1. Fundamentals of Biochemistry
Third Edition
Donald Voet • Judith G. Voet • Charlotte W. Pratt
Chapter 13
Biochemical Signaling
Copyright © 2008 by John Wiley & Sons, Inc.

2. There are many forms that biochemicals are used to signal systems to start or stop functioning. An obvious example are the class of compounds called hormones, produced by endocrine glands.

3. For instance, the adrenal medulla synthesizes catecholamines, one of which is norepinephrine, which is methylated to become epinephrine
These chemicals enter the bloodstream and interact with cells that have α and β adrenergic receptors in their membranes. These chemicals can act as agonists or antagonists.

4. Protein tyrosine kinases (PTKs) are a class of enzymes that activate other enzymes by covalent modification — phosphorylating a serine residue

5. But to get PTKs to work, you first need to bind a ligand
But to get PTKs to work, you first need to bind a ligand. For example, the receptor tyrosine kinase (RTK), which is imbedded in a cell membrane (a transmembrane protein), binds insulin and switches conformation.

6. Kinetics of binding a ligand

7. Scatchard plot (b) yields the ligand binding constant KL
B = [bound ligand] = [RL]; F = [free ligand] = [L]
George Scatchard, 1949

8. The Ras signaling cascade regulates cell growth and differentiation: starts with an RTK

10. Another group of signal transduction molecules are heterotrimeric G proteins
The structure of a heterotrimeric G protein, showing a bound GDP molecule

11. Adenylate cyclase (AC) catalyzes the production of cyclic AMP (cAMP) from ATP
AC is activated by the binding of a heterotrimeric G protein

12. G protein coupled receptors contain 7 transmembrane helices

13. Figure 13-18

14. Adenylate cyclase synthesizes cAMP that activates protein kinase A (PKA)

15. Figure 13-21

16. Figure 13-21b

17. The adenylate cyclase (AC) signaling system

18. Box 13-4a

19. Box 13-4b

20. Page 436

21. Figure 13-24

22. Figure 13-25

23. Figure 13-26

24. Figure 13-27

25. Figure 13-28

26. Figure 13-29

27. Page 441

28. Figure 13-30

29. Figure 13-31

30. Box 13-5a

31. Box 13-5b