Concept 11.2

1. 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

2. 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.

3. 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

4. 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

5. -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.

6. 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.

7. G Protein-Coupled Receptors (GPCRs) • 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.

8. 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

9. G Protein- Coupled Receptor • GDP is inactive. • A signalling molecule binds to the extracellular side of the receptor, making it active. GTP binds to the cytoplasmic side. • GTP moves to the enzyme, changing the enzyme’s shape and activity. It leads a cellular response. • The GTP leaves the enzyme and changes to GDP, which is now inactive.

10. 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.

11. 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.

12. Receptor Tyrosine Kinases • There are two inactive monomers. • Signaling molecules go to the binding site. The two monomers come together and form a Dimer. • 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. • The receptor is activated. Proteins bind to a specific phosphorylated tyrosine, undergoing a structural change. It leads to a cellular response.

13. 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.

14. Ion Channel Receptors • The ligand-gated ion channel remains closed until a ligand binds to the receptor. • The ligand binds to the receptor. The gate opens and ions can flow through. It leads cellular response. • The ligand leaves the receptor. The gate closes and the ions can not pass through.

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