Cytoskeletal Systems: Microtubules Part 1

Microtubules

• The primary function of cytoplasmic microtubules in a cell is to provide structural support, shape, and movement.

Axonemal Microtubules

• Axonemal microtubules are organized and stable in cilia and flagella.
• The axoneme is the internal structure of cilia and flagella, composed of microtubules.
• Axonemal microtubules in eukaryotic flagella are responsible for movement and motility.

Types of Microtubules

• There are two types of microtubules involved in various cell functions: cytoplasmic microtubules and axonemal microtubules.
• Cytoplasmic microtubules are not involved in cell motility.

Microtubule Structure

• The basic subunit of a protofilament in a microtubule is a dimer of α-tubulin and β-tubulin.
• Protofilaments in microtubules have an inherent polarity.
• Cilia and flagella contain 13-protofilament microtubules with one complete tubule and one or two incomplete rings.

Microtubule Assembly

• Nucleation is the process of microtubule assembly.
• The dynamic equilibrium between assembly and disassembly balances the growth of microtubules when the mass reaches a point where the amount of free tubulin is diminished.
• Microtubule-associated proteins (MAPs) and microtubule-organizing centers (MTOCs) serve as 'nuclei' from which new microtubules grow during assembly.
• The plateau phase of microtubule assembly represents a state of dynamic equilibrium.

Tubulin

• Each α-tubulin and β-tubulin has a globular domain.
• Tubulin heterodimers are made of one α-tubulin and one β-tubulin molecule.
• Protofilaments in microtubules consist of tubulin heterodimers arranged head-to-tail.

Test your knowledge on the first part of the lecture series by Kathleen Fitzpatrick at Simon Fraser University, covering the topic of microtubules as a component of the cytoskeletal system.