Cell Communication

Page
9

different

protein

kinases

Slide 66

Termination of the Signal

Inactivation mechanisms are an essential aspect of cell signaling

When signal molecules leave the receptor, the receptor reverts to its inactive state

Slide 67

Concept 11.5: Apoptosis (programmed cell death) integrates multiple cell-signaling pathways

Apoptosis is programmed or controlled cell suicide

A cell is chopped and packaged into vesicles that are digested by scavenger cells

Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells

Slide 68

Fig. 11-19

2 µm

Slide 69

Apoptosis in the Soil Worm Caenorhabditis elegans

Apoptosis is important in shaping an organism during embryonic development

The role of apoptosis in embryonic development was first studied in Caenorhabditis elegans

In C. elegans, apoptosis results when specific proteins that “accelerate” apoptosis override those that “put the brakes” on apoptosis

Slide 70

Fig. 11-20

Ced-9

protein (active)

inhibits Ced-4

activity

Mitochondrion

Receptor

for death-

signaling

molecule

Ced-4

Ced-3

Inactive proteins

(a) No death signal

Ced-9

(inactive)

Cell

forms

blebs

Death-

signaling

molecule

Other

proteases

Active

Ced-4

Active

Ced-3

Nucleases

Activation

cascade

(b) Death signal

Slide 71

Fig. 11-20a

Ced-9

protein (active)

inhibits Ced-4

activity

Mitochondrion

Ced-4

Ced-3

Receptor

for death-

signaling

molecule

Inactive proteins

(a) No death signal

Slide 72

Fig. 11-20b

(b) Death signal

Death-

signaling

molecule

Ced-9

(inactive)

Cell

forms

blebs

Active

Ced-4

Active

Ced-3

Activation

cascade

Other

proteases

Nucleases

Slide 73

Apoptotic Pathways and the Signals That Trigger Them

Caspases are the main proteases (enzymes that cut up proteins) that carry out apoptosis

Apoptosis can be triggered by:

An extracellular death-signaling ligand

DNA damage in the nucleus

Protein misfolding in the endoplasmic reticulum

Slide 74