Carboxylic Acids Esters, Amines and Amides

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Chemical Messengers
Neurotransmitters Hormones
4/13/2013
Supplemental
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Chemical Messengers for coordination of
biological processes within an organism

• Terms and Definitions
• neuron a nerve cell.
• neurotransmitter a chemical messenger between a
  neuron and another target cell neuron, muscle
  cell or cell of a gland.
• - the molecule acts over a short distance
• (across a synapse, 0.1 µm)
  Eg, Acetylcholine
• hormone a chemical messenger released by an
  endocrine gland (secretary organ) into the
  bloodstream and transported there to reach its
  target cell (its site of action).
• over a long distance ( 20cm).
  Eg, Insulin

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Chemical Messengers

• Five Classes
• Cholinergic Messengers Acetylcholine, and likes
• Amino acid Messengers Glutamate, GABA, etc.
• Adrenergic Messengers Monoamines
• Peptidergic Messengers Insulin, Glucagon, etc.
• Steroid Messengers Androgen, Estrogen,
  etc.
• Messengers are also classified by how they work
• activate enzymes.
• affect the synthesis of enzymes.
• affect the permeability of membranes.
• act directly or through a secondary messenger.

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Chemical Communication

• Many drugs used in medicine influence chemical
  communication
• Antagonist a molecule that blocks a natural
  receptor and prevents its stimulation.
• Agonist a molecule that competes with a natural
  messenger for a receptor site it binds to the
  receptor site and elicits the same response as
  the natural messenger.
• A drug may decrease or increase the effective
  concentration of messenger.

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• A neurotransmitter

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Amine (Quaternary) as well as Esther
Acetylcholine (ACh) the main cholinergic
messenger

• the first neurotransmitter found (1914)
• by Henry Dale Otto Loewi (NP, 1936)
• communicate between the nervous system and the
  muscle.
• When stimulated, it releases into the synapse
  where it binds to muscle cell receptors causing
  the muscles to contract.

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Acetylcholine

• The main cholinergic messenger is acetylcholine.
• Cholinergic receptors
• There are two kinds of receptors for
  acetylcholine.
• We look at the one that exists in motor end
  plates of skeletal muscles or in sympathetic
  ganglia.

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Acetylcholine

• Storage and release of acetylcholine (ACh).
• The nerve cells that bring messages contain ACh
  stored in vesicles.
• The receptors on muscle neurons are called
  nicotinic receptors because nicotine inhibits
  them.
• The message is initiated by calcium ions, Ca2.
• When Ca2 concentration becomes more than about
  0.1 mM, the vesicles that contain ACh fuse with
  the presynaptic membrane of nerve cells and empty
  ACh into the synapse.
• ACh travels across the synapse and is absorbed on
  specific receptor sites.

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Acetylcholine

• Action of the acetylcholine (contd)
• The presence of ACh on the postsynaptic receptor
  triggers a conformational change in the receptor
  protein.
• This change opens an ion channel and allows ions
  to cross membranes freely.
• Na ions have higher concentration outside the
  neuron and pass into the cell.
• K ions have higher concentration inside the
  neuron and leave the cell
• This change of Na and K ion concentrations is
  translated into a nerve signal.
• After a few milliseconds, the ion channel closes.

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Acetylcholine in Action
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Acetylcholine

• Removal of ACh
• ACh is removed from the receptor site by
  hydrolysis catalyzed by the enzyme
  acetylcholinesterase.
• This rapid removal allows nerves to transmit more
  than 100 signals per second.

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Acetylcholine

• Acetylcholine is linked to Alzheimers disease
• In Alzheimers disease, ACh levels may decrease
  by 90.
• Aricept, an Alzheimers medication, slows the
  breakdown of ACh in order to elevate the
  acetylcholine levels in the brain.

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Catecholamines

• Include dopamine, norepinephrine, and epinephrine
• All of these are closely related in structure and
  all are synthesized from the amino acid tyrosine.

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Dopamine

• produced in the nerve cells of the midbrain and
  acts as a natural stimulant to give us energy and
  feelings of enjoyment.
• Control muscle movement, improve, cognition,
  memory, learning
• Cocaine and amphetamine block the reuptake of
  dopamine resulting in a longer lifetime in
  synapse.

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Norepinephrine and Epinephrine

• Norepinephrine (noradrenaline) and epinephrine
  (adrenaline) are hormonal neurotransmitters that
  play a role in sleep, attention and focus, and
  alertness.
• Epinephrine is synthesized from Norepinephrine.
• Both are normally produced in the adrenal glands.
• Both are highly produced during the
  fight-or-flight response, increasing blood
  pressure, heartv rate, constrict blood vessel,
  dilate airways, stimulating breakdown of
  glycogen.
• Administered during cardiac arrest.broncodialator.
  
• Low level leads to Attention Deficit
  Disorder(ADD)

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Serotonin (5-Hydroxytryptamine)

• Serotonin helps us relax, sleep deeply and
  peacefully, think rationally, and it provides us
  a feeling of well-being and calmness.
• Serotonin is synthesized from the amino acid
  tryptophan.
• Psychedelic drugs stimulate the action of
  serotonin at its receptors.
• Low serotonin levels may be associated with
  depression, anxiety disorders, etc.
• Prozac and Paxil (antidepressant drugs) are
  selective serotonin reuptake inhibitors (SSRIs).

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Prozac and Paxil
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Histamine

• synthesized in the nerve cells in the
  hypothalamus from the amino acid, histidine.
• is produced by the immune system in response to
  pathogens and invaders, or injury.
• When it combines with histamine receptors, it
  produces allergic reactions inflammation,
  watery eyes, itchy skin,.etc.

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Amino Acid Neurotransmitters

• Glutamate
• the most abundant neurotransmitters in the
  nervous system.
• stimulates the synthesis of nitrogen monoxide
  (NO).
• Both Glutamate NO involved in learning and
  memory
• Too much glutamate in the spinal cord causes
  degeneration of nerve cells (Lou Gehrigs disease
  of Muscular atrophy).
• Too rapid uptake of glutamate may results in
  schizophrenia

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Gamma(g)-Aminobutyric Acid (GABA)

• the most common inhibitory neurotransmitter in
  the brain.
• produces a calming effect by inhibiting the
  ability of nerve cells to send electrical signals
  to nearby nerve cells.
• Alcohol, sedatives increases the inhibitory
  effects.
• Caffeine decreases the GABA levels in the
  synapses
• causing opposite effects.

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Gamma(g)-Aminobutyric Acid (GABA)

• GABA
• the most common inhibitory neurotransmitter in
  the brain.
• produces a calming effect by inhibiting the
  ability of nerve cells to send electrical signals
  to nearby nerve cells.
• Alcohol, sedatives increases the inhibitory
  effects.
• Caffeine decreases the GABA levels in the
  synapses
• causing opposite effects.

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