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Biology 2382B Lecture Notes - Guanine, Cyclic Adenosine Monophosphate, Transcription Preinitiation Complex

Course Code
BIOL 2382B
Jessica Kelly

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Lecture 15 Cell Signalling
Signal Transduction
Signal Transduction - taking one cellular signal and converting it into another signal
External signals external molecules/stimuli (light, neurotransmitters, GF’s, ,
cytokines, etc…)
Signal transduction plays very important roles in development and physiology of
an organism
Disruptions in normal function can result in a host of diseases and conditions
including diabetes, heart disease, & cancer
Complex mechanisms that have only recently been begun to be understood
(began to be researched heavily in 70’s and 80’s)
Phosphorylation found to play a large role in many of these pathways…
Examples of Some of The Players:
G-protein Coupled Receptors (GPCR’s)
Receptor Tyrosine Kinases (RTK’s)
Proto-oncogenes (Ras)
Mitogen Activated Protein Kinases (MAPK)

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Basic Elements of Cell Signaling
No cells live in isolation thus they must be able to communicate with one another as
well as receive & respond to signals from their environment (even single-celled
organism communicate)…this is mediated main by extracellular signaling molecules…
(heat, light, other physical signals are also used)…
Signal or Signaling molecule (ligand, primary messenger)
o Small molecules epinephrine, acetylcholine, steroids, peptides,
hormones, etc
o Large molecules growth factors, cytokines (proteins), etc…
Receptors for signaling molecules
o Cell-surface receptors -
o Intracellular receptors
Intracellular Signaling and Effector Proteins
o Perform the function of transmitting the signal inside of the cell
(i.e. G proteins, protein kinases and phosphatases, etc…)
Second messengers usually small molecule or ions involved in amplifying the
signal/aid in transmission
o Ca2+, cAMP, cGMP, IP3, DAG, NO, etc.

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Binding At Cell Surface or Intracellular
Cell-surface receptors transmembrane proteins that contain both an extracellular and
cytosolic domain
They bind hydrophilic signaling molecules that can freely diffuse in the
extracellular space but cannot pass through the PM (due to hydrophilic nature)
Mechanism must be available to transduce the signal from this molecule from the
cell surface to the inside of the cell
Carrier proteins must be used to transport small hydrophobic signaling
molecules to the PM (can’t freely diffuse through hydrophilic extracellular space)
where they can diffuse into the cell and directly transfer their signal (able to
cross PM due to hydrophobic nature)
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