Cell Communication & Cell Junctions

Located within the epithelia (between epithelial cells, seal adjacent epithelial cells and prevent molecule and ions to pass, cell membranes are connected by transmembrane proteins (protein strands)

interact with each other in intercellular matrix, act like rivets and keep cells together, keratin fibres (interact with intracellular matrix) and partially embedded proteins

span between to adjacent cell membranes, let water and small dissolved molecule pass ,specialised protein channels (connexins) composed of 5 subunits,

Consists of pores or channels between plant cells, create gaps that connect plant cells, allows molecules and substances to move between adjacent cells, desmotubule (ER that links cells together)

Surface of the plasma membrane that faces towards the lumen, tight junctions seal adjacent epithelial cells underneath the apical surface

oriented away from the lumen (cell membrane)

attached to underlying tissue, ???

specialised for interaction, "sticky" carbohydrate section sticks out the PM to connect to other molecules and is anchored in the PM and able to move around on lipid layer

Glycoproteins in membranes, collectively secrete enzymes, produce antibiotics, bioluminesence

1.Bacteria synthesizes molecules and sectrete into medium

2.Need glycoproteins to interact with ligands (recognition)

3.Response to this interaction

1. Receptor-ligand binding (ligands = molecule with -amine-group -> peptides, sterioids and nucleotides (a lot of hydrophobic regions and carbohydrate groups)

2. Signal transduction (transducer molecule with active and inactive site)

3. Short term cellular responses (increased enzyme activation or cellular movrement)

OR

4. Long term activity -> causes change in DNA transcription

Molecules alter from active to inactive (or the opposite)  by adding or removing a phosphate group from nucleotides (like ATP or GDP in the cell)  

Enzyme which adds a phosphate 

Enzyme which removes phosphate 

If ATP gives away a phosphate group it becomes ADP 

Some proteins are activated by adding a phosphate group and inactivated by removing a phosphate group. Others are activated by removing the phosphate group and inactivated by adding a phosphate group

Small or non-polar ligand cross the membrane and interact with receptor in the cytoplasm 

Large and polar ligands can't cross membrane -> bind to transmembrane proteins with a extracellular binding region

Ion channel receptors, g-protein coupled receptors, protein kinases

Only opens when a ligand binds to it -> causes conformational change -> enables ions to diffuse through the channel

1.GPCR is inactive when g protein is GDP bound 

2. Signalling molecule binds to GPCR to activate g-protein

3. G-protein binds to GPCR and nucleotide exchange of swapping GDP with GTP (activates g-protein)

4. Active g-protein binds to inactive enzyme -> causes cellular response

Phosphorelation of proteins to activate or deactivate them -> incstructs cell to do work (grow, divide)

Related to glands which secrete hormones or other products directly in the bloodstream

Relating to a hormone which only affect adjactent parts near the gland

Relating to a cell-produced substance that only has an effect on the cell by which it is secreted (auto=self)

Signal cell = target cell

signalling via neurons to the target cells

Target cell is local to target cell 

Target cells have fix ligand in membrane which binds to membrane bound receptor of signalling cell