Describe, in detail, what second messengers are and what their function is with regard to signal- transduction pathways. Solution Cell signalling is initiated with the release of messenger molecule by the cell which is engaged in sending messages to other cells in the body. Cells can only respond to an extracellular message if they ezpress receptors that specificallt recognizes and bond that particular messenger molecule. In most cases the messenger molecule or logand binds to a receptor at the extracellular surface of the responding cell. This interaction causes a signal to be relayed across the mebrane to the receptors cytoplasmic domain. Once it has reached to the inner surface of the plasma membrane, there are two routes by which the signal is transmitted into cell interior where it elicits the appropriate response. The particular route takendepends on the type of receptor that is activated. One type of receptor transmits a signal drom its cytoplasmic domain to a nearby enzyme which generates a molecule called as second messenger. Because it vrings about (effects) the cellular response by generating a second messenger, the enzyme responsible is called as effector. Another type of receptor transmits a signal by transforming its cytoplasmic domain into a r3cruiting station for cellular signalling protiens. Signalling patways therefore are the information superhighways of the cell. Each cell signalling pathway consists of a series of distinct protiens that operate in sequence. Signals transmitted along such signalkibg pathways ultimately reach target protiens involved in celkular process . Depending upon the type of cell and message, the response initiated by the target protien may involve change in gene expression,an alteration of activity of metabolic enzymes, an increase or decrease in cell motility, a change in ion permeability. This over all process in which information carried by extracelkular messenger molecules is translated into changes that occur inside the cell is referred as signal transduction. Second messengers are molecules that relay signals received at receptors on the cell surface — such as the arrival of protein hormones, growth factors, etc. — to target molecules in the cytosol and/or nucleus. Second messengers are intracellular signaling molecules released by the cell to trigger physiological changes such as proliferation, differentiation, migration, survival, and apoptosis. Secondary messengers are therefore one of the initiating components of intracellular signal transduction cascades. The cell releases second messenger molecules in response to exposure to extracellular signaling molecules termed as first messengers. First messengers therefore are extracellular factors, often hormones or neurotransmitters, such as epinephrine, growth hormone, and serotonin. There are 3 major classes of second messengers: Cyclic AMP is the second messenger that is capable of diffusing to other sites within the cell. The synthesis of cyc.

1. Describe, in detail, what second messengers are and what their function is with regard to signal-
transduction pathways.
Solution
Cell signalling is initiated with the release of messenger molecule by the cell which is engaged in
sending messages to other cells in the body. Cells can only respond to an extracellular message if
they ezpress receptors that specificallt recognizes and bond that particular messenger molecule.
In most cases the messenger molecule or logand binds to a receptor at the extracellular surface of
the responding cell. This interaction causes a signal to be relayed across the mebrane to the
receptors cytoplasmic domain. Once it has reached to the inner surface of the plasma membrane,
there are two routes by which the signal is transmitted into cell interior where it elicits the
appropriate response. The particular route takendepends on the type of receptor that is activated.
One type of receptor transmits a signal drom its cytoplasmic domain to a nearby enzyme which
generates a molecule called as second messenger. Because it vrings about (effects) the cellular
response by generating a second messenger, the enzyme responsible is called as effector.
Another type of receptor transmits a signal by transforming its cytoplasmic domain into a
r3cruiting station for cellular signalling protiens.
Signalling patways therefore are the information superhighways of the cell. Each cell signalling
pathway consists of a series of distinct protiens that operate in sequence. Signals transmitted
along such signalkibg pathways ultimately reach target protiens involved in celkular process .
Depending upon the type of cell and message, the response initiated by the target protien may
involve change in gene expression,an alteration of activity of metabolic enzymes, an increase or
decrease in cell motility, a change in ion permeability. This over all process in which information
carried by extracelkular messenger molecules is translated into changes that occur inside the cell
is referred as signal transduction.
Second messengers are molecules that relay signals received at receptors on the cell surface —
such as the arrival of protein hormones, growth factors, etc. — to target molecules in the cytosol
and/or nucleus. Second messengers are intracellular signaling molecules released by the cell to
trigger physiological changes such as proliferation, differentiation, migration, survival, and
apoptosis. Secondary messengers are therefore one of the initiating components of intracellular
signal transduction cascades.
The cell releases second messenger molecules in response to exposure to extracellular signaling
molecules termed as first messengers. First messengers therefore are extracellular factors, often
hormones or neurotransmitters, such as epinephrine, growth hormone, and serotonin.
There are 3 major classes of second messengers:

2. Cyclic AMP is the second messenger that is capable of diffusing to other sites within the cell.
The synthesis of cyclic AMP follows the binding of a first messenger - a hormone or other ligand
-to a receptor at the outer surface of the cell.
Whereas first messenger binds exclusively to single receptor molecule, the second messenger
often stimulates a variety of cellular activities as a result second messenger enables cell to mount
a large scale coordinated response following stimulation by a single extracelluar ligand.