Chapter 11Cell Communication

Question? How do cells communicate? By “cellular” phones. But seriously, cells do need to

communicate for many reasons.

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 Communication

How?

Direct Contact May also occur by cell surface molecules

that project from the surface and “touch” another cell.

How?

Direct Contact When molecules can flow directly from

cell to cell without crossing membranes. Plants - plasmodesmata Animals - gap junctions

How?

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 C.S.1. Reception - receiving the signal.2. Transduction - passing on the signal.3. Response - cellular changes because

of the signal.

Reception

Transduction

Response

Reception The target cell’s detection of a signal

coming from outside the cell. May occur by:

Direct Contact Through signal molecules

Signal Molecules

The actual chemical signal that travels from cell to cell.

Often water soluble. Usually too large to travel through

membranes. Double reason why they can’t cross cell

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 Mechanisms1. G-Protein linked2. Tyrosine-Kinase3. Ion channels4. Intracellular

G-protein linked receptors Very widespread and diverse in

functions. Ex - vision, smell, blood vessel

development.

G-protein linked receptors Many diseases work by affecting g-

protein linked receptors.

Ex - whooping cough, botulism, cholera, some cancers

G-protein linked receptors Up to 60% of all medicines exert their

effects through G-protein linked receptors.

Tyrosine-Kinase Receptors Extends through the cell membrane. Intracellular part functions as a “kinase”,

which transfers Pi from ATP to tyrosine on a substrate protein.

Tyrosine-Kinase Receptors Often activate several different

pathways at once, helping regulate complicated functions such as cell division.

Ion-channel Receptors Protein pores in the membrane that

open or close in response to chemical signals.

Allow or block the flow of ions such as Na+ or Ca2+.

Ion-channel Receptors Activated by a ligand on the

extracellular side. Causes a change in ion concentration

inside the cell. Ex - nervous system signals.

Intracellular Signals Proteins located in the cytoplasm or

nucleus that receive a signal that CAN pass through the cell membrane.

Ex - steroids (hormones), NO - nitric oxide

Intracellular Signals Activated protein turns on genes in

nucleus.

Comment Most signals never enter a cell. The

signal is received at the membrane and passed on.

Exception - intracellular receptors

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.