Connections between Cells and their Environment

The Extracellular Matrix

• The protein collagen forms long collagen fibers;
• These collagen fibers are modified with carbohydrates and interwoven with proteoglycan;
• Proteoglycan is a protein heavily modified with carbohydrates and form branched proteoglycan complexes.
• ECM components attach to membrane proteins called integrins and also connects to surrounding cells.
• The ECM provides strength and structure to tissues.

Cell Junctions and Adhesions

• Gap junctions
• Tight junctions
• Desmosomes
• Plasmodesmata

Gap Junctions

• From channels between cells.
• Allows the passage of fluid and molecules between their borders through the channel.
• The channels are called connexons and each one is composed of six connexin proteins.

Tight Junctions

• Form a tight seal between cells, preventing the passage of fluids and molecules between their border.
• Cells are held together by tight junction proteins.
• Main proteins are claudins and occludins.

Desmosomes

• Form links between cells (not water tight) and give strength to tissues.
• Cadherins are proteins located on the cell membrane.
• They connect with intermediate filaments on the inside of the cells and with other cadherins on the neighbor cell.

Plasmodesmata

• Neighboring plant cells are separated by two thick cell walls and the middle lamellae.
• Plasmodesma is a channel between the cell walls of two plant cells adjacent to each other.
• Allows for the sharing of cytoplasm between plant cells.