2. OVERVIEW
• Cells typically communicate using chemical signals.
• These chemical signals, which are proteins or other molecules produced by
a sending cell, are often secreted from the cell and released into the
extracellular space.
• There, they can float – like messages in a bottle - over to neighbouring cells.
• Not all cells can "hear" a particular chemical message.
• • In order to detect a signal (that is, to be a target cell), a neighbor cell must
have the right receptor for that signal.
3. • When a signaling molecule binds to its receptor, it alters the shape or activity of the
receptor, triggering a change inside of the cell.
• Signaling molecules are often called ligands, a general term for molecules that bind
specifically to other molecules (such as receptors).
• The message carried by a ligand is often relayed through a chain of chemical
Messenger inside the cell.
• Ultimately, it leads to a change in the cell, such as alteration in the activity of a gene
or even the induction of a whole process, such as cell division. Thus, the original
intercellular (between-cells) signal is converted into an intracellular (within-cell)
signal that triggers a respanse
4. INTRODUCTION
• Cell signaling is part of a complex system of communication that governs basic
cellular activities and coordinates cell actions.
• The ability of cells to perceive and correctly respond to their microenvironment is
the basis of development, tissue repair, and immunity as well as normal tissue
nomeostasis.
• Cell signaling is a process through which living cells interact with the cellular
environment and neighbouring cells.
• Intracellular signalling is the key to the evolution of multi-cellular organism,
• This involves determining the function of the individual cells within the context of the
organism as well as the response of specific cells or group of cells to the
environment.
5. IMPORTANCE OF SIGNALS
• Intracellular signalling is essential to the survival of organisms providing opportunity to adapt stability
following important functions may be attributed
1.maintain off homeo status
2.Control of cell division and cell death
3.Adaptation to environmental conditions
4.Control of development and growth
5.Release and production of hormone and other regulatory molecule
6.Response elicited between organism-including establishment of pathogenesis ,activation of defences
,establishment of symbiosis etc
6. SIGNAL TRANSDUCTION
• signalling refers to the process by which cells release ,receive, propageted and
responded to information from their environment and from each other
• It is an important part of the cell signalling process and refer to the conversion of the
signal from one from to another
• The receptor transmitted the signal across the membrane converting the extracellular
signal to on the intracellular signal
• in most cases, additional protein and the small molecules participate in relaying the
messages to its ultimate destination in the cell where are responses Is evoked
• the responses could be of any imaginable cellular activity. however ,many drugs
interfere or exacerbate the responses to signalling pathways.
7. STEPS IN SIGNALLING
1. Biosynthesis and release of
the signal
2. Transport of signal to target
cell
3. Transduction in target cell
4. Alterations of cell growth and
metabolism pertaining to
response
5. Termination of signal
8. SYNTHESIS OF SIGNALLING MOLECULES
RELEASE OF SIGNALLING MOLECULES
TRANSPORT OF SIGNAL TO TARGET CELLS
DETECTION & BINDING OF SIGNAL BY SPECIFIC RECEPTOR
CHANGES DUE TO RECEPTOR-SIGNAL COMPLEX
SIGNAL REMOVAL & RESPONSE TERMINATION
9.
10. Broadly classified as
• Pathway initiated by
hydrophobic massangers
• Messengers bind to
INTRACELLULAR
PROTEINS
• Eg : steroid hormone
:thyroid hormone
:steroid
derivatives
• Pathways initiated by
HYDROPHILIC MESSENGERS
• Messengers bind to EXTRACELLULAR
PORTIONS of membrane protein
• Eg :most of hormones
neuro-transmitters
paracrine
autocrine compounds
• 4sub types:
-ligand gated ion channels
-intrinsic enzymatic activity
-bounded to janus kinases
-G –protein coupled recepters
11. pathways initiated by lipid soluble messenger
Signal enters the cell
Binds with inactive recepter
Activate the inactivated protein/recepter
Hormone recepter complex
Binds to specific sequence near a gene
Act as transcription factor
Aitersthe rate of gene trancription
mRNA
tRNA
Protein synthesis
13. AUTOCRINE SIGNALLING
• Autocrine signals target the cell itself .sometimes autocrine cell can
target cells close by if they are the same type of cell as the emiting
cell
• An example of these are immune cells
• autocrine signalling is important in the immune system and it also
frequently contribute to uncontrolled growth of the cancer cells in the
situations cancer cells produce a factor to which they respond deriving
their on an regulated proliferation
14.
15. PARACRINE SIGNALLING
• Paragon signals target the cells in the vicinity of the emiting cell
• Neurotransmitters present an example
16.
17. ENDOCRINE SIGNALLING
• Endocrine signal Stargate a distance cells
• produce hormones that travel through the blood to reach all the parts
of the body
• For example:the pancreas is an endocrine gland and produce the
hormone insulin which regulate the uptake of glucose in a cell all over
the body for example of hormones that function in an endocrine
manner include the testosteron progesterone and gonadotropins
18.
19. JUXTACRINE SIGNALLING
• Juxtacrine signals target adjacent (touching) cells
• transmitter along cell membranes via protein or lipid components
integral to the membrane
• Capable of affecting either the Emitting cell or cell immediately
adjacent
20. • this does not involve the release of secreted molecule and only occur over a short
distance the molecule make a directly physical contact through the signal molecule
found into the plasma membrane ofthe signalling cell and the receptor proteins
present in the plasma membrane of the targeted cell
• This type of signalling is extremely important during the embryonic development and
cell fate determination (when similar cell that are close to each other specialise to
form a specific cell type)
• The notch pathway mediate the juxtacrine signalling between Adjacent cells
• Ligand binding results in a proteolytic cleavage of the notch receptor which release
an intracellular domain that is translocated to the nucleus where it regulate gene
expression
22. WHAT ARE RECEPTORS
• Receptors are protein associated with cell membranes or located
within the cell
• Receptors recognize signaling molecules by binding them
• Binding of receptors by signaling molecules—cell behaviour changes
23. • RECEPTORS are roughly categorised into two:
• 1.Extracellular receptors/cell surface receptors
• 2.Intracellular receptors
24. INTERNAL RECEPTORS
• internal receptors also known as intracellular or a cytoplasmic
receptors are found in the cytoplasm of the cell and respond to
hydrophobic ligand molecules that are able to travel across the
plasma membrane
• once inside the cell menu of this molecule bind to proteins that act as
a regulator of Mrna synthesis to mediate gene expression
• gene expression is the cellular process of transforming the information
in the cells DNA into a sequence of the amino acid that ultimately
forms a protein
25. • The ligand receptor complex more
into the nucleus by two specific
regulatory region of the
chromosome DNA and promotes
the initiation of transcription
• The internal receptors can directly
influence gene expression without
having to pass the signal on to
other receptors or a messengers.
26. CELL SURFACE RECEPTORS
• Cell surface receptors also
known as the transmembrane
receptors are cell surface
membrane-anchored ,or integral
proteins that bind to external
ligand molecules.
27. • This type of receptors spans the plasma membrane and perform signal transduction,
converting an extracellular signals to intracellular signal
• Ligand that interact with cell surface receptors do not have to enter the cell that they
affect
• cell surface receptors are also called cells specific receptors or a markers because they
are specific to individual cell types
• Which cell surface receptors has a three main components an external ligand-binding
domain (extracellular domain), hydrophobic membrane – spanning region, and an
intracellular domain inside the cell
• The size and extent of each of these domains vary widely, depending on the type of
receptors
28. • Cell surface receptors are involved in most of the signalling in
multicellular organism
• There are three general categories of cell surface receptors: ion
channel linked receptor, G- protein linked receptor, enzyme linked
receptor.
29. ION CHANNEL LINKED RECEPTORS
• ion channel linked receptors bind a ligand and open the channel through the membrane that
allowed the Specific ions to pass through
• full form of channels this type of cell surface receptor has on the extensive membrane spanning
region
• In order to Interact with the phospholipid fatty acid tails that form the centre of the plasma
membrane, many of the amino acids in the membrane-spanning region are hydrophobic in nature
• Conversely, the amino acids that line the inside of the channel are hydrophilic to allow for the
passage of water or iron
• when a ligand binding to the extracellular region of the channel there is the conformational
changes in the protein structure that allows ions such as a sodium calcium magnesium and
hydrogen to pass through
30.
31. ENZYME LINKED RECEPTORS
• Enzyme linked the receptor are either the enzyme themselves for a
directly associated with enzyme that they activate
• These are usually single pass transmembrane receptors with the
enzymatic portion of the receptor being the intracellular
• The majority of enzyme linked receptors are protein kinase or
associated with the protein kinase
32. 1TYROSINE KINASES
• The general method of activation following ligand binding to the receptor tyrosine kinases , which allow
their kindness domain to dimerize.
• The dimerization then invites the phosphorylation of their tyrosine kinase domains that, in turn, allow
intracellular proteins to bind the phosphorylated site and become active
• an important function of receptor tyrosine kinase are their role in mediates growth pathway(epidermal
growth factors, fibroblast growth factors)
33. G PROTEIN COUPLED RECEPTOR
• Largest category
• G protein
- hetrotrimeric protein
-3 sub units;. Alfa,beta, gamma
- alfa binds with GDP and GTP
. - beta and gama anchor to membrane
36. WHAT IS ION CHANNELS?
• Transmembrane glycoproteins pores that open and close in a
regulated manner and allows passage of ions through it
• Highly selective in type of ions transported
• Very high rate of ion transfer
• Ions are transported across the electrochemical gradient
• Passive mechanism
37. SELECTIVITY
• Permit ions of a specific size and charge
• The permeating ions will lose their dissociated water molecules and
pass through the hole in the channel which is known as selectivity
filter
• This limits their rate of passage
38. Schematic diagram of an ion channel
1- Channel domains(typically four per
channel),
2- Outer vestibule,
3- Selectivity filter,
4- Diameter of selectivity filter,
5- Phosphorylation site,
6- Cell membrane.
39. Types of ion channels
1.voltage gated ion channel: Open and close in response to membrane
potential
2.Ligand gated ion channel: open in response to specific ligand
molecules binding to the extracellular domain of the receptor protein
40.
41. • These channels are responsible for the rapid influx of sodium ions during the
action potential in nerve, muscle, and endocrine cells.
41
42. Voltage gated calcium channel
• Voltage-gated calcium channels mediate calcium influx in response
membrane depolarization and regulate intracellular processes such
as contraction, secretion and neurotransmission
• There are several different types of voltage gated
calcium channels:
L-type: skeletal, smooth, cardiac muscle (contraction) and for
aldosterone secretion in endocrine cells of the adrenal cortex
43. N-type: pre synaptic terminal and involved in neurotansmission
T-type : neurons, bones(osteocytes) Control the pacemaking activity
activity of the SA Node within the heart.
R-type: neurons, dendrites Control of firing pattern
P/Q-type channel: purkinje neurons in the
44. Voltage gated potassium channels
• Voltage-gated K+ channels are one of the key components in
generation and propagation of electric impulses in nervous system.
Upon changes in transmembrane potential, these channels open and
allow passive flow of K+ ions from the cell to restore the membrane
potential
45. Volatge gated chloride channel
These channels are present in every type of neuron, where they
control excitability, restore the resting membrane potential and
help regulate cell volume
48. Types of ligand gated ion channels
1.Extracellulalry activated ligand gated ion channel:
• The receptors of the cys-loop family(nicotinic receptors, 5-HT, GABA,
glycine and serotonin
• The glutamate activated cationic channels(NMDA, AMPA, kainate
receptors
51. 3.Ionotropic glutamate receptor
• Competitive NMDA antagonists bind directly to the glutamate site of the NMDA
receptor to inhibit the action of glutamate. Non-competitive antagonists block
the NMDA-associated ion channel in a use-dependent manner. Other sites on
the NMDA receptor susceptible to antagonism are the glycine site and the polyamine
site
53. Intracellular signal transduction pathways.
• The chains of molecules that relay signals inside a cell are known
as intracellular signal transduction pathways.
• Here, we’ll look at the general characteristics of intracellular signal
transduction pathways, as well as some relay mechanisms commonly
used in these pathways.
54. Binding initiates a signaling pathway
• When a ligand binds to a cell-surface receptor, the receptor’s intracellular domain
(part inside the cell) changes in some way. Generally, it takes on a new shape,
which may make it active as an enzyme or let it bind other molecules.
• The change in the receptor sets off a series of signaling events. For instance, the
receptor may turn on another signaling molecule inside of the cell, which in turn
activates its own target. This chain reaction can eventually lead to a change in the
cell's behavior or characteristics, as shown in the cartoon below.
55.
56. • Because of the directional flow of information, the term upstream is often used to
describe molecules and events that come earlier in the relay chain,
while downstream may be used to describe those that come later (relative to a
particular molecule of interest). For instance, in the diagram, the receptor is
downstream of the ligand but upstream of the the proteins in the cytosol. Many
signal transduction pathways amplify the initial signal, so that one molecule of ligand
can lead to the activation of many molecules of a downstream target.
• The molecules that relay a signal are often proteins. However, non-protein
molecules like ions and phospholipids can also play important roles.
57. Phosphorylation
• The cartoon above features a bunch of blobs (signaling molecules)
labeled as “on” or “off.” What does it actually mean for a blob to be on
or off? Proteins can be activated or inactivated in a variety of ways.
However, one of the most common tricks for altering protein activity is
the addition of a phosphate group to one or more sites on the protein,
a process called phosphorylation.
58. • Phosphate groups can’t be attached to just any part of a protein. Instead, they are typically
linked to one of the three amino acids that have hydroxyl (-OH) groups in their side chains:
tyrosine, threonine, and serine. The transfer of the phosphate group is catalyzed by an
enzyme called a kinase, and cells contain many different kinases that phosphorylate different
targets.
• Phosphorylation often acts as a switch, but its effects vary among proteins. Sometimes,
phosphorylation will make a protein more active (for instance, increasing catalysis or letting it
bind to a partner). In other cases, phosphorylation may inactivate the protein or cause it to be
broken down.
• In general, phosphorylation isn’t permanent. To flip proteins back into their non-
phosphorylated state, cells have enzymes called phosphatases, which remove a phosphate
group from their targets.
59.
60. MAP kinase
https://www.youtube.com/watch?v=thLsxvqDZ04
• To get a better sense of how phosphorylation works, let’s examine a
real-life example of a signaling pathway that uses this technique:
growth factor signaling. Specifically, we'll look at part of the epidermal
growth factor (EGF) pathway that acts through a series of kinases to
produce a cellular response.
61.
62. • When growth factor ligands bind to their receptors, the receptors pair up and act as
kinases, attaching phosphate groups to one another’s intracellular tails.
• The activated receptors trigger a series of events ,These events activate the kinase
Raf.
• Active Raf phosphorylates and activates MEK, which phosphorylates and activates
the ERKs.
• The ERKs phosphorylate and activate a variety of target molecules. These include
transcription factors, like c-Myc, as well as cytoplasmic targets. The activated targets
promote cell growth and division.
• Together, Raf, MEK, and the ERKs make up a three-tiered kinase signaling pathway
called a mitogen-activated protein kinase (MAPK) cascade. (A mitogen is a signal
that causes cells to undergo mitosis, or divide.) Because they play a central role in
promoting cell division, the genes encoding the growth factor receptor, Raf, and c-
Myc are all proto-oncogenes,
63. p38 MAPK
• p38 MAPKs (α, β, γ, and δ) are members of the MAPK family that are activated by a
variety of environmental stresses and inflammatory cytokines.
• As with other MAPK cascades, the membrane-proximal component is a MAPKKK,
typically a MEKK or a mixed lineage kinase (MLK).
• The MAPKKK phosphorylates and activates MKK3/6, the p38 MAPK kinases.
MKK3/6 can also be activated directly by ASK1, which is stimulated by apoptotic
stimuli.
• p38 MAPK is involved in regulation of HSP27, MAPKAPK-2 (MK2), MAPKAPK-3
(MK3), and several transcription factors including ATF-2, Stat1, the Max/Myc
complex, MEF-2, Elk-1, and indirectly CREB via activation of MSK1.
64.
65. JNK Pathway
• The c-Jun N-terminal kinase (JNK) pathway is one of the major
signaling cassettes of the mitogen-activated protein kinase (MAPK)
signaling pathway. It functions in the control of a number of cellular
processes, including proliferation, embryonic development and
apoptosis.
66. • Activation of JNK is mediated by a MAP kinase module, i.e.,
MAP3K→MAP2K→MAPK , through sequential protein phosphorylation. So far, two
MAP2Ks (JNKK1/MKK4/SEK1 and JNKK2/MKK7) for JNK have been identified .
JNKKs are dual-specificity protein kinases, which phosphorylate JNK at Thr183 and
Tyr185, leading to its activation. However, these two JNKKs appear to have different
preferences for the phosphate-acceptor sites, with JNKK1 preferring Tyr185 , and
JNKK2 Thr183 Although phosphorylation of JNK at both Thr183 and Tyr185 is
required for its full activation, Tyr185 phosphorylation seems to be a predominant
one in TNF-α induced JNK activation .
67.
68. PI3K PATHWAY
• PI3K-Akt-Mtor Pathway is an intracellular signal transduction pathway.
• Promotes metabolism, proliferation, cell survival, growth and angiogenesis in
response to extracellular signals.
• Key proteins are AKT and PI3K.
69. • The key molecules involved in this pathway are
• Receptor tyrosine kinase (RTKs).
• Phosphatidylinositol 3-kinase (PI3K)
• Phosphatidylinositol-4,5-bisphosphate (PIP2)
• Phosphatidylinositol-3,4,5-triphosphate (PIP3)
• AKT/protein kinase B.
70. PI3Ks are a family of intracellular lipid kinases
• PI3K consisted of two domains:
• a catalytic domain P110 and a
regulatory domain P85.
• Activation of PI3K typically occurs as a
result of ligand binding to receptor
• PI3K can also be activated by a GTP
binding RAS protein.
71. PIP2 AND PIP3
• PIP2 and PIP3 are minor phospholipid component of cell membranes.
• In PI3K-AKT pathway, the 3 position phosphate group of PIP3 can
bind to AKT protein and recruiting AKT protein at the plasma
membrane.
• AKT can also be activated by
• PDPK1.(Phosphoinositide-dependant protein kinase)
72. AKT pathway
https://www.youtube.com/watch?v=Mc61VOhhNk
g
• AKT also named as protein kinase B.
• Serine/threonine-specific protein kinase
• Role in multiple cellular processes.
• Once activated, at threonine-308 and at serine 473 it regulates the function via
phosphorylation activation or suppression of a broad array of proteins .
• Involved in different functions.
73.
74. RAS
https://www.youtube.com/watch?v=L7U9QrGPkM
• RAS is a monomeric G-protein
• Contains only a single subunit
• Acts as a GTPASE switch i.e converts GDP TO GTP
• RAS was first identified as transducer for the tyrosine kinase linked receptors where
it functions to relay information to mitogen activated receptor kinase(MAPK)
signalling pathway
• It is now known the activated RAS is able to relay information to number a signalling
pathways
