The document provides an overview of various signaling mechanisms in cells, including autocrine, paracrine, endocrine, and juxtacrine signaling. It discusses G protein-coupled receptors, receptor tyrosine kinases, and ionotropic receptors, detailing their structures, functions, and roles in signal transduction processes. Additionally, it highlights how these signaling pathways impact cellular responses and activities, such as growth and differentiation.

3. Synthesis
of
signaling
molecule
Release
of
signaling
molecule
Transport
of signal
to target
cell
Detection
and
binding of
signal by
specific
receptor
Changes
due to
receptor-
signal
complex
Signal
removal
and
response
terminatio
n

5.  Autocrine signaling
 Paracrine signaling
 Endocrine signaling
 Juxtacrine signaling

18.  An agent which activates a receptor to
produce an effect similar to that of the
physiological signal molecule

19.  An agent which activates a receptor to
produce an effect in the opposite
direction to that of the agonist

20.  An agent which prevents the action of
an agonist on a receptor or the
subsequent response, but does not
have any effect of its own

21.  An agent which activates a receptor to
produce submaximal effect but
antagonizes the action of a full agonist

22.  To propagate regulatory signals from
outside to within the effector cell when
the molecular species carrying the
signal cannot itself penetrate the cell
membrane
 To amplify the signal
 To integrate various extracellular and
intracellular regulatory signal

26.  Their signaling protein partners are
called G proteins because they bind to
the nucleotide GTP to regulate their
shape and activity
 When activated, they can trigger the
activation of several copies of the same
G protein. Because activated G proteins
dissociate from the GPCR, leaving the
binding site available to bind and
activate, thereby amplifying the effect of
a single signal molecule

27.  Gs subgroup which stimulate
adenylyl cyclase
 It includes Golf coupled to olfactory
receptors
 Gi subgroup which inhibit adenylyl
cyclase and activate some Ca²+ and
K+ channels

28.  Gq subgroup which couple receptors
to calcium mobilisation through
phospholipase Cβ that in turn generates
the two second messengers inositol
triphosphate (IP3) and diacylglycerol
(DAG)
 Gt subgroup which stimulate
phosphodiesterase following light
stimulation of the retina involving
transducin

31.  The receptor protein forms seven
transmembrane α helices connected
by alternating cytosolic or
extracellular loops
 The N – terminus of the protein is
exposed to the extracellular fluid,
while the C – terminus resides in the
cytosol

32.  The extracellular portion of each G
protein – linked receptor has a unique
messenger – binding site, and a
cytosolic loop connecting the fifth and
sixth transmembrane α helices is
specific for a particular G protein

33. Activation of G
protein receptors

34. First
messenger
Change in
conformation
of G-protein
Increase
affinity for
α to GTP

35. Activated α
binds to other
EFFECTOR
PROTEIN
Dissociates
from other
sub-units
α binds
with GTP

36. GTPase of α
cleaves GTP
to GDP
Inactivation
of α subunit
Recombining
β with and γ
units

39.  These are transmembrane proteins
that are composed of at least two
subunits and therefore have a
quaternary structure
 Each of the subunits contains a single
α-helical transmembrane domain, so
they can diffuse relatively easily in the
membrane

40.  The subunits of inactive receptors
dissociate from one another, and only
bind to one another when they come into
contact with the proper ligand
 Their cytoplasmic tails contain protein
kinase domains
 A protein kinase is an enzyme that
attaches phosphate groups to the side
chains of specific amino acids

41.  Serine/threonine kinase receptor are
more heterogeneous in structure than
tyrosine kinases, and most do not
undergo transautophosphorylation;
instead, they phosphorylate a
separate signaling protein

42.  Tyrosine kinase receptor, which
contain two subunits. Each of the two
subunits contains a tyrosine kinase,
and in many cases, each
phosphorylates tyrosines on the
opposite subunit, a behavior called
transautophosphorylation

44.  Many receptor tyrosine kinases (RTKs)
trigger a chain of signal transduction
events inside the cell that ultimately
leads to cell growth, proliferation, or the
specialization of cells in a process
known as differentiation
 These processes are tightly controlled ,
so that only specific cells respond when
the appropriate ligand is available

45.  Examples of RTKs include the insulin
receptor, the nerve growth factor
receptor and the epidermal growth
factor (EGF)

46.  These receptors often consist of a single
polypeptide chain with only one
transmembrane segment
 The extracellular portion of the receptor
contains the ligand – binding domain
 Inactive receptors are separate
polypeptides with inactive tyrosine
kinase domains

47.  Binding to a signaling molecule
causes the two subunits of the
receptor to join together, also called
dimerize
 The resulting phosphotyrosine amino
acids are binding sites for additional
signaling proteins that pass the signal
along the pathway

48.  When the cytoplasmic tail of one
subunit is brought close to the
tyrosine kinase domain of the other
subunit, it is phosphorylated on
specific tyrosine amino acids

49.  They are actually located in the
cytoplasm and migrate to the nucleus
after binding with their ligands
 They are composed of a C – terminal
ligand – binding region, a core DNA –
binding domain (DBD) and an N-
terminal domain that contains the AF1
(activation function 1) region

50.  The core region has two zinc fingers that
are responsible for recognizing the DNA
sequences specific to this receptor
 The N – terminus interacts with other
cellular transcription factors in a ligand –
independent manner
 Depending on these interactions , it can
modify the binding / activity of the
receptor

51.  Membrane – permeable signals adhere to
receptor proteins in the cytosol
 These receptors typically have very
short signal transduction pathways they
move directly into the nucleus once they
are bound and activated . These are
called nuclear receptors for this reason

53.  It is commonly known as ionotropic
receptors, are a group of
transmembrane ion channel proteins
which open to allow ions such as Na+,
k+, Ca²+ and Cl¯ to pass through
membrane in response to the binding
of a chemical messenger such as a
neurotransmitter

54.  When a presynaptic neuron is excited, it
releases neurotransmitter from vesicles
into the synaptic cleft
 The neurotransmitter then binds to
receptors located on the postsynaptic
neuron. If these receptors are ligand -
gated ion channels, a resulting
conformational change opens the ion
channels, which leads to a flow of ions
across the cell membrane

55.  This, in turn, results in either a
depolarization, for an excitatory
receptor response, or a
hyperpolarization, for an inhibitory
response

56.  These proteins are typically composed
of at least two different domains: a
transmembrane domain which
includes the ion pore, and an
extracellular domain which includes
the ligand binding location

58.  Ionotropic glutamate receptors
 NMDA receptors
 GABA receptors
 5-HT receptors

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 Rastogi Bala Veer, Aneja R. K. , principles of
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International Pvt. Ltd. NEW DELHI, fifth edition,
page no. 211 - 219
 Plopper George, cell biology, published by jones
& bartlett learning, second edition, 2016, page
no. 372 – 380
 https://www.cancer.gov/publications/dictionaries/
cancer-terms?cdrid=633297
 http://encyclopedia2.thefreedictionary.com/intra
cellular +signaling+ pathway