Lec 15/16 Cell Signaling

Flashcards covering key vocabulary related to cell signaling principles discussed in the lecture.

1st step in cell signaling

extracellular signal (primary messenger is created)

2nd step in cell signaling

Cell surface receptor binds to the extracellular signal

3rd step in cell signaling

Second messenger molecules relay signals

4th step in cell signaling

mediators that transmit the signal inside the cell to elicit a response.

5th step of cell signaling

Cellular responses are activated, resulting in physiological changes.

Modes of extracellular signaling

Paracrine
Endocrine
Contact dependent
Synaptic

Paracrine signaling

Local signaling where a cell produces a signal to induce changes in neighboring cells.

Endocrine signaling

Long-distance cell signaling using hormones released into the bloodstream to generate systematic response

Contact dependent signaling

Highly specific signal is transmitted from one cell to another using membrane bound signal receptors

Synaptic signaling

Highly specific neurotransmitters are released across a synapse to transmit signals directly to target cells.

Which 2 modes of cell signaling are the most specific

Contact dependent signaling and synaptic signaling are the most specific modes of cell signaling, as they directly involve interactions between particular cells.

Properties of cell signaling

Speed of response
Signal processing

Speed of electrical signals

~msecs

Speed of protein phosphorylation

~sec - mins

Speed of gene expression

Hrs

Types of signal processing

Hyperbolic
Sigmoidal
All or None

Which type of curve represents all or nothing response

A steep L shaped curve that indicates a rapid transition between low and high response levels.

Which curve represents sigmoidal

S curve that describes a gradual increase in response once effector concentration reaches threshold and eventually levels off as saturation occurs.

Example of sigmoidal response

Activation of protein kinase A (PKA) occurs when cAMP levels increase, leading to a gradual enhancement of signaling.

Which type of curve represents a hyperbolic response

A curve that shows a continuous, gradual increase in response with increasing concentration of an effector, typically plateauing as saturation is reached.

Positive feedback

A process that enhances or accelerates changes in a system, leading to a greater response.

Strong positive feedback induces which cell response

leads to abrupt, all/nothing cellular behavior (bistable), which can generate lasting effects even after initial signal is gone

Negative feedback

A process that dampens or reduces changes in a system, promoting stability or homeostasis.

Negative feedback- Short delay

Short lived response with rapid return back to normal

Negative feedback- Long delay

generates an oscillatory behavior where the system alternates between states over a longer period, allowing gradual adjustments.

Circadian rhythm

Generated by delayed negative feedback, which causes cellular oscillatory behavior over 24 hr period

Signal processing

The mechanisms by which cells respond to signals; includes gradual, abrupt, and oscillatory responses.

Cyanobacteria clock

-Kai-A,-B,-C constitutes the simplest signaling circuit of circadian rhythm

Cyanobacteria clock step 1

Kai C slowly phosphorylates with help of Kai A

Cyanobacteria clock step 2

Phosphorylated Kai-C activates Kai-B which inhibits further phosphorylation (negative feedback)

Adaptation/desensitization

enables cells to respond to changes in the concentration of an extracellular signal molecule (rather than to the absolute concentration of the signal)

How does Adaptation/desensitization occur

Negative feedback mechanisms

Mechanisms of Adaptation/desensitization

• Receptor sequestration

• Receptor downregulation

• Receptor inactivation

• Inactivation of signaling proteins

• Production of inhibitory proteins