QCM : Cell Cytoskeleton Fundamentals — 11 questions

Explication

The cytoskeleton's main role is to provide structural support, maintain cell shape, and organize the internal components of the cell, enabling cell motility, division, and environmental sensing.

Explication

Intermediate filaments are characterized by their solid, rope-like structure formed by twisted protein strands, providing mechanical strength. In contrast, microtubules are hollow tubes made of tubulin dimers, involved in cell organization and transport. This fundamental difference in structure distinguishes the two filament types.

Explication

Intermediate filaments assemble through a hierarchical process where monomers first form coiled-coil dimers, which then associate in an antiparallel fashion to form tetramers. These tetramers further organize into a staggered, filamentous structure that elongates into mature intermediate filaments. The process involves specific steps, not direct assembly from monomers or random aggregation, and it is distinct from microtubule assembly.

Explication

The nuclear lamina, composed of lamins, primarily provides mechanical support to the nuclear envelope and maintains nuclear integrity. Mutations in lamins can lead to structural defects and disease, highlighting its structural support role. It does not primarily facilitate DNA replication, regulate gene expression directly, or serve as the main pathway for molecular transport.

Explication

Disrupting SUN/KASH complexes via gene editing allows researchers to study their specific role in connecting the cytoskeleton to the nuclear envelope, which is essential for nuclear positioning and integrity. This application directly leverages the understanding of linker proteins' function in nuclear-cytoskeletal linkage and can help elucidate disease mechanisms or develop targeted therapies.

Explication

The understanding that microtubules are organized by centrosomes through γ-tubulin rings was established in the 1970s, marking a significant milestone in cell biology research.

Explication

γ-tubulin rings within the centrosome act as nucleation sites for microtubule growth, initiating the polymerization process that leads to microtubule formation. This role is essential for organizing the microtubule network within the cell.

Explication

Theodor S. S. is credited with early research identifying the centrosome as the main microtubule-organizing center in animal cells, particularly through the discovery of γ-tubulin rings that nucleate microtubule growth.

Explication

Actin filaments polymerize at the cell's leading edge, which directly causes the formation of protrusions such as lamellipodia and filopodia. These structures are essential for cell crawling, environmental sensing, and motility. The other options are unrelated to actin polymerization at the leading edge: microtubule networks are organized separately, intermediate filaments support nuclear and cellular integrity, and tight junctions involve cell-cell adhesion proteins, not actin polymerization.

Explication

Actin in cell movement is a dynamic and flexible filamentous protein that polymerizes at the leading edge of the cell, forming protrusions such as lamellipodia and filopodia, which are essential for crawling and motility. Unlike stable support proteins or rigid structures, actin actively drives movement through its polymerization and interaction with motor proteins.

Explication

Signals regulate the organization and formation of actin protrusions by promoting actin polymerization at the leading edge, enabling cell movement. Protrusions are structural extensions of the cell membrane driven by actin dynamics, not formed independently of signals. Therefore, the key similarity is that signals control protrusions, but they are distinct concepts: signals are external cues, while protrusions are physical cell structures.