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Cell BiologyLecture 3
Function of Plasma MembraneMechanical SupportCell SignalingSelective permeabilityActive transportBulk TransportMetabolic activity
Signaling cell
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General principle signaling1. Synthesis of signaling molecules by the
signaling cells2. Release of signaling molecules3. Transport of the signal to the target cell4. Detection of a signal by a specific
receptor protein present on the target cell5. 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 effectReceptor present on Plasma or nuclear
membrane has ligand binding sitesSignaling 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 signalingChanges 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, creatininePTH: parathyroid hormone
In the absence of EPO, CFU-E undergoes apoptosis
JAK/STAT pathwayMutation 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
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