Cell Communication: A Review

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

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

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

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

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.

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.

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

Most signal receptors are plasma membrane proteins

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

Skeletal muscle contraction is a complicated “chemical cascade”.

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.

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

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

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.

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

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

What’s the Big Deal about Kinases?

Activating a kinase cascade also amplifies the response

The End