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Cellular Communication

The ligand isn't important.

The Response is!

What kind of feedback?

Simplicity leads to Complexity

It's All About Signal Reception!

Make Sure You Can

Big Questions

Why do cells communicate?

What does cellular communication look like?

How is cellular communication utilized in unicellular and multicellular life?

Explain why and how cells communicate with the environment.

Explain the common features shared among cellular communication processes.

Compare the purpose of cellular communication in unicellular and multicellular organisms

Describe the major features of signal transduction pathways in cells.

Connect cellular signaling pathways to actual examples as discussed in this presentation.

Discuss the evolutionary/adaptive considerations of cellular signaling pathways.

Theory:

Applications

Why Cells Communicate: Some Examples

How Cells Communicate: Signal Transduction

Note: We will only look at unicellular examples in this lesson (animals and plants later!)

Signaling Pathways

Epinephrine:

An Example

Epinephrine

The 3 Phases of Signal Reception

An Epinephrine Receptor

Widely conserved among all domains (why?)

Quorum Sensing

Yeast Mating

  • Aka "Adrenaline"
  • A common hormone in vertebrates.
  • Involved in short term stress ("fight or flight") response.

Apoptosis

G-Protein Linked Reception

G-proteins:

proteins activated by the transfer of a phosphate from a molecule of GTP.

The first step in the protein relay

What kind of hormone is epinephrine (polar or non-polar)?

communication among microbes that triggers group response once particular population densities are reached

Epinephrine is a polar amine ligand

"ligand"

Programmed cell death is programed because of the signaling pathway that it is programmed to.

Vibrio fischeri

Epinephrine signal transduction is mediated by G-Protein linked receptors.

It has multiple effects, but one response is the inhibition of glycogen synthesis and the acceleration of glycogen breakdown (why?)

A bacterium that lives inside organs in marine animals.

When population density hits a threshold, they begin to produce a light-producing protein.

This gives the host animal bioluminescence.

Tyrosine Kinases

Mating type in (haploid) yeast is genetically determined.

Two mating types (a and alpha). Each makes signaling molecules that the other receives.

The reception of a mating factor leads to the production of a mating "Shmoo"

Fusion of shmoo's = diploid yeast cell.

Meiosis soon ensues

Model of quorum sensing in V. fischeri.

Don't worry about the specifics, focus on the big picture

High density

Low density

Kinase: A protein that "phosphorylates" (adds a phosphate) to another molecule

Tyrosine Kinases:

proteins that form dimers. Tyrosine amino acid residues are active in the transfer of phosphates to relay proteins.

Remain active as long as the ligand is attached.

Amplification

How Signals Are Sent

More from less

Biofilms

Local Signals

Long Distance Signals

Cells Amplify A Message

Ligand-gated Ion Channels

Graphic Yeast Sex

Biofilms are bacterial ecosystems that are established and maintained due to elaborate quorum sensing networks

The incoming ions trigger the response

The Nervous and endocrine systems handle these things in animals. We will talk about them in depth, later in the course

Notice that death proteins are present in an inactive form prior to signal reception (Why?)

Yeast shmoo mutants & the shmoo formation pathway

Plaque Biofilm All Up On Your Teeth!

Other Signals

Second Messengers

Fruiting Body Formation in Soil Bacteria in response to poor environmental conditions

Complication

Here's an example:

Pretty much any chemical or energy source could serve as a biological signal...

...though most are biologically created molecules

Internal signaling molecules released due to external ("first") signals. Trigger sub-response pathways.

A "Branching Network"

How Signals are Recieved

Cyclic AMP: A typical second messenger that affects metabolism.

Things Get Complicated Quickly

Different Reception

Different Chemistry

Different Responses

Calcium ions are another common second messenger.

How can this kind of behavior evolve?

Things

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