Concept 11.2
Reception: A signaling molecule binds to a receptor
protein, causing it to change shape.
Presenters: Siena DeBenedittis, Daniel de Leon, Isaiah Galarza,
Amy Mercado, Ronan Murphy, Yasmeen Qureshi, Orlando
Santiago, Christina Valeros, Yao Xu
Period: A
Date: 12/16/14
Reception
-The term used to describe the target cell’s
detection of a signaling molecule outside of the
cell.
-This detection occurs when the signaling
molecule binds to a certain site on the receptor
protein.
Ligands
-Ligands are molecules that specifically bind to others.
-Ligand bonding usually causes the receptor proteins to
change shape.
-This shape change could either:
-allow the receptor to interact with other cellular
molecules
-or bring together two or more receptor molecules
Intracellular Receptors.
-Intracellular receptor proteins are found in the cytoplasm or nucleus
of target cells.
-Signaling molecules, a.k.a. chemical messengers can permeate through
the membrane to reach these receptors
Signaling molecules are hydrophobic or small enough to cross the
membrane.
For example:
Steroid or thylakoid hormones are hydrophobic, and therefore can
cross the membrane.
Nitric acid (NO) is a molecule small enough to cross the membrane
-Hormones like the steroid testosterone have the ability to bind to a receptor
protein, activating it. The receptor protein then enters the nucleus and can turn
on specific genes.
-Special proteins called transcription factors are able to turn on specific genes,
that it is able to turn on genes that are to be transcripted to mRNA.
-The testosterone receptor which acts as a transcription factor carries out
complete transduction of the signal.
-Almost all other intracellular receptors function the same, but the only
difference here is that the signal molecule reaches these receptors when they
are in the nucleus.
-Many intracellular receptors are similar in structure.
Receptors in the Plasma Membrane
-Receptor proteins embedded in the cell membrane contain
sites onto which many water-soluble signal molecules are
able to bind to.
-These receptors transmit information into the cell when a
ligand binds to it.
-There are three types of receptors in the plasma
membrane: G protein-linked receptors, receptor tyrosine
kinases, and ion channel receptors.
G Protein-Coupled Receptors (GPCRs)
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-
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A G protein-coupled receptor is a receptor
protein located within the plasma
membrane that functions along with the
help of a G protein.
A G protein is a protein that binds GDP and
a phosphate group to form GTP, an energy
rich molecule that functions similar to ATP.
GPCRs are all made up of a single
polypeptide chain coiled into seven α helices
that span the plasma membrane.
Slight changes in basic structure creates
different GPCRs that bind to different
signaling molecules and G proteins.
GPCRs Cont.
FUNCTIONS OF GPCRs
GPCRs are extremely diverse in their functions
-Has a role in embryonic development and sensory reception
-In humans, taste, smell and vision all depend on these systems
-Involved in many human diseases, mainly bacterial infections
~Cholera, pertussis, botulism, and other bacteria produces toxins that
interfere with G proteins
G Protein- Coupled Receptor
1) GDP is inactive.
2) A signalling molecule binds
to the extracellular side of
the receptor, making it
active. GTP binds to the
cytoplasmic side.
3) GTP moves to the enzyme,
changing the enzyme’s
shape and activity. It leads
a cellular response.
4) The GTP leaves the enzyme
and changes to GDP, which
is now inactive.
Receptor Tyrosine Kinases (RTKs)
- Receptor tyrosine kinases belong to a major class of plasma
membrane receptors. These receptors are characterized by
enzymatic activity.
- A kinase is an enzyme that catalyzes the transfer of phosphate
groups.
- The part of the receptor protein going inside the cytoplasm
functions as a tyrosine kinase, an enzyme that catalyzes the
transfer of a phosphate group from ATP to the amino acid
tyrosine.
RTKs continued.
-
One receptor tyrosine kinase complex can activate ten or more
different transduction pathways and cellular responses, helping the
cell regulate growth and reproduction.
The ability of a single ligand-binding event to trigger so many
pathways is a key difference between receptor tyrosine kinases and
G protein-coupled receptors.
Abnormal RTKs that operate in the absence of signaling molecules
are related with many kinds of cancer.
Receptor Tyrosine Kinases
1) There are two inactive monomers.
2) Signaling molecules go to the
binding site. The two monomers
come together and form a Dimer.
3) Dimerization activates the tyrosine
region of each monomer. Each
tyrosine kinase adds a phosphate
from an ATP molecule to a tyrosine
on the tail of the other monomer.
4) The receptor is activated. Proteins
bind to a specific phosphorylated
tyrosine, undergoing a structural
change. It leads to a cellular
response.
Ion Channel Receptors
- A ligand-gated ion channel is a membrane receptor containing
a region that acts as a "gate" when the receptor changes shape.
-Binding of a signaling molecule to a receptor protein causes the
gate to open or close, allowing or blocking the flow of ions.
-Important to the nervous system
→ Neurotransmitters released at a synapse between two
nerve cells bind as ligands to ion channels, causing the channel
to open. Ions flow in/out, triggering an electrical signal.
-Voltage-gated ion channels are gated ion channels controlled by
electrical signals instead of ligands.
Ion Channel Receptors
1) The ligand-gated ion channel
remains closed until a ligand
binds to the receptor.
2) The ligand binds to the receptor.
The gate opens and ions can flow
through. It leads cellular
response.
3) The ligand leaves the receptor.
The gate closes and the ions can
not pass through.
Thanks :)