CELL CONNECTIONS & COMMUNICATION AP Biology Ch.6.7; Ch. 11

Intercellular Junctions Multicellular organisms have cells neighboring other cells Cells interact!!!

Plasmodesmata (plant cells) In plant cells, channels that connect cells Pass chemicals along Water Small solutes (glucose)

Tight Junctions (animal cells) Specific proteins tightly bind cells Function: prevent leakage

Desmosomes (animal cells) Anchor cells together Function: create strong sheets of cells

Gap Junctions (animal cells) Channels connecting cells Function: pass chemicals along

Cell Communication It’s easy to communicate when you are next to the cell you need to communicate with but… Multicellular organisms need to be able to communicate long distance Example: hormones

Signal Transduction Pathway Reception – cell receives signal Transduction – cell transfers signal to nucleus Response – cell responds

recognition Performed by receptors Ligand will produce response only in cells that have receptors for that particular ligand Each cell has a specific set of receptors

Transduction Activated receptor interacts with other intracellular signaling molecules and Directly changes cellular activity OR Produces some intermediates (secondary messengers) that change cellular activity

Response Ensures that crucial activities occur in the right cell at the right time and in proper coordination with other cells Examples: Metabolism Gene expression Growth and differentiation (cell cycle) Secretion of proteins Structure (cytoskeleton rearrangement)

Extracellular Signal Found on cell membrane For molecules that cannot cross the membrane It can’t work if it can’t get in, but it can send a messenger When activated, a receptor on the surface “passes” the signal to messengers inside the cell

Second messengers Molecules inside a cell that: Change of function of the cell Signal to the nucleus for genomic effects

Signaling strategies G protein-coupled receptors Activate intracellular second messengers

Signaling strategies Ion channels receptors Ligand gated ion channels

Signaling strategies Receptor tyrosine kinases Uses kinase enzymes to transfer phosphate groups Phosphate groups activate receptor Relay proteins recognize activation Transduction pathway triggered

Intracellular Signal For molecules that can cross the cell membrane and enter the cell Found in cytoplasm or on nucleus Initiate transcription factors Control if genes are “on” or “off” Examples: steroid hormones