The Cytoskeleton - Practice Questions & MCQ

The Cytoskeleton

• Cytoskeleton refers to the network of protein fibres that help in maintaining the shape of the cell and help in the movement of the cell. 
• There are three types of protein fibres within cytoskeleton:

1.                  microfilaments,
2.                  intermediate filaments, and 
3.                  microtubules

Microfilaments

• These are the narrowest fibres made up of two intertwined strands of F-actin protofilaments. They are also called actin filaments.
• F-actin protofilaments are made up of G-actin subunit. 
• F-actin is the filamentous actin while G-actin is the globular actin. 
• The individual strands of F-actin protofilaments are wound together with the help of tropomyosin. 
• Tropomyosin is a double-stranded alpha-helical coiled-coil protein. 
• It bears a protein complex, called troponin, which is interspersed along the length of the coil.

Functions of Microfilaments:

• Microfilaments provide shape and rigidity to the cells. They can depolymerize (disassemble) and reform quickly, thus enabling a cell to change its shape and move.

Intermediate Filaments

• They are called the intermediate filaments because their diameter (8 to 10 nm) is between those of microfilaments and microtubules. 
• These are structural in function. 
• They do not perform any role in the movement. 
• They maintain the shape of the cell by bearing the tension. 
• Their main function is to maintain the shape of the cell and provide tensile strength. 
• These are formed through the process of polymerization. 

Microtubules

• These are small hollow tubules. 
• Their walls are made up of polymerised dimers of a-tubulin and B-tubulin. 
• They have a diameter of 25 nm. They are the widest component of the cytoskeleton. 
• They help the cell resist compression, provide a track along which vesicles move through the cell and pull replicated chromosomes to opposite ends of a dividing cell. 
• Like microfilaments, microtubules can dissolve and reform quickly.