What are the primary mediators that determine if a cell will proceed through the cell cycle or arrest? G proteins and G protein coupled receptors B microtubules and actin claudins and occludins cyclins and cyclin-dependent kinases @ the Map kinases pathway Some necessary cellular reactions are energetically unfavorable, that is, they have a positive delta G. Within a cell, how can these be made to occur? they only occur when the cell heats up reactions with a positive delta G only occur in cancer cells or diseased cells they are coupled to favorable reactions with a negative delta G and common intermediates reactions with a positive delta G never occur in cells they only occur when there are very few reactants available Many cancer cells have abnormal numbers of chromosomes or chromosome instability. What is the most likely explanation? A they have mutations in genes that result in synthesis of multiple copies of chromosomes before dividing cancers that are caused by viruses will have viral chromosomes that attach to human chromosomes, which will activate viral replication of all chromosomes they have mutations in genes that cause them to divide before replicating DNA they have mutations in genes that arrest cells the spindle assembly checkpoint, so cells can proliferate without segregating the proper number of chromosomes cancer cells tend to fuse back together after dividing, doubling the DNA content each time

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