Cell Signalling and Signal Transduction: Chapter 10
Cell Signaling and Signal Transduction
-Extracellular messenger molecules communicate between cells
-Messengers can travel short distances and stimulate close cells, or they can travel through the body to
stimulate cells that are farther away
-Many different ways for cells to signal:
Autocrine Signalling occurs when the cell producing the messenger expresses receptors to respond to the
Paracrine signaling is more limited as they cannot travel as far and may be unstable
Endocrine signalling is when the messenger molecules reach target cells through the bloodstream. These
messengers are called hormones and they act on target cells
-Cells can only respond to extracellular messages if they have receptors that will recognize and bind to the
messenger molecule. The molecule that binds to the receptor is a ligand.
-Activities a cell engages in depends on stimuli as well as intracellular machinery.
-Two major routes of signalling for cells:
Type One: A receptor sends a signal to an enzyme which sends a secondary messenger which will activate
or inactivate specific proteins.
Type Two: Receptor will send a signal by transforming the cytoplasmic domain into a station for proteins to
interact with each other.
-Alterations to signaling proteins are often caused by protein kinases or phosphatases which add or remove
phosphate groups from proteins
-Protein phosphorylation changes protein behaviour by activating or inactivating an enzyme, increasing or
decreasing protein-protein interactions, inducing a protein to move from one compartment to another
initiating protein degradation.
Signal transduction is defined by the way information carried by extracellular messenger molecules is
translated into changes within a cell. Almost all activity a cell engages in is from signals originating on its
-Large variety of molecules can be carriers of information such as:
Amino acids and their derivatives: Neurotransmitters and hormones
Gases: NO, CO
Steroids: Made from cholesterol
Eicosanoids: non polar molecules from fatty acid which regulates pain, inflammation, blood clotting etc.
Polypeptides and proteins
-Receptors that mediate signal transduction are:
G-protein coupled receptors: Huge family containing trans membrane helices which activate GTP binding
proteins that are responsible for many processes.
Receptor protein tyrosine kinases
Ligand gated channels: Conduct flow of ions are membrane Steroid hormone receptors: increases or decreases gene transcription rate
B and T Cell receptor: Involved in foreign antigen response
Apoptosis: Programmed Cell Death
-Different from necrosis which is cell death by trauma or biochemical insult. Necrosis causes swelling of
cell and organelles, leaking of contents and inflammation.
-Apoptosis is involved in the elimination of cells that have genomic damage which is important as if
these cells are not eliminated, unregulated cell division and cancer may occur
-Caspases are activated early on in apoptosis and trigger most of the changes that cause cell death
Intrinsic pathway of apoptosis: Internal stimuli, such as genetic damage, lack of oxygen, high