Telomerase, a reverse transcriptase that contains an RNA template, repeatedly adds TTAGGG repeats

#Id: 7928

#Unit 2. Cellular Organization

Muscle cells have an abundant, modified smooth ER called the sarcoplasmic reticulum.

The release and reuptake of Ca2+ by the sarcoplasmic reticulum trigger myofibril contraction and relaxation, respectively

#Id: 7929

#Unit 2. Cellular Organization

The ER captures selected proteins from the cytosol as they are being synthesized. These are of two types:

Transmembrane proteins

Water-soluble proteins

#Id: 7930

#Unit 2. Cellular Organization

#Id: 7931

#Unit 2. Cellular Organization

#Id: 7932

#Unit 2. Cellular Organization

Signal sequence

ER targeting sequence, located at the N-terminus of the protein

#Id: 7933

#Unit 2. Cellular Organization

Signal sequences

contain one or more positively charged amino acids adjacent to a continuous stretch of 6–12 hydrophobic residues (known as the hydrophobic core)