Mechanism of Peptide hormone action, Secondary Messenger

1. Zoology Department
Yashpal Singh Chundawat

2. Peptide Hormone
Peptide hormones or protein hormones are hormones whose
molecules are peptide, or proteins, respectively. These hormones
have an effect on the endocrine system of animals, including
humans. These Hormones are water-soluble and act on the
surface of target cells via second messengers

3. Mechanism of Peptide Hormone Action.
• Receptor is found on the Target cell's plasma Membrane. Which is
called membrane receptor.
Q. Why Membrane Receptor ?
• Peptide hormone made of protein means it is not lipid solution or
lipophilic molecule.Thats receptor is found on the plasma membrane
of the target cell and receptors are called membrane receptors.

4. Receptor Is made of 3 Things :-
1. R-U : Recognition Unit
2. T-U : Transduction Unit
3. C-U : Catalytic unit

5. R-U
• Which Recognises Hormone.
• It Has Binding Site Facing Towards Exterior.
T-U
• Made Of G-protein Made By Alpha , Beta and Gama Sub unit Together.
• Alpha Attached With GDP Calling It Alpha GDP.
• Beta and Gama Are associated With each other.
• This complete unit is Called Transduction Unit .
C-U
• It Is Enzyme Because enzyme will Form Product.
• The product made by this enzyme will be called 2nd messenger.

6. R-U
GDP
Alpha
beta gamma
C-U
When Peptide hormone is
not Present.

7. When Peptide Hormone Arive.
Peptide Hormone
Hormone binds on binding side of
recognition unit. Means recognition
unit recognise the peptide hormone.

8. As Peptide Hormone binds on
binding site of the recognition
unit.
Phosphorisation of Alpha GDP
occurs.
Means Alpha GDP is converted
into Alpha GTP.

9. GDP
ALPHA
BETA GAMMA
Phosphorylation
GTP
ALPHA BETA GAMMA
Activate Transduction unit.

10. • After Converting into GTP Alpha it dettach from recognition unit and
associate with beta and Gamma.
• This combination or association of GTP alpha and beta and gamma is
called as activated transduction unit.
• Activated Transduction Unit will activate Catalytic Unit means
Activated T-U will associate with C-U.
• There comes the Conformational Change in C-U.

11. Active site
• This confermational change Result in formation of active site on C-U.
• Because it is a enzyme there for the active site is formed.
• Now, ENZYME will form product .

12. • For making product it will use ATP (substrat ) To form product and this
product will be called c-AMP.
• and cAMP is called Second massenger.
• Second messenger will activate enzyme so that biochemical activity
could be started in target cell. Means Physiological Function could
occur.

13. Thats Why We call that Peptide Hormones
acts via Second Messenger System.

14. What is Second Messenger ?
• it is a inracellular molecule which is formed by Binding of First
messenger (Peptide Hormone) in cell’s cytoplasm.
• It activates Diiferent enzymes from which biochemical activity is
started.

15. Does Only cAMP act as secondary
Messenger?
• No, Like cAMP cGMP ,DAG, IP3, Calmadaline. These all acts as second
messenger.