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Cell Signaling
•Cells of multicellular organisms are specialized in order to perform
specific functions.
• Many biological processes require that cells work in a
coordinated manner.
• The coordination occurs by means of cellular signaling
mechanisms.
• For their survival cells must communicate with surrounding cells,
control the conditions of their environment and respond to various
stimuli that come to their surface.
• Cell signaling may be related to any aspect of the structure and
function of the cell.
Cell Signaling
 The communication or cell signaling involves
signals incoming and outgoing
 The signals are agents that affect cell properties
 The signals affect the conformation of a receptor
causing a response in the cell
Alberts et al., L’ESSENZIALE DI BIOLOGIA MOLECOLARE DELLA CELLULA, Zanichelli editore S.p.A. Copyright © 2005
Why cells must respond to the signals?
1.
Need to respond to environmental changes
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The adaptation or cellular response is critical for
survival
Activation of specific metabolic pathways (catabolic
and / or anabolic)
2. It is required to coordinate cellular activities in a
multicellular organism
3. An important reason of cellular communication
is the promotion of cell division
Alberts et al., L’ESSENZIALE DI BIOLOGIA MOLECOLARE DELLA CELLULA, Zanichelli editore S.p.A. Copyright © 2005
Cell communicate with each other through the
signaling mechanisms of:
1.
direct intracellular
Cell junctions allow signal molecules to move from one cell to
another
2. contact-dependent
Some molecules are bound to the surface of cells and act as
signals for the cells that come in contact with them
Signaling with direct contact
Different ways of hormonal signals
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ENDOCRINE: Hormone produced by the pituitary
cells passes into circulation and acts distantly on
the target gland (eg. Thyroid);
Neuroendocrine: the hormone is secreted by a
neuron directly into circulation and reaches a
target organ (eg. Kidney);
Paracrine: the hormone acts on a cell present in
the same gland;
Autocrine: the hormone acts on the same cells
from which it was secreted.
Local Signaling w/o Direct Contact
Paracrine signaling
Communicate using local regulators
Synaptic signaling
Long Distance Signaling
Both plants and animal use hormones
THE TWO SYSTEMS OF COMMUNICATION
• Hormones diffuse long distance,
through the blood where they
are diluted. They act at low
concentration (10-8 M);
• Neurotransmitters are released
at high concentrations in the
synapses (5 x 10-4 M).
ENDOCRINE SYSTEM
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1.
2.
3.
4.
The endocrine system is a communication system
aimed to adjust, integrate and coordinate various
physiological processes such as:
Digestion, use and storage of nutrients
Growth and development
Electrolyte metabolism
Reproductive function
Hypothalamic-pituitary axis
HORMONE
• Regulator and coordinator of multiple biological
functions powerful and specialized organic molecule
produced by endocrine cells in response to specific
stimuli that exerts its action on specific TARGET CELLS;
• CELL TARGET: cell with receptor that recognizes with
specificity and affinity the hormone;
• RECEPTOR: protein molecule or glycoprotein that
placed on the cell surface or inside recognizes and
binds to the hormone.
HALF-LIFE, ONSET AND DURATION OF
HORMONE ACTIVITY
1. The concentration of a hormone reflets its rate of release
and the rate of inactivation and removal from the body;
2. The half-life of a hormone is the duration of time a
hormone remains in the blood and is shorter for a watersoluble hormones;
3. Target organ response and duration of response vary
widely among hormones
MAIN ENDOCRINE ORGANS
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PITUITARY
THYROID
THYME
PARATHYROIDS
ENDOCRINE PANCREAS
ADRENAL GLANDS
OVARIES AND PLACENTA FOR WOMEN
TESTICLES FOR MEN