Question

First outline the general scheme for signal transduction or the "players" involved in transmitting a signal across a membrane. Explain how a signal transduction system amplifies the original signal. Then explain how membrane fluidity and induced changes in protein structure are critical for this signaling mechanism.

Answer 1

ANS: Signal Transduction : The binding of a ligand to its receptor triggers a series of events by which extracellular signals are transduced into the cell resulting in changes in gene expression.

cell signaling can be divided into 3 stages---------Reception ,Transduction, Response

outside signaling molecule detect by cell and then these signal molecule binds to the receptor protein in or inside the cell.

this binding changes the receptor protein and initiates the process of transduction. In this transduction pathway each relay molecule changes the pathway of the next molecule and this signal triggers a specific cellular response.

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COMPONENTS of signal transduction pathway are -

1. Ligands

2. Receptors

3. second messengers

4. Transcription factors

Ligands is the primary messenger (Signal molecule) and binds on Receptor-ligand binding site (receptor protein ) ,in the cell membrane and causes conformational changes in the proteins and this conformational change( in the form of second messengers (cAMP, Ca) etc. this results in the amplification of the signal, secondary messengers are free to move around the cell ,this mean they influence the processes in different compartments of the cell which activate secondary effectors transmitted to the cytoplasmic domain and then pass through the nuclear membrane into the nucleus ,altering gene expression.

IN case of membrane receptors ,receptors transmit information from the external environment to inside the cell by changing the confirmation. example of membrane receptor is receptor Tyrosine kinase.

IN case of intracellular receptors ,mainly present inside the cell ---cytoplasm---nucleus ,these signal molecules are hydrophobic in nature so easily pass to the plasma membrane and binds to the intracellular receptors.

These activated receptor can initiates cellular response ,change in gene expression.

Signal transduction amplifies the original signal ---

.Release of appropriate signal molecule act as a primary messengers and then binding of the primary messengers (signal molecule)to its receptor brings conformational change in the structure .

Once the information is transduced across the cell membrane ,the cell reacts by increasing the production of some sort of intercellular molecule called a secondary messengers i.e cAMP. This results in amplification of the signal and then these secondary messengers are free to move around the cell ,means they can influence the process in different compartments of cell.

Membrane fluidity induced the affect of the function of biomolecules that are associated with the membrane structure

Membrane is 50% proteins ,depends upon cell type .

Types of membrane proteins--

1. Integral membrane proteins

2. anchored membrane proteins

3. Peripheral protein

but the presence of saturated or unsaturated fatty acids determine the fluidity in the membrane at low temperature and temperature increases fluidity also increases the presence of cholesterol functions as a buffer and maintain the fluidity .presence of protein in membrane act as receptor and relay the signal among the cell between inside or outside the environment of the cell ,act as a facilitator for ions or responsible for active transport across cell membrane.

but membrane fluidity mainly associated with lipid bilayer of a cell membrane and the viscosity of membrane affects the diffusion of protein and rotation .If fluidity is not proper then carrier protein donot perform their function and it also affect the transporation of protein across the membrane