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Lecture 5

BIOL 2160 Lecture Notes - Lecture 5: Secretion, Membrane Transport Protein, Codocyte


Department
Biological Sciences
Course Code
BIOL 2160
Professor
Cross- Eyed
Lecture
5

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CHAPTER 5: CHEMICAL SIGNLAING
Direct and Indirect Intercellular Communication
o Direct: two cells that are physically connecting, joined by protein channel called
connexon.
Ions, small signaling molecules, transfer easy between two cells…. Called
gap junction.
Advantage: Quick. Disadvantage: bad for long distance. (need to be
touching)
Cells in heart connected by gap junctions (coordinated activation…
activate one cell and have it spread throughout heart)
o Indirect: involves chemical messenger (ligand) and receptor. Most common way.
Secretory vesicle secretes chemical message and target cell has to have
receptor for message to bind to. (have receptor for ligand ALWAYS)
Chemical Messengers:
Paracrine: close to each other, right next to each other, released
from one cell and binds to another. Ex: pancreas
o Advantage: Speed
Neurotransmitter: signaling molecule is neurotransmitter, target
cell is another neuron/muscle cell/gland. Neuro signaling NEEDS
secretory cell to be neuron.
o Advantage: Speed
Endocrine (Hormones): involves molecule entering blood stream.
No blood inside cells or around cells (closed circulatory system),
blood stays in blood vessels. Every living cells no more than 1 mm
away from blood supply.
o Advantage: long distance (can affect every single cell in
body)
o Disadvantage: Takes longer than every other way of
transmitting. (speed is necessary for reflexes)
o Hormones doesn’t know where to bind, just binds wherever
it can. (doesn’t know what target cell it’s going to bind
with).
o Can be Hydrophobic or Hydrophilic:
Hydrophobic: repels water, binded with carrier
protein to shield water around it in blood stream.
Hydrophilic: dissolves in blood stream without
carrier protein.
Receptor Proteins (MUST KNOW FOR TEST)
o A target cell receives a signal because it has receptor proteins specific to it on the
plasma membrane or inside the cell.
Nonpolar signal molecules such as steroid hormones can penetrate the
plasma membrane and interact with receptors inside the cell.
If it likes waterdoesn’t like membrane (nonpolar)
Hydrophilic ligand CAN’T just cross membrane, receptor has to be on
outside of cell. All it can do is activate receptor.
Hydrophobicdissolves through membrane bc like dissolves like.
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Binds on inside, hydrophilic is outside.
o Specificity: Each type of receptor only binds one type of ligand/molecule
o Affinity: Strength of binding between a ligand and its receptor
o
Messenger 1: hydrophilic. Messenger 2: hydrophobic.
If it has to compete w more than one ligand: opposites attract.
o RECEPTOR ACTIVATION
Concentration of ligand
Expression level of receptor (# of receptors)
Affinity of receptor for ligand.
If you add more messenger or ligand you get higher percent of activation.
Once they’re all boundadding ligand doesn’t change anything.
o How Can Receptors Change?
Receptor Synthesis Receptor Turnover
Synthesis: makes more receptors.
Turnover: take down form mem. Put into lysosome and are
destroyed.
Upregulation: increase in receptor synthesis. (making more receptors)
Downregulation: decrease in receptor synthesis. (making fewer receptors)
Turnover: destroy some you’ve made already.
o Drug Interaction
Drugs take advantage of receptors in body: binds to receptor that already
has purpose in body.
Every addictive drug available today takes advantage of pre-existing
receptors in the human body.
Binding of the drug to these receptors often activates a network of
dopaminergic cells in the mesolimbic region of the brain that are involved
in emotional reward
o Drug Addiction
Opiates: painkillers such as codeine, morphine, oxycodone, oxycontin,
heroin, etc.
Activate natural G-protein coupled receptors for endorphins in the brain.
Endorphin concentration is usually extremely low.
Triggers receptor downregulation, as well as de-sensitization resulting
from functional un-coupling of G-protein receptors to their effector
molecule.
Alexander the Great smoked opium in China and gave it to his
soldiers to get them to push themselves when they were hurt.
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