Cell Signaling
Signal Transduction Pathways
Cellular Signaling
• Autocrine Signals
– Diffuse from one part of a
cell to another part of the
same cell
• Synaptic signaling
– Neurotransmitter is the
signaling molecule
– Occurs in the animal
nervous system
– Paracrine signals- send
messages to nearby cells
by diffusion
– Endocrine signals, or
hormones, travel
anywhere in the blood to
reach their target cells.
Signal Transduction Pathways
•
Coordinates the activities within, among, and between all individual cells, which supports the entire
organism
• Ligands
– Chemical in low
concentrations that
reach target cells by local
diffusion or via the
circulatory system
• Ligands bind to
receptors
– On cell membrane or
inside the cytoplasm of
the target cell
• Examples include ion channel receptors, G-protein –coupled receptors, and
protein kinase receptors
• End product of the signal transduction pathway is a change in gene expression, a
change in protein activity, or apoptosis (cellular death)
Secondary Messengers
• Once the signal is transmitted from outside
the cell to the cytoplasm, a secondary
messenger propagates the signal
• Most common example: cAMP (cyclic AMP)
– The ligand, or first messenger, is not able to enter
the cell
The Cascade Effect
• The multi-step cascade uses a small number of
extracellular signal molecules to produce a major
cellular response.
• Amplifies the signal and provides numerous
opportunities for cellular control, coordination,
and regulation
• Diversity of organisms with such similar pathways
suggests that signal transduction pathways
evolved from a common ancestor millions of
years ago!!!
What do I NEED to know?
• Signal transduction pathways …
– Are Characterized by a signal, a transduction, and
a response
– Are Highly specific and regulated
– One signal molecule can cause a cascade effect
– Evolved millions of years ago in a common
ancestor
Can you make the connections?
• Imagine you just got a splinter! How does
your body protect itself from the “foreign
invader” and keep you healthy?
Pause for discussion
The Human Immune System
• We live in a world of germs! We must protect
ourselves, so…
• The three levels of the immune system are:
– Nonspecific defenses, or barriers (innate)
– Nonspecific defenses (inflammatory response)
– Adaptive Immunity
First Line of Defenses
• Non-specific to help prevent pathogens from
entering
• Like soldiers patrolling the area
•
•
•
•
Skin
Mucous
Tears- lysozyme
Stomach acid
Question to Ponder
Can you think of a time in which you used any of
these defenses? How do you think it worked?
Second Line of Defense
• Non-specific
• Inflammatory response
– Histamines trigger vasodilation
– Release of phagocytes and prostaglandins
• White blood cells attack invaders
• Prostaglandins increase blood flow
– Chemokines are secreted
• Attracts phagocytes to site
Third Line of Defense
• Adaptive Immunity
– B lymphocytes and T lymphocytes (both arise from stem
cells)
• Both recognize specific antigens
– Specific responses
• Recognition
– B and T cells recognize specific antigens on APC (antigen presenting cells)
• Activation phase
– Rapid cell division
– Makes effector and memory cells
• The effect phase
– B cells produce humoral response
– T cells produce cell-mediated response
Interferons
• Interferons are protein signals released by
cells infected by viral pathogens
• http://www.dnaftb.org/35/animation.html
Question to Ponder
• Discuss with your partner how adaptive
immunity could utilize cell signaling pathways.
• How is your second line of defense like a
signal transduction pathway?
– What parts of the inflammatory response are
represented in the cell signaling pathway? Can
you draws parallels between the parts of this
response to the parts of a signaling pathway?
Are you ready…
• Which of the following is directly responsible
for humoral immunity?
Keep it up…
• Of all the following, what part does not
participate in nonspecific immune defense?