1. How do you think cells communicate?
Cell Communication Ch. 11
Cell-to-cell communication is essential for multicellular organisms
How do you think cells communicate?

2. Cell Signaling Animal cells communicate in many ways:
Direct contact (gap junctions)
Secreting local regulators (growth factors, chemical messengers, neurotransmitters)
Long distance (hormones)

3. Local
Autocrine signaling respond to molecules they produce themselves. Examples include many growth factors.

4. In local signaling, animal cells May communicate via direct contact
Figure 11.3
(b) Cell-cell recognition. Two cells in an animal may communicate by interaction
between molecules protruding from their surfaces.

5. diffuses across synapse
In other cases, animal cells
communicate using local regulators
(a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid.
(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
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

6. Long-distance signaling
A hormone is a chemical released by a cell in one part of the body, that sends out messages that affect cells in other parts of the organism
All multicellular organisms produce hormones
Hormones in animals are often transported in the blood
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
Figure 11.4 C

7. Signal Transduction Pathways
Convert signals on a cell’s surface into cellular responses
Are similar in microbes and mammals, suggesting an early origin

8. Earl W. Sutherland’s Three Stages of Cell Signaling
- suggested that cells receiving signals went through three processes
Reception
Transduction
Response

9. Step One - Reception Receptor protein is on the cell surface
Reception occurs when a signal molecule binds to a receptor protein, causing it to change shape
Receptor protein is on the cell surface

10. The binding between signal molecule (ligand) and receptor is highly specific
A conformational change in a receptor is often the initial transduction of the signal

11. Step Two - Transduction
The binding of the signal molecule alters the receptor protein in some way
The signal usually starts a cascade of reactions known as a signal transduction pathway
Multistep pathways can amplify a signal

12. Step Three - Response
Cell signaling leads to regulation of cytoplasmic activities or transcription
Signaling pathways regulate a variety of cellular activities

13. 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

14. Example of Pathway Steroid hormones bind to intracellular receptors
(testosterone)
EXTRACELLULAR
FLUID
Receptor
protein
DNA
mRNA
NUCLEUS
CYTOPLASM
Plasma
membrane
Hormone-
receptor
complex
New protein
Figure 11.6 1
The steroid
hormone testosterone
passes through the
plasma membrane.
Testosterone binds
to a receptor protein
in the cytoplasm,
activating it. 2
The hormone-
receptor complex
enters the nucleus
and binds to specific
genes. 3
The bound protein
stimulates the
transcription of
the gene into mRNA. 4
The mRNA is
translated into a
specific protein. 5

15. Receptors in the Plasma Membrane
There are three main types of membrane receptors:
G-protein coupled
Tyrosine kinases
Ligand gated Ion channel

16. G protein
G proteins ( guanine nucleotide-binding protein) act as molecular switches inside cells, and are involved in transmitting signals from outside a cell to its interior.
These proteins change between an active conformation when bound to GTP, and an inactive conformation when bound to GDP.
IN the absence of a signal they are bound to GDP.
Signal results in the release of GDP and the binding of abundant GTP. After a short period of time they hydrolyze GTP and come back to their “off” state.

17. Protein Kinases
Upon activation they add phosphate groups to themselves and/or other proteins at either serine/threonine, or at tyrosine residues.
Their activity can be regulated by second messengers, interaction with other proteins, or by phosphorylation itself. They are opposed by phosphatases that remove phosphate groups from specific phosphorylated proteins.

18. G-Protein-Coupled Receptor

19. Ion channel receptors Cellular response Gate open Gate close
Ligand-gated
ion channel receptor
Plasma Membrane
Signal molecule (ligand)
Gate closed
Ions

20. Intracellular receptor model
For a signal molecule to bind with an intracellular receptor it must be able to pass through the cellular membrane.
Generally signal molecules that enter the cell are nonpolar and fat soluble.
These signal molecules can pass through the lipid bilayer of the cell membrane.