Dosage compensation

Equalization in males and females of the amount of protein produced by X-linked genes.

Each female cell one of the two X chromosome becomes inactive. Which X chromosome is inactivated is random.

The Xist (X inactive specific transcript) gene located on the X chromosome, in required for inactivation. 

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#Id: 3239

#Unit 4. Cell Communication and Cell Signaling

miR-21 targets tumor-suppressor gene PTEN phosphatase

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#Id: 10390

#Unit 4. Cell Communication and Cell Signaling

Four stages of the evolutionary progression of cancer:

Initiation→Cancer progression → Evasion of cancer cell elimination  → Tumor growth and dispersal 

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#Unit 4. Cell Communication and Cell Signaling

Cancer cells 

acquire a drive to proliferate 

does not require an external inducing signal

fail to sense signals that restrict cell division

survive when they should die

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#Unit 4. Cell Communication and Cell Signaling

Tumors are detected only after they have reached 1cm3 in size.

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#Id: 10393

#Unit 4. Cell Communication and Cell Signaling

Precancerous cells have: 

lost contact inhibition

less adherent and more rounded than normal cells

continue to divide

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#Id: 10394

#Unit 4. Cell Communication and Cell Signaling

Malignant tumors are classified by their embryonic

tissue of origin:

Carcinomas -derive from epithelia such as endoderm

(gut epithelium) or ectoderm (skin and neural epithelia) 

Sarcomas - derive from mesoderm (muscle, blood, and

connective tissue precursors)