Ch. 5 Chemical Receptors

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gap junctions chemical messengers: All cell in the body use ____ ________ and ________ _________ to communicate with one another
connexins: Gap junctions link adjacent cells and are formed by plasma membrane proteins called _________.
connexons: These ________ form channels that allow ions and small molecules to pass directly fro one cell to another.
couples: The movement of ions through gap junctions electrically _______ the cells, such the electrical signals in one cell are directly transmitted to the neighboring cells.
gap junctions: ___ _______ are also found in some glands and btwn some neurons in the brain and retina, where they function in communication.
metabolically: The movement of small molecules through gap junctions __________ couples the cells, such that one cll can provide necessary nutrients to reach certain bone cells.
Paracrines Autocrines Cytokines Neurotransmitters Hormones Neurohormones: What are the 6 functional classifications of chemical messengers?
Paracrines: What is the functional classification of eicosanoids?
Autocrines: Local effect on the SAME cell that secretes it.
Cytokines: interferons
interleukins
Neurotransmitters: chemical released into the interstitial fluid from nervous system cells called neurons.

Released from a specialized protion of the neuron called the axon terminal, which is very close to the target cell.
Hormones: are chemicals released from endocrine glands into the interstitial fluid, where they can diffuse with the blood.

Travels in blood to get to its target cell.

Bloodstream distributes these to all cells of body, BUT cell only have specific receptors for specific _________.
Neurohormones: Messengers released by neurosecretory cells at their axons. Carried by the BLOODSTREAM to target cell.

Target cells are NOT neurons.
If they are lipophilic or lipophobic.: How are chemical messengers classified? (2)
Lipophilic: May be lipid soluble

Receptors usually inside the target cell.
lipophobic: May be water soluble

Receptors usually part of the cell membrane.
AA Amines Peptides Steroids Eicosanoids: What are the 5 chemical classifications of messengers?
Amino Acids: Act as a messenger in the ner. sys.

Lipophobic
Ex. neurotransmitters
Amines: derived from A.A.s
Peptides: multiple AAs bonded together. Length of chain is variable (2-100)

Lipophobic
Ex. many neurotransmitters, hormones, all cytokines.
Steroids: derived from cholesterol
Lipophilic
Eicosanoids: derived from fatty acids
Lipophilic
Act as paracrine messengers
Signal transduction mechanisms: Mechanisms that allow a messenger molecule to act on target cells to change their function.
Messenger binds to receptors on or in the target cell. The receptors then change the activity of enzymes in the cells, changing cell function.
Properties of receptors: 1. show specificity - react only with certain molecules
2. Many types of receptors on or in 1 cell.
3. The more interactions btwn messengers and receptors the greater the effect.
messenger concentration # of receptors present (they change) receptor affinity (how strong): Interactions effected by :
(3)
intercellular receptor function: Messenger must be lipophilic
STEROIDS or EICOSANOIDS
Effects on target cells are slow, but it lasts a long time.
They control protein synthesis which is a slow process.: Why are intercellular receptors' effects slow on target cells?
Membrane receptor function: Messenger must be lipophobic

Receptors are part of the cell membrane.

Have 3 categories of receptors (Channel-linked, Enzyme-linked, G-protein linked)
membrane receptors: Channel-linked
Enzyme-linked
G-protein linked
Channel-linked receptors: Acts as a receptor and a channel
Involved in ion movement across cell membrane.
A gated channel
When receptor interacts w/messenger the channel will open.
Will change cell function
All INTERNAL changes in cell
Enzyme-linked receptors: Receptor act as both a receptor and an intracellular enzyme
Enzyme function is inactive unless a messenger molecule is attached.
G-protein linked receptors: Receptor is linked to a group of proteins found in the cell membrane.

The second messenger molecule may be CA++ or cAMP.

Messenger moleucle acting on the receptor activates the _ ________ which in turn act on another protein found in the cell membrane.
Long distance communication: Utilizes nervous & endocrine systems

Neurons can be over 1 meter in length

used for rapid communication (signal speed up to 100 meter/sec.

Endocrine system secretes hormones often control protein synthesis which is a slow process and it takes time to reach the target cells.
Effects can be long lasting
receptor: A target cell has certain proteins that specifically recognize and bind the messenger.
Presynaptic neuron: The neuron which conducts an action potential toward a synapse.
Postsynaptic neuron: The neuron which receives the signal at a synapse.
Insulin: a hormone secreted by the pancreas and acts on target cells throughout the body to regulate energy metabolism.
Plasma membrane: What is the location of receptors on target cells of peptide/proteins?
cytosol: What is the location of receptors on target cells of eicosanoids?
Paracrines Autocrines Neurotransmitters Hormones Neurohormones: What are the functional classification of amines?
Paracrines Autocrines Neurotransmitters Hormones Neurohormones Cytokines: What are the functional classification of peptides/proteins?
A.A. messengers: glutamate
aspertate
glycine
GABA
Eicosanoid messengers: prostaglandins
leukotrienes
thromoboxanes
Catecholamine: A type of organic compound that contains a benzene ring structure and an amine group. Dopamine, norepinephrine epinephrine and are _____________.
transmitters: Dopamine are NE are primarily _________.
hormone: E is primarily a __________.
Amino acid synthesis: neurotransmitters must be synthesized in the neuron.
Glycolysis
Pyruvic acid turns into Aceytl CoA
Krebs cycle
neurotransmitters are then transported into vesicles where they are stored until they are released by exocytosis.
Peptide & protein synthesis: Ribosome attached to rough E.R. is where translation occurs. Polypeptide is formed inside the lumen of rough E.R. (prepropeptide)

In lumen of e.r., proteolytic enzymes cleave off A.A.s from prepropeptide, now called propeptide.

In smooth e.r. the propeptide is packaged into transport vesicle.

Vesicle is transported to golgi apparatus.

Golgi apparatus packages propeptide in secretory vesiclefor storage until release is triggered. More A.A.s are cleaved off in golgi apparatus now called a _______.
steroid synthesis: All _______ are capable of crossing the plasma membrane because they are membrane-permeant, _______ cannot be stored prior to release and instead diffuse out of the cell into the interstitial fluid as soon as they are synthesized.

Are synthesized on demand and released immediately.
Eicosanoid synthesis: Phospholipase A2 catalyzes the conversion of a membrane phospholipid to arachinodonic acid, the precursor for all eicosanoids. Arachidonic acid is converted into _________ via 2 ways:
1. the cyclooxygenase-dependent pathway leads to the production of prostaglandins, prostacyclins, and thromboxanes
2. lipoxygenase-dependent pathway leads to the production of leukotrienes.
half-life: the time it take for half of the hormone in the blood to be degradaded.
Carrier proteins: Messengers can be transported in the nlood either in dissolved form or bound to _______ ________.
hydrophilic: To be transported in dissolved form, the messenger must be a _________ messenger.
albumin: carrier protein that is NOT specific and can transport many different hormones.

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