Chapter 15 Baboon text
Cell Signaling and Communication
15.1 What Are Signals, and How Do
Cells Respond to Them?
Cells receive signals from
1. Physical environment
Ex: light, temperature, touch, sound and
chemicals
2. Other cells- primarily in the form of
chemicals and touch.
15.1 What Are Signals, and How Do Cells Respond to Them?
Autocrine signals affect the cells that made them.
Paracrine signals affect nearby cells.
Hormones travel to distant cells, usually via the
circulatory system.
Local Diffusion
e.g., Histamine released from damaged cells in inflammation
e.g., Interferon release by viral-infected cells
LIGANDS
Receptor proteins have very specific binding
sites for chemical signal molecules, or
ligands.
Binding the ligand causes receptor protein to
change shape.
The binding is reversible.
LIGANDS
• Ligands can bind to
– Cytoplasmic receptor- located in the cytoplasm or
nucleus. Ligand must be small and non-polar (lipid
soluble)
• Cytoplasmic- causes change in protein regulation
– Ex: glycogen breakdown
• Nuclear- stimulates or inhibits transcription
– Membrane receptor- located within the membrane.
Ligand is large and/or polar (water soluble)
• Leads to stimulation or inhibition of transcription;
either stopping, starting, increasing or decreasing
production of particular activity
Ligands
Extracellular Reception
e.g., insulin and
epinephrine
Intracellular Reception
e.g., nitric oxide and
steroid hormone
Examples of Surface Receptors
Three Stages of Signal Transduction
1. Reception of extracellular signal by cell
2. Transduction of signal from outside of cell
to inside of cell—often multi-stepped
Note not necessarily transduction of ligand
3. Cellular Response
Response is inititiated and/or occurs
entirely within receiving cell
Three Stages of Signal Transduction
Three Stages
1. Reception
2a. Transduction
2b. Transduction
3. Response
Three Stages
1. Reception
2a. Transduction
2b. Transduction
2c. Transduction
2d. Transduction
3. Response
Responses usually involve increasing or decreasing some Protein’s Function
Various Responses
Note that more than one
response can result from the
reception of a single ligand
Various Responses
A signal transduction pathway:
A signal transduction pathway:
• The signal causes receptor protein to
change conformation.
• Conformation change gives it protein
kinase activity.
• Phosphorylation alters function of a
responder protein.
Various Responses
15.2 How Do Signal Receptors
Initiate a Cellular Response?
Types of plasma membrane receptors:
• Ion channels
• Protein kinases (Tyrosine-kinase receptors)
• G protein-linked receptors
Ion-Channel Receptors
15.2 How Do Signal Receptors
Initiate a Cellular Response?
Ion channel receptors: channel
proteins that allow ions to enter or
leave a cell.
Example: acetylcholine binds which
allows Na+ into cell. This causes a
muscle to contract
• Ion-Channel Receptors
Figure 15.5 A Gated Ion Channel
Ion-Channel Receptors
G Protein-Linked Receptors
15.2 How Do Signal Receptors
Initiate a Cellular Response?
G protein-linked receptors: the
seven-transmembrane-spanning G
protein-linked receptors.
G proteins: mobile membrane
proteins with three subunits.
G Protein-Linked Receptors
15.2 How Do Signal Receptors
Initiate a Cellular Response?
Signal outside cell activates G protein linked
receptor which activates G protein inside
cell.
This then activates the protein and it moves
through plasma membrane until it encounters
an effector protein.
Binding activates the effector which causes a
change in cell function
(activation/inhibition).
• G Protein-Linked Receptor
Figure 15.7 A G Protein-Linked Receptor (Part 1)
Effector protein can
cause amplification
G Protein-Linked Receptors
the more ligand
binding, the more
K+ in cytoplasm
note how activation
is reversible
• Protein Kinase & Phosphatase
15.3 How Is a Response to a Signal
Transduced through the Cell?
Protein kinase receptors—catalyze the
transfer phosphate from ATP to a target
protein causing conformation and
activity.
Ex: Insulin (ligand) binds to receptor
which phosphorylates and activates
glucose transporters.
• Protein Kinase & Phosphatase
Figure 15.10 A Protein Kinase Cascade
Signal Amplification
(Direct Cascade)
15.3 How Is a Response to a Signal
Transduced through the Cell?
Direct
transductionthe receptor
causes the
change and
occurs at
membrane.
15.3 How Is a Response to a Signal
Transduced through the Cell?
Signal Amplification
(Indirect Cascade)
Indirect transduction- involves
a second messenger.
15.3 How Is a Response to a Signal
Transduced through the Cell?
Second messengers were discovered in
research on the liver enzyme glycogen
phosphorylase, and how it is activated by
epinephrine. (Read up on Sutherland’s
investigations with epinephrine p. 340-41)
Binding of the hormone to the membrane
receptor caused production of a small
molecule (cyclic AMP, or cAMP) that
diffused into the cytoplasm to activate the
enzyme.
15.3 How Is a Response to a Signal
Transduced through the Cell?
The signal is the first messenger.
The second messenger is released into the
cytoplasm after signal binds to receptor.
Second messengers affect many processes in
the cell.
Also amplify the signal—one epinephrine
molecule leads to production of many
cAMP.
Second Messengers
Specificity of Cell Signaling
1. Note how same ligand gives rise to different
responses
2. Cells differ in terms of their proteins
3. Different proteins respond differently to the same
environmental signals
4. (note, though, same receptors, different relay)
5. Different cells behave differently because some,
but not all proteins can differ between cell types
Chemical Signaling Between Cells
15.4 How Do Cells Change in
Response to Signals?
• In your trifold book add the following
information:
Reception
Transduction
Response
Ion channels
G-Protein Linked
Protein Kinase
• Include details on the front and examples
for each on the back.
Acknowledgements
biology.ucf.edu/courses/bsc2010/08-2010C-02.PPT
www.aw.com/bc/ppt/marieb_ap/chap03c.ppt
http://zeus.uwindsor.ca/courses/biology/zielinski/204/comm1.ppt
http://vaccine.chonbuk.ac.kr/images/cell/Chapter%2015%20Cell.ppt
http://faculty.uca.edu/~jmurray/BIOL1440/lec/lec15.ppt
\http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/7-signal.ppt
http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/9-glycogen.ppt
http://homepage.smc.edu/chen_thomas/Bio21/Chpt%2011%20Cell%20Comm.ppt
Putting the information to work
Cell Cycle Control System
• How is the cell cycle controlled
• Restriction Checkpoints- sites where cell
division are either prevented or stopped
• Locations
–
–
–
–
G1- commits the cell to division
G2
M
Ex: At the G1 checkpoint, if the cycle is
stopped, cell will enter G0
Cell Cycle Control System
• Checkpoints are controlled by protein
activity
– 2 main proteins
• Cyclins- proteins continually produced in cells
• Kinase-proteins that activate or inactivate target
proteins by phosphorylating them
– Phosphorylation: breaking down ATP and adding a
phosphate group
» This changes the shape of the target protein
Target proteins –directly regulate the cell cycle
Cell Cycle Control System
• Ex: G1 checkpoint
• Proteins involved
– Cyclin
– Cyclin dependent kinase (Cdk)
– Rb (target protein) normally inhibits the cell cycle at G1 checkpoint
How it works
When Cdk binds with a cyclin, it becomes activated
Cdk/cyclin complex phosphorylates RB
Rb becomes inactive and can no longer inhibit the cell cycle
Cell proceeds to stage Synthesis
NOTE: RB and other target proteins in the cell cycle control system act as
tumor suppressors by stopping uncontrolled cell division.
LOOK AT FIGURE 9.6 IN YOUR BABOON TEXT
• LOOK AT FIGURE 9.6 IN YOUR
BABOON TEXT