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Cell Communication
Keri Muma
Bio 6
Types of Cellular Communication

Direct contact between cells

Gap junctions – cells are connected by tunnels
formed by connexons


Allows ions and small water soluble chemicals to pass
between cells
Cardiac and smooth muscle
Types of Cellular Communication

Direct contact between cells

Cell to cell recognition – interaction of cellsurface molecules

Immune cells – recognize self vs. non-self
Types of Cell Communication

Through extracellular chemical messengers

Cells release ligands that bind to receptors on
target cells to initiate a desired cellular
response
Types of Cell Communication

Local Regulators



Paracrine – through diffusion, ligands affect cells
in the local vicinity
Autocrine – chemicals act on the cell that
produced it
Examples: histamine, cytokines, prostaglandins
Local Regulators

Neurotransmitters – secreted by neurons


Diffuse across the synaptic cleft and target the
adjacent cell (neuron, gland, muscle)
Short-lived
Types of Cellular Communication

Long-range (distant) regulators


Hormones – secreted into the blood by
endocrine glands to travel to distant target
cells
Neurohormones – neurons secretes hormones
into the blood
Cellular Effects of Chemical Signals

Example of various effects chemical
signals may have on the target cell




Activate or inhibit enzymes
Direct protein synthesis through activation
of transcription factors
Stimulate cell division
Alter membrane permeability – membrane
potential or opening/closing of ion channels
How do hormones work?
Hormones are chemical substances that
travel through the blood to a target cell
 Target cells must have specific receptors
to which the hormone binds
 These receptors may be intracellular or
located on the plasma membrane
 They trigger a change in cellular activity

Types of Hormones

Amines – amino acid derivatives


Peptides – proteins


Vasopressin, insulin
Steroids – cholesterol based


Catecholamines (NE and E), T3, T4, serotonin,
melatonin
Cortisol, aldosterone, estrogen, testosterone
Eicosanoids –derived from arachidonic
acid

Prostaglandins, leukotrienes
Transport of Hormones

Hydrophilic (water-soluble) hormones –
transported dissolved in the plasma


Peptide and catecholamines
Lipophilic (lipid-soluble) hormones –
circulate bound to plasma proteins such as
albumin

Steroids and thyroid hormones
Mechanism of Signaling Molecules

Lipid soluble hormones


Move through the plasma
membrane and bind to an
intracellular receptor in
the nucleus
Binding of the HRC to the
DNA triggers transcription
of a specific gene and the
synthesis of a protein that
initiates a cellular
response
Mechanisms of Signaling Molecules



Water soluble hormonesutilize a membrane bound
receptor
Binding of hormone causes a
conformational change in the
receptor
Two affects of ligands binding
to membrane bound receptors:
1.Triggers the opening or
closing of ion channels
Mechanisms of Signaling Molecules
OR
2.Transfers the signal to a secondary messenger
within the cell which triggers a cascade of
biochemical events
Types of Receptors
Signal Transduction
Secondary Messenger Pathways

G-protein linked
receptor – spans the
membrane and is
associated with a G
protein on the cytoplasmic
side



Ligand binds to the
receptor
Receptor then activates a
G protein
G proteins are
considered relay proteins
that cycle between an
inactive and active form
Cyclic AMP Secondary Messenger Pathway
1.
2.
3.
4.
G protein activates the
enzyme adenylate
cyclase (the effector)
Converts ATP to cyclic
AMP
Activates protein
kinase A which
phosphorylates other
proteins
Trigger cellular
responses
Cyclic AMP Secondary Messenger Pathway
Signaling Pathways Amplify the Cells
Response to Signals
Molecules in second
messenger system
Total number
of molecules
Extracellular
chemical messenger
bound to membrane
receptor
Activated
adenylyl cyclase
1
Amplification
(10)
10
Amplification
Cyclic AMP
(100)
Activated
protein kinase
Phosphorylated
(activated) protein
(e.g., an enzyme)
Products of
activated enzyme
1,000
1,000
Amplification
(100)
100,000
Amplification
(100)
10,000,000
Calcium Secondary Messenger Pathway
1. Binding of extracellular messenger to a G protein
linked receptor or a tyrosine kinase receptor
2. Activates phospholipase C which converts PIP2 to
DAG and IP3
Calcium Secondary Messenger Pathway
3. DAG will activate protein kinase C in another
signaling pathway
4. IP3 binds to calcium channels triggering the release
of calcium from the ER into the cytoplasm
Calcium Secondary Messenger Pathway
5. Calcium binds to and activates calmodulin
which can alter other proteins to bring about
a cellular response
Calcium Secondary Messenger Pathway
Calcium Secondary Messenger Pathway
Summary of Signaling Pathways