Cell Communication Ch 11 Notes

Cellular Internet  Cell to Cell communication essential for multicellular organisms  Coordinates activities of cell  Help fertilized egg to become entire organism

External Signals  Yeast  Send signal to other yeast cell for mating  Use Signal Transduction Pathway  Bacteria  Use signals for survival  Aggregate (group) with other bacteria to survive harsh conditions  Make walled fruiting body when food is scarce

Local Signaling  For cells in Direct or Close contact  Through Cell Junctions  Gap junctions – animal cells  Plasmodesmata – plant cells  Cell-Cell Recognition  Molecules on cell surface interact together

Cell-Cell Recognition Molecules on cell surface interact together (usually glycolipids and glycoproteins)

Paracrine Signaling Local regulators travel short distances Growth factor stimulates growth and division in neighbor cells Synaptic signaling Electrical signal along a nerve triggers secretion of chemical signal Neurotransmitter (chemical signal) travels across to target cell Example – animal nervous system

Long Distance Signaling Hormones travel long distances to target cells In animals – travel through blood or hemolymph In plants – travels through air (gas) or through plasmodesmata

Stages of Cell Signaling 1. Reception a. Signaling molecule binds to a protein on cell membrane 2. Transduction a. Several steps using a Signal Transduction pathway to cause changes in next molecule 3. Response a. A specific response is triggered in a cell

Reception  Receptor Proteins on or in target cell allow a response to a signal  Very specific  Signaling molecule works like a Ligand  Causes change in receptor protein

Membrane Receptors  G Protein-Coupled Receptor  Works with a G protein using GTP (like ATP but with guanine instead of adenine)  Causes 1 response only

Membrane Receptors  Receptor Tyrosine Kinases  Have Enzyme Activity  Kinase catalyzes transfer of phosphate groups  Cause MANY responses

Membrane Receptors  Ion Channel Receptors  Region that acts as a gate when receptor changes shape  When gate opens – ions move

Intracellular Receptors  Found in cytoplasm or nucleus of target cells  Must pass through plasma membrane  Hydrophobic or small molecules  Ex – Steroid Hormones like testosterone move into cell, bind to receptor in cytoplasm and move to nucleus to turn on a gene  Ex – Thyroid hormone enters cell and finds receptor in nucleus

Transduction  Usually multiple steps involved  Many activate proteins by adding phosphates  Signal can be amplified for a bigger reaction  Opportunities for coordination and regulation of cellular activities  Works using Signal Transduction Pathway  Often makes a Phosphorylation Cascade

Transduction o Protein Kinase o Enzyme that phosphorylates a protein (adds a P i ) o Changes shape of protein to activate it o Protein phosphatase o Removes a phosphate from a protein (dephosphorylate) o Inactivates a protein

Transduction – 2 nd Messengers  Small molecules and ions  Can spread rapidly through cell by diffusion

2 nd Messenger  Cyclic AMP  cAMP is made from ATP by an enzyme  cAMP activates Protein Kinase A to initiate a response in the cell  Does NOT use phosphorylation cascade

cAMP - examples  Ex – Cholera – bacteria keeps GTP stuck onto a G Protein – makes cAMP and causes constant release of salt in intestines – draw in water – give you diarrhea  Ex – Viagra  cGMP is second messenger - relaxes smooth muscles by keeping cycle on  Dilates blood vessels in all over body

2 nd Messengers  Calcium  Concentration in cytosol lower than outside cell (10000x less)  Reception signal hits cell  Activates enzyme  Makes IP3 (2 nd messenger)  IP3 connects to protein in ER  Gate opens  Ca2+ is released  Activates a protein to make a response  Ex – muscle contraction, nervous signals

Response  Signal transduction pathway leads to regulation of one or more cellular activities  Can act as a transcription factor to turn a gene on or off  Might regulate the activity of a protein  Open/close channel  Cause change in cell metabolism  Cause change in cell shape – growth of microfilaments/microtubules

Response  Amplification  Once an enzyme is activated, it can make lots of product  The more steps involved in a pathway, the more the signal can be amplified  Small amount of signal can lead to lots of response

Response  Specificity of Cell Signaling  Different cells have different collections of proteins  The response of a cell to a signal depends on the type of receptor proteins, relay proteins, and response proteins

Response  Scaffolding Proteins  Help to hold a pathway together to make it faster and more efficient

Response  Termination of the Signal  Binding of original signal is reversible  Less signal molecule = less response

Apoptosis  Programmed Cell Death  Chop DNA and fragment organelles  Cell shrinks  Parts are packaged in vesicles and digested by scavenger cells  Protects neighboring cells from damage

Apoptosis  Signal received  Starts a pathway that turns on a C death gene (Ced)  Activates a protease (eats proteins) or a nuclease (eats nucleic acids)  Signal might come from  Another cell  Nucleus if there are problems with DNA  ER if there is a protein folding problem