The document discusses second messengers, which are small molecules that transmit signals within cells from one location to another. Specifically, it discusses how cyclic AMP was discovered as a second messenger that transmits signals from hormones like glucagon and epinephrine to affect glycogen metabolism in the liver. It also discusses calcium ions as another important second messenger. The document outlines the four major classes of second messengers and their properties, such as being synthesized and degraded by enzymes, able to diffuse quickly within cells, and able to amplify signals.

2. They were discovered by Earl Sutherland and Ted Rall as heat
stable factor that mediated the intracellular actions of the
hormones glucagon and epinephrine on glycogen metabolism
in the liver
That factor was- cyclic AMP, a discovery that earned
Sutherland a Nobel Prize in 1971
The next signaling molecule to be officially considered as a
second messenger was the calcium ion by pioneering work of
London-based physiologist Sydney Ringer. The acceptance of
the general signal transduction function of Ca2+, as originally
proposed by Lewis Victor Heilbrunn

7. Second messengers fall into four major classes:
1. cyclic nucleotides, such as cAMP and other
soluble molecules that signal within the cytosol;
2. lipid messengers that signal within cell
membranes;
3. ions that signal within and between cellular
compartments; and
4. gases and free radicals that can signal
throughout the cell and even to neighboring cells.

8. They are also known as intracellular messengers,
share common properties :
1. They can be synthesized/released and broken down
again in specific reactions by enzymes or ion
channels.
2. Some (such as Ca2+) can be stored in
special organelles and quickly released when
needed.
3. Their production/release and destruction can
be localized, enabling the cell to limit space and
time of signal activity.

9. Second messengers are small molecules can be synthesized
and destroyed quickly.
They can be made readily
Act at high and low concentrations of target proteins
Low affinity permits rapid dissociation.
They also can diffuse quickly within the cell, although many
cells have developed mechanisms to spatially restrict such
diffusion.
Second messengers are, thus, superior to proteins in
mediating fast responses, particularly at a distance
They can be addressed to large numbers of target proteins
simultaneously.
These advantages often overcome their lack of catalytic
activity and their inability to bind multiple molecules
simultaneously

10. They can amplify the signal

11. 11
Activated G proteins activate effector proteins -Adenylyl
cyclases

13. Synthesis and degradation of cAMP

16. Many protein activated by secondary messengers
1.Relay proteins.
2.Messenger proteins
3.Adaptor proteins
4.Amplifier proteins,.
5.Transducer proteins.
6.Bifurcation proteins
7.Integrator proteins
8.Latent gene regulatory proteins
Anchoring proteins
Scaffold proteins
Modulator proteins

17. The activation of cyclic-AMP-dependent protein kinase
(PKA)

19. 19

20. 20

21. 21
Coordinate Control of Glycogen Metabolism

22. Signal response via GPCR activate A.cyclase