3 teams - ~ 8 students in each

Have to create a skit to physically model one of the 3 types of receptor proteins G-protein linked receptors Tyrosine kinases Ligand gated ion channels

As we take notes today, starting thinking about what you could do to “act” it out.

We will plan and rehearse today and perform next week

Your skits You need: a narrator, a signaling cell, ligand, receptor cell, protein receptors, transduction pathway, and some sort of cell response

Skits

1. G protein linked receptor proteins with cAMP as a second messenger

2. Tyrosine kinase receptors with a phosphorylation cascade

3. Ligand gated ion channels with IP3 as a second messenger

Transduction of a Signal is Usually a Multi-Step Pathway

In this case, there are two advantages:1. A small number of extracellular signal

molecules can produce widespread cellular response. 2. Provides more opportunities for

coordination & regulation than in simpler systemsAnalogy:

vs.

On/off switchis like a singlestep pathway Dimmer=

multi-step

Cell Communication –Signal Transduction

Ch. 11Section 11.3

Signal Transduction Pathways

•The binding of a specific signal to its receptor triggers a chain reaction that leads to a response.•Relay molecules are the proteins that “carry the message” down a reaction chain

Ligand doesn’t enter cell

Remember: the Remember: the signal molecule signal molecule itselfitself doesn’t doesn’t physically physically get passed down get passed down the pathway.the pathway.

Instead, at each step of transduction a protein undergoes a conformational change, which in turn transduces the next protein.

Quick Think

How does a message get “passed” along from receptor to response?

Protein Phosphorylation & Dephosphorylation:

Phosphorylation= the transfer of a phosphate group from ATP to a protein; a mechanism for regulating protein activity

Protein kinase is the enzyme that transfers phosphate groups from ATP to proteins

Phosphorylation Phosphorylation CascadeCascade

Many relay molecules in signal transduction pathways are protein kinasesAs phosphates are passed from one protein to another, the newly phosphorylated protein undergoes a shape change and is now active.

Quick Think

Describe what a phosphorylation cascade is – try to use the term “conformation” in your response

Protein kinases are numerous and help regulate cell reproduction. Therefore, abnormal kinase activity can contribute to cancer.

In addition to protein kinases, protein phosphatases also play a role in the cascade

Protein phosphatases are enzymes that dedephosphorylate proteins

Phosphate removal causes protein inactivation, therefore protein phosphatases turn off signal transduction

Phosphatases also make kinases available for re-use

QUICK THINKQUICK THINK

Explain how a phosphorylation cascade gets turned off

Small Molecules & Ions as Second Messengers:

Second messengers: small, nonprotein, water-soluble molecules or ions; the signal molecule being the “first messenger.”

The two main second messengers are1. Cyclic AMP (cAMP)2. Calcium ions (Ca+)

Cyclic AMP

cAMP= cyclic adenosine monophosphate; a ring shaped molecule made from ATP by an enzyme, adenylyl cyclase

Example ofcAMP as a Second Messenger

The binding of epinephrine,the first messenger, activates adenylyl cyclase, which then catalyzes the synthesis of cAMP in a liver cell. The response isthe breakdown of glycogen within the cell.

Boosts your energy!

cAMP Malfunctioning

Vibrio cholerae produces a toxin that modifies the G protein, which is now stuck in the on position.

G protein is unable to hydrolyze GTP to GDP

Now high concentrations of cAMP cause intestinal cells to secrete water & salts- may lead to death w/in hours

cAMP’s role in cells1. It is short lived – rapidly converted back to

AMP (adenosine monophosphate) by phosphodiesterase

2. Once epinephrine binds, cAMP levels increase 20X in cell

3. Caffeine artificially boosts your energy by blocking the conversion of cAMP to AMP, keeping you alert even without epinephrine

4. It is involved in many pathways

Quick Think

What’s cAMP?

Calcium Ions & Inositol Triphosphate (IP3) as Second Messengers

•Some signal molecules such as neurotransmitters, growth factors, & certain hormones stimulate an increase in calcium ion concentration. •Increases in Ca2+ concentrations cause cellular responses including muscle contraction, secretion, & cell division.

Because the relative concentration of Ca2+ is so much lower in the cytosol than in the extracellular fluid, slight changes in concentrationeasily elicit a response

How?

IP3, inositol triphosphate, stimulates the ER to release Ca2+ into the cytosol

IP3 attaches to an ion-gated channel receptor protein in the membrane of the ER. The ion-gated channel opens and Ca ions rush out

QUICK THINKQUICK THINK

Describe what a second messenger is

Use IP3 as an example