Chapter 11 Cell Signaling

Lecture 38

Cell signaling

How cells communicate with each other

Functions of cell signaling

Development

Immune system function

Nervous system function

Homeostasis

Response to hormones

Types of signaling in multicellular organisms

1. Direct cell-cell contact

2. Local signaling

3. Long distance signaling

1. Direct cell-cell contact (plant, animal)

Cell junction, cell-cell recognition

Cell junctions

Direct connection of the cytoplasm of adjacent plant or animal cells

Cell-Cell recognition (animal cells)

Direct contact of membrane proteins (in immune system, devolpment)

2. Local signaling (animals)

Paracrine signaling

Synaptic signaling

Synapse

Paracrine signaling

A secretory cell releases a signal that binds target cells closely nearby

Ex; Growth factors; stimulate cell growth

Synaptic signaling

In nervous system

Neurons release a neurotransmitter that stimulates a target cell

Synapse

A tiny gap between nerve and target cell

Long distance signaling (Plants, animals)

Hormones: used for long distance signaling

Endocrine signaling (in animals)

Gland secretes hormones into the bloodstream and binds cells far away

Ex; insulin, adrenaline (epinephrine)

Growth regulators (in plants)

Can travel in vessels, in the air, or through cells

Ex; ethylene gas- promotes ripening

3 stages of cell signaling

Earl W. Sutherland (1971 nobel prize)

Studied how epinephrine stimulates an enzyme that breaks down glycogen

It only worked if the cells were intact, not if you added epinephrine directly to the enzyme

Thus, the cell has a signaling mechanism

Cell signaling

Changes that occur on the inside of the target cell in response to a extra cellular signal

3 steps in signaling (sutherland)

1. Reception-signaling molecule binds a receptor on the cell surface or inside the cell

2. Signal transduction- the receptor changes shape and starts a cascade of intracellular signals

3. Response- cell responds to signals

Reception

Signal molecule (ligand) binds a receptor

Binding between ligand and receptor is highly specific

Receptor changes shape and starts a signal

Ligand

A general term for a molecule that activates a receptor

Types of receptors (know)

1. Intracellular receptors

2. Membrane receptors

Intracellular receptors

In the cytoplasm or the nucleus

Bind small hydrophobic ligands such as steroid hormones or thyroid hormones

Receptor goes to nucleus and activates gene expression

Membrane receptors 3 types

1. G-protein-coupled receptors

2. Receptor tyrosine kinases

3. Ligand-gated ion channels

Membrane Receptors - GPCRs

G-protein-coupled receptors (GPCRs)

All GPCRs have 7 transmembrane spanning regions

Internal site binds to G proteins

G protein activates an effector

Example of GPCR functions

Autonomic nervous system (blood pressure, heart rate, digestion)

Vision, taste, smell

Mood and behavior (serotonin, dopamine)

Beta-blockers bind GPCRs, which block the effect of epinephrine

Half of all pharmaceuticals affect G-protein pathways

Receptor Tyrosine Kinases

Kinase: enzyme that adds a phosphate group to a protein

Receptor tyrosine kinases