Revision 2010 Unit 3 Cell Communication

Cell Communication

Unit 3 AOS2 Review

Types of SignalsPhysical stimuli• Light• Heat• Touch/mechanicalChemical stimuli – specific signalling

molecules• Nutrient molecules – glucose• Hormones: in animals and plants• Neurotransmitters• Pheromones• Electrical signals

Communication Systems Involve Signal Transmission

• Signals are transmitted to targeted cells via:

• The Nervous System• A system of specialised cells providing rapid and precise signalling

between parts of the organism.

• Chemical signals (defined by the distance travelled) • Chemical messengers secreted by cells and carried via a transport

system to finally diffuse into the extra cellular fluid surrounding the target cell. (The Endocrine system is only one part)

Long Distance Communication Can be Fast!

Signal initiated Signal transmitted Signal received

Nerve Cells (neurons) form nerve pathways. Information passes along a neuron as an electrical current. The impulse is unidirectional and fast!

Or slow… such as in the Endocrine System.

Hydrophobic and Hydrophilic Signals

A return to the nature of molecules, importance of shape and binding specificity.

Membrane bound receptor

Intracellular receptor molecule

Hydrophilic signalling molecules

Neurotransmitters

Growth Factor HormonesInsulin

Hydrophobic Signalling MoleculesSteroid hormonesThyroid hormones

Types of Plasma Membrane Receptors

Ion Channel Receptors (milliseconds)

Binding of ligand causes a shape change that opens the channel so ions enter or leave the cell. Eg: Acetycholine at nerve/muscle junctions

G protein-couple receptors (Seconds)

Binding of ligand activates a G protein which activates or inhibits an enzyme or modulates an ion channel that generates secondary messengers. Eg. Receptor for glucagon.

Tyrosine kinase-linked receptor (hours)

Binding of ligand to TK causes a shape change that activates enzymes within the cell. Eg: Human Growth Factor.

Signal Transduction

• Applying the stimulus response model to the cell at a molecular level

• Is the signal hydrophobic or hydrophillic?• Does the cell have the correct receptor

molecules?• How is the signal transformed into a response

by a effector molecule?

Intracellular receptors for hydrophobic signals

Steroid hormones activate receptors which regulate gene expression.

•Steroid hormones moves through the lipid bilayer

•Steroid binds with intracellular receptor

•The ligand-receptor complex moves into the nucleus to regulate gene expression

•Proteins are the products of gene expressions

Hydrophilic signals

• The signal is received by a receptor on the cell membrane

• The signal passes along relay molecules – signal transduction.

• At the end of the relay effector molecules produce the cellular response

The Cellular Response

• Effector molecules bring about a cellular response. These responses include:

• Activates or inhibits enzyme action.• Regulates protein production by switching

genes on or off.• Opens or closes protein channels.• Moves transport vesicles to the plasma

membrane to secrete cellular products.

2006 Exam – Short Ans 2.

2006 Exam – Short Ans 2.

2006 Exam – Short 2

2007 – MC Q 21