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 signal 2. Transduction - passing on the signal 3. 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 - plasmodesmata Animals - 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 soluble Usually 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 protein Change shape when bind to a signal molecule Transmits information from the exterior to the interior of a cell

Receptor Molecules 1. G-Protein linked 2. Tyrosine-Kinase 3. Ion channels 4. Intracellular **You must research these on your own.

Comment Most signals never enter a cell ◦The signal is received at the membrane and passed on Exception - 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 diffusion Activates relay proteins Ex: cAMP, Ca +2

Response

Responses May involve: ◦Regulation of cytoplasmic activities OR ◦Regulation of transcription

Cytoplasmic Regulation/Response Rearrangement of the cytoskeleton Opening or closing of an ion channel Alteration 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 amplification Identify how cells respond to signals. Recognize the role of cell signaling in apoptosis.