Chapter 11: Microtubule Flashcards
Microtubules have a ______ arrangement in the main body of a flagellum
Circular, 9 pairs in the outer layer and 1 pair in the inner layer; often called the “9+2” arrangement.
In the main body of a flagellum, the microtubules are organized in a specific pattern called the “9+2” arrangement. This arrangement refers to a central pair of microtubules surrounded by nine pairs of microtubules forming a ring-like structure. The central pair is connected to the outer microtubule doublets by radial spokes, creating a cylindrical structure. This arrangement provides structural support and allows for the coordinated bending and movement of the flagellum.
Describes the concept of “dynamic instability” as it applies to the microtubules.
Dynamic instability in microtubules refers to their ability to undergo reversible cycles of growth and shrinkage. Tubulin subunits are added during polymerization, causing growth, while subunit loss leads to depolymerization and shrinkage. This dynamic behavior allows microtubules to rapidly adapt and participate in cellular processes.
Dynamic instability allows the cell to rapidly reorganize the cytoskeleton when necessary. This is important because cells change/divide frequently. This can occur several different ways, but essentially is the result of a lost GTP cap which results in peeling.
What are the common features of the motor proteins kinesin and dynein?
Kinesin and dynein are both motor proteins that walk along the microtubules. They are different in structure and the direction that they walk however. Kinesins move toward the plus end (the membrane) and the dyneins move toward the negative end (the MTOC or center).
What is a motor protein?
Proteins that use repeated cycles of ATP hydrolysis to power continuous movements along the side of microtubules; like walking.
Do motor proteins undergo conformational changes when the motor travels?
These conformational changes enable motor proteins to “walk” or “step” along the filament, converting chemical energy from ATP into mechanical work.
Both types of motor proteins step from one tubulin to another, an 8 nm “step.” True or False
True. Both types of motor proteins walk in 8 nm steps, which is the length of a single tubulin heterodimer.
Tubulin dimers may assemble at the plus end and disassemble at the minus end simultaneously in a process known as _____________.
Treadmilling. or dynamic instability.
The truth is that addition and removal of heterodimers is constantly occuring at both ends but the plus end grows and the minus end shortens at the same rate, creating a conveyor belt effect.
What is dynamic instability?
Dynamic instability allows the cell to rapidly reorganize the cytoskeleton when necessary.
Dynamic instability refers to the ability of microtubules to switch between phases of growth (polymerization) and shrinkage (depolymerization) in response to cellular signals and environmental cues. During the growth phase, tubulin subunits are added to the microtubule, extending its length. In the shrinkage phase, tubulin subunits are lost from the microtubule, causing it to shorten.
What is treadmilling of microtubules?
The plus end of the microtubule grows longer while the minus end shortens at the same rate. This creates a conveyor belt effect and can only occur at critical concentration of tubulin heterodimers (Cc). This process can be used to transport vesicles, etc. across the cell.
What is the definition of critical concentration of purified tubulin dimers?
The critical concentration of purified tubulin dimers refers to the concentration of tubulin subunits in a solution at which microtubule assembly and disassembly are in equilibrium. It is the concentration at which the rate of tubulin subunit addition to the microtubule (polymerization) equals the rate of tubulin subunit loss from the microtubule (depolymerization), resulting in no net change in microtubule length.
The microtubule-organizing center (MTOC) nucleates microtubule assembly. True or False
True
the MTOC functions to nucleate microtubules; the most common MTOC in animals is the centrosome.
he microtubule-organizing center (MTOC) is responsible for nucleating or initiating the assembly of microtubules. The MTOC serves as a focal point for the nucleation and organization of microtubules in the cell. The primary MTOC in animal cells is the centrosome, which contains a pair of centrioles surrounded by pericentriolar material. The centrosome acts as the main MTOC during interphase and plays a critical role in cell division.
What acts as an anchor for both ends of the microtubule?
The centrosome acts as an anchor for both ends of the microtubule.
The centrosome, which is the primary microtubule-organizing center (MTOC) in animal cells, plays a crucial role in microtubule organization and serves as an anchor for both ends of the microtubule. The centrosome contains a pair of centrioles surrounded by pericentriolar material.
According to the current model, what is the sequence of microtubule assembly?
Dimers join to form oligomers -> protofilaments -> sheets of protofilaments -> closing of microtubule -> elongating microtubule.
What serves as a site for microtubule and microfilament assembly?
Microtubule Organizing Center; usually the centrosome
What acts as a motor for driving chromosomes apart during mitosis?
Microtubules attach to the chromosomes and then shorten to pull them apart.
During mitosis, microtubules attach to the chromosomes and then shorten to pull them apart. The microtubule structures that interact with chromosomes are called kinetochore microtubules.
GTP cap in a microtubule is found only on the plus end of the microtubule. True of False
True.
The GTP cap is found on the plus end of a microtubule.
The GTP cap is typically present on the plus end of a growing microtubule. The tubulin subunits at the plus end are GTP-bound, providing stability to the microtubule structure.
GTP cap in a microtubule is spontaneously lost over time by hydrolysis of GTP to GDP in the tubulin subunits. True or False
True.
The hydrolysis of GTP to GDP is a cause of dynamic instability.
The hydrolysis of GTP to GDP in the tubulin subunits is a key factor contributing to dynamic instability in microtubules. The hydrolysis weakens the tubulin-tubulin interactions, making the microtubule more prone to depolymerization or disassembly.
GTP cap in a microtubule promotes the elongation of the microtubule in which it is found. True or False
False.
The GTP cap is not necessary for microtubule elongation, but it influences the growth rate.
While the GTP cap itself is not required for microtubule elongation, it does have an impact on the growth rate. The GTP-bound tubulin subunits at the plus end have a higher affinity for each other, promoting the addition of new subunits and faster growth compared to the minus end. However, microtubules can still elongate in the absence of a GTP cap, albeit at a slower rate.
