Cell Biology: Gap Junctions

What are communicating junctions primarily responsible for?

Which of the following is true about gap junctions?

How is the diameter of the channels in gap junctions regulated?

What is the main function of chemical synapses?

What is the size of the intercellular space at gap junctions?

What do connexins or connexons comprise in gap junctions?

Which substances can pass through gap junctions?

What happens to the diameter of gap junction channels when intracellular calcium concentration increases?

Communicating Junctions

Permits intercellular exchange of ions and molecules.
Includes gap junctions and chemical synapses.

Gap Junctions

Also known as nexus.
Facilitate direct passage of ions and smaller molecules between adjacent cells.
Found in the heart and basal epithelial cells of the intestinal mucosa.

Structure of Gap Junctions

Membranes of adjacent cells are closely aligned, reducing the intercellular space to 2.5 to 3 nm.
Cytoplasm of cells is interconnected via channels formed by membrane proteins.
Channel structure consists of two halves, each made of six protein subunits called connexins or connexons.
Channel diameter ranges from 1.5 to 3 nm, allowing passage of substances with molecular weight less than 1,000.

Functions of Gap Junctions

Enables exchange of chemical messengers between cells.
Facilitates rapid propagation of action potentials between cells.
Diameter of the channel is regulated by intracellular calcium ion concentration, pH levels, electrical potential, hormones, and neurotransmitters.

Chemical Synapse

Junction between a nerve fiber and a muscle fiber or between two nerve fibers.
Signal transmission occurs through the release of chemical transmitters.

This quiz covers the concept of cell junctions, specifically focusing on communicating junctions like gap junctions. You'll learn about their structure, function, and significance in intercellular communication, particularly in tissues such as the heart and intestines.