Lecture 6 Flashcards
Common Types of Cell-to-Cell Signaling
- Direct intercellular signaling via cell junctions
- Contact dependent signaling
- Local signaling (autocrine and paracrine
signaling) - Long-distance signaling (endocrine, aka
hormonal signaling)
Direct
Signaling
- Direct cytoplasmic
connection - Mediated by
proteins - Almost universal
in multicellular
tissues
– Exception:
skeletal muscle
Contact Signaling
Cells must have membrane-membrane contact
Cell attached molecules
Used in immune system
Local Signaling
- Autocrine: affects BOTH themselves and nearby target cells.
- Paracrine: affects nearby target cells, but NOT themselves.
– Synaptic signaling: a specialized paracrine signal unique to
nerve cells, stimulate another nerve or muscle cell.
Four Categories of Receptors
- Membrane receptors
– G protein-coupled receptors
– Receptor tyrosine kinases
– Ion channel receptors - Intracellular receptors
Endocrine Signaling
- Travels long distance, and signals between tissues and
organs. - Endocrine signaling molecules are called hormones.
Three stages of cell signaling
- Signal Reception
– Signaling molecule binds to and
activates receptor - Signal Transduction
– Activated receptor stimulates
sequence of changes- signal
transduction pathway - Cellular Response
– Alter activity of enzymes
– Alter structural protein function
– Change gene expression
G-protein coupled receptors (GPCR)
- Extremely widespread and diverse in their functions
- Activated receptor binds to G protein
- Activated (GTP bound) G protein leave the receptor, and activate
downstream enzymes.
Proteins and Phosphate Groups
- Many proteins only active when bound to a
phosphate group - Kinases
– Class of enzymes that attach phosphate groups
to other proteins
– Proteins that activate other proteins - Phosphatases
– Class of enzymes that remove phosphate groups
from other proteins
Receptor tyrosine kinases (RTKs)
- Membrane receptors that catalyze the transfer of phosphate groups from ATP to another protein
- Extracellular domain binds to signaling molecules, causing intracellular domain to become functional catalyst (activated)
- Abnormal functioning of RTK s is associated with many types of cancers
Ligand-gated ion channels
- Acts as a gate that opens and closes when the receptor
changes shape - Ligand binding causes ion channels to open and ions to flow
through the membrane - Animals- signals between nerve and muscle cells or between
2 nerve cells
Intracellular Receptors
- Hormone-receptor complex
interacts directly with DNA
to affect gene expression
Phosphorylation Cascade
- Usually
associated with
RTKs - Regulated by
protein
phosphatases
*Chain of proteins constantly transmitting signal down chain
G-Protein-Coupled Receptor Signal
Transduction
- Protein activated by G-protein
– May directly trigger cellular
response
– May initiate signal
transduction pathway into the
cell - Signal transduction often involves
production of second
messengers, such as cAMP
1. G-protein activates adenylyl
cyclase
2. Adenylyl cyclase converts ATP
to cyclic AMP (cAMP)
3. cAMP activates a protein
kinase
Signal transduction via cAMP
- A small molecule produced from ATP
- One of the most widely used second messengers
- G protein activates adenylyl cyclase, which converts
A TP to cAMP
Long term response
– Induce cell differentiation etc (via differential gene
expression)
- Quick/Intermediate response
– Alter cell motility, shape, etc (via changing
structural proteins such as cytoskeleton)
- Quick response
– Alter metabolism and other cell function (via
changing enzymatic activities)
Quorum Sensing
(autocrine)
-high cell density leads to more behaviors
-low cell density leads to less group activities
- allows bacteria to detect and respond to cell population density by gene regulation
