Spindle fibers are made up of
A. Proteins
B. Cellulose
C. Lipids
D. Pectin

Hint: They help in maintaining the structure of the cell along with microfilaments and intermediate filaments and hold the chromosomes in place.

Complete answer:
The spindle fibers are also called the mitotic spindle. It refers to the cytoskeletal structure of eukaryotic cells that forms using division to separate sister chromatids between daughter cells. They are composed of proteins called microtubules.

Additional Information: -Spindle fibers are the thread-like structure made up of numerous microtubules.
-Microtubules are the polymers of tubulin that form part of the cytoskeletal and provide structure and shape to eukaryotic cells.
-Microtubules also make up the internal structure of cilia and flagella.
-Microtubule is a type of cytoskeletal protein made of protein subunits called tubulin.
-The attachment of microtubules to chromosomes is structured by kinetochores.
-The microtubules are originated from the centrioles during cell division and help in the movement of chromosomes towards the pole.
-They provide the rigid, organized components of the cytoskeletal that give shape to many cells.
-Microtubules can grow as long as 50 micrometers and are highly dynamic.
So, the correct answer is ‘Proteins’.


Note: A kinetochore is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. They are important elements of a mitotic checkpoint. Proteins are the basic building block of the human body which is composed of amino acids. Cellulose is the substance that is found mainly in the cell walls which makes the cell walls hard, stiff, and rigid. It prevents the cell from breakage when the osmotic pressure is high. Pectin is a heteropolysaccharide that is found in the various layers of the cell wall, especially the middle layer and the primary wall. Lipids are the main component of which the body is composed of. It comprises various hormones, vitamins, fats, etc.