kinesin motors move?

<p>Plus end directed (D)</p> Signup and view all the answers

Which kinesin family is noted for being a unique minus end directed motor?

<p>NCD family (A)</p> Signup and view all the answers

What triggers the conformational change in dynein's microtubule binding domain?

<p>ATP hydrolysis (B)</p> Signup and view all the answers

How does ATP binding affect dynein's interaction with microtubules?

<p>It causes the dynein head to release from the microtubule. (D)</p> Signup and view all the answers

How are the motor domains in a homodimeric dynein coordinated during movement?

<p>They alternate in a hand-over-hand fashion. (B)</p> Signup and view all the answers

What is the function of the light chains associated with most kinesin motors?

<p>They enable cargo binding specificity. (C)</p> Signup and view all the answers

Which domain of dynein consists of the ATPase activity?

<p>Motor region (B)</p> Signup and view all the answers

What happens during the power stroke of dynein's movement?

<p>The linker region moves, positioning the rear head forward. (A)</p> Signup and view all the answers

What is the primary function of the centrosome in cell biology?

<p>To orchestrate the growth of microtubules (A)</p> Signup and view all the answers

What are the two main components of a centrosome?

<p>Centrioles and pericentriolar material (D)</p> Signup and view all the answers

What role does γ-tubulin play in microtubule polymerization?

<p>It serves as a seed for microtubule nucleation (A)</p> Signup and view all the answers

How are microtubules described once they start to grow from the centrosome?

<p>They exhibit dynamic instability (C)</p> Signup and view all the answers

What characteristic orientation do microtubules have when growing from a centrosome?

<p>The plus end is oriented towards the cytoplasm (C)</p> Signup and view all the answers

What is the structure of centrioles within the centrosome?

<p>Barrel-shaped organelles made of bundled triplet microtubules (B)</p> Signup and view all the answers

Where are the minus ends of microtubules typically located in a cell?

<p>At the centrosome, anchored by γ-tubulin (A)</p> Signup and view all the answers

What happens to microtubules during the process of dynamic instability?

<p>They alternate between phases of growth and shrinkage (A)</p> Signup and view all the answers

What is the main role of dynactin in dynein function?

<p>It links dynein to cargoes. (B)</p> Signup and view all the answers

How does dynein differ from kinesin in terms of step size?

<p>Dynein can take varied step sizes of 8, 16, and 32 nm. (C)</p> Signup and view all the answers

What occurs to dynein homodimers when they are not bound to dynactin?

<p>They enter an autoinhibited state. (D)</p> Signup and view all the answers

What is the process called when kinesins transport cargo to the cilia tip?

<p>Anterograde transport (A)</p> Signup and view all the answers

Which structures use IFT trains for cargo transport?

<p>Cilia (D)</p> Signup and view all the answers

How are cargos transported in a neuron?

<p>Both dynein and kinesin can be attached to the same cargo but behave differently. (B)</p> Signup and view all the answers

What role do microtubules play in organelle positioning within a cell?

<p>They act as tracks for motor proteins. (D)</p> Signup and view all the answers

What happens to dyneins during anterograde transport?

<p>Dyneins are inactivated while kinesins are active. (D)</p> Signup and view all the answers

What structure is formed by the microtubules in cilia and flagella?

<p>Axoneme (B)</p> Signup and view all the answers

How do motile cilia and flagella differ?

<p>Flagella are present in 1 or 2 copies per cell. (C)</p> Signup and view all the answers

What role do axonemal dyneins play in cilia?

<p>They generate the power strokes for beating. (A)</p> Signup and view all the answers

Which of the following describes the motion cycle of cilia?

<p>They alternate between power strokes and recovery strokes. (D)</p> Signup and view all the answers

Which type of cilia are involved in sensory detection?

<p>Non-motile cilia (B)</p> Signup and view all the answers

What is the primary function of motile cilia in the respiratory tract?

<p>To sweep particulate matter out of airways. (C)</p> Signup and view all the answers

Which statement is true regarding cilia on tracheal cells?

<p>They beat in synchrony to perform filtration functions. (A)</p> Signup and view all the answers

What determines the directionality of movement for dynein or kinesin complexes on microtubules?

<p>The number of motors attached. (B)</p> Signup and view all the answers

Flashcards

Kinesin movement

Kinesin moves along microtubules towards the plus end, taking 8nm steps.

Dynein movement

Dynein moves along microtubules, taking variable steps (8, 16, 32 nm) and can switch protofilaments.

Dynactin

Dynactin is an adaptor protein that links cytoplasmic dynein to cargoes.

Microtubule transport direction

Microtubules often have a fixed direction in cells, allowing for specific cargo transport.

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Cargo transport

Cargoes are moved along microtubules in either anterograde (away from the center) or retrograde (towards the center) direction, often using kinesins and dyneins.

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Cilia transport

Cilia use IFT trains for cargo transport, with kinesin for anterograde and dynein for retrograde movement.

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Organelle positioning

Motor proteins move organelles (e.g., ER, Golgi) along microtubules to specific locations in the cell.

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Bidirectional transport

Sometimes, a single cargo is moved in both directions along a microtubule.

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Centrosome

A nucleating organelle where microtubules grow in most cells.

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Centrioles

Barrel-shaped organelles within centrosomes, made of bundled triplet microtubules.

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Pericentriolar material

A protein matrix surrounding centrioles in the centrosome; crucial for microtubule nucleation.

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γ-tubulin

A type of tubulin that acts as a seed for microtubule nucleation in the pericentriolar material.

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Kinesin motor protein

A motor protein that moves along microtubules towards the plus end.

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Microtubule nucleation

The process of forming new microtubules from existing structures, often at the centrosome.

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Dynein motor protein

A motor protein that moves along microtubules towards the minus end.

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Microtubule plus end

The end of a microtubule where kinesins move.

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Microtubule polymerization

The assembly of tubulin proteins into microtubules.

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Dynamic instability

The ability of microtubules to grow and shrink.

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Microtubule minus end

The end of a microtubule where dyneins move.

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Radial organization of microtubules

Microtubules growing outward from the centrosome in a radial pattern.

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ATP Hydrolysis

The process of breaking down ATP to fuel motor protein movements along microtubules.

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Motor protein homodimer

Two identical motor protein chains working together.

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In vitro assay

An experiment performed outside a living organism to study the behavior of a motor protein.

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Motor speed

The rate at which a motor protein moves along a microtubule

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Cilium Power Stroke

The phase of ciliary movement where the cilium extends fully, moving fluid over the cell surface.

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Axoneme Structure

The core microtubule-based structure within cilia and flagella, arranged in a 9+2 array.

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Ciliary Movement Cycle

A complete back-and-forth movement of a cilium (or flagellum), taking approximately 1/10th of a second.

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Dynein Motor Function

Dynein proteins within cilia/flagella use ATP to move along microtubules, causing the microtubule bundles to bend, driving movement.

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9+2 Array

Arrangement of microtubules in cilia and flagella: 9 outer doublet microtubules surrounding 2 central singlet microtubules.

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Kinesin motor domains

Kinesin motors, often homodimers, coordinate their ATP hydrolysis cycles, enabling coordinated movement and alternating 'steps' similar to walking.

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Kinesin family diversity

The kinesin family includes various types of motor proteins, including homodimers and tetramers that are involved in microtubule-based movement. Many are plus-end directed; others, such as the NCD family, are minus-end directed.

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NCD kinesin

A specialized kinesin motor protein that moves towards the minus end of microtubules.

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Dynein structure/ATP

Dynein, often a homodimer, comprises an ATPase domain (that binds ATP) and a microtubule binding region. ATP binding and hydrolysis cause a conformational change that affects microtubule adhesion.

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Dynein sliding helices

ATP hydrolysis in dynein causes the sliding of two alpha-helices in opposite directions, leading to changes in the binding conformation for microtubules

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Dynein's power stroke

After ATP hydrolysis, dynein undergoes conformational change, resulting in a power stroke that propels its movement. This involves a moving linker region

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Dynein's direction of movement

Dynein moves toward the minus end of microtubules, in contrast to kinesin's movement to the plus end.

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Cytoplasmic Dynein

Cytoplasmic dynein, a molecular motor, moves cargo towards the microtubule minus end.

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Motile Cilia Function

Motile cilia sweep away particles in the respiratory tract, and help move the egg in the oviduct

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Dynein Role in Cilia

Axonemal dynein drives the beating of cilia and flagella, providing cellular movement.

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Cilia and Flagella Structure

Both cilia and flagella have microtubules arranged in an axoneme, but differ in number and length.

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In Vitro Motility Assay

Testing motility of motor proteins (kinesin, dynein) on microtubules outside a living cell.

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Microtubule Dynamics

Microtubules can grow and shrink constantly; this is analyzed by kymography.

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Kymography Analysis

Kymography visualizes microtubule movement to see speed, direction, pauses and changes of direction.

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Axoneme Structure

The core structure of cilia and flagella, composed of microtubules arranged in a specific pattern.

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Flagella vs. Cilia

Flagella are long and usually present in one or two copies per cell. Motile cilia are much shorter and numerous, typically in 10–100 copies per cell. Flagella move the cell, and cilia move the fluids around the cell, or cells.

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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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Lecture 19: Microtubule Motors 2024 PDF

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.

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