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Gwendolyn Quintana @0118723504.18.13 Class Assignment1. Give the function of ras, raf, p53, p21. Ras proteins are proto-oncogene products that are critical components of signaling pathways leading from cell-surface receptors to the control of cellular proliferation, differentiation, or cell death.Raf proteins are a family of kinases that serve as an intermediary in transmitting extracellular signalsfrom growth factor receptors in the RAS-RAF pathway, a type of MAPK signaling pathway. This pathway controls cell growth, cell proliferation, and cell differentiation.P53 can activate DNA repair proteins when there is DNA damage. It can induce growth arrest by holding the cell cycle at G1/S regulation point on DNA damage recognition. It can also initiate apoptosis, the programmed cell death, if DNA damage proves to be irreparable. P21 can bind to and inhibit the activity of cyclinCDK2 or CDK1 complexes and so functions as a regulator of cell cycle progression at G1. Its expression is controlled by P53. It can also interact with proliferating cell nuclear antigen and polymerase necessary factor and play a necessary role in S phase DNA replication and DNA damage repair. 2. Explain how cells determine whether they go from G1 to G0 of G1 to S. In most cells, checkpoints in the cell cycle prevent a cell from entering one phase if the events ofthe preceding phase have not been completed. At the G1 checkpoint, the cell checks for damaged DNA. Arrest at the G1 checkpoint allows repair of the damage to take place before the cell enters S phase, where the damaged DNA would be replicated. The S point checkpoint provides continual monitoring of the integrity of DNA to ensure that damaged DNA is repaired before it is replicated. In addition, the S phase checkpoint provides a quality control monitor to promote the repair of any errors that occur during DNA replication, such as the incorporation of incorrect bases or incomplete replication of segments of DNA. A DNA damage checkpoint is G2 also leads to the cell cycle arrest in response to unreplicated or damaged DNA. This checkpoint prevents the initiation of mitosis until DNA replication is completed. Another checkpoint, called the spindle assembly checkpoint, arrest mitosis of the chromosomes are not properly aligned onthe mitotic spindle and therefore not organized for equal distribution to daughter cells. These cell cycle checkpoints function to ensure that complete genomes are transmitted to daughter cells. 3. Trace the steps in cytokinesis. Cytokinesis in plant cells is different from that in animal cells. In early telophase in plants, vesicles carrying cell wall precursors from the golgi associate with remnants of the spindle microtubules and accumulate t the former site of the metaphase plate. These vesicles then fuse to form a large, membrane-enclose, dislike structure, and their polysaccharide contents assemble to form the matrix of new cell wall, called a cell plate. The cell plate expands outward,perpendicular to the spindle, until it reaches the plasma membrane. The membrane surroundingthe cell then fuses with the parental plasma membrane, dividing the cell in two. Connections, called plasmodesmata, between the daughter cells are formed as a result of incomplete vesicle fusion during cytokinesis. 4. Define and differentiae an oncogene and a tumor suppressor. Give examples of each. Tumor suppressor turn OFF or DECREASE the rate of cell division, repair DNA mistakes and play a role in apoptosis. If these genes mutate or are inactivated, cells pass through the checkpoints and divide in an uncontrolled manner, which may lead to abnormal cell growth and defective apoptosis -all which can cause cancer. P 53An oncogene does not respond to normal growth restraints, leading to uncontrolled cell proliferation. When a mutation occurs in a proto-oncogene that permanently "turns it on" it can become an oncogene. Ex. Mdm2.An important difference between oncogenes and tumor suppressor genes is that oncogenes result from the activation (turning on) of proto- oncogenes, but tumor suppressor genes cause cancer when they are inactivated (turned

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UTSA CLA 2033 - Class Assignment

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