CELL JUNCTIONS AND BASEMENT MEMBRANE

What is epithelial tissue?

A body tissue that covers the body surface, lines hollow organs, cavities and ducts and forms the glands of the body

What are the key functions of epithelial tissues?

Selective barriers (limit or aid transfer)

Secretory (onto a free surface)

Protective (especially from abrasion)

What type of cell junction is this?

Tight

What type of cell junction is this?

Adherens

What type of cell junction is this?

Desmosome

What type of cell junction is this?

Gap

What type of cell junction is this?

Hemidesmosome

What is the function of a tight junction?

Holds membranes of cells together tightly

Prevents ions and other molecules pass down between the cells in an uncontrolled way

Where are the tight junctions located on the cell?

Near the apical section

What are the proteins that bind and sew the membranes together tightly?

Claudins and occludins

What does the orientation of tight junctions allow?

Allows polarity - cell can have different functions at top vs bottom as the environment is controlled

Describe the structure of adherens junction

Plaque of proteins forms linear structure that traverses around the cell and provides belt like interaction between the 2 cells

Protein structure spans the gap

Where are adherens junctions located?

more basal than tight junctions

What is the protein bridge in adherens junctions?

cadherins

What protein does the cadherins protein bridge link to in adherens junctions?

catenin

What does catenin do in adherins junctions?

locks cadherin to actin (microfillaments)

What is the function of adherens junction?

Locks cells cytoskeletons together - keeps structure and resists tension

What is the function of demosome junction?

Where are desmosome junctions located

What is the structure of desmosome?

plaque of proteins like adherens junctions

isolated points of contact between the cells (more discrete)

What proteins spans the gap in desmosome junctions?

cadherin

What does cadherin bind to in desmosome junctions?

desmoplakin

What does desmoplakin lock into in desmosome junctions?

keratin (intermediate filaments)

What is the function of desmosome junctions?

Security of cell

What is the function of the gap junction?

coordinated communication between cells

allows ions, RNA etc to pass between cells

What are gap junctions made of?

6 proteins - each called a connexin (6 together = connexon/hemichannel)

2 hemichannels make up a gap junction

Describe how gap junctions form

hemichannels will form in cell membranes

they migrate around the membrane until they find another on a different cell

dock together on a chemical level

forms an opening between the cells - has special molecules that control what goes between cells (RNA, ions)

What is the function of hemidesmosome?

connect epithelial cells to basement membrane

locks cytoskeleton of cells onto basement membrane

Where are hemidesmosome located?

basal layer of cell/bottom

What protein spans the gap of hemidesmosome junctions?

integrin

What does the protein spanning the gap of hemidesmosomes bind to?

laminin in basement mebrane

What is the basement membrane made of?

Basal lamina and reticular lamina

What is the basal lamina secreted by?

epithelial cells

What is the reticular laminar made by?

cells of underlying connective tissues known as fibroblasts

Where is the basement membrane located?

between epithelial and connective tissue

What is the function of basement membrane?

diffusion - allows oxygen and nutrients to diffuse through it to epithelia.

supports epithelium

provides a surface along which epithelial cells migrate during growth and wound healing