Cell Communication - Cell Response

Ch. 11Section 11.4

““Output Response” - - The Final Output Response” - - The Final Step in a Signaling PathwayStep in a Signaling Pathway

Responses in the cytoplasm:•May open an ion channel or cause a change in cell metabolismRecall the response of liver cells to epinephrine

Notice that 1 1 signal moleculeis producing a response thatcan metabolize 101088 glycogen molecules!!

Many phosphorylation cascades end in an activated molecule that serves as a transcription factor which regulate the functioning of one or more genes….

The final kinase in the cascade phosphorylates, and, thus, activates a transcription factor in the nucleus

Responses in the nucleus:

Why are there so many steps between the Why are there so many steps between the original signal molecule and the cell original signal molecule and the cell

response?response?

1. One reason is: with this system, the one original signal molecule can be amplified many times

•This results from the fact that once a molecule is activated, it remains activated long enough to affect many molecules , and then each of those molecules activate several other molecules, and so on.

Much more efficient for cells A small number of signal molecules

released from just a few signaling cells can lead to a huge output from the target cells

Quick ThinkQuick Think

How is it that the message from a How is it that the message from a single signal molecule can be single signal molecule can be

amplified more than a millionfold??amplified more than a millionfold??

A second advantage is 2. signal specificity The same signal

molecule can generate different responses in different cells

Each type of cell may contain different types of proteins, thus they will respond to the same signal molecule differently

Signal Specificity: An Advantage to Signal Specificity: An Advantage to Multi-Step Signaling PathwaysMulti-Step Signaling Pathways

Different types of Different types of cells contain different cells contain different proteinsproteins

Why does epinephrine cause a livercell to metabolize glycogen, but cause a muscle cell to contract??

Another advantage…

3. Different receptor and internal proteins allows cells to interpret signals originating from other sources – leads to “cross talk”

QUICK THINKQUICK THINK

Explain why cells can respond differently to the same signal

molecule

Signaling EfficiencySignaling EfficiencyScaffolding Proteins-facilitate facilitate the action of relay proteins in the intermediate steps of signal transduction

Proteins are large and move slowly through thick cytosol

Scaffolding proteins help speed things up by holding proteins involved in the same pathway near each other

Problems arise when scaffolding Problems arise when scaffolding proteins are missingproteins are missingThe absence of a single scaffolding protein causes the disease Wiskott-Aldrich Syndrome

The absence or malfunction of the WAS protein causes a breakdown in the signaling pathway. Result: the cytoskeletons of immune cells do not have the correct configuration for cell division, leading to the symptoms of WAS

Eczema and abnomal bleeding are symptoms of Wiskott-AldrichSyndrome

QUICK THINKQUICK THINKExplain how scaffolding proteins work &

how they assist in cellular response mechanisms

Signal TerminationSignal Termination

All of the reactions in a signal transduction pathway must be reversible so that the cell’s receptor molecules can receive a continuous flow of information…The molecules involved need to be able to turn off, so they are ready to receive the next call

As in the case of the G-proteins in cholera patients, a pathway stuck in the on or off position may result in dire consequences