Lec 04 Flashcards
Physiological signals
-Electrical signals
Changes membrane potential
-Chemical signals
Molecules secreted by cells into ECF
Bind to specific receptor on or in target cells
Communication method between cells
1- Local(gap junction, autocrine(myself), paracrine(neighbor))
2- Long distance (neuronal, endocrine)
Autocrine and Paracrine examples
Hormones
Neurotransmitter
Hormone are secreted by endocrine into —
Blood. Only target cells with receptors for the hormone will respond
Endocrine hormone example
Insulin secreted from pancreatic betta cells and binds to insulin receptors throughout body enable glucose enter these cells
Neurotransmitters
-Long distance
-Secreted by neurons that Diffuse across a small gap to the target cell
Neurotransmitter example
Acetylcholine that elicit skeletal muscle contraction
Neurohormones
Chemicals released by neurons into blood for action at distant targets
Neurohormones examples
Oxytocin is released by posterior pituitary gland into blood and stimulates (Uterus smooth muscles) uterine contractions during labor
Major classes of chemical signals
Amino acids — glutamate, glycine
Amines — epinephrine, norepinephrine, dopamine
Peptides — insulin, glucagon
Steroids — derived from cholesterol, estrogen
Receptor Location
Intracellular signal receptors:
— receptor in cytosol or nucleus
— SLOWER RESPONSE
Extracellular signal receptor:
— cell membrane receptor
— RAPID CELLULAR RESPONSE
Membrane receptors categorize
1- channels
2- Enzyme(receptor)
—— insulin
3- G protein (receptor)
4- Anchor protein (integrin)
—— adherents junctions
Signal transduction
1- Signal molecule (hormone/neurotransmitter) binds to membrane receptors proteins
2- Which activates intracellular signal molecules
3- which alter target protein
4- create response
Signal transduction
1-Signal molecule bind to membrane receptor
2- Initiate signal transduction by proteins
3- amplifier enzymes produce second messenger molecules
**4.1- protein kinases or phosphatases
**4.2- increase intracellular ca ion
***4.3- MAYBE alter ion channels
5- cell response
Kinases
Phosphorylate protein
Phosphatases
Dephosphorylated proteins
Signal amplification two key factors
1- volume
2- sensitivity
Cascade
Tightly regulated to not accidentally turn on safety
Enzyme-linked receptors
Ligands binds to receptor, which activates associated enzyme
Ex. Insulin receptors
G protein coupled receptors
-Ligand binds to receptor that is physically coupled to a Guanosine nucleotide-binding (G) protein
-Largest family of cell surface receptor
-G protein made up three subunits: alpha, betta, gamma
-After activation they may:
—— directly alter ion channel
——alter activity of another enzyme
-Type of G protein will determine which intracellular cascade is initiated
GS
GPCR—adenylyl cyclase—produce cyclic cAMP shows us —activates protein kinase A—phosphorylated protein—cell response
GI
GPCR—GI(inhibitory)—inhibit Adenylyl cyclase—cyclic cAMP level decrease—kinase activity fall
Gq
Gq activates phospholipase C—(break triphospholipid)—IP3 (O-head) AND DAG (tail)—DAG activates PKC (protein kinase c) that will phosphorylated proteins— IP3 will open ligand-gated ca ion channels in ER
Gq
1- Signal molecule activates receptor and associated G protein.
2- G protein activates phospholipase C (PLC), an amplifier enzyme.
3- PLC converts membrane phospho- lipids into diacylglycerol (DAG), which remains in the membrane, and IP3, which diffuses into the cytoplasm.
4- DAG activates protein kinase C (PKC), which phosphorylates proteins.
5- IP3 causes release of Ca2+ from organelles, creating a Ca2+ signal.
Ligand-gated channel
Ligand binds to its receptor. Receptor is ion channel that is gated by ligand binding
Ion channels can be activated during gpcr by ——
Camp,Ca ion,G protein
Indirect gating
Slower change
Ca ion can enter the cell via
1- voltage-gated channel
2- ligand-gated channel
3- mechanically-gated channel
4- released from stores by secondary messengers
When Ca ion conc. in cytosol Increase
Ca ion binds to protein:
Calmodulin — alter protein activity
Other proteins — Exocytosis/movement
