15. What is meant by the term signal transduction? (5 marks) 16. Normal cells gr
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15. What is meant by the term signal transduction? (5 marks) 16. Normal cells greatly slow their rates of cell division after filling a culture dish with a layer that is one cell deep (a monolayer). If a circular group of cells is removed from the middle of the filled culture dish, the cells on the edges of the ''wound'' will begin to divide, fill the space, and then stop dividing again. How is the behaviour of transformed cells different from that? (6 marks) 17. Assume that a signalling pathway in the cell is initially triggered by protein phosphorylation, leading to decreases in cell division. What would be the effect of a mutation that results in the overexpression of an oncogene coding for a protein phosphatase that works at the same step in this pathway? (6 marks)Explanation / Answer
15.
Signal transduction: It is transmission of molecular signals from a cells exterior to cell interior, to activate or inactivate a specific gene expression. Signal transduction involves the following:
Cytoplasmic proteins or polypeptides that are associated with cytoplasmic domains of the receptor
Cytoplasmic domains of receptors are associated with proteins that are in their inactive or pro-enzyme form. When a ligand binds to its receptor, cross-linking of receptor with ligand brings the cytoplasmic proteins close together, and they mutually activate one another by means of phosphorylation (mostly involves phosphorylation of tyrosine) (such motifs are called receptor tyrosine based activation motifs). Phosphorylation of these attached proteins triggers a cascade of events, which involves activation/deactivation of a series of proteins. Ultimately, this leads to activation of a transcription factor in the cytoplasm, which enter nucleus, and initiates or inhibits expression of a gene or a set of genes.
16.
Transformed cells do not show adherence dependence, they do not show contact inhibition. Transformed cells grow as suspension cultures.
17.
There will be tremendous decrease in cell division, as there is high level of phosphorylation.
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