cell-signaling: signal transduction pathways

Cell-Signaling: Signal Transduction Pathways

• Bacteria produce and excrete signal proteins

• Bacteria have receptor proteins on their cell membranes

• When the signal protein binds with the receptor protein, single-celled bacteria can communicate & coordinate to produce group behaviors

• A few bacteria do not produce enough signal

• A quorum (group) produces enough signal to reach a threshold

Quorum Sensing in Bacteria

Signaling molecule

Response = light

The gray molecule is the protein receptor (lock) it is also a large organic molecule with a complex shape.

The colored molecule is the signal molecule (hormone)

Fit is lock-key based on complex chemical shape

Evolutionary Significance of Cell-Signaling • The same small set of cell-signaling mechanisms

shows up again and again in diverse species from bacteria (quorum sensing) to humans (hormones, embryonic development, cancer)

• These similarities provide evidence for evolutionary relatedness of all life

• A stimulus triggers the release of hormones from endocrine cells

• Hormones travel throughout the body via the blood stream

• Hormones bind only to specific target cells

• Binding of the hormone to a receptor triggers a response

Signaling in Human Cells - Hormones

AutocrineJuxtacrine

Paracrine

Endocrine

Autocrine –(auto = self)

Juxtacrine -(juxta = beside, next to, touching)

Paracrine -(para = nearby)

Endocrine –(endo – within)

Quorum-sensing in Bacteria

Plasmodesmataallow hormones to travel between plant cells

Morphogens determines head vs. tail-end of embryo

Juxtacrine – the cells are touching each other and the signal moves between cells without having to travel a long distance

Paracrine – the ligands only travel the length of a small embryo, so the cells are fairly close

Paracrine – the signal does not need to move very far, only to the adjacent cell or cells nearby

Endocrine – the insulin moves throughout the body to all cells, even those far from the pancreas

#1

#1

#2

#2

#3

#3

#4

#4Signal/Hormone

Signal/Ligand

Receptor

ReceptorTransduction via Relay Molecules

Transduction via Relay Molecules

Response

Response

• Step 1 = Signal reception: hormone/ligand binds to receptor and initiates/triggers/induces signaling

• Step 2 = Transduction: intercellular cascade transduces/amplifies/transfers the signal from plasma membrane to nucleus via a series of relay molecules

• Step 3 = Response: transcription/expression of target genes is stimulated/repressed

Signaling

Reception

Transduction

ResponseAmplification

ATP ADP + P

Reception

Steps 2 – 6 = Transduction

ResponsePP

PP

Facilitated diffusion

Second Messenger: Cyclic AMP

• Relay molecules & secondary messengers have the same job

• Relay molecules are almost always proteins that require activation. They are large and do not diffuse through the cell quickly.

• Secondary messengers are small, water soluble molecules that can diffuse quickly.

https://www.youtube.com/watch?v=FkkK5lTmBYQ

Insulin Signal-Transduction Pathway

1

B

D

AC

Identify the following from the model:1. Signaling molecule (the hormone insulin)2. Protein receptor3. Relay molecules (transduction)4. Response5. Describe the response:

1. Use the diagram to describe: signal, reception, transduction & response.

2. Discuss how this process would be altered if there was no insulin present:

3. What would be the consequence to blood [glucose]?

Signaling molecule

Receptor

Transduction

Response

Glucagon Signal-Transduction Pathway

• Animals store glucose as glycogen = branched chains of glucose molecules

• Glycogen is stored in the liver and muscles

1. What triggers the fight or flight response?2. What are some symptoms associated with it?3. What is the adaptive (evolutionary significance)

of this response?4. How would the breakdown of glycogen to

release glucose into the blood aid the response?

Signal Transduction Case-Study: Epinephrine

• Second messengers are often essential to the transduction

Example: Cyclic AMP

http://www.youtube.com/watch?v=ejq99wLEMTw

Signal Transduction Case-Study: Epinephrine

Many transduction pathways include:• Phosphorylation

cascades

• Protein kinasesactivated by CyclicAMP- add a phosphate group to the next protein in the cascade sequence thus activating it

http://www.youtube.com/watch?v=ejq99wLEMTw

• Hormones like epinephrine/adrenaline are proteins (peptides)

• Thus they can not diffuse through the lipid bilayer

• They are too large to use protein channels

• Thus they must use the signal-transduction pathway

• Cyclic AMP (cyclic AMP) is a second messenger, its small size allows it to diffuse quickly within the cell

• Steroid hormones (like testosterone) are lipid soluble

• Thus, they can diffuse through the lipid bilayer

• Thus, they do not need a receptor on the cell membrane

• The receptor is within the cell

• Here, testosterone is causing a gene to be transcribed

Select signaling by: hormones, neurons or both

1. Involves a stimulus2. Involves a chemical

messenger3. Involves a signal

transduction pathway4. Triggers a response5. Involves an action

potential6. Signal travels to a specific

target location7. Signal travels everywhere8. Chemical signal travels

through blood stream