1. Biological Hierarchy:

2. Cell to Cell Communication
Involves (and you should review):
Structure of plasma membranes
Diffusion vs. active transport
Hydrophobic vs. hydrophilic compounds
Proteins
Surface vs. intermembrane proteins
Enzyme activity

3. Figure 8.7 The structure of a transmembrane protein

4. Figure 8.9 Some functions of membrane proteins
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Receptor protein
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Receptor protein

5. Cells can communicate by direct contact between cells

6. Cells can communicate by sending chemical signals to other cells:
Mating in yeast cells depends on cell to cell communication

7. Chemical signals can be sent to cells at various distances from each other

8. Once a chemical signal reaches its target cell:
Signal molecule binds to a receptor protein on the target cell (it is a ligand)
The receptor molecule changes shape
The shape change causes a series of reactions (transduction) to take place in the cytoplasm of the cell
This series of reactions leads to a response of the cell to the chemical signal
This process is called a signal-transduction pathway

9. Figure 11.5 Overview of cell signaling (Layer 1)

10. Figure 11.5 Overview of cell signaling (Layer 2)

11. Figure 11.5 Overview of cell signaling (Layer 3)

12. Common Types of Receptors
G-protein-linked receptors
Tyrosine-kinase receptors
Ligand-gated ion-channel receptor
Intracellular receptors

13. G-protein-linked receptors

14. When G-protein-linked receptors receive a signal, they will activate a “G protein” inside the cell The G-protein starts the transduction pathway leading to the cell response

15. Tyrosine-kinase receptors act as an enzyme, using ATP to start several transduction pathways simultaneously

16. Ligand-gated ion-channel receptors open or close in response to a chemical signal, allowing ions to DIFFUSE in or out of the cell based on relative concentrations

17. Lipid-soluble chemical signals, such as steroid hormones, can pass through the plasma membrane, and bind to an intracellular receptor Inside the cell, the activated receptor may turn on or off certain genes (a transcription factor)

18. Once the signal has been received by the receptor, this triggers the transduction pathway, that eventually leads to the cell’s response
Fig : A phosphorylation cascade

19. Some signal-transduction pathways involve the use of small, non-protein molecules or ions. These are called second messengers Second messengers often bind to and activate other enzymes in the pathway

20. Cyclic AMP (cAMP) is a common second messenger

21. Calcium ions are also used as second messengers
The concentration of calcium is kept low in the cytoplasm of animal cells by actively pumping them into the mitochondria and the ER and out of the cell

22. Calcium is used by both G-protein and tyrosine-kinase pathways as a second messenger

23. Inositol triphosphate (IP3) opens a channel that releases Ca2+ into the cytoplasm

24. Calcium activates calmodulin which turns on or off other proteins

25. An example of an entire pathway
In times of physical stress, the adrenal glands release the hormone epinephrine
Fuel reserves are mobilized by the breakdown of glycogen to individual glucose molecules

26. The response of a cell to signal can be varied: 1
The response of a cell to signal can be varied: 1. Turning on certain enzymes 2. Turning on/off genes and protein production 3. Muscle contraction 4. Cell division etc…

27. The response of a cell to a signal depends on what type of cell it is and what other types of proteins are present in the cell