SA node has an unstable resting membrane potential.

The “resting membrane potential” of the sinus nodal fiber between discharges has a negativity of about −55 to −60 millivolts.

TLS Online TPP Program

#Id: 7927

#Unit 2. Cellular Organization

Function of the ER:

most eukaryotic cells is to sequester Ca2+ from the cytosol (High concentration of Ca2+-binding proteins in the ER facilitates Ca2+ storage)

TLS Online TPP Program

#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

TLS Online TPP Program

#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

TLS Online TPP Program

#Id: 7930

#Unit 2. Cellular Organization

Secretory pathway

pathway of protein trafficking that flows through the ER

TLS Online TPP Program

#Id: 7931

#Unit 2. Cellular Organization

Microsomes

when cells are homogenized, the rough ER breaks up into small closed vesicles with ribosomes on the outside

TLS Online TPP Program

#Id: 7932

#Unit 2. Cellular Organization

Signal sequence

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