Hormones are molecules that are produced in one cellular
location in an organism, and whose effects are seen in another tissue or cell
type. In mammals hormones can be proteins or steroids. Hormones are usually either peptide (protein) or steroid
in the body.
Hormones produce their effects on target tissues by binding to specific
proteins called hormone receptor, specific for a particular hormone located in
the target tissues only. These hormone receptors present on the cell membrane
of the target cells called membrane bound receptors /extracellular/surface
receptors. The hormone binds to the receptor forming hormone receptor
complex. The hormones are not able to enter the target cells. Hence they
generate second messengers that regulate the cellular metabolism. Second
messengers are cyclic AMP,Ca2+, IP3 ( Inositol
triphosphate). Second messengers act as interacting between the hormone and the
cell. They carry the information from the hormones and transfer it to the cell.
Each receptor is specific to one hormone only and hence receptors are specific
hormone receptor complex formation leads to certain biochemical changes in the
target tissue.
Peptide hormones bind extracellular receptors because they have hydrophilic
elements and are lipid insoluble, cannot pass through cell membrane and relay
an internal message via multiple methods (G-protein cascade signaling,
phosphorylation of internal proteins, etc) via second messengers. The action of
hormone is performed by method is Non-steroidal.
A steroid hormone directly initiates the production of proteins within a
target cell. Steroid hormones diffuse into the cytosol of cell membrane of
target cells as they are lipid soluble due to which they can directly enter the
cell because they are hydrophobic and may even enter the nucleus of the
receptor cells and the receptors present inside the nucleus of target cell
called intracellular receptors, mostly nuclear receptors. Steroid
hormones are slow acting, smaller in size and are able to cross cell membrane.
This hormone action is known as Steroid hormone action. Physiological
functions are regulated by steroid hormone in the target tissue of body is
cortisol, testosterone, estrogen, progesterone etc.
Ultimately, the two actions produce
the same effect in that the intracellular response leads to increased
transcription of DNA creates a m-RNA (messenger RNA) that is translated into
the desired protein within the cytoplasm (protein synthesis). As soon as
proteins are synthesized, they start working on the action. The effect
increases/decreases protein levels which lead to the observed response (DNA
expression). Proteins are responsible for "traits".
Working of Estrogen:
Estrogen is released from follicular cells and the place where its action takes
place are uterine cells (target cells). Estrogen is a group of hormone and the
acting hormone is β-estradiol. In the cytoplasm, intracellular receptor of
estrogen called as Estrophillin. This hormone is slow acting and is fat
soluble. That why estrogen can cross the cell membrane and come inside the
cells and bind to receptor which is present in the cytoplasm leads to formation
of estrogen receptor complex (Estrophillin II). This complex diffuses into the
nuclear membrane and come into the nucleus. Inside the nucleus, it binds to
target gene on DNA. The DNA undergoes modified changes leads to formation of
m-RNA (transcription), m-RNA (messenger RNA)is present in the cytoplasm and it
can help to form protein with the help of ribosomes. This is the place where
translation takes place. The protein formed
can be ovalbumin and ovovitinin. These two bring about the division of
follicular cells and the effect is seen (gene expression).
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