Question

Cancer cells grow uncontrollably and do not die. Do you think that the following defect would lead to a cancerous cell phenotype?  

"A gain of function mutation in growth factor signaling pathway RTK that causes constitutive (constant) kinase activity"

"A p53 protein that cannot be imported into the nucleus."

"A deletion of the polyadenylation signal sequence in the gene of growth factor signaling pathway protein TFa."

"A deletion in the TATA box in the promoter for the CDK inhibitor gene."

"The DNA in the region of the Rb gene is highly methylated and the histone tails are not acetylated."

"A frameshift mutation early in the protein coding region in the gene for G1 cyclin."

Answer 1

Cancer cells grow uncontrollably and do not die. Do you think that the following defect would lead to a cancerous cell phenotype?  

"A gain of function mutation in growth factor signaling pathway RTK that causes constitutive (constant) kinase activity"

RTK or receptor tyrosine kinases are involved in cell grwoth and development. Their signaling has to be regulated otherwise uncontrolled cell growth will result. A constitutively active RTK means that it will result in uncontrolled cell growth leading to cancerous phenotype.

"A p53 protein that cannot be imported into the nucleus."

p53 is a transcription factor that has tumor suppressor function. If it cannot be imported in to nucleus it cannot function as a transcription factor thus loosing its tumor suppressor function leading to cancerous phenotype.

"A deletion of the polyadenylation signal sequence in the gene of growth factor signaling pathway protein TFa."

A deletion of polyadenylation signal in the gene means that mRNA of that gene will be unstable, and will not lead to translation of the mRNA and the protein TFa will not be produced by the cell. Given that TFa is a gene in growth factor signaling, lack of TFa protein will result in inhibition of cell growth and division. This will lead to programmed cell death or cell cycle arrest and not to any cancerous phenotype.
"A deletion in the TATA box in the promoter for the CDK inhibitor gene."

CDK or cyclin dependent kinases are important proteins involved in cell cycle regulation. Their epression needs to be in check to controll every phase of cell cycle other wise check points in cell cyle to repair DNA damages will be affected. This function of keeping the CDK activity in check is done by CDK inhibitors. Hence a deletion of TATA box of CDK inhibitor gene will result in non expression of this inhibitor protein leading to accumulation of mutation, uncontrolled cell growth and cancer.

"The DNA in the region of the Rb gene is highly methylated and the histone tails are not acetylated."

This will read to non expression of Rb protein which is a tumor supressor. Lack of Rb protein will lead to retinoblastoma a cancer of the retina of the eye.

"A frameshift mutation early in the protein coding region in the gene for G1 cyclin."

This mutation will lead to an entirely different protein instead of G1 cyclin. and in the presence of a non functional G1 cyclin the cell cannot move into G1 phase and it will be arrested in G0 phase. This will not lead to any cancerous phenotype.

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