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Chapter 5

Chemical Messengers

Long distance communication centers of the body: Nervous system and Endocrine system.
What is the Nervous System made up of? Neurons and supporting cells.
T/F: A particular neuron can span a long distance? True
How does the Nervous System communicate signals? Transmit signals down the length of their axon; turns into chemical signal at the axon terminals.
T/F: Fast communication but is over quickly too? True
Endocrine System relies on ___________ ___________ to deliver hormones. Circulatory System
T/F: Endocrine System has direct contact with its' target. False, relies on hormones.
What is the Endocrine System able to offer that Nervous System does not? SLOW acting, but able to offer prolonged communication which is important for coordination homeostasis (metabolism, cell growth) and for specialized processes like reproduction and lactation.
Direct communication Gap Junctions - connexin: plasma proteins that come together to form channels.
Indirection communication Chemical Messengers
What is the general method of communication? via Chemical Messengers
T/F: Ligand is a chemical messenger? True
What does the ligand do? Ligand binds to its receptor on target cells.
What happens when the Ligand binds to the receptor? It causes signal transduction.
Signal Transduction causes physiological response:
What are types of physiological response of signal transduction? a. induces changes w/n proteins already existing inside of the cell. b. induces the cell to make new protein (transcription/translation)
Distance B/W ligand released and target cell determines action: Autocrine, paracrine, and endocrine.
Autocrine Fast-acting, short-lived.
How does Autocrine regulate its own cellular activity (usually inhibitory; short negative feedback loop): by secreting ligand into ISF; diffuses back to self.
Paracrine Fast-acting, short-lived.
T/F: Paracrine regulates neighboring cellular activity? True
How does Paracrine regulate neighboring cellular activity? by secreting ligand into ISF; diffuses into neighbor cells.
What is an example of Paracrine in action? Delta cells of the pancreas modulate the production of glucagon and insulin through somatostatin.
Define Somatostatin Growth hormone- inhibiting hormone; regulates Endocrine system...
Alpa cells secretes glucagon.
Beta cells secretes insulin.
Delta cells secretes somatostatin.
Endocrine Longer time to action, Longer half life.
How does Endocrine regulate a distant target? by releasing a hormone into the bloodstream.
Lipophilic/hydrophobic Can easily cross membrane.
Where are the receptors for lipophilic/hydrophobic located? Intracellularly (cytosol or nucleus),
Lipophobic/hydrophilic Cannot cross the plasma membrane without assistance.
Where are the receptors for lipophobic/hydrophilic located? Plasma membrane.
Define Half-Life: Time it takes for half of the ligand in the plasma to be degraded.
T/F: Half-Life measure of ligand lifespan in the brain? False, measures of ligand lifespan in the body.
What is the Half-Life of autocrine and paracrine ligands? Short.
What is the Half-Life of endocrine hormones? Longer.
T/F: Time to degradation depends on how the ligand is transported? True
Which ligand does not require carriers? Lipophobic/hydrophilic
Which ligand use carrier proteins? Lipophilic/hydrophobic
Why does lipoPHILIC/hydroPHOBIC use carrier proteins? Protect them from degradation (prolong their half-life), allow them to travel in ISF and plasma, Ligand must separate from its carrier to be active.
Active ligand amounts to... "free"
Type of carriers: 1. specific: only shuttle a specific ligand or class of ligands. 2. general: carry a variety of ligands. a. albumin
What are the 5 chemical classes of ligands? 1. Amino Acids, 2. Amines, 3. Protein/peptides, 4. Steroids, 5. Eicosanoids.
Amino Acids... ACT AS, Synthesized inside, Stored in: Neurotransmitters, Neurons, stored in vesicles until needed; released by exocytosis.
Where are the receptors located in amino acids? Plasma membrane; lipophobic
Examples of Amino Acids? Gluatmate, Aspartate, Glycine, and GABA (gamma-aminobutyric acid).
Amines... Derived from, Synthesized in, Stored in: AA, Cytosol (created by enzymatic reactions), stored in vesicles until needed; released by exocytosis.
T/F: Amines are lipophobic? True, except the thyroid hormones.
Examples of Amines? Catecholamines: norepinephrine (Neurotransmitter), epinephrine (hormone), dopamine (N), serotonin (N), thyroid hormones, histamine (paracrine).
Peptides are huge class of ligands: hormones, neurotransmitters, cytokines.
Peptides are... Synthesized, Stored in, Classified by: Classical translation (rough ER and ribosomes), stored in vesicles until needed; released by exocytosis, and are classified by size.
T:F: Peptides are lipophilic? False, it is lipophobic.
Steroid... Derived from, Synthesized on, Stored in: Cholesterol; series of enzymatic reactions converts cholesterol into desired steroid. Synthesized on demand and immediately released. CAN'T BE STORED inside cell; when made, they diffuse out of cell.
Steroids lipophilic; nuclear receptors.
Eicosanoids Paracrines secreted by many different cell types.
Eicsanoids... Synthesized, Stored in: On demand and immediately released. CAN'T be stored inside cell.
Examples of Eicosanoids Prostaglandins, leukotrienes.
T/F: Eicosanoids are lipophilic. True
Steroid Action 1: Steroid diffuses through cell and binds to its receptor in the nucleus (nuclear receptor) = hormone-receptor complex (HR).
Steroid Action 2: The HR binds to DNA to drive transcription of a particular gene.
Steroid Action 2a: HR binds to hormone response element (HRE).
Steroid Action 2b: HRE is located at the starting sequence of the desired gene.
Steroid Action 3: Transcription proceed-->mRNA; mRNA travels into cytosol.
Steroid Action 4: Translation process.
Eicosanoid 1: Eicosanoid binds to its receptor in the cytosol= HR
Eicosanoid 2: HR diffuses into nucleus.
Eicosanoid 3: The HR binds to DNA to drive transcription of a particular gene.
Eicosanoid 3a: HR binds to hormone response element (HRE).
Eicosanoid 3b: HRE is located at the starting sequence of the desired gene.
Eicosanoid 4: Transcription proceeds--> mRNA; mRNA travels into cytosol.
Eicosanoid 5: Translation process.
HR Hormone-receptor complex
HRE Hormone-response element
What are the types of receptors on the plasma membrane? Channel- linked receptor, enzyme-linked receptor, and G protein-linked receptor.
Which are the fast receptors? Channel-linked and enzyme-linked.
Which one is a slow receptor? G protein-linked.
What can FAST ligand-gated channels do? When it binds to R, opens channel. R and channel are same protein. ONLY OPEN a channel. Immediate response but the channel will open ONLY BRIEFLY.
What can SLOW ligand-gated channels do? G-protein-linked R. R and channel are separate proteins, but are linked by another protein (G protein). OPEN AND CLOSE a channel. Slower response but the channel can remain regulated for a LONG PERIOD OF TIME.
Ions enter through a channel, physiological responses: Contraction, secretion, change the electrical properties of the cell (alters the electrical potential), ion can act as a 2nd messenger.
What is a 2nd messenger? an intracellular messenger that is produced by a ligand (1st messenger) binding to its receptor.
Tyrosin Kinase System Insulin uses this signaling system to trigger the increase of GLUCOSE transporters to the plasma membranes of cells throughout body and increases anabolic processes w/n liver, SKM, and fat cells.
TKA 1: Ligand (insulin) binds to its receptor.
TKA 2: The receptor undergoes a conformational change and becomes an activated enzyme (tyrosine kinase).
TKA 3: The enzyme phosphorylates proteins-->physiological response.
Calcium-Camodulin System 1: Ligand binds to its receptor.
Calcium-Camodulin System 2: The receptor udnergoes a conformational change and becomes a calcium channel.
Calcium-Camodulin System 3: CA++ flows into the cell.
Calcium-Camodulin System 4: Working as a second messenger, it binds to Calmodulin creating a CA-Calmodulin complex.
Calcium-Camodulin System 5: This complex activate Protein kinase (an enzyme).
Calcium-Camodulin System 6: The enzyme phosphorylates proteins-->physiological response.
This system can trigger muscle contraction, and can affect metabolism and transport. Calcium-calmodulin system.
G protein signaling cascades 1: Ligand will bind to its receptor (causing a change of shape in G protein will become loose, dissociates-->then back to normal.)
G protein signaling cascades 2: causes the conversion of GDP-->GTP (alpha subunit dissociates.)
G protein signaling cascades 3: Activate G protein alpha subunit will dissociates and bind to target protein (a channel or enzyme) (activates enzymes, go inside cell, and activates 2nd messenger.)
G protein signaling cascades 4: The channel or enzyme is now activated. (Tell more enzymes)
G protein signaling cascades 5: Phosphorylate proteins-->physiological response. (Increased #s of whatever protein it wants)
cAMP (cyclic monophosphate) 2nd messenger system: LH, FSH, TSH, Glucagon, PTH, calcitonin, ADH, ACTH etc. all use this signaling cascade to cause their physiological response.
cAMP 1: The ligand binds to its receptor, activating the G protein.
cAMP 2: The alpha subunit binds and activates adenylate cyclase.
cAMP 3: Adenylate cyclase converts ATP to cAMP.
cAMP 4: Acting as a 2nd messenger, activates protein kinase A (PKA)
cAMP 5: Causes the phosphorylation of proteins-->physiological response.
Created by: r_saelee



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