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