so now let's take a closer look
at how hormones activate genes
since they cannot go directly into the
cell
because of their because they're not
lipid-based amino acid-based hormones
except for our thyroid hormone are going
to exert their effects
through something called second
messengers
there are two main types of second
messenger systems
that we find in our cells the first
second messenger is going to be cyclic
amp
the second is the pip2 calcium second
messenger system
if we take a closer look at the cyclic
amp
signaling mechanism we find that
first our messenger is going to bind to
the receptor
on the target cell so the messenger in
this case is the hormone
binding of this hormone to the receptor
is going to activate a g-protein since
this receptor is usually something
called a
g-protein coupled receptor
once the g-protein is active it's going
to
activate or inhibit other enzymes
known as the adenylate cyclase
the adenylate cyclase is then going to
convert
atp in the cell to the second messenger
which is cyclic amp
cyclic amp can then go on to activate
other proteins known as protein kinases
these are enzymes that are going to
phosphorylate or add a phosphate
to other proteins this usually happens
in a signal transduction pathway or kind
of like a
relay where each message is going to be
passed from one molecule
to the next until we get to our actual
target
activity the phosphorylated proteins are
then going to be
activated or inactivated
the cyclic amp is then rapidly degraded
by another enzyme that's pretty much the
opposite of a protein kinase
known as a phosphodiesterase this is
going to
stop that signal transduction pathway
cascade
cascades have the ability to have
huge amplification effects and so this
second messenger system
allows for one hormone signal to cause a
very big effect in our target cell
the second second messenger system that
we find in our cells is the pip2
calcium signaling mechanism in this
mechanism
a hormone is going to bind to a jeep
coupled protein receptor
in the membrane of the target cell
and this is going to activate a g
protein
that is going to then activate a
different effector enzyme
known as phospholipase c
this activated phospholipase is then
going to split
the membrane protein pip2 into
two different second messengers the
first
is diacylglycerol or dag which is going
to activate
protein kinases which can subsequently
phosphorylate proteins the second
is inositol triphosphate or ip3
this is going to cause calcium to be
released
from intracellular storage sites inside
of the cell
the calcium is then going to act as
another
second messenger or a second second
messenger
the calcium alters the enzyme activity
and channels or it binds to regulatory
proteins
such as calmodulin
once calcium is bound to calmodulin
this is going to activate enzymes which
will then
amplify the cellular response
so now that we've discussed how second
messengers work
let's take a closer look at how genes
are
activated by these proteins
lipid soluble steroid hormones and
thyroid hormone can actually diffuse
directly
into the target cell and bind to
receptors
inside of the cell or your intracellular
receptors
from here they make a receptor hormone
complex
that enters the nucleus and then binds
to a specific region
of the dna inside the nucleus
from there this initiates dna
transcription
to produce certain mrnas
once the mrna is produced it is then
translated
into specific proteins in the cytoplasm
of that cell
proteins that are synthesized have
various functions
including things like inducing metabolic
activity
or creating structures or
being exported or secreted from the cell
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