Cell Biology Lecture 3

Function of Plasma Membrane Mechanical Support Cell Signaling Selective permeability Active transport Bulk Transport Metabolic activity

Signaling cell

General principle signaling 1. Synthesis of signaling molecules by the signaling cells 2. Release of signaling molecules 3. Transport of the signal to the target cell 4. Detection of a signal by a specific receptor protein present on the target cell 5. A change in cellular metabolism, function or development triggered by the receptor- signal complex 6. Removal of the signal, which often terminate the cellular response

Receptor protein exhibit ligand binding effect Receptor present on Plasma or nuclear membrane has ligand binding sites Signaling molecules (hormones, pheromones or neurotransmitters) act as ligands Confirmational change occurs in the receptor that initiate a sequence of chemical reactions Receptor proteins are specific for each horomone

Cellular responses due to cell signaling Changes in the activity or function of specific enzymes and other proteins present in the cells Changes in the amount of protein produced by a cell e.g. modification of transcription factors that stimulate or repress gene expression

Erythropoietin and formation of RBCs Optimal red blood cell (RBC) production requires both erythropoietin (as the controlling factor) and iron (as the raw material). Several factors can impair RBC production; inhibit iron availability, and/or shorten RBC life span. BFU-E, burst-forming unit erythroid; CFU-E, colony- forming unit erythroid. Uremic toxins: products of metabolism that accumulate in the body with renal failure e.g. urea, creatinine PTH: parathyroid hormone In the absence of EPO, CFU-E undergoes apoptosis

JAK/STAT pathway Mutation in EPOR leads to embryonic cell death due to severe anemia, study was conducted on mice Janus kinase (JAK) Signal Transducer and Activator of Transcription (STAT)

Types of signaling

Different cells have different sets of receptor for the same ligand and each of which induces a different response Different cells respond in a variety of way to the same ligand (e.g. acetylcholine) Different ligands can induce the same cellular response in some cells (glucagon/epinephrine) In most receptor-ligand system, the ligand do not have any function except to bind to receptor Upon binding it changes the properties of receptor which then produce signals to the cell that a specific product is present Target cells often degrade or modify the ligand to terminate or modify their response

The same signaling molecule can induce different responses in different target cells

Involvement of G- Protein in Cell Signaling

Opening of ion channels

GPCRs that activate adenylyl clase

Lecture prepared from Molecular Cell Biology, Lodish and co 5Edition, Chapter 15