Module 4

6. In animal cells a cleavage furrow forms during cytokinesis. While in plant cells a cell plate forms in the middle of the cell. The furrow in animal cells is a contractile ring of actin microfilaments associated with molecules of the protein myosin. Action reacts with myosin causing ring to contract. The furrow deepens until parent cell divides into two producing two separate cells with their own nucleus and share of cytosol, organelles, and other subcellular structures. In plant cells vesicles from the Golgi apparatus move along the microtubules to the middle of the cell, where they coalesce, producing a cell plate. The plate enlarges until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell. Two daughter cells result, each with its own plasma membrane. Meanwhile, a new cell wall arising from the contents of the cell plate has formed between the daughter cells.

7. Eukaryotic cells have a true nucleus, bound by a double membrane Prokaryotic cells have no nucleus. Eukaryotic DNA is linear; prokaryotic DNA is circular (it has no ends). Eukaryotes go through every phase of Mitosis including prophase, metaphase, anaphase, and telophase. Prokaryotic cell simply divides by cytokinesis after DNA replication which is known as binary fission.

8. Checkpoints make sure that the eukaryotic cell completes each phase with no problems. Without checkpoints it may affect cell growth which is very important.

9. The Hershey-Chase experiments by Alfred Hershey and Martha Chase helped confirm DNA as genetic material. Using bacteriophages, Hershey and Chase added radioactive elements into the bacteriophages by adding the isotopes. The phage coats remained on the outside of the bacteria, while genetic material entered. Centrifugation allowed for the separation of the phage coats from the bacteria. These bacteria were lysed to