Problem 19 - Biology

Question

Which of the following have the ability to disassemble and reform quickly? a. microfilaments and intermediate filaments b. microfilaments and microtubules c. intermediate filaments and microtubules d. only intermediate filaments

Step-by-Step Solution

Answer

b. microfilaments and microtubules

Step 1 - Understand the components

Identify the components mentioned in the question. The cell's cytoskeleton is made up of microfilaments, intermediate filaments, and microtubules. Each has distinct characteristics.

Step 2 - Characteristics of Microfilaments

Microfilaments are composed of actin and are known for their ability to assemble and disassemble quickly. They are involved in various functions such as muscle contraction, cell motility, and division.

Step 3 - Characteristics of Microtubules

Microtubules are made up of tubulin and also have the ability to rapidly disassemble and reform. They play key roles in cell division, intracellular transport, and the maintenance of cell shape.

Step 4 - Characteristics of Intermediate Filaments

Intermediate filaments, composed of various proteins like keratin, are more stable and do not disassemble and reform as quickly as microfilaments and microtubules. They provide mechanical support and maintain cell integrity.

Step 5 - Compare the options

From the understanding above, compare the options: a) microfilaments and intermediate filaments - only microfilaments disassemble/reform quickly, b) microfilaments and microtubules - both can disassemble/reform quickly, c) intermediate filaments and microtubules - only microtubules disassemble/reform quickly, d) only intermediate filaments - incorrect as they do not disassemble/reform quickly.

Step 6 - Conclusion

The correct answer is 'b. microfilaments and microtubules' as both have the ability to disassemble and reform quickly.

Key Concepts

Microfilaments

Microfilaments are essential components of the cytoskeleton, composed primarily of a protein called actin. These thin, thread-like structures have a diameter of about 7nm and are remarkably dynamic.
They can rapidly assemble and disassemble, which is crucial for various cellular functions. For example:

• **Cell motility:** Microfilaments allow the cell to move by forming and depolymerizing in response to changes in the cell's environment.
• **Muscle contraction:** In muscle cells, actin filaments interact with myosin to cause contraction, essential for movement.
• **Cell division:** During cytokinesis, microfilaments form a contractile ring that pinches the cell into two daughter cells.

Their dynamic nature makes microfilaments integral in maintaining cell shape and enabling cells to respond rapidly to internal and external signals.

Microtubules

Microtubules are another vital part of the cytoskeleton. These hollow tubes are made of tubulin protein dimers and have a larger diameter of about 25nm. Just like microfilaments, microtubules can also quickly assemble and disassemble.
Some key roles of microtubules include:

• **Cell division:** They form the mitotic spindle, essential for segregating chromosomes during mitosis and meiosis.
• **Intracellular transport:** Microtubules provide tracks for the movement of organelles and vesicles within the cell, facilitated by motor proteins like kinesin and dynein.
• **Cell shape:** They help maintain cell shape by resisting compressive forces.

The ability of microtubules to rapidly change length allows them to adapt quickly to the needs of the cell, making them indispensable for cell function and structure.

Intermediate Filaments

Intermediate filaments, unlike microfilaments and microtubules, do not disassemble and reform as quickly. They are approximately 10nm in diameter and are made from a variety of proteins, such as keratins, vimentin, and lamins.
Their main functions include:

• **Mechanical support:** Intermediate filaments provide tensile strength to cells, helping them withstand mechanical stresses.
• **Cell integrity:** They contribute to maintaining cell integrity by anchoring organelles and stabilizing the cytoskeleton.
• **Tissue resilience:** In tissues, such as the skin, they provide structural support, preventing cells from tearing under stress.

Intermediate filaments are less dynamic compared to microfilaments and microtubules. This stability is crucial for long-term support and resilience, particularly in cells that need to endure physical stress.