Chapter 11: Cell Communication

Essential Knowledge

2.e.2 – Timing and coordination of physiological events are regulated by multiple mechanisms (11.1).

3.b.2 – A variety of intercellular and intracellular signal transmissions mediate gene expression (11.1 & 11.4).

3.d.1 – Cell communication processes share common features that reflect a shared evolutionary history (11.2 & 11.2).

3.d.2 – Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling (11.1 & 11.2).

Essential Knowledge

3.d.3 – Signal transduction pathways link signal reception with cellular response (11.3).

3.d.4 – Changes in signal transduction pathways can alter cellular response (11.4).

Question?

How do cells communicate?◦By “cellular” phones

But seriously, cells do need to communicate for many reasons.

Cell Communication

Why do cells communicate?

Regulation - cells need to control cellular processes

Environmental Stimuli - cells need to be able to respond to signals from their environment

Cell Signaling (C.S.)

Is a relatively “new” topic in Biology and AP Biology

Appears to answer many questions in medicine

Is a topic you’ll be hearing more about in your future

Stages of cell signaling

1. Reception - receiving the signal2. Transduction - passing on the signal3. Response - cellular changes because of

the signal

Reception

Reception

The target cell’s detection of a signal coming from outside the cell

May occur by:◦Direct contact◦Through signal molecules

Direct Contact

When molecules can flow directly from cell to cell without crossing membranes

Plants - plasmodesmataAnimals - gap junctions

Direct Contact

May also occur by cell surface molecules that project from the surface and “touch” another cell

Signal Molecules

The actual chemical signal that travels from cell to cell

Often water solubleUsually too large to travel through

membranes

Signal Molecules

Behave as “ligands” ◦A smaller molecule that binds to a larger one

Receptor Molecules

Usually made of proteinChange shape when bind to a signal

moleculeTransmits information from the exterior to

the interior of a cell

Receptor Molecules

1. G-Protein linked2. Tyrosine-Kinase3. Ion channels4. Intracellular**You must research these on your own.

Comment

Most signals never enter a cell ◦The signal is received at the membrane and

passed onException - intracellular receptors

Transduction

Signal-Transduction Pathways

The further amplification and movement of a signal in the cytoplasm

Often has multiple steps using relay proteins such as Protein Kinases

Protein Phosphorylation

The addition of Pi to a protein, which activates the protein

Usually adds Pi to Serine or Threonine amino acids

Protein Kinase

General name for any enzyme that transfers Pi from ATP to a protein

About 1% of our genes are for Protein Kinases

Amplification

Protein Kinases often work in a cascade with each being able to activate several molecules.

Result - from one signal, many molecules can be activated.

Secondary Messengers

Small water soluble non-protein molecules or ions that pass on a signal

Spread rapidly by diffusionActivates relay proteinsEx: cAMP, Ca +2

Response

Responses

May involve:◦Regulation of cytoplasmic activities

OR◦Regulation of transcription

Cytoplasmic Regulation/Response

Rearrangement of the cytoskeletonOpening or closing of an ion channelAlteration of cell metabolism

Transcription Regulation/Response

Otherwise known as nuclear regulation/reponse

Activating protein synthesis for new enzymes

Transcription control factors are often activated by a Protein Kinase

Comment

Chapter focused only on activating signals

There are also inactivation mechanisms to stop signals◦We will learned about these with the cell cycle

Summary

Recognize several examples and importances of cell communication.

Identify the three stages of cell signaling.Recognize how signals are received.Recognize how signals are transduced.Recognize the role of protein kinases and

phosphorylation in signal amplificationIdentify how cells respond to signals.Recognize the role of cell signaling in

apoptosis.