Question

briefly mention the mechanism of action of FSH
or
illustrate the difference between the mechanism of action of protein and steroid hormone

Answer 1

Fixed membrane receptor mechanism

The hormones that are protein or amines in compositions such as Growth hormone, ADH, oxytocin, Insulin, Adrenaline, FSH, TSH etc shows this mechanism of action.

These hormones are water soluble and cannot passes through the lipid membrane and they have their target receptor on the cell membrane. The receptor are fixed on the cell membrane, so hormone can bind on the specific receptor.

Binding of hormone on specific receptor on target cell activates the enzyme Adenylcyclase in the cell membrane and causes production of cyclic AMP (cAMP).

cAMP act as secondary messenger. It diffuse through the cell membrane and activates (Protein Kinase) various enzymatic reaction to cause biochemical changes. After the target cell responded to the changes, cAMP is deactivated by a group of enzyme Phosphodiesterase



Figure: Fixed membrane receptor mechanism of hormone action( Eg. FSH)

Mobile receptor mechanism

The lipid soluble hormones such as steroid hormones and Fatty acids hormones can easily passes through the plasma membrane.

They have their receptor inside the cell, freely floating in the cytoplasm. Binding of hormone to the specific receptor activates the enzymatic activity of the cell for biochemical changes.

Some hormones (testosterone, progesterone, estrogen, cortisol, thyroxine) have their receptor localized inside the nucleus, the hormone-receptor complex are carried inside the nucleus.

The hormone-receptor complex initiate transcription of the DNA to form specific mRNA.

mRNA initiate protein synthesis in the cytoplasm. The protein (enzyme) causes biochemical changes in the cell.

Answer 2

THE MECHANISM OF HARMONE ACTION :

the hormone is produced by the endocrine gland hormones produces their effects on target tissue by binding to specific proteins which are termed as the hormone receptors they are located in target tissue only
the hormone receptors are found on cell membrane of target cells and they are known as the membrane bound receptors receptors found inside target cells are named as intracellular receptors nuclear receptors occurs in nucleus of cell only

A) THE BINDING OF A HARMONE TO IT'S RECEPTORS:

its results in formation of a hormone receptor Complex each receptor is specific to one to another hormone only the receptors are specific for hormones the hormone receptor complex formation occurs due to the biochemical change in the target tissue in a Cell only

B) TARGET TISSUE METABOLISM:


the physiological functions of body are regulated by hormones Almonds are divided into four groups on chemical basis
a)polypeptide ,protein hormones example: insulin ,glucagon, pituitary hormones ,hypothalamic hormones etccc
b) the steroids example : coristol , testosterone,eatra- diol and progesterone
c) iodothyronines( thyroid hormone)
d) amino - acid derivatives such as epinephrine

There are two cases :
•the hormones interacting with membrane bound receptors generally do not enter target cell they generate second messengers like cyclic AMP,IP3 ,Ca++ .these regulate cellular metabolism also .
• the hormones that interact with intracellular receptors such as the seat steroid hormones
idothyronines regulate gene expression or chromosome function by interaction of hormone receptor Complex with the genome of the organism

finally the cumulative biochemical action cause physiological as well as the development effect occur in our body


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