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Biol 212 Cell Signaling Notes
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Detailed and Easy to follow notes on Cell Signaling and Signal Transduction: Communication between Cells. *Essential Study Material!!
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Cell Signaling and Signal Transduction: Communication between Cells Cells must respond adequately to external stimuli to survive via cell signaling
Cell signaling
o Involved in the regulation of cell growth and division
o Affects virtually every aspect of cell structure and
function
o Signal molecules enter cells or bind to surface
receptors
Cells can only respond to a signal if they posses the correct
receptor
o Extracellular signals may bind to cell-surface
receptors or intracellular receptors
**NOTE CHECK**
o Define:
Receptor:
Second messenger:
Effector:
GPCR:
o What are some classes of proteins common to signaling cascades?
o What are some typical outcomes of signaling cascades?
Basic elements of cell signaling systems
o Extracellular messenger molecules: transmit messages between cells
Types of signaling:
o (a) Autocrine: the cell has receptors on its surface that respond to the messenger
o (b) Paracrine: messenger molecules travel short distances through extracellular
space
o (c)Endocrine: messenger molecules reach their target cells through the
bloodstream
Receptors on or in target cells receive the message. Two major routes or mechanisms by
which the signal is transmitted to the cell interior, in general.
o Some cell surface receptors generate an intracellular second messenger through
an enzyme called an effector.
o Other surface receptors recruit proteins to their intracellular domains.
, 2 types of signaling pathways: General Properties
o Overview of the major signaling pathways by which extracellular messenger
molecules can elicit intracellular responses
Two types of pathways
1) a signaling pathway is activated by a diffusible second
messenger
2) signaling pathway is activated by recruitment of proteins to the
plasma membrane
**most involved a combination of these mechanisms
They are not linear tracts—but are branched and interconnected to form
a complex web (refer to text)
Signal transduction via a kinase cascade system
o Signaling pathways consist of a series of proteins.
Each protein in a pathway alters the conformation of the next protein.
Protein conformation is usually altered by phosphorylation.
Kinases add phosphate groups while phosphatases remove them.
Target proteins ultimately receive a message to alter cell activity.
This overall process is called signal
transduction.
Referring to the figure to the right
o protein kinase 2 is activated by protein kinase 1.
o Once activated, protein kinase 2 phosphorylates
protein kinase 3, activating the enzyme.
o Protein kinase 3 then phosphorylates a
transcription factor, increasing its affinity for a site
on the DNA.
o Binding of a transcription factor to the DNA
affects the transcription of the gene in question.
Each of these activation steps in the pathway is
reversed by a phosphatase.
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