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Cell Biology
Lecture 3
Function of Plasma Membrane
Mechanical Support
 Cell Signaling
 Selective permeability
 Active transport
 Bulk Transport
 Metabolic activity
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Signaling cell
General principle signaling
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Synthesis of signaling molecules by the
signaling cells
Release of signaling molecules
Transport of the signal to the target cell
Detection of a signal by a specific receptor
protein present on the target cell
A change in cellular metabolism, function
or development triggered by the receptorsignal complex
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
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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
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Erythropoietin and formation of RBCs
In the absence of EPO, CFU-E undergoes apoptosis
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, colonyforming unit erythroid.
Uremic toxins: products of metabolism that accumulate in the body with renal failure e.g. urea,
creatinine
PTH: parathyroid hormone
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
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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
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Molecular Cell Biology, Lodish and co
5Edition, Chapter 15