1. Cell Communication

2. The “Cellular Internet”
All multicellular organisms must “communicate and cooperate” to maintain homeostasis
Science has identified universal mechanisms of cell-to-cell communication.
Communication in cells is similar to communication in general. Cells communicate by sending/receiving signals and then converting the signals into a response

3. Overview of cell signaling
EXTRACELLULAR
FLUID
Receptor
Signal
molecule
Relay molecules in a signal transduction pathway
Plasma membrane
CYTOPLASM
Activation
of cellular
response
Figure 11.5
Reception 1
Transduction 2
Response 3

4. Cell Signaling Animal cells communicate by:
Locally by direct contact (gap junctions)
Locally by secreting local regulators (growth factors, neurotransmitters)
Long distance (hormones)

6. LOCAL SIGNALING EXAMPLES
Direct transport between cells
protein tunnels directly connecting adjacent cells allow material to pass through (e.g. chem signals or water) and be shared
gap junctions in animal cells
plasmodesmata in plants);
Plasma membranes
Plasmodesmata
between plant cells
Gap junctions
between animal cells
Figure 11.3
(a) Cell junctions. Both animals and plants have cell junctions that allow molecules
to pass readily between adjacent cells without crossing plasma membranes.

7. LOCAL SIGNALING EXAMPLES
local regulators- messenger molecules that travel only short distances
Local regulator
diffuses through
extracellular fluid
Target cell
Secretory
vesicle
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across synapse
is stimulated
Local signaling (Left: Paracrine, Right: Synaptic)

9. LONG DISTANCE SIGNALING EXAMPLES
Used by all multicellular organisms to coordinate effort between cells that are not close together
Hormones travel through the circulatory system abd can go anywhere in the body or even to another organism
Target cells contain surface receptors that recognize and respond to the specific hormone
Slow method of communication, but it can cause changes in a lot of cells simultaneously
Hormone travels
in bloodstream
to target cells
(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood Hormones may reach virtually all body cells.
Long-distance signaling
Blood
vessel
Target
cell
Endocrine cell

10. Stage One: Reception
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane 1 1
Reception
The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!)
Receptor
Signaling
molecule
The shape determines function!
Only cells that contain the right receptor can receive the signal

11. Stage Two: Transduction
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane 1 1
Reception 2
Transduction
Receptor
2nd Messenger!
Relay molecules in a signal transduction pathway
Signaling
molecule
Reception sets off a “relay team” of INTERIOR communication molecules; proteins and/or second messengers (non-proteins) carry the original exterior signal to the inside of the cell

12. Stage Three: Response
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane 1
Reception 2
Transduction 3
Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signaling
molecule
The cell will respond to the signal as directed (e.g. make a protein, produce more energy, enter mitosis, etc.)

13. Termination of Communication
Inactivation mechanisms are an essential aspect of cell signaling
When signal molecules leave the receptor, the receptor reverts to its inactive state