There are 4 genes (I, Z, Y, A), 2 Promoters and 3 lac operators in Lac operon

The major O1 lac operator lies adjacent to promoter

The O1 operator extends from position -5 just upstream of the mRNA start point to position +21 within the transcription unit.

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#Unit 4. Cell Communication and Cell Signaling

CAMs fall into one of four major families: 

Cadherins

Immunoglobulin (Ig) superfamily

Integrins

Selectins

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The adhesiveness of cadherins depends on the presence of extracellular Ca2+

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#Unit 4. Cell Communication and Cell Signaling

Two type of Cadherins:

1. Classical cadherin proteins

2. Nonclassical cadherin proteins

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#Unit 4. Cell Communication and Cell Signaling

Extracellular region of a classical cadherin contains five copies of the cadherin domain separated by flexible hinge regions

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Ca2+ ions bind to sites near each hinge and prevent it

from flexing, so that the whole string of cadherin domains behaves as a rigid and slightly curved rod to generate cell–cell adhesion

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In absence of Ca2+, 

the hinges can flex, the structure becomes floppy & adhesion fails