Microtubules part 4

Summary

The video script delves into the intricate dynamics of microtubules, their role in cellular processes, and the mechanisms involved in transporting cargo within cells. It highlights how microtubules interact with motor proteins like kinesin and myosin to transport vesicles to the cortex of the cell. The script also covers the structure and function of flagella and cilia, detailing how doublet microtubules and proteins like dynein and radial spokes facilitate their movement. Furthermore, it explores the organization and function of the centrosome, which plays a crucial role in cell division, forming various types of microtubules that help separate chromosomes during mitosis.

Takeaways

• 😀 The transportation of vesicles within cells involves microtubules and motor proteins like kinesin and myosin. Microtubules transport vesicles to the cell cortex, where they are transferred to myosin for movement along microfilaments.
• 😀 The cargo transported via microtubules is often secretory in nature, and in glandular cells, it must be moved to the membrane for secretion after reaching the cell cortex.
• 😀 Microtubules play a significant role in the formation of structures such as flagella and cilia. These are made of doublet microtubules arranged in a circular pattern beneath the membrane.
• 😀 The central part of flagella and cilia contains singlet microtubules, and these are linked by radial spokes to the axoneme structure, which is crucial for their function.
• 😀 Dynein, a type of protein, is attached to the doublet microtubules of flagella and cilia and works together with radial spokes to generate motion.
• 😀 Centrosomes, which are also known as microtubule organizing centers (MTOC), duplicate during the G2 phase of the cell cycle and are responsible for organizing microtubules during mitosis.
• 😀 During mitosis, centrosomes move to opposite poles of the cell and help form a microtubule network that aids in aligning chromosomes along the equator of the cell.
• 😀 The process of mitosis involves the shortening of microtubules to pull chromatids toward opposite poles, ultimately resulting in the formation of two identical daughter cells.
• 😀 There are different types of microtubules involved in mitosis: astral microtubules, polar microtubules, and kinetochore microtubules, each playing distinct roles in chromosome movement.
• 😀 Kinetochore microtubules interact with the kinetochore, a protein complex on the chromosome, to facilitate proper chromosome separation during cell division.

Q & A

What is the role of microtubules in the cell cortex?

Microtubules are limited in the cell cortex area, where they are almost absent. This region is mainly dominated by microfilaments, which are responsible for cargo transportation within the cell's cortex.

How is cargo transported to the cortex if microtubules are not present?

Cargo is initially transported by microtubules using motor protein kinesin. Upon reaching the cortex, the cargo must be transferred to microfilaments, and motor protein myosin II is responsible for recognizing and moving the cargo along these filaments.

What happens when cargo reaches the cortex in terms of its transport system?

Once the cargo reaches the cortex, the kinesin protein is no longer effective, so the cargo is transferred to myosin II. This allows the cargo to travel along microfilaments, enabling it to reach its final destination in the cell, such as when a gland secretes substances.

What are flagella and cilia made of?

Flagella and cilia are composed of microtubules arranged in a specific structure. They are built from doublet microtubules, with 9 doublet microtubules forming a ring around the membrane of the structure, and two single microtubules in the center.

What is the axoneme, and what is its role in flagella and cilia?

The axoneme is the central structure of flagella and cilia, composed of doublet and singlet microtubules. The doublets are connected by a protein complex called 'nexin,' and the structure is further stabilized by radial spokes that interact with the central microtubules.

What is the role of dynein in flagella and cilia movement?

Dynein, a motor protein, is attached to the microtubule doublets in flagella and cilia. Its interaction with radial spokes leads to bending and movement, allowing flagella and cilia to perform their function of propulsion or fluid movement around the cell.

How does the centrosome play a role in cell division?

The centrosome, also known as the microtubule-organizing center, duplicates during the G2 phase of the cell cycle. It helps in organizing microtubules that are crucial for chromosome alignment during cell division, particularly in mitosis.

What is the role of microtubules during mitosis?

During mitosis, microtubules form the mitotic spindle, which is essential for aligning chromosomes at the cell's equator. As the cell progresses, microtubules help pull chromatids toward opposite poles of the cell.

What are the different types of microtubules involved in mitosis?

There are three main types of microtubules during mitosis: astral microtubules, polar microtubules, and kinetochore microtubules. Astral microtubules help orient the spindle, polar microtubules push the poles apart, and kinetochore microtubules connect to the chromosomes and move them.

What is the kinetochore, and how does it function during mitosis?

The kinetochore is a protein structure located at the centromere of chromosomes. During mitosis, kinetochore microtubules attach to it, facilitating the separation of chromatids as the microtubules shorten and pull the chromatids toward opposite poles.