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Lecture 10

BIOL 151 Lecture Notes - Lecture 10: Autocrine Signalling, Transmembrane Protein, Protein Kinase A


Department
Biology
Course Code
BIOL 151
Professor
Josephbattistelli
Lecture
10

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BIOL 151 Chapter 9
9.1 Principles of Cell Communication
Cells communicate using chemical signals that bind to specific receptors
o There are four essential elements involved in communication between all cells,
whether prokaryotic or eukaryotic
Signaling Cell
Signaling Molecule
Receptor Molecule
Responding Cell
o The source of the signaling molecule, which binds to a receptor molecule on or in
the responding cell
Signaling involves receptor activation, signal transduction, response, and termination
o After a signaling molecule binds to a receptor on the responding cell, the receptor
is turned on, or Activated
o Once activated, the receptor transmits the message through the cytoplasm by
intracellular signaling in a process called Signal Transduction
The message is carried from outside the cell into the cytosol or nucleus
The initial signal is usually amplified along the way
o Afterwards, there is a cellular Response, which can take different forms
depending on the nature of the signal and the type of responding cell
o At the end, the cell with experience Termination, meaning that it will then allow
the cell to respond to new signals
9.2 Types of Cell Signaling
Endocrine signaling acts over long distances
o Endocrine Signaling: signaling by means of molecules that travel through the
bloodstream
An example of this are the mammalian steroid hormones estradiol (an
estrogen) and testosterone (an androgen)
It travels from the ovaries and tests, respectively, through the
bloodstream, to target cells in various tissues throughout the body
Paracrine and autocrine signaling act over short distances
o Paracrine Signaling: involves two cells that are close together
A signaling molecule needs to diffuse only a short distance to the nearest
neighboring cell in order to bind to its receptor and deliver its message
These molecules can travel up to 20 cell diameters
The signal is usually a small, soluble molecule, such as a Growth Factor
These factors have effects (stimulation of cell growth, cell
division, and changes in gene expression) that are confined to
neighboring cells
o Autocrine Signaling: signaling molecules that are secreted by a cell and then
bound to receptors on the very same cell
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BIOL 151 Chapter 9
o Both paracrine and autocrine signaling are ESPECIALLY important in multi-
cellular organisms
Juxtacrine signaling depends on direct cell-to-cell contact
o Contact-Dependent (Juxtacrine) Signaling: cell communication through direct
physical contact, without a chemical signal that diffuses or circulates through an
eternal medium
A transmembrane protein on the surface of one cell acts as the signaling
molecule, and a transmembrane protein on the surface of an adjacent cell
acts as the receptor
9.3 Receptors and Receptor Activation
Ligand: when the signaling molecule binds noncovalently to its appropriate and usually
highly specific receptor protein
Ligand Binding Site: the specific location that the signaling molecule binds to on the
receptor protein
Receptors can be on the cell surface or in the interior of the cell
o The location of a particular receptor in a cell depends largely on whether the
signaling molecule is polar or nonpolar
o Many proteins, like growth factors, are small, polar proteins that cannot pass
through the hydrophobic core of the plasma membrane
Receptor proteins for growth factors and other polar ligands are
transmembrane proteins with an extracellular domain, a short
transmembrane domain, and a cytoplasmic domain
o Some nonpolar signaling molecules don’t need a receptor on the cell surface in
order to relay information to the interior of the cell
An example are the steroid hormones involved in endocrine signaling
There are three major types of cell-surface receptor, which act like molecule switches
o G Protein-Coupled Receptor
This receptor couples to, or associates with, G Proteins: proteins that bind
to the guanine nucleotides GTP and GDP (almost like ATP and ADP)
When a G protein is bound to GTP, it’s active, and when a G protein is
bound to GDP, it’s inactive
o Receptor Kinase
Kinase: enzymes that add a phosphate group to another molecule in a
process called phosphorylation
Usually a protein becomes active when phosphorylated by kinase
Phosphatases: enzymes that remove a phosphate group in a process called
dephosphorylation
Proteins usually become inactive by phosphatases
o Ligand-Fated Ion Channels
They alter the flow of ions across the plasma membrane when bound by
their ligand
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