Atomic radii: The atomic radii of an atom depends on its position in the periodic table.

We can never determine the atomic radius of an atom because there is never a zero probability of finding an electron, and thus never a distinct boundary to the atom.

All that we can measure is the distance between two nuclei (internuclear distance).

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#Section 2: General Biology

Fas-L on the cytotoxic T cell binds to its receptor, the Fas protein on the tumor cells, an apoptotic signaling pathway in the tumor cells becomes activated, which also leads to tumor cell death. 

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#Section 2: General Biology

The tumor cells may acquire additional oncogenic mutations that allow them to escape the immune system.

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#Section 2: General Biology

The tumor down regulates the expression of class I MHC proteins

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#Section 2: General Biology

Sometimes the tumor cells up-regulate the expression of anti-apoptotic proteins like BCL-2.

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#Section 2: General Biology

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#Section 2: General Biology

PD-1 has a structure similar to CTLA-4 and when activated negatively regulates T-cell function by inducing apoptosis of activated T cells.