Question

Which type of cytoskeletal fiber is important in the formation of the nuclear lamina? a. microfilaments b. intermediate filaments c. microtubules d. fibronectin

Short answer

b. intermediate filaments

Step-by-step solution

- Understand the Options

Analyze each of the given cytoskeletal fibers to understand their primary functions: microfilaments, intermediate filaments, microtubules, and fibronectin.

- Define Nuclear Lamina

The nuclear lamina is a dense fibrillar network inside the nucleus of eukaryotic cells, providing structural support and regulating important cellular events.

- Match Fiber to Function

Intermediate filaments are known for providing tensile strength and structural support in cells. They form the nuclear lamina, which underlies the nuclear envelope.

- Eliminate Incorrect Options

Microfilaments (option a) are primarily involved in cell movement and shape. Microtubules (option c) are responsible for maintaining cell shape, intracellular transport, and segregation of chromosomes. Fibronectin (option d) is a glycoprotein that helps cells attach to the extracellular matrix.

- Final Selection

Given that intermediate filaments form the nuclear lamina, it is the correct choice.

Key concepts

Intermediate Filaments

Intermediate filaments are one of the three main types of cytoskeletal fibers. They are named 'intermediate' because their diameter, at around 10 nanometers, is between that of microfilaments and microtubules. Intermediate filaments provide structural support and mechanical strength to cells. They are highly durable and help maintain the integrity and shape of cells, especially when under external stress.

Intermediate filaments are composed of a variety of proteins, such as keratins, vimentin, and lamins. Each type of protein is specific to certain cell types. For example:

• Keratins are found in epithelial cells and are essential for the formation of hair, nails, and the outer layer of skin.
• Vimentin is present in connective tissue cells.
• Lamins are found in the nucleus and form the nuclear lamina.

Lamins play a crucial role in stabilizing the nuclear envelope.

Without intermediate filaments, cells would be vulnerable to mechanical stress, which could lead to structural damage or cell death.

Nuclear Lamina

The nuclear lamina is a dense fibrillar network located just inside the inner nuclear membrane of eukaryotic cells. It is composed mainly of intermediate filaments known as lamins. The nuclear lamina provides structural support to the nucleus, maintaining its shape and integrity.

In addition to structural support, the nuclear lamina plays several vital roles:

• It anchors chromatin, the complex of DNA and proteins, to the nuclear envelope.
• It regulates DNA replication and transcription, which are essential for cell division and function.
• It helps in organizing nuclear pores, which control the import and export of molecules between the nucleus and the cytoplasm.

Defects in the nuclear lamina can lead to a range of diseases, collectively known as laminopathies. These can affect muscle function, cause premature aging, and even result in sudden cardiac death.

The importance of the nuclear lamina underlines the critical role of intermediate filaments in maintaining cellular health and functionality.

Eukaryotic Cells

Eukaryotic cells are highly complex cells with a true nucleus enclosed by a nuclear envelope. They are found in all multicellular organisms, including animals, plants, fungi, and protists. Eukaryotic cells are distinct from prokaryotic cells, which lack a defined nucleus and other membrane-bound organelles.

Key features of eukaryotic cells include:

• The presence of organelles such as mitochondria, the endoplasmic reticulum, the Golgi apparatus, and lysosomes, each with specialized functions.
• A cytoskeleton composed of microfilaments, intermediate filaments, and microtubules, providing structural support and facilitating intracellular transport.
• A dynamic plasma membrane that controls the movement of substances in and out of the cell.

The nucleus is the defining feature of eukaryotic cells. It houses the cell's genetic material (DNA) and is the site of DNA replication and transcription. The nuclear envelope, composed of two lipid bilayers, surrounds the nucleus. Just beneath this envelope lies the nuclear lamina, which provides mechanical support and plays roles in cellular regulation.

The complexity and organization of eukaryotic cells enable them to perform a wide variety of functions essential for the growth, development, and survival of multicellular organisms.