Mechanism of Hormone action, Role of Secondary Messengers cAMP, cGMP , Ca and Calmodulin
1. Mechanism of Hormone action,
Role of Secondary Messengers
cAMP, cGMP , Ca and Calmodulin.
PRESENTED BY
JYOTI DEVENDRA ADALA
MSc PART 1
2. Coordination is the process through
which two or more organs interact and
complement the function of one
another.
Coordination is brought by the two
following system:-
a) Nervous system
b) Endocrine system
3. INTRODUCTION TO HORMONES AND SECONDARY
MESSENGERS
Hormones in Greek means to excite. Hormones are
defined as the organic substance produced in small
amounts by the endocrine glands secreted into the
blood stream to control metabolic and biological
activities in the target cells.
Functions of the hormone include control of many
metabolic pathway of various constituents, regulate
secondary sexual characteristics and so on.
4. Secondary messengers are the molecules that relay
signals from the receptors on the cell surface to target
molecules inside the cell.
They greatly amplify the strength of the signal, cause
some kind of change in activity of the cell.
Earl Wilbur Sutherland Jr.,
discovered secondary
messengers for which he won
the 1971 Noble Prize in
medicine.
5. Hormones can classified into two groups
i) Based on their chemical nature
ii) Based on mechanism of action
a) Group 1 hormones- Bind to intracellular receptor to
form complex and carry out biochemical function.
b) Group 2 hormones- Bind to cell surface receptor and
stimulate the release of certain molecule namely
secondary messengers which in turn perform
biochemical function.
7. Quick recap..
Being lipophilic, these hormone can easily pass across the
plasma membrane. They act through intracellular receptors
( cytosol or nucleus).
They form hormone receptor complex binds to the specific
regions on the DNA called HRE and cause increased
expression of specific genes.
It is believed that the interaction of hormone receptor
complex with HRE promotes initiation , elongation and
termination.
The ultimate outcome is the production of specific proteins
( translation) in response to hormonal action.
8. GROUP 2 HORMONE ACTION
Hormones that bind to surface receptors of the cells, communicate
through intermediary molecules called second messenger which are
generated as consequences of the hormone action.
Example:- The heterotrimeric G protein. G protein was discovered
by Alfred Gilman and Martin Rodbell in 1990.
9. MECHANISM OF SECOND MESSENGER
1) Cyclic AMP ( adenosine 3’ 5’ monophosphate)
cAMP synthesized from nucleotide ATP by the enzyme adenylate
cyclase .
10. 2) Cyclic GMP
cGMP (guanosine 3’ 5’ monophosphate)
synthesized from nucleotide GTP by the
enzyme guanylyl cyclase. Cyclic GMP carries
different messages to different tissues:
1) In the kidney and intestine,
2) In the cardiac muscle it signal relaxation,
3) Nitric oxide stimulates the synthesis of cyclic
GMP.
11. 3. CALCIUM AND/ OR PHOSPHOINOSITIDES
AS SECONDARY MESSENGER
In many cells that respond to extracellular signals, calcium
serves as a second messenger.
Certain hormone receptor interaction result in activation of the
enzyme phospholipase C through a specific G protein.
Intracellular enzyme phospholipase C hydrolyzes
phosphotidylinositol-4,5 bisphosphate (PIP2) which is found in
inner layer of the plasma membrane. Hydrolysis of PIP2 yield
two products
a) Diacylglycerol ( DAG)
b) Inositol -1,4, 5 triphosphate ( IP3)
13. 4. CALMODULIN AS SECONDARY MESSENGER
Calcium calmodulin second messenger system operates in response
to the entry of calcium into the cells.
Calmodulin is an acidic protein with highly conserved single
polypeptide chain has four high affinity for calcium binding sites.
Binding of calcium causes profound conformational changes in
calmodulin’s affinity for its effector molecules.
Calmodulin, when activated, causes contraction of smooth muscles.
14. CONCLUSION
Hormones are the chemical messengers that bind to intracellular receptor or
cell surface receptor to form complex and carry out biochemical function.
Hormones that bind to surface receptors of the cells, communicate through
intermediary molecules called second messenger which are generated as
consequences of the hormone action.
Signal transduction pathways allow cells to respond to environmental signals.
In these pathways, a signal is amplified.
This signal amplification is brought about by second messengers like cAMP,
cGMP, calcium ions, calmodulin, DAG and IP3.
Second messengers essentially serves as chemical relays from the plasma
membrane to cytoplasm, thus carrying out the intracellular signal transduction.
15. REFERENCES
- ESSENTIALS OF MEDICAL BIOCHEMISTRY- SECOND
EDITION BY R C GUPTA
- ESSENTIALS OF BIOCHEMISTRY BY PANKAJA NAIK
- PHYSIOLOGY BY JOSHI MENDHURWAR
- PRINCIPLES OF BIOCHEMISTRY BY LEHNINGER
- PRINCIPLES OF ANATOMY AND PHYSIOLOGY BY
TORTORA
- CELL AND MOLECULAR BIOLOGY BY KARP GERALD
