Our muscles are made of long chains of cytoskeleton comprised of two filaments – actin and myosin. Of these, actin is a microfilament, while myosin is a motor protein. If actin degenerates, then our muscles would not contract, thus, our answer is E. The spindle fibers radiating from the centrioles are microtubules. A lysosome is an organelle that is involved in phagocytosis. The extracellular matrix consists of protein fibers and glycosaminoglycans. Chromosomes are made of nucleic acids.

A.Spindle fibers radiating from centrioles
The spindle fibers radiating from centrioles are composed primarily of microtubules, and not microfilaments; therefore the answer choice is incorrect. While similar in name, these are completely separate structural units that should not be confused. To test your knowledge, it may be helpful to now ask yourself which stage of the cell cycle would be disrupted if the question had instead asked about a toxin that promotes the degeneration of microtubules during cell division. These microtubules shorten during anaphase, which causes chromosomes to be pulled apart into separate chromatids.

B. Lysosomes
Lysosomes are vesicles produced from the Golgi that contain digestive enzymes for breaking down nutrients, cell debris, and bacteria. These activities do not rely upon microfilaments; therefore the answer choice is incorrect. In plants, the central vacuole is known to carry out functions performed by the lysosome.

C. The extracellular matrix
The extracellular matrix, found in the area between adjacent animal cells (beyond the plasma membrane and glycocalyx), does not contain a significant amount of microfilaments; therefore the answer choice is incorrect. This answer may have been tempting to choose because it contains many structural proteins (most abundantly collagen, in addition to proteoglycans and fibronectin). However, none of these structural proteins are composed of microfilaments. The extracellular matrix primarily functions to provide mechanical support and helps bind adjacent cells.

D. Chromosomes
A chromosome is composed of tightly condensed chromatin, which is the general packaging of DNA around proteins in eukaryotes. Microfilament is a component of neither DNA nor the histone proteins that DNA wraps around; therefore the answer choice is incorrect. Knowing the structure, components, and packaging of a chromosome is important for the DAT!

E. Muscle cells
Microfilaments are primarily made of actin filaments and are primarily involved in motility. Substantial amounts can be found in skeletal muscle (where microfilaments are a key component of the sliding filament model of contraction), the pseudopod of amoeba (used for cell motility), and the cleavage furrow during animal cell division (actin and myosin microfilaments shorten and pull the plasma membrane towards the center of the cell); therefore the answer choice is correct. Microfilaments, along with microtubules and intermediate filaments, are key components of the cell’s cytoskeleton.