Cells communicate with each other and their environment through chemical signaling. The basic processes of cell communication are shared across species and have evolved to ensure signals and responses are correctly targeted. Cell signaling directs complex processes like cell differentiation and physiological behaviors. Signaling can occur through direct cell contact or over long distances via hormone signals. Receptors allow cells to have specific responses to signaling molecules. Understanding signaling pathways allows for manipulation of biological systems and development of medicines.

1. A P B I O L O G Y
Cell Communication

2. Cells Communicate with Chemical Signals
 For cells to function in a biological system, they must
communicate with other cells and respond to their
external environment.
 Cell-to-cell communication occurs among all cells in
all species.
Question:
How do you
communicate with
others?

3. Processes in Cell Communication are the Products of
Evolution
 The basic chemical processes by which cells
communicate are shared across evolutionary lines of
descent, and communication schemes are the
products of evolution.
 Correct and appropriate signal pathways are
generally under strong selective pressure.
Question:
What is “strong selective pressure”?

4. Cell Communication Directs Complex Processes
 Cell-to-cell (and environment-to-cell) signaling
pathways direct complex processes.
 Ex: Cell and organ differentiation and physiological
behaviors.
Question:
What is an
example of a
physiological
behavior?

5. Direct Cell-to-Cell Contact
 Certain signal pathways involve direct cell-to-cell
contact or they may operate over very short
distances.
 Ex: Immune cells interact by cell-to-cell contact,
antigen-presenting cells (APCs), helper T-cells, and
killer T-cells.
Question:
Why do we need
such a complex
system to combat
infection?

6. Signaling Across Distances
 Chemical signals allow cells to communicate without
physical contact.
 The distance between the signal-generating cell and
the responding cell can be small or large.
 In this type of signaling pathway, there is often a
gradient response. Often, certain concentrations
must be reached to trigger the response.
Question:
What would be an example of a signal-
generating cell?

7. Cell Communication Over Short Distances
 Cells communicate over
short distances by using
local regulators that
target cells in the vicinity
of the emitting cell (the
cell that releases the
chemical).
 Ex: neurotransmitters

8. Cell Communication Over Long Distances
 Signals released by one cell type can travel long
distances to target cells of another cell type.
 Ex: endocrine signals are produced by endocrine
cells that release signaling molecules (such as
insulin, human growth hormone, testosterone
estrogen).
 These hormones are specific.
 Hormones may travel long distances
through the blood to reach all parts
of the body.

9. Endocrine System

10. Properties of Molecules Involved in Signaling
 Chemical signaling pathways in cells are determined
by the properties of the molecules involved, the
concentrations of signal and receptor molecules and
the binding affinities (fit) between signal and
receptor.
Question:
How could a drug like
heroin or cocaine
affect a cell?

11. Signals may be a Molecule or an Environmental
Factor
 The chemical signal may be either a specific molecule
that fits the receptor, or it may be a change in the cell
(or organisms’) environment.
Question:
How does
temperature
affect the genes
that produce
pigment in
these Arctic
Hares?

12. Receptors
 At the cellular level, the receptor is a protein with
specificity for the signal molecule; this allows the
response pathway to be specific and appropriate.
Question:
What shape/type of
molecule would bind to
this receptor?

13. Signal Cascade
 The receptor protein often is the initiation point for a
signal cascade that ultimately results in one of the
following: a change in gene expression, protein
activity, or physiological
state of the cell or organism
(even including cell death).
Question: How
does a cascade
of water
resemble a
signal cascade?

14. Defects in the Signal Pathway
 Defects in any part of the
signal pathway often lead
to severe or detrimental
conditions such as faulty
development, metabolic
diseases, cancer or death.
This shows the affects of increased
alcohol exposure on the
development of zebrafish embryos.
Question:
How could a defect interfere with
normal operation of a cell?

15. Understanding Signaling Pathways
 Understanding signaling pathways allows humans to
modify and manipulate biological systems and
physiology.
 An understanding of the endocrine system, for
example, allowed the development of birth control
methods, as well as medicines that control
depression, blood pressure and metabolism.
Question:
Should research
continue that allows
humans to modify and
manipulate biological
systems?

16. Transduction of Signals
 Cell communication
involves transduction of
stimulatory or inhibitory
(start or stop) signals
from other cells,
organisms or the
environment.
Question:
What is transduction?

17. Signaling in Single Celled Organisms
 In single-celled organisms (such as bacteria), signal
transduction pathways influence how the cell
responds to its environment.
 Ex: Use of chemical messengers by microbes to
communicate with nearby cells and to regulate
specific pathways in response to population density.
Question:
Why would bacteria need to
communicate with other
bacteria cells regarding
population density?

18. Signaling in Multi-Cellular Organisms
 In multi-cellular
organisms, signal
transduction pathways
coordinate the activities
within individual cells
that support the function
of the organism as a
whole.
 Ex: Temperature
determination of sex in
some vertebrate
organisms.
In some reptile species, the temperature of the
nest will allow development of more females
than males in a brood (or vice versa).

19. Signaling in Multi-cellular Organisms
 Ex: Epinephrine stimulation of glycogen breakdown
in mammals.
Glycogenolysis (the breakdown of
glycogen) takes place in the cells of
the muscle and liver tissues in
response to hormonal and neural
signals. In particular, glycogenolysis
plays an important role in the fight-
or-flight response and the regulation
of glucose levels in the blood.
Question:
Why would the body need to break
down glycogen if experiencing a
fight-or-flight response?