1. Modified slides from knuffke and biology in focus (campbell)
Cell communication
Modified slides from knuffke and biology in focus (campbell)

2. Eukaryotic cells may communicate by direct contact (local signaling)
Animal cells = gap junction
Plant cells = plasmodesmata

3. Animal cells also communicate via cell-to-cell recognition – important for immune response and embryonic development
Glycoproteins serve as ID tags that are specifically recognized by membrane proteins of other cells

4. More examples of short distance local signaling
Paracrine signaling: a cell secretes a messenger molecule
Local regulator- travels short distance
Ex: growth factors (these stimulate nearby cells to grow)
Synaptic signaling: an electrical signal causes the secretion of a neurotransmitter carrying a chemical signal
signal crosses synapse between the two cells
Causes a response in the target cell
Ex: occurs in animal nervous system

5. Long Distance Signaling
Use hormones (endocrine signaling)
Animals: Cells release hormones which travel in circulatory system to the target cell where it recognizes and responds
Plants: no circulatory system- so hormone moves through xylem and pholem (vascular tissue) or travels through the air as a gas

6. Plant hormones

7. Examples of long distance signalers
Insulin derived from e.coli:
C257H383N65O77S6
The animal hormone insulin- regulates sugar levels in the blood
Can consist of thousands of atoms
Nervous system can have long distance signals as well- ex: signal travels from brain to big toe
The plant hormone ethylene (a gas) - promotes fruit ripening.
Consists of 6 atoms

8. Basics of cell-to-cell communication
Reception: target cell’s detection of a signaling molecule coming from outside the cell
Signal molecule binds to a receptor protein at the cell’s surface or inside the cell
Transduction: step or series of steps that converts the signal to a form that can bring about a response
Requires a sequences of changes in a series of different molecules (signal transduction pathway)
Response: triggered cell reacts

9. CELL COMMUNICATION

10. This is important because…
It ensures that crucial activities occur in the right cells, at the right time, and in proper coordination with the activities of other cells of the organism
Multicellular organisms are amazingly complex!!!!

11. Any signaling molecule is called a ligand
Ligands are complementary in shape to a specific site on the receptor and attaches there like a key in a lock
Reception depends on the chemistry of the signal
A signaling molecule can bind to the receptor protein located:
at the cells surface or
inside the cell

12. Ligand chemistry
Most signal receptors are plasma membrane proteins. Their ligands are water-soluble and generally too large to pass freely through the plasma membrane.

13. Ligand chemistry
Other signal receptors are located inside the cell. Their ligands are lipid-soluble so the pass through the membrane and into the cell.

14. STEP 1- RECEPTION
BEFORE
AFTER
Ligand 
Ligand binding causes the receptor protein to CHANGE SHAPE
Transmembrane receptors transmit information from the extracellular environment to the inside of the cell by changing shape when a specific ligand binds to it.

15. STEP 2- TRANSDUCTION
After the cell is received then the message is TRANSDUCED.
The transduction stage converts the signal to a form that can bring about specific cellular responses
This is like falling dominoes
Often it AMPLIFIES the message

16. Second Messengers
2nd messengers are small non-protein water-soluble molecules or ions that can readily diffuse
The “first messengers” are the signaling molecule that bind to the membrane receptor. 2nd messengers trigger sub-response pathways
2nd messengers participate in pathways initiated by both G protein-coupled receptors and receptor tyrosine kinases
The 2 most widely used 2nd messengers are cyclic AMP (cAMP) & calcium ions Ca2+

17. Calcium functions as a 2nd messenger more often than cAMP.
Increasing the cytosolic concentration of Ca2+ causes many responses in animal cells, including muscle cell contraction, secretion of certain substances, and cell division.

18. Step 3- RESPONSE

19. The responses can be complex. What is the big picture
The responses can be complex! What is the big picture?! : The response may trigger a gene to turn on or off or it may just regulate the activity of an enzyme…

20. The L

21. DIFFERENT RECEPTOR SYSTEMS THAT YOU SHOULD BE FAMILIAR WITH:
G proteins
Ligand gated ion channels
Tyrosine kinases
You don’t have to know many details about them- but you should know general info about them

22. G protein-coupled receptor systems
ONE TYPE OF MEMBRANE RECEPTOR: G-Protein coupled receptors (GPCR)
Many signaling molecules such as epinephrine, other hormones and neurotransmitters use GPCRs
G-proteins: proteins activated by the transfer of a phosphate from a molecule of GTP (an energy rich molecule like ATP).

23. G protein-coupled receptor systems
GPCR and G proteins are remarkably similar in structure – suggesting they evolved very early in the history of life
Widespread and diverse in their functions. Ex: These proteins are instrumental in human embryonic development, vision, and smell
Also play a role in human disease- bacteria that causes cholera, pertussis, and botulism make their victims ill by producing toxins that interfere with G-protein function.
Up to 60% of all medicines used today exert their effects by influencing G-protein pathways

24. G-protein-linked receptors form the largest family of cell-surface receptors and are found in all eukaryotes.

25. Ligand-gated ion channel is a type of membrane receptor that can act like a gate when the receptor changes shape.
Incoming IONS trigger the response
The gates only open to specific ions which may directly affect the activity of the cell in some way.

26. TYROSINE KINASES are the cell surface receptors for many polypeptide growth factors and hormones.
KINASE: An enzyme that catalyzes the transfer of phosphate groups (It “phosphorylates” (adds a phosphate to) another molecule).
#2: The binding of a signaling molecule (such as a growth factor) causes the 2 receptors to associate closely (forms a dimer)

27. TYROSINE KINASE
#3: Dimerization activates the tyrosine kinase region of each polypeptide.
#4: receptor protein is fully activated and is recognized by specific relay proteins inside the cell. The Tyrosine kinases attaches phosphates to the relay proteins. This leads to a cellular response.
The complex remains ACTIVE as long as LIGAND is attached

28. Specific examples

30. The first messenger activates a G protein-coupled receptor
This activates a specific G protein.
In turn, the G protein activates adenylyl cylcase, which catalyzes the conversion of ATP to cAMP.
The cAMP then acts a second messenger and activates another protein (transduction), usually protein kinase A,
This leads to a cellular RESPONSE
animation of this process (click here)

31. MORE EXAMPLES Why cells communicate?
Multicellular examples:
Wound healing (click for animation)
APOPTOSIS- Programmed cell death
Unicellular examples:
Yeast mating
Biofilms
Quorum sensing

32. APOPTOSIS “Cell suicide”
Why are “Death proteins“ present in inactive form?

33. Cell-communication is IMPORTANT in unicellular organisms as well

35. QUORUM SENSING