Microtubules part 1

Summary

This lecture delves into the structure and function of microtubules, key components of the cytoskeleton. Microtubules are made of tubulin dimers, forming cylindrical structures crucial for cell shape, intracellular transport, and cell division. They are more rigid than other cytoskeletal elements, aiding in the movement of organelles and chromosomes. The polymerization of microtubules is influenced by temperature, with higher temperatures promoting their formation. The motor proteins kinesin and dynein move cellular components along microtubule tracks. The lecture also covers how microtubules contribute to processes like the movement of chromosomes during cell division and the formation of cellular projections like cilia and flagella.

Takeaways

• 😀 Microtubules are a type of cytoskeleton made of tubulin, a globular protein, and have a cylindrical shape with a diameter of approximately 25 nm.
• 😀 The length of microtubules varies, ranging from a few micrometers to hundreds of micrometers.
• 😀 Microtubules are more rigid compared to other cytoskeletal elements like intermediate filaments and microfilaments due to their thicker diameter and cylindrical structure.
• 😀 Microtubules are involved in cell shape maintenance, the movement of organelles and vesicles, and chromosome separation during cell division.
• 😀 Microtubules can be either stable or unstable, with the unstable type involved in organelle and vesicle transport, and the stable type found in structures like axons.
• 😀 The polymerization of microtubules is influenced by temperature, with higher temperatures promoting polymerization and lower temperatures causing disassembly.
• 😀 Microtubules contribute to the movement of cilia and flagella, which are built from tubulin dimers arranged in a specific structure.
• 😀 Tubulin dimers consist of alpha-tubulin and beta-tubulin, and their polymerization forms protofilaments that assemble into microtubules.
• 😀 Microtubules have polarity, with a positive and a negative end, affecting the direction of vesicle and organelle movement along them.
• 😀 The addition of tubulin dimers to the plus end of microtubules occurs twice as fast as at the minus end, influencing the overall dynamics of microtubule growth.
• 😀 Microtubules play a crucial role in cell division, particularly during mitosis, where they help in moving chromosomes towards the poles of the dividing cell.

Q & A

What is the basic structure of a microtubule?

A microtubule is a cylindrical structure with a diameter of about 25 nanometers. It is formed by the polymerization of tubulin protein monomers.

How does the stability of microtubules compare to other cytoskeletal elements?

Microtubules are stiffer and more rigid compared to intermediate filaments and microfilaments, making them stronger and able to push cellular structures like the cell membrane without bending.

What role do microtubules play in cell division?

During cell division, microtubules help in the movement of chromosomes by attaching to the centromere and pulling them toward the poles of the cell during mitosis.

What is the function of microtubules in the axon of nerve cells?

In nerve cells, microtubules run along the axon and help in the stable organization and transportation of cellular components and vesicles.

How do microtubules contribute to the movement of organelles and vesicles within the cell?

Microtubules serve as tracks for motor proteins, such as kinesin and dynein, which transport organelles and vesicles along the microtubules. Kinesin moves them toward the positive end, while dynein moves them toward the negative end.

What is the role of microtubules in the formation of cilia and flagella?

Microtubules form the structural basis of cilia and flagella. In these structures, microtubules are arranged in a '9+2' configuration, with nine doublets surrounding two central microtubules.

What determines the polarity of microtubules?

The polarity of microtubules is determined by their structure, with one end being the 'plus' end (fast-growing) and the other the 'minus' end (slow-growing).

How does temperature affect microtubule polymerization?

Microtubule polymerization is temperature-dependent. Higher temperatures promote polymerization, while lower temperatures cause the microtubules to depolymerize.

What are the key subunits that make up microtubules?

Microtubules are composed of tubulin dimers, specifically alpha-tubulin and beta-tubulin. These dimers form protofilaments, which in turn make up the microtubule structure.

What is the significance of the 'minus' and 'plus' ends of microtubules?

The 'plus' end of a microtubule is where polymerization is faster, and it is typically oriented toward the cell's periphery. The 'minus' end is more stable and often anchored to microtubule-organizing centers (MTOCs).