1. Cell Communication: A Review

2. Communication may occur by direct contact between cells.
Where have you seen these pictures before?

3. Or it might involve a signaling system
This should look familiar- we studied this in the nervous and endocrine system

4. The signal may be “local”, only travel short distances

5. Or it may travel a long distance, as in the endocrine system

6. The importance of cell signaling-
Cardiac muscle cells must function as a unit,
not individually
Acetylcholine initiates skeletal muscle contraction
Epinephrine signals the liver to break down
glycogen, increasing blood glucose levels
Testosterone turns on genes that promote
“maleness”
These are just a few reasons that cellular
communication is vital to homeostasis; many
metabolic disorders and cancers are a result of
malfunctioning communication among cells.

7. Communication gone wrong-
Normally, cells in the pancreas release a signal, called insulin, that tells your liver, muscle and fat cells to store this sugar for later use. In type I diabetes, the pancreatic cells that produce insulin are lost. Consequently, the insulin signal is also lost. As a result, sugar accumulates to toxic levels in the blood. Without treatment, diabetes can lead to kidney failure, blindness and heart disease in later life.

8. Types of Signaling Molecules
Polypeptides- insulin
Amines- thyroxine (hydrophobic), epinephrine, dopamine, serotonin
Steroids- testosterone
Gases- nitric oxide, ethylene
The chemical class will determine how the molecule enters the cell; for example, thyroxine and the steroids are hydrophobic and can pass through the cell membrane. Insulin and epinephrine are hydrophilic and must utilize a receptor on the cell membrane and activate a second messenger

10. Most signal receptors are plasma membrane proteins

11. Let’s start with a simple example- this could be the beginning of the chemical cascade that leads to skeletal muscle contraction. Ach is the signaling molecule, Na+ ia the ion enters the cell

12. Skeletal muscle contraction is a complicated “chemical cascade”.

13. The receptor is a G protein linked receptor
The receptor is a G protein linked receptor. The signaling molecule in this case might be epinephrine affecting cells of the liver, or the heart- notice that the epinephrine doesn’t enter the cell- it initiates a series of chemical reactions that results in the response.

14. What do you remember about epinephrine?
Produced in the adrenal medulla
Neurotransmitter of the sympathetic nervous system (fight or flight)
Acts on the liver to promote the breakdown of glycogen
Acts on the heart to increase the heart rate

15. Since epinephrine doesn’t enter the cell, it must utilize a
“second messenger”. In this case the second messenger is
Cyclic AMP (cAMP)

16. Growth factors utilize a type of receptor called a tyroxine kinase receptor. Notice the similiarity with the first example- the signaling molecule doesn’t enter the cell. Also notice the term “kinase”- we will look at it later.

17. Recall the unit on the endocrine system
Recall the unit on the endocrine system. The action of some hormones is to act as a transcription factor. Notice that the receptor for testosterone
is in the cell; the hormone-receptor
complex acts as a transcription factor

18. In cell signaling, how is the flow of specific ions
regulated?
Opening and closing of ligand-gated channels
Transduction
Cytoskeleton rearrangement
Endocytosis

22. What’s the Big Deal about Kinases?

25. Activating a kinase cascade also amplifies the response

27. The End