Biology Chapter 11: Cell Communication (2/2)
Summary
TLDRThis YouTube video script delves into cell communication, focusing on the three stages: reception, transduction, and response. It explains how signaling molecules initiate communication by binding to receptor proteins on the cell surface, triggering a conformational change. Key receptor types like G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors are discussed. The script then details the transduction process, emphasizing the role of phosphorylation and dephosphorylation in signal amplification and regulation. Finally, it touches on the response stage, where signals regulate cellular activities like transcription or cytoplasmic functions, ensuring precise cellular responses.
Takeaways
- 🔬 Cell communication involves three stages: reception, transduction, and response.
- 🔔 Reception is the initial stage where a signaling molecule binds to a receptor protein, causing a conformational change.
- 🔄 Receptor proteins are typically transmembrane and have specific shapes and chemical properties to bind only to certain signaling molecules.
- 🔗 G protein-coupled receptors interact with G proteins to relay messages inside the cell upon ligand binding.
- 📡 Receptor tyrosine kinases (RTKs) become activated upon ligand binding, leading to dimerization and activation of the kinase activity.
- 🚪 Ion channel receptors act as gates for ions to move across the cell membrane, activated by ligand binding or membrane potential changes.
- 📈 Intracellular receptors, found within the cell, require signaling molecules to pass through the plasma membrane to bind and initiate a response.
- 🔄 Transduction involves a cascade of molecular interactions that relay signals from receptors to their targets, often involving phosphorylation events.
- ⚙️ Phosphorylation and dephosphorylation are key mechanisms in regulating protein activity and signal transduction within cells.
- 🏁 The response stage is the final step where the signal transduction pathway leads to the regulation of cellular activities, such as gene transcription or protein synthesis.
Q & A
What are the three stages of cell communication?
-The three stages of cell communication are reception, transduction, and response.
What happens during the reception stage of cell communication?
-During the reception stage, a signaling molecule binds to a receptor protein, causing it to change shape and initiating a series of intracellular signaling events.
What is the role of receptor proteins in cell communication?
-Receptor proteins play a crucial role in cell communication by binding to specific signaling molecules and initiating a response within the cell.
How does the binding of a signaling molecule to a receptor protein cause a conformational change?
-The binding of a signaling molecule to a receptor protein causes a conformational change by interacting with the extracellular domain of the receptor, which then alters its shape and activates the intracellular domain to interact with signaling proteins.
What are the different types of receptor proteins mentioned in the script?
-The script mentions G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors as different types of receptor proteins.
How do G protein-coupled receptors work?
-G protein-coupled receptors work by interacting with G proteins upon ligand binding, which leads to a conformational change that activates the intracellular signaling pathway.
What is the role of receptor tyrosine kinases in cell communication?
-Receptor tyrosine kinases play a role in cell communication by activating their intrinsic kinase activity upon ligand binding, leading to receptor dimerization and the initiation of intracellular signaling.
How do ion channel receptors contribute to cell communication?
-Ion channel receptors contribute to cell communication by acting as gates for the movement of ions across the cell membrane in response to ligand binding or changes in membrane potential.
What is the purpose of the transduction stage in cell communication?
-The transduction stage is where a series of molecular interactions relay signals from receptors to their targets, often involving multi-step pathways that amplify the signal and provide control points for regulation.
What is the role of phosphorylation and dephosphorylation in cell signaling?
-Phosphorylation and dephosphorylation play a critical role in regulating protein activity and signal transduction by adding or removing phosphate groups, which can activate or inhibit enzymes and affect protein conformation.
How does the response stage of cell communication lead to cellular activities?
-The response stage leads to cellular activities by regulating protein synthesis or other cytoplasmic activities, often through the activation of transcription factors that turn genes on or off.
Outlines
🔬 Introduction to Cell Communication
The script begins by introducing the topic of cell communication, specifically focusing on chapter 11. The presenter, Iman, recaps the previous discussion on self-communication and the three stages of cell communication: reception, transduction, and response. The current session aims to delve deeper into each stage, starting with reception. Reception is defined as the first step where a signaling molecule, or ligand, binds to a receptor protein on the cell surface, causing a conformational change. This change initiates intracellular signaling events. Receptor proteins are transmembrane proteins with specific shapes and chemical properties that allow them to bind only to specific signaling molecules, likened to a lock-and-key mechanism. The ligand binds to the extracellular domain of the receptor, triggering a conformational change that sends a message to the intracellular part of the cell, setting off the next steps in the communication process.
🧬 Receptor Proteins and Their Functions
This paragraph discusses different types of receptor proteins involved in cell signaling. The first type mentioned is G protein-coupled receptors (GPCRs), which are transmembrane proteins that interact with G proteins upon ligand binding, leading to a conformational change and activation of intracellular signaling pathways. G proteins function as molecular switches, changing from an inactive GDP-bound state to an active GTP-bound state upon receptor activation. The activated G protein then interacts with and activates an enzyme, initiating a series of events that culminate in a cellular response. The temporary nature of this activation is due to the G protein's ability to hydrolyze GTP back to GDP, resetting the process. The paragraph also introduces receptor tyrosine kinases (RTKs) and ion channel receptors, setting the stage for further discussion on their roles in cell signaling.
🌐 Ion Channel Receptors and Intracellular Receptors
The script continues by explaining ion channel receptors, which are transmembrane proteins that control the flow of ions across the cell membrane. These receptors can be activated by ligand binding or changes in membrane potential, leading to the opening of ion channels and the flow of ions like sodium, potassium, or calcium. The paragraph also discusses intracellular receptors, which are found within the cell, either in the cytoplasm or the nucleus. Signaling molecules must pass through the plasma membrane to reach these receptors. Once inside, they can bind to intracellular receptors, initiating a response that may involve gene regulation. The paragraph emphasizes the multi-step nature of signal transduction, which allows for signal amplification and regulation, ensuring a coordinated and controlled cellular response.
🔋 Phosphorylation and Dephosphorylation in Signal Transduction
This section delves into the mechanisms of phosphorylation and dephosphorylation, which are critical for regulating protein activity and signal transduction within cells. Phosphorylation, the addition of a phosphate group to a protein by a kinase enzyme, can activate or inhibit enzyme activity, change protein conformation, or affect protein localization. Dephosphorylation, carried out by phosphatases, is a reversible process that removes phosphate groups. These processes are key components of intracellular signaling pathways, allowing for the conversion of extracellular signals into a series of intracellular events leading to a cellular response. The paragraph uses a phosphorylation cascade as an example to illustrate how a signaling event can initiate a series of phosphorylation events, culminating in a cellular response.
🌀 The Final Stage: Cellular Response
The final paragraph discusses the response stage of cellular communication, where signal transduction pathways lead to the regulation of cellular activities. These activities can occur in the nucleus or cytoplasm and involve the regulation of protein synthesis or gene expression. The response is not a simple on-off switch but is regulated in multiple ways, including amplification of the signal, control points for regulation, enhancement through proteins like scaffolding proteins, and the termination of the signal. The paragraph emphasizes the importance of these regulatory mechanisms in ensuring that cells function correctly and that the right amount of substances, such as proteins and enzymes, are produced. The discussion concludes with a summary of the three stages of cell communication: reception, transduction, and response, highlighting the importance of communication in cellular processes.
Mindmap
Keywords
💡Cell Communication
💡Reception
💡Transmembrane Proteins
💡Conformational Change
💡G Protein-Coupled Receptors (GPCRs)
💡Receptor Tyrosine Kinases (RTKs)
💡Ion Channel Receptors
💡Intracellular Receptors
💡Transduction
💡Phosphorylation
💡Response
Highlights
Introduction to cell communication chapter 11.
Explanation of the three stages of cell communication: reception, transduction, and response.
Reception is the first step where a signaling molecule binds to a receptor protein causing a conformational change.
Receptor proteins are typically transmembrane proteins with specific shapes and chemical properties for binding.
The binding of signaling molecules to receptors is likened to a lock and key mechanism.
Conformational change in the receptor protein initiates intracellular signaling events.
Types of receptor proteins include G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors.
G protein-coupled receptors interact with G proteins to relay messages upon ligand binding.
Receptor tyrosine kinases have intrinsic kinase activity activated upon ligand binding.
Ion channel receptors act as gates for ion movement across the cell membrane.
Intracellular receptors are found within the cell and are activated by signaling molecules that pass through the plasma membrane.
Transduction is the multi-step pathway that relays signals from receptors to their targets.
Phosphorylation and dephosphorylation are key mechanisms in regulating protein activity and signal transduction.
The transduction pathway can amplify the signal through a series of molecular interactions.
The response stage is the final step where the signaling pathway leads to the regulation of cellular activities.
Signaling pathways can regulate protein synthesis by turning genes on or off.
The final activated molecule can function as a transcription factor to regulate gene expression.
Regulation of the response includes amplification, control points, efficiency enhancement, and signal termination.
Summary of cell communication stages: reception, transduction, and response.
Transcripts
hello everybody my name is Iman welcome
back to my YouTube channel today we're
continuing chapter 11 cell communication
last time we sort of motivated the idea
of self communication we introduced the
three stages of cell communication which
is a reception transduction and response
and today we want to dive into the
details of each of these stages starting
off with stage one reception all right a
signaling molecule binds to a receptor
protein causing it to change shape so
let's dive into this all right reception
like we said is the first step in cell
signaling where a signaling molecule or
ligand ligand sorry binds to a specific
receptor protein usually located on the
surface of the target cell all right The
Binding of the signaling molecule to the
receptor protein is going to cause a
conformational change in that receptor
protein at I did too and what this does
is it initiates a series of
intracellular signaling events now
receptor proteins they're typically
transmembrane or plasma membrane
proteins that will span the cellular
membrane
with an extracellular domain that binds
to the signaling molecule and an
intracellular domain that will interact
with intracellular signaling proteins
all right the extracellular domain of
the receptor protein it usually has a
specific shape and a specific chemical
properties that are going to allow it to
bind to only specific signaling
molecules all right so it kind of works
like a lock and key mechanism all right
so what we're saying is that these
receptor proteins usually found
um
in the plasma membrane can have a
extracellular component a part of it
that kind of peeks out of the membrane
and a part of it that's embedded in the
membrane usually the outer part of this
this receptor protein will interact with
with with a signaling molecule they have
specific shapes so that they only bind
to specific signaling molecules all
right
so there there's usually a specificity
to receptor proteins that they're only
binding to the kind of signaling
molecules that they bind to that they
can respond to all right now the
signaling molecule lands in the receptor
protein that it needs to get to all
right in the extracellular part and then
a conformational change happens some
sort of conformational change happens
right like uh it changes all right this
change
in itself
lets the cell know
all right sends a a message the change
in the receptor protein carries a
message with it it carries a message to
the intracellular part of of the cell to
to enact something right
that's going to be the next step
essentially but this reception part all
right you have a signaling molecule that
will interact with its specific receptor
protein these are usually like I said
transmembrane or plasma membrane
proteins that will span the cell
membrane all right and the extracellular
domain the extracellular part of that
receptor protein is going to have a
specific shape in chemical properties
that will allow it to only bind to
specific signaling molecules now
The Binding of the signaling molecule to
the receptive protein protein is going
to induce a conformational change in the
receptor Protein that's going to either
activate or inhibit the intracell the
intracellular signaling pathway all
right it's either gonna
activate some further steps that happen
within the the the inside part of the
cell the intracellular uh on part of the
cell or it's going to inhibit some
signaling pathway inside of the inside
of the cell this conformational change
may involve the rearrangement of
intramolecular bonds or the the exposure
of previously hidden domains that will
interact with intracellular signaling
proteins so this change in this receptor
protein can then send
um
signals to proteins that happen to lie
inside of the cell to carry the message
all right now with that being said let
me erase this all right with that being
said there are some important types of
receptor plasma membrane proteins that
we want to just talk about a little bit
all right one of them is called a g
protein coupled receptors another type
that we'll talk about
um are receptor tyrosine kinases and the
third type that we'll we'll briefly talk
about are ION channel receptors all
right now
first we'll start with
G protein coupled receptors all right
these are a large and diverse family of
transmembrane proteins that play a
really critical role in cell signaling
and they're named this way because they
interact with a class of intracellular
signaling proteins called G proteins
all right so this trans membrane protein
g-protein-coupled receptor Works
alongside other G proteins that are
inside the cell to relay
um
to relay messages so upon ligand binding
the receptor is going to undergo a
conformational change which activates
the intracellular signaling pathway
inside the cell to relay the message so
here let's read let's read the steps
that they break down here this Loosely
attached to the cytoplasmic side of the
membrane the G protein functions as a
molecular switch that is either on and
off depending on which of the two
guanine nucleotides are attached all
right
now when GDP is bound to the G protein
as shown above the G protein is inactive
the receptor and the g protein work
together with another protein usually an
enzyme now when the appropriate
signaling molecule finally binds to this
G protein-coupled receptor all right the
receptor is activated and what happens
is it changes shapes it's cytoplasmic
side the inside part of this protein
then binds to an inactive G protein all
right so in its inactive form
all right the G protein-coupled receptor
and the g protein themselves they're not
bound together
all right but when a signaling molecule
comes ahead and binds to this
g-protein-coupled receptor it sends it
relays a message that leads to the G
protein being binded to the
g-protein-coupled receptor and it
activates the G protein what happens
when the G protein is activated well the
activated G protein dissociates from the
receptor diffuses along the membrane and
then binds to an enzyme altering the
enzymes shape and activity so then
um
it moves and binds to an inactive
enzyme and this enzyme becomes activated
once activated the enzyme can trigger
The Next Step leading to a cellular
response all right now the changes in
the enzyme and the g protein are only
temporary because the G protein also
functions as a gtpase enzyme in other
words it then hydrolyzizes its bound GTP
to GTP and now it's inactive again
allowing this whole process to be
repeated if need be
all right so that's one kind of receptor
protein the G protein-coupled receptor
fantastic another kind of receptor
protein is this tyronease kinases these
receptor tyrosine kinases I'm sorry
they're also a family of transmembrane
proteins that play a critical role in
cell signaling and they're named this
way because they have intrinsic protein
kinase activity which is activated upon
ligand binding to the receptor let's
also work through this figure all right
so many receptor thyroidase kinases have
the structure that's depicted here all
right these are two these are receptor
Tyrone tyrosine kinase proteins I'm so
sorry
all right
um before the signaling molecule binds
the they exist as individual units all
right so this is one
um rtk uh protein and this is another
rtk protein I'm going to use the acronym
all right notice that each of them has
an extracellular ligand binding site
they each exist as different units and
they each have a binding site
all right Now The Binding of a signal
signaling molecule to one of these
causes the two receptor monomers or
actually The Binding of signal molecules
to both of these
um like a growth factor causes the two
receptor monomers to associate closely
with each other and they form a complex
that we now call a rtk dimer
all right this dimerization activates
the TK uh the tyrosine kinase region of
each monomer each tyranny tyrosine
kinase then adds a phosphate from an ATP
molecule to a tyrosine on the tail of
the other monomer all right and now the
receptor is fully activated and it is
recognized by specific relay proteins
inside the cell to relay the message
each activated protein triggers a
transduction pathway that leads to a
cellular response alright so this is
another example of a receptor protein
our last example are these ION channel
receptors they're also transmembrane
proteins that act as a gate for the
movement of ions across the cell
membrane they're activated by binding of
a by binding of a specific ligand ligand
or by changes in membrane potential too
so when they're activated an ion Channel
receptor will usually allow ions like
sodium potassium calcium to flow across
the membrane either into or out of the
cell all right so here what we see is we
see the ligand-gated Ion channel
receptor where the the gate is closed
until you have a signaling molecule that
comes and binds to the Ion channel and
this signaling molecule will result in
the Ion channel opening and allowing
ions to pass through in One Direction or
the other
all right fantastic so those are three
examples of receptor proteins now there
are other kinds of receptor specifically
intracellular receptors intracellular
receptor proteins are receptor proteins
you'll find inside the cell not
necessarily just in the membrane right
there's other kinds of receptors
um these intracellular receptors are
found in either the cytoplasm or the
nucleus of target cells and to reach a
uh such a receptor right because they're
not on the membrane
um they're inside the cell what happens
is
a signaling molecule has to pass through
the target cells plasma membrane to
reach these intracellular receptors a
number of important signaling molecules
can do this because they are either
hydrophobic enough to pass through the
plasma membrane or they're small enough
to enough to cross the hydrophobic
interior of a membrane all right these
hydrophobic chemical Messengers can
include things like steroid hormones and
thyroid hormones of animals and another
chemical signaling molecule with a
intracellular receptor is nitric oxide
and gas it's a very small molecule that
can readily pass through the membrane's
phospholipids now regardless once the
signaling molecule or hormone has
entered the cell it can then bind to an
intracellular receptor in the cytoplasm
or the nucleus
and of course the binding changes the
receptor into some sort of complex
that's going to be able to cause a
response many cases this can be turning
on or off of particular genes
all right so that's the first stage of
cell communication all right let's move
on to our next objective which is
talking about the second
um stage of cellular communication this
is transduction all right Cascades of
molecular interactions can then relay
signals from receptors to their targets
so when receptors for signaling
molecules are plasma membrane proteins
like most of those we've discussed then
the transduction cell stage of a cell
signaling is usually a multi-step
pathway that involves many molecules and
it usually happens inside this cell so
steps often include the activation of
proteins by either the addition or
removal of phosphate groups or something
like the release of other small
molecules or ions that will act as
Messengers one benefit of this
multi-step
transduction pathway is the possibility
of greatly amplify buying a signal so if
each molecule in this pathway transmits
the signal to numerous molecules at the
next step in the series then the result
is a geometric increase in the number of
activated molecules by the end of the
pathway and so multi-step Pathways
provide more opportunities for
coordination and control than do simple
systems and this really allows for the
regulation of a response
and so like we said the first step is
reception your signaling molecule will
bind to a receptor protein this is going
to have some change to this receptive
protein and this results in
the a couple of next steps that we call
transduction that will continue to
happen until the message finally reaches
its Target all right most of the time it
involves multiple steps it's not usually
a one-step thing and again like we said
this is usually a good thing it's good
that it's multi-step because that means
more molecules in each step are
activated making sure that there's a
geometric increase in the number of
activated molecules through this pathway
ensuring that the target reaches the
response it needs
all right now the phosphorylation and
dephosphorylations of protein is a
widespread as a widespread cellular
mechanism for regulating protein
activity and transducing a a message so
let's talk about this a little more now
phosphorylation and dephosphorylation
are key mechanisms of post-translational
Pros post-translational modification
that actually regulates protein activity
and it's usually very critical it's a
very critical component of intracellular
signaling transductions so if you're
wondering okay we understand reception
you have a signaling molecule that binds
to your receptor protein it changes and
then that somehow initiates a
transduction multi-step Pathway to to
relay the message all right but what is
what is happening usually in those
transduction steps well one thing that
usually happens is phosphorylation and
dephosphorylation of proteins these are
the key mechanisms of how
how
intracellular signal transduction
pathways are are are moved along
phosphorylation usually involves the
addition of a phosphate group to a
protein typically like a c serine or
threonine or a tyrosine residue and it's
usually done by an enzyme called a
kinase this process is usually
reversible it can be counteracted by an
enzyme
um called phosphatase which removes the
phosphate group from the protein and so
phosphorylation dephosphorylation that's
a reversible process
now like we said phosphorylation and
defosphorylation it plays a critical
role in cell signaling by regulating the
activity of enzymes
um by regulating the activity of enzymes
as we move through a transduction
pathway for example
um
phosphorylation can activate or inhibit
enzyme activity by changing the
conformation of the protein or by
creating or disrupting docking sites for
other signaling proteins phosphorus
phosphorylation can also regulate the
subcellular localization of proteins or
or Target them for degrade degradation
all right so essentially this process of
phosphorylation dephosphorylation is a
really key component of intracellular
signaling transduction Pathways where
your extracellular signal or stimuli is
converted into a series of intracellular
signaling events that finally lead to a
cellular response okay one more time
because this is really important and
it's probably a very new idea that
you're learning here
okay let's erase this and let's work
through this figure all right we know we
understand reception now let's Circle
this in purple this is our reception
step signaling molecule binds to the
receptor protein causes a change and it
initiates a transduction pathway all
right this transduction pathway is
usually several steps all right this is
one example of a phosphorylation Cascade
all right which is an example of a
transduction pathway that can happen all
right what you can have here is you can
have a relay molecule that activates
protein kinase one
all right so this this change in your
receptor protein
results in this activated relay molecule
that interacts with this inactive
protein kinase when these two things
interact what happens oh what happens is
now we have an active protein kinase one
all right now this active protein kinase
one what can it do it can transfer a
phosphate from ATP to an inactive
molecule of protein kinase II all right
so what
what what kinase one does is
it adds a phosphate group to kinase II
and now kinase II is also an activated
protein okay what does kinase 2 do it
does it initiates another
phosphorylation where we take one
phosphate group from ATP slap it onto
kinase 3 and now kinase 3 is also
activated and finally this kinase 3 it
brings the cell
uh signal the cellular message to our
active protein our Target protein
finally which will finally result in a
cellular response which is the final
stage of cellular communication
all right fantastic that leads us to
actually being able to talk to our
finals talk about our final stage of
cellular communication and that's the
response stage cell signaling leads to a
regulation of either transcription or
other cytoplasmic activities so now what
we can do is take a closer look at the
cell's subsequent response to an
extracellular signal all right this is
what some researchers call the output
response what is the nature of the final
step in the signaling pathway ultimately
a signal transduction pathway leads to
the regulation of one or more cellular
activities the response at the end of
the pathway can occur either in the
nucleus or the cytoplasm but the point
is that fine that response
tells the Targets target molecule or
Target organelle or Target
um
protein that it needs to go and do a
specific thing and that specific thing
keeps the cell working in the way that
it needs to all right ultimately keeping
your bodies working the way that they
need to all right many signaling
Pathways will regulate protein synthesis
usually by turning G's on or off in the
nucleus all right like an activated
steroid receptor the final activated
molecule in a signaling pathway can also
function as a transcription Factor all
right it can
um
it can signal transcription the
synthesis of one or more specific mrnas
which will be translated into the
cytoplasm into specific proteins it can
regulate
um
many different things in this cell all
right and as for regulation of a signal
whether the response occurs in the
nucleus or the cytoplasm it's not just
simply turned on and off rather the
extent and the specificity of this
response are regulated in multiple ways
all right and here we'll consider four
aspects of this regulation actually
first signaling Pathways generally
amplify the cell's response to a single
signaling event and the degree of
amplification depends on the function of
the specific molecules in the pathway
all right second the many steps in a
multi-step pathway provide control
points at which the cell's response can
be further regulated which contributes
to the specificity of the response and
it allows for coordination with other
signaling pathways
third the overall efficiency of the
response is enhanced by the presence of
proteins like scaffolding proteins and
finally a crucial point in regulating
the response is the termination of the
signal all right
so the way that the signal passes
through the transduction uh pathway and
and reaches its Target cell and then
communicates some sort of of job that
the cell needs to do is is ultimately
important in in regulating different
things within the cell that keep the
cell functioning that keep the cell
alive
um
and it's important for the synthesis of
things like proteins and enzymes all
right so most signaling Pathways
ultimately regulate things like protein
synthesis or turn genes on and off all
right the final activated molecule can
function even as a transcription factor
and ultimately everything's regulated
all right everything's regulated through
communication so enough of something is
produced and not too much all right
and and so on and so forth all right so
that's cell communication for us
reception transduction and finally
response I hope this was helpful let me
know if you have any questions down
below other than that good luck happy
studying and have a beautiful beautiful
day
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