Cell Communication

Chapter 11

Trillions of cells in multicellular organisms must communicate with each other to coordinate their activities.

In unicellular organisms signaling is important in finding different mating types for sexual reproduction.

Inside the cells there are a series of chemical changes that cause the response. This series of chemical events that occur is called the signal- transduction pathway.

These pathways are common to both humans and yeast cells suggesting that this strategy evolved very early on.

LOCAL Signaling Description –Cell secreting a chemical that

acts on a nearby target cellExample: 1.Panacrine signaling (Growth factors) – compoundsthat stimulate nearby cells to grow and divide

LOCAL Signaling Description –Cell secreting a chemical that acts on a nearby target cell

Example: 2. Synaptic signaling - Neurons secrete neurotransmitters that diffuse across an intercellular space (synapse) and interacts with a another neuron.

Long-Distance Signaling Description –Use of hormones (is a chemical secreted by one cell but exerts is effect on another cell some distance away). Example:1.Animal Cells - hormone is released into the

vessels of circulatory system and the molecules travel to target cells.

2.Plant Cells - hormones may travel in vessels or diffuse the air as a gas.

Types of Animal Hormones

Modified amino acids- i.e. epinephrine is a modified tyrosine.

Proteins-i.e. insulin is a large protein

Steroid Hormones- i.e. testosterone and estrogen are steroids.

Pheromones are chemicals secreted by one animal to affect the behavior of another animal.

Direct Contact Signaling Description –Cells have cell junctions where

direct contact of the cytoplasms of adjacent cells occur. This allows for signaling substances in the cytosol to pass feely between the adjacent cells.

Example:1.Animal Cells - communicate via direct

contact between molecule on their surface of their cell membranes.

2.Plant Cells – Between plasmodesmata.

The three stages of cell signaling are:

1. Reception

2. Transduction

3. Response

Signal begins when signal interacts with a receptor site located on the outside surface of the plasma membrane Signal is a ____Ligand_

-When the ligand (signal) attaches it will cause a change in the shape of the receptor site. Receptors are usually proteins inserted into the plasma membrane

Ligands (signals) can be: hormones, neurotransmitters, or growth factors.

Receptors can be: kinases

Processing the signal Protein process the signal Brings about a cellular response Protein kinases - are proteins that transfer

phosphate groups from ATP to another protein.(Approximately 1% of all our genes code for various protein

kinases)

Cascade effect- one protein kinase will activate another protein kinase by transferring a phosphate group on to it

Extremely Important

Transduce signal finally triggers a cellular response.

Response could be:-activating an exzyme

- activation of gene in nucleus - synthesis of protein

Bottom line – Cell-signaling process helps ensure that crucial activities occur in the right cells, at the right time, and in the proper coordination with the other cells of the organism!!

d. Intracellular receptors-Some signal receptors are NOT found in the plasma membrane. Instead they are dissolved in the cytoplasm. This means the signal must be lipid soluble to make into the cytosol. These signals are usually steroids hormones, thyroxin, and nitric oxide. i.e. Testosterone enters the cell and binds with a receptor protein found in the cytoplasm. This complex now moves to the nucleus where is acts a transcription factor and helps transcribes certain genes. Only targeted cells have intracellular receptors.

Types of cellular responses

1. Ultimately activating an enzyme

2. Synthesis of a particular enzyme or protein

1. Activating an enzyme-

Usually when cAMP, Ca++ or IP3 is activated then it will interact with a specific enzyme to start the cascading effect.

A biochemical pathway usually has a cascading effect where one protein kinase will activate another protein kinase by transferring a phosphate group on to it. These protein kinases are extremely important. Approximately 1% of all our genes code for various protein kinases. Protein phosphatase is a protein that will remove a phosphate group from proteins and can deactivate a protein kinase.