lecture 13

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Questions and Answers

What is the primary mechanism of action of colchicine in treating acute gouty arthritis?

Enhancing the movement of organelles along microtubules

Binding to tubulin to prevent microtubule polymerization (correct)

Inhibiting the formation of microfilaments

Promoting leukocyte migration and phagocytosis

Which family of motor proteins moves vesicles toward the minus end of microtubules?

Kinesin

Dynein (correct)

Actin filaments

Tubulin

What structural feature distinguishes centrioles from other microtubule-associated structures?

Formed during cytokinesis

Composed of microfilaments

Involved in phagocytosis

Consist of nine microtubule triplets (correct)

Which function is NOT attributed to microtubule-associated proteins (MAPs)?

Catalyzing the polymerization of actin filaments Signup and view all the answers

During cell division, what critical role do centrioles play?

Forming the spindle apparatus Signup and view all the answers

What drives the movement of kinesin along microtubules?

The presence of ATP Signup and view all the answers

Which of the following statements about actin filaments is incorrect?

They provide structural support to the centrosome. Signup and view all the answers

What is the role of the centrosome in relation to microtubules?

Organizing and forming microtubules Signup and view all the answers

Which statement accurately describes the dynamics of microtubules?

Microtubules frequently change their length, typically having a half-life of about 10 minutes. Signup and view all the answers

What is the primary role of the centrosome in relation to microtubules?

It serves as the main activation site for microtubule growth. Signup and view all the answers

How do microtubules contribute to intracellular movement?

They act as pathways that facilitate the transport of organelles and vesicles. Signup and view all the answers

Which of the following correctly describes the structural composition of microtubules?

They consist of 13 parallel protofilaments made up of heterodimers of alpha- and beta-tubulin. Signup and view all the answers

What critical role do microtubules play during cell division?

They undergo rapid polymerization to form the mitotic spindle. Signup and view all the answers

What is one of the effects of microtubules' dynamic nature?

They allow for rapid reorganization to respond to cellular demands. Signup and view all the answers

In what way do microtubules support ciliary and flagellar motion?

They assist in the bending and movement of cilia and flagella. Signup and view all the answers

Why are microtubules considered important targets for drug action?

Their dynamic instability can be manipulated to affect cell division and motility. Signup and view all the answers

Study Notes

Cytoskeletal Microtubules & Microfilaments & Motility

Students will be able to correlate the molecular organization of microtubules to their dynamic nature, interpret structural adaptations of microtubules (MTs) to their function, correlate motor proteins in cell trafficking to MTs, appraise the importance of microtubules as a drug target, and correlate the molecular structure of actin to its function.

Cytoskeleton

The cytoplasm of animal cells contains a complex three-dimensional protein filament network (cytoskeleton) maintaining cell shape.
The cytoskeleton is active in cell and organelle movement.
It has three components: microfilaments, intermediate filaments, and microtubules.

Microtubules

Microtubules (MTs) are long, hollow structures acting as intracellular pathways.
Centrosomes, near the nucleus, contain y-tubulin ring complexes that nucleate microtubules.
Microtubules are dynamic, frequently changing length by growing and shrinking at the plus end (away from nucleus). The average half-life is about 10 minutes.
Each microtubule consists of 13 parallel protofilaments made of a- and b-tubulin heterodimers.

Functions of MTs

Provide cell shape rigidity and maintain structure.
Regulate organelle and vesicle movement.
Form the basis of cilia and flagella.
Create intracellular compartments.
Essential for cell division (mitotic spindle).

Clinical Correlation

Drugs like colchicine can disrupt microtubule formation, affecting leukocyte function (migration, phagocytosis) and having anti-inflammatory effects (e.g., acute gouty arthritis).

Microtubule-Associated Proteins

Motor proteins (e.g., kinesin and dynein) move organelles and vesicles along microtubules.
Kinesin moves toward the plus end, and dynein moves toward the minus end, both driven by ATP.

Centrioles

Centrioles are small cylindrical structures (nine triplets) forming the microtubule organizing center (or centrosome).
They are perpendicular to each other.
Centrioles are important in cell division by forming the spindle apparatus, also forming cilia and flagella.

Actin Filaments (Microfilaments)

Thin filaments (microfilaments) are composed of two intertwined chains of globular actin (G-actin).
These form a filamentous protein (F-actin).
Filaments have a plus and minus end with different growth rates.

Functional Forms of Actin

Contractile Bundles: Loosely parallel bundles for cytokinesis, movement of organelles, and vesicles.
Gel-Like Networks: Structural basis for the cell cortex.
Bundles: Form the core of microvilli.
Focal Points/Focal Adhesions: Cell-matrix contact points.

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Description

This quiz focuses on the organization and function of microtubules and microfilaments in the cytoskeleton. Students will learn about the dynamic nature of microtubules, their role in cell motility, and the significance of motor proteins. Additionally, it highlights the importance of microtubules as potential drug targets.