CELL CONNECTIONS&COMMUNICATIONAP 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