An experiment was performed to study the progress of cells through the mitotic cell cycle. The compounds listed below were used individually to study their effects on the cell cycle. The cells on the left are examples of the cells at the beginning of the experiment. The cells at the right are representatives of three different experimental treatments using the compounds listed below. a. cytochalasin: b. an inhibitor of actin microfilament assembly colchicine: c. an inhibitor of microtubule formation aphidicolin: d. an inhibitor of DNA polymerase activity emetine: e. an inhibitor of ribosome activity (and therefore protein synthesis)

Mitotic Cell Cycle

Explanation:

a. Cytochalasin: an inhibitor of actin microfilament

Cytokinesis is the process by which cytoplasm is divided into two cells hence generation of two daughter cells In animal cells the division of cytoplasm starts with the assembly of contractile ring Contractile band consists of actin and myosin and catalyze cleavage furrow formation Cytochalasin is a drug that blocks the polymerization of actin filament When cytochalasin is added dividing cell fails to undergo in cytokinesis due to defective assembly of contractile band

b. Colchicine: an inhibitor of microtubule formation

Colchicine tightly binds with free tubulin dimer and prevents its polymerization In this case mitotic spindle apparatus do not assemble and cells unable to do partitioning of chromosomes into two groups Thus cell division is arrested

c. Aphidicolin: an inhibitor of DNA Polymerase activity

Aphidicolin is used to induce cell cycle arrest via specific inhibition of DNA Polymerase α It blocks the cell cycle at early synthesis (S) phase

d. Emetine: an inhibitor of ribosome activity

It blocks the protein synthesis in eukaryotic cells by binding to small subunit (40 S) of ribosomes It interferes with the synthesis and activities of DNA and RNA