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1. MSCDFSM
BIOCHEMISTRY
HORMONES -II

2. SIGNAL TRANSDUCTION : An organism makes homeostatic adaptations to constantly changing environment
.achieved by altering the activity and amount of proteins.this is achieved by the action of hormone. The interaction
between hormone receptors generates intracellular signal .These can regulate the activity of genes that will alter the
amount of protein .it affect the activity of specific proteins including enzymes and transporter or proteins
The signal can influence the formation of protein in cell and can affect protein synthesis .it is by influencing gene
expression. The stimulus can be a challenge or threat to organism to an organ or integrity of single cell with in that
organism .at an organism level it involves the nervous system like including sight ,light, pain ,smell ,touch etc.in
cellular level ,it involves physicochemical factors like ph, oxygen tension etc .according to stimulus ,one or more
hormones would be secreated that will bring desired adaptive responses.

3. SIGNAL GENERATION :
1. Group I hormones : for group I hormones, ligand receptor complex is the signal .these hormones are
lipophilic ,easily diffuse through the plasma membrane of all cells these receptors can be located in cytoplasm
or in nucleus of target cells .the hormone receptor complex undergo activation reacton that occur by 2
mechanism :
2. In case of glucocorticoid hormone ,receptor are present in cytoplasm bound to protein called heat shock
protein 90 .when hormone gets binds to receptor,there is dissociation of hsp 90 from receptor .the receptor
contain nuclear localizationsequence that helps in this process of translocation from cytoplasm to nucleus this
activated receptor moves into nucleus.it binds with high affinity DNA at specific sequence called hormone
receptor element (HRE).when the hormone is glucocorticoid ,the region is also called glucocorticoid response
element (GRE) .once the activated hormone receptor is bound to HRE ,protein acts as coactivators and bind
to its region and result in gene transcription.
3. Thyroid hormone and retenoids : it diffuse from the extracellular fuid across the plasma membrane and go to
nucleus .here receptor already bound with HRE that can also called thyroid response element (TRE).This
DNA bound receptor fails to activate transcription as it is complexed with corepresser .this receptor
corepresser complex is active repressor of gene transcription .when hormone bind to complex ,there is
dissociation of corepressor .this hormone receptor complex now binds with high affinity it results in
acceleration of gene transcription .

4. GROUP II : These are water soluble ,it cannot cross plasma membrane .they have receptors in plasma membrane
and have to use intracellular messenger molecule to communicate their message to cell .these second messengers are
the intracellular signal they generate and effect gene transcription as well as other process in cell..receptor of Group
II hormone work in collaboration with G protein .these receptor are also called G.protein coupled receptors r
GPCR. The G protein is called transducer.the action of the effector molecule generate second messanger that is
usually a molecule like Camp,Cgmp. etc .the diffusible second messanger carries the signal to destination.that may be
in nucleus or intracellular compartment or cytosol.

6. G –Protein receptors (gpsr) :
Receptors of group II hormones have seven domains (areas) spanning the plasma membrane .The seven domains
are depicted as seven interconnected cylinders that extended through the lipid bylayer of member .
Plasma membrane consists of protein layer in between 2 lipid layer.the protein consist 3 polypeptide .The
polypeptide are denoted by alpha, beta, gamma . The G – protein is inactive in this form .Further the g protein is
inactive in this form and is anchored to plasma membrane but not linked to receptor. When groupII hormone
,there is a conformational change in receptor .GTPreplaces GTP attached to alpha subunit .the Beta and gamma
subunit then dissociate ,it activates G protein .the alpha then binds to E molecule that is also present on plasma
membrane .the E can be either Ca +2 , Na +.
Alpha subunit has intrinsic GTPase activity and it act as enzyme Gtpase and hydrolyse GTP into GDP and pi ,the
proten gets deactivated then trimeric complex is reformed again and start for another process. Cholera toxin
catalyses ADP ribosylation of alpha subunit .and alpha subunit cannot reassociate with beta and gamma and is
irreversibly activated.
SECOND MESSANGERS:
1.These are divided on the basis of intracellular signals.they generate . They function as Cyclic AMP..Cyclic AMP
,GMP ,calcium are all second messangers.these are :
1.Cyclic AMP
a) Adenylyl cyclase b).Protein kinase c )phosphoproteins d)phospodiesters
2.Cyclic GMP :
1.Calcium or phospharidylinositols : calcium ,phosphotidylinositols, protein kinase cascade