The site of cleavage/polyadenylation in most pre-mRNAs is flanked by two cis-acting signals:  An upstream AAUAAA motif, which is usually located 11 to 30 nucleotides from the site, and  A downstream U-rich or GU-rich element. 

he AAUAAA is needed for cleavage and polyadenylation because deletion or mutation of the AAUAAA hexamer prevents generation of the polyadenylated 3’ end

TLS Online TPP Program

#Id: 2246

#Unit 11. Evolution and Behavior

Some people have an allele called Δ32 at the CCR5 locus in which 32 bp are deleted.

CCR5 that plays a role in inflammatory response. Unfortunately, this protein is also a key to human immunodeficiency virus (HIV) infection. The virus binds to a loop of the CCR5 protein and then enters the cell.

The missing part of the gene codes for the loop in the protein to which the virus attaches. 

TLS Online TPP Program

#Id: 6366

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 1765

#Unit 4. Cell Communication and Cell Signaling

The possibility of damage from self-reactive lymphocytes is further limited by the life span of activated lymphocytes, which is regulated by programs that induce cell death (apoptosis).

TLS Online TPP Program

#Id: 8762

#Unit 1. Molecules and their Interaction Relevant to Biology

Thermostable proteins have such a high incidence of salt bridges.

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#Id: 5286

#Unit 7. System Physiology – Animal

When the cholinergic vagal fibers to nodal tissue are stimulated, the membrane becomes hyperpolarized and the slope of the prepotentials is decreased