Lecture 21 - Cell communication and cell signaling I

Cells can act as both ___ cells and ____ cells

target; signaling

______ ______ is the process whereby one type of signal is converted into another

signal transduction

Describe signal transduction

receptor on a target cell receives an extracellular signal and the produces intracellular signal molecule that alter cell behavior

____ ______ encompasses the mechanic of signal reception and transduction

cell signaling

5 types of cell signaling

• endocrine

• paracrine

• autocrine

• neuronal

• contact-dependent

Endocrine signaling

• signaling cell:

• signaling molecule:

• communication distance:

• communication mode:

endocrine cell, hormones, long, public broadcast to whole body

Paracrine signaling

• signaling cell:

• signaling molecule:

• communication distance:

• communication mode:

many cell types, cytokines & interferons, local, semi-public

Example of paracrine signaling

• regulate inflammation at the site of infection

• promote cell proliferation at a wound site

Define autocrine signaling

a specialized form of endocrine signaling in which cells respond to signaling molecules they secrete themselves

Autocrine signaling

• signaling cell:

• signaling molecule:

• communication distance:

• communication mode:

many cell types, cytokines & interferons, local, semi-public

examples of autocrine

cancer cells promote their own survival and proliferation

Neuronal signaling

• signaling cell:

• signaling molecule:

• communication distance:

• communication mode:

nerve cell, neurotransmitter, long, private

In contact-dependent signaling, signals are transmitted through _____ _____ _____ between neighboring cells

direct physical contact

Contact-depending signaling

• signaling cell:

• signaling molecule:

• communication distance:

• communication mode:

several (epithelial and mesenchymal), several, very short, private

Example of contact-dependent signaling

during embryonic development, adjacent cells are initially similar then become specialized

Two types of signaling receptors

• large and/or hydrophillic

• small and/or hydrophobic

How do large/hydrophillic molecules signal to other cells

bind and rely on surface receptors to relay their message

How do small/hydrophobic molecules signal to other cells

bind to intracellular receptors

(T or F) the same signal molecule can induce different responses in different target cells

True

How does the cell limit the type of of signals that can affect it

By producing only a limited set of receptors

Is it possible for the same receptor to induce a different intracellular signaling response?

Yes

Examples of cell signals that are typically fast

changes in cell movement, secretion, or metabolism

Examples of cell signals that are typically slow

cell differentiation and increased cell growth or division

Cell-surface receptors relay extracellular signals via ____ _____ ______

intracellular signaling pathways

5 functions of the intracellular signaling pathways

• relay

• amplify

• integrate

• distribute

• modulate

What does it mean to integrate an extracellular signal

detect from more that one signaling pathway and integrate them before passing it on

What does modulation mean in an intracellular pathway

the activity of upstream signaling molecules provides feedback

Some intracellular signaling proteins act as molecular ______

switches

What can turn molecular switches on or off

addition or removal of phosphate groups

Kinases ____ phosphate groups while phosphates _____ them

add; remove

Class 1 molecular switch proteins

protein phosphorylation

Class 1 switch protein is ___ by protein kinase and ______ by protein phosphatase

activated; deactivated

Class 2 switch protein

GTP-binging proteins

Class 2 molecular switch proteins are _____ upon binding to GTP and ____ by the exchange of GTP for GDP

activate; deactivates

2 types of G-proteins

• large heteromeric G-proteins

• small monomeric G-proteins

Subunits of large, heteromeric proteins

alpha, beta, gamma

Another name for small, monomeric G-proteins

Ras proteins

3 main classes of cell-surface receptors

• ion-channel-coupled receptors

• G-protein-coupled receptors

• enzyme-coupled receptors

G-coupled protein receptor structure

• seven alpha-helix domain

• cytosolic G protein binding loop - specific for a particular G protein

G protein structure

Heterotrimeric G-proteins with subunits being a,B, and y

G proteins are a type of _____ _____ whose on or off states depends on whether the G protein is bound to GTP or GDP

molecular switch

Did you watch video for G proteins

Yes

_____ _____ binds receptor triggering a conformational change, thus starting the activation process of the G-protein

signal molecule

How is G-protein activated

alpha subunit releases GDP and binds to GTP → activates G-protein

When an activated a subunit interacts with its target protein → it activates that target protein and activates that protein for as long as the two …

remain in contact

How does the alpha subunit inactivate G protein

a subunit hydrolyzes its bound GTP to GDP

(T or F) the GPCR pathway must be tightly regulated

True

3 mechanisms that allows GPCR pathway to be shut down

1. GTP on a subunit is hydrolyzed to GDP

2. arrestin binds to phosphorylated GCPR

3. primary signal (ligand of the GPCR) is removed