1) Botulinum toxin produced by Clostridium botulinum bacteria binds to and blocks G-protein coupled receptors, preventing the release of acetylcholine at neuromuscular junctions. 2) This inhibition of acetylcholine signaling prevents muscle contraction and can cause botulism poisoning in humans. 3) Botulinum toxin is also used medically in controlled doses as Botox to temporarily paralyze muscles for cosmetic or medical purposes by similarly blocking acetylcholine receptor signaling at neuromuscular junctions.

1. Cell Communication - Signal
Reception
Ch. 11
Section 11.2
Whiteboards please

2. How cells “hear” the call
• The target cell has a
receptor protein that
recognizes the chemical
signal
 Recognition happens when
the signal molecule binds
to the receptor
 They fit together like lock
and key

3. signal specificity
 The same signal
molecule can generate
different responses in
different cells
 Each type of cell may
contain different types
of proteins, thus they
will respond to the
same signal molecule
differently

4. Signal SpecificitySignal Specificity
Different types of cellsDifferent types of cells
contain differentcontain different
proteins and soproteins and so
respond differently torespond differently to
signal moleculessignal molecules
Why does epinephrine cause a liver
cell to metabolize glycogen, but
cause
a muscle cell to contract??

5. QUICK THINKQUICK THINK
Explain why cells can respond
differently to the same signal
molecule

6. Critical Vocab!!
• Signal molecule =
ligand

7. Signal Reception
• Ligand binds to receptor
• Receptor protein changes shape
• This starts the transduction pathway
• Leads to cell response

8. Quick Think
•How do cells “hear” the
message from other
cells?

9. Ligands – 2 types
Large and/or Polar Ligands
• Proteins
• Ions
• Cannot pass
through cell
membrane
• Bind to
protein
receptor on
exterior of
cell
membrane
Non-polar Ligands
• Lipids –
Steroid
Hormones
• Can pass
through
cell
membrane
• Bind to
receptor
protein
inside cell

10. Testosterone - a steroid signal
molecule
• Testosterone is a hormone, a
steroid, secreted by the testis
• It travels through the blood stream
• It enters all kinds of cells
• But the only cells that can “hear” it
are the target cells that have the
right receptor molecule inside the
cell
• Once inside, testosterone binds to
the receptor and helps turn on
genes that control male sex
characteristics

12. Example Cell Response
• Many ligands are
transcription factors
• Direct the cell to DNA
 mRNA  protein

13. Quick Think
• Where are intracellular reception
proteins?
• Why can their chemical signals
pass into the cell?

14. Quick Think
• Nerve Growth Factor (NGF) is a
water-soluble signal molecule.
Would you expect the receptor for
NGF to be intracellular or in the
cell membrane? Why?

15. Most signal receptor proteins
are in the cell membrane
• There are 3 main types
of cell membrane
signal receptors
 G-protein-linked
receptors
 Receptor tyrosine
kinases
 Ion-channel receptors

16. G-protein linked receptors
• Made up of a receptor
protein + a G protein
• They have 7 α helices

17. The G-protein part
• The G-protein part is like
an on/off switch for the
receptor protein
• When GDP (cousin of
ATP) is bound to it, the G
protein is inactive

18. G-Protein Linked
Receptors
1.Ligand attaches to
receptor protein
2.G-protein activated
3.G protein activates an
enzyme
4.Transduction & cell
response

19. The G-protein
• G-protein receptor systems
are really common and play a
role in lots of different cell
processes
 Development of embryos
 Vision & Smell
• Lots of diseases involve G-
proteins
 Bacterial infection like botulism
and cholera interrupt G-protein
function
 Most drugs (medicines) work by
influencing a G-protein pathway

20. Quick Think
•How does a G-protein linked
receptor function?

21. Tyrosine-kinase receptors
• Best when the cell needs to trigger several
cell responses at once

22. Tyrosine-kinase receptors
• kinase - enzyme that
catalyzes the transfer
of phosphate groups
• So it is an enzyme
that functions to
transfer a phosphate
group from ATP to
tyrosine

23. Tyrosine-kinase receptors
• Has 3 parts:
 Extracellular (outside
the cell) signal-
binding site
 1 α helix
 An intracellular
(inside the cell) tail
with a bunch of
tyrosines on it

24. Tyrosine-kinase receptors
• Once 2 signal molecules binds to 2
tyrosine-kinase receptors, they pair up to
form a dimer

25. Tyrosine-kinase receptors
• Once this happens, this
causes the tyrosine-kinase
part of the receptor to take
phosphate from ATP and
add it to the tyrosine tail
• This makes the receptor
protein “fully activated”

26. Tyrosine-kinase receptors
• Once the tyrosine-kinase
receptor is fully activated, it
is recognized by other
proteins in the cell
• Each tyrosine-kinase
receptor may activate
many different proteins that
may lead to many different
cell responses

27. 1. 2 ligands bind to 2 receptor
proteins
2. 6 Pi (from 6 ATP) added to
receptor protein tails
3. Each Pi can activate a different
cell response

28. Quick Think
•Summarize how a
tyrosine-kinase receptor
functions.

29. Ligand-gated ion channel
protein
• Receptor protein that acts
as a gate for entry into the
cell
• When a signal molecule
binds to the receptor
protein, the gate opens to
allow specific ions (like
sodium or calcium) to flow
through it

30. Ligand-ion-gated channel
protein
1. ligand binds & protein
channel opens
• ions flow through
• ligand dissociates & gate
closes

31. Ligand-gated-ion channel
protein
• Important in the nervous
system
 Neurotransmitter binds as a
ligand
 Ion-channel proteins open
 Ions flow into cell
 Triggers an electrical signal
that moves down the length
of the cell

32. Quick Think
•Summarize how a Ligand-
gated ion channel functions.

33. Cell Communication Research
• Create an infographic about a disease or drug that
disrupts cell communication