CHAPTER 13: Signal-Transduction Pathways (Problems: - - PowerPoint PPT Presentation

CHAPTER 13: Signal-Transduction Pathways

(Problems: 1-5,7,13,15-18,21,25,29)

• 1. Primary messenger.
• Signal, first messenger, ligand.
• 2. Reception of primary messenger.
• Protein receptor of primary messenger.
• 3. Relay of information.
• Transmembrane protein, transducer.
• 4. Activation of effectors.
• Transducer, effector enzyme,

second messenger, effectors.

• 5. Termination of signal.
• Phosphatases

13.2. Receptor Proteins

Transmembrane proteins

Seven transmembrane helices (7TM proteins) Ligand binding on

• utside leads to

conformational change (new activity) on inside

• f cell.

Ligand Binding

ligand 7TM receptor Transducer (G-protein) Effector enzyme Second messenger Effector

Gs

Ligand Binding → Activation of G-Proteins → Activation of Effector Proteins

Activation of Effector Proteins → Phosphorylation of Proteins

Protein kinase A Protein kinase A phosphorylates Ser and Thr residues in numerous proteins resulting in activation or inhibition of their functions.

Control of Activation

X

GTPX Chlorera (Vibrio cholorae) Choleragen → stabilizes Gs ↓ Open Cl‐ channel ↓ Inhibits Na+‐H+ exchange ↓ NaCl loss G-cycle Whooping Cough (Bordertella pertussis) Toxin → prevents Gi ↓ Closes K+ channel ↓ Opens Ca2+ channel

Reversible Ligand/Receptor Binding

Other Second Messengers

Ligand/Receptor binding leads to G‐protein activation

2nd messenger 2nd messenger

Phosphorylation

• f Ser and thr
• n many proteins

The Phosphoinositide Cascade

Ligand + Receptor  Active G‐Protein  Activates C

13.3. Tyrosine Kinases

Epidermal Growth Factor Signaling

Adaptor proteins

Pi

Tumors

X

13.4. Insulin Signaling

Akt is a mobile protein kinase

Insulin-receptor substrates

Phosphorylate enzymes in glycogen synthesis and glucose transport (GLUT4) Signaling terminated by protein phosphatases

13.4. Calcium Ion is a Cytoplasmic Messenger

CaM-Ca2+ CaM-Kinase + Inactive CaM-Ca2+ CaM-Kinase Active Phosphorylation of proteins resulting in regulation of fuel metabolism, ion permeability, neurotransmitters