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Intercellular communication
Cells communicating with each other
Types of Intercellular Communication
Direct
Indirect
Direct Intercellular Communication
Gap junctions: pores (formed from → connexons) connecting adjacent cells together
Ex: cardiac muscle
“Sharing same cytoplasm, ions, and communicating fast with one another”
Indirect Intercellular Communication
Chemical messengers
Classification of Chemical Messengers
Functional
“How it’s functioning”
Chemical Properties
“usually lipophilic or lipophobic aka nonpolar or polar”
Chemical Class
“5 different chemical classes”
Functional Classifications
Paracrines
Neurotransmitters
Hormones
Paracrines
Chemicals that communicate with neighboring cells (cells that are very close not directly attached) (tissue level)
Distance: short
Mode of transportation: diffusion (high → low conc.)
Includes:
Autocrines: chemicals that act on the same cell that secreted them
Examples of Paracrines
Growth factors
Clotting factors
Cytokines
“Chemical messengers that are essential for a lot of different immune responses”
Neurotransmitters
Chemicals released by neurons → synapse (connection site between) → target cell
“Neuron Anatomy: Axon and Soma. Released @ Axon Terminal”
Distance: short
Mode of transportation: diffusion
Example of Neurotransmitter
Acetylcholine
“Major autonomic neurotransmitters”
Hormones
Chemicals released from endocrine glands, or neurosecretory neuron → ISF → blood
Neurosecretory neuron: a neuron that releases hormones
ISF: interstitial fluid = fluid between cells
Distance: long
Mode of transportation: blood
Chemical Properties Classifications
Lipophilic
Lipophobic
Lipophilic
Lipid soluble
Acts on receptors inside the cell
“lipid loving”
“nonpolar” = no trouble crossing membrane so receptors are inside cell
“doesn’t mix well w/water b/c fats don’t mix well with water”
Lipophobic
Usually water soluble
Acts on receptors on the cell membrane
“lipid fearing”
“polar” = hard to cross membrane
Chemical Classes
Amino acids
Amines (modified aa’s)
Peptide and proteins (chains of aa’s)
Steroids
Eicosanoids
Amino Acids
Basic monomer for proteins
“building block for proteins”
“Proteins mix well w/water b/c they are polar”
Chemical property: lipophobic
Functional classification: neurotransmitter (NT)
Examples of Amino Acids
Glutamate
“Excitatory neurotransmitter”
Aspartate
“Excitatory neurotransmitter”
Glycine
“Inhibitory”
GABA
“Inhibitory”
Amines
Derived from amino acids
Contains -NH2 group
Chemical property: lipophobic (except thyroid hormones)
Functional classification: Paracrine, NT, and hormones
Examples of Amines
Dopamine
“elicits feeling of reward”
Serotonin
“Happiness”
Norepinephrine and Epinephrine
“fight or flight sympathetic NS response”
“can even bond to same type of receptor”
Norep: used more like NT
Epi: used more like hormone
Histamine
“Local immune response like bug bite”
Thyroid hormones
“metabolism increases if you increase thyroid hormones”
Peptides and Proteins
Chain of amino acids
Most common
Chemical property: lipophobic
Functional classification: paracrine, NT, and hormones
Examples of Peptides and Proteins
Cytokines
“chemical messengers used in your immune response”
Variety of NT and Hormones
Steroids
Derived from cholesterol
“example of a lipid”
Chemical property: lipophilic
“cuts through membrane, receptor for steroids is inside the cell”
Functional classification: hormones
“will travel thru blood”
Examples of Steroids
Testosterone
Cortisol
“stress hormone”
Aldosterone
“increases BP”
Progesterone
Eicosanoids (type of lipid)
Derived from arachidonic acid (fatty acid)
“fatty acid derived from phospholipid”
Chemical property: lipophilic
“Non-polar, so cuts through the membrane, receptor likely inside the cell”
Functional classification: Paracrine
Examples of Eicosanoids
Prostaglandins
“helps perceive pain”
Prostacyclins, Thromboxanes, and Leukotrienes
“associated w/blood and blood clotting”
Signal Transduction Mechanism
Source releases a ligand (chemical messenger)
Travels to target cell
“could be by diffusion, by blood, long or short distances”
Ligand binds to receptors on/in target cell → functional change
“has to do with chemical property of chemical messenger (lipophilic [in] or lipophobic [on])”
Properties of Cell Receptors
Messenger specific
Multiple receptors types present on/in a cell
The more interactions (between messengers and receptors) → the greater the effect
Factors affecting interactions between messengers and receptors
Messenger concentration
“increased concentration = more interactions”
# of receptors
“more = higher likelihood of bonding to a particular messenger”
Affinity
“how much does that receptor want to bind to that chemical messenger?”
Intracellular Mediated Response
Receptors: inside cell
Messenger: lipophilic
“Has to cut thru membrane”
Response: gene activation or inhibition
“activate or inhibit DNA”
Effects of Intracellular Mediated Response
Slow → Protein synthesis takes time
Long-lasting → Proteins last a while
Membrane Receptor Mediated Response
Receptors: on membrane
Messenger: lipophobic
“Can’t cut thru membrane”
Categories of Membrane Receptor Mediated Response
Channel-linked
“receptor is linked to a channel”
Enzyme-linked
“receptor is linked to a specific enzyme”
G protein-linked
“receptor linked to a G protein”
Channel-linked Receptor
Receptor also acts as a (protein) channel
Response: opens channels in membrane
Enzyme-linked Receptor
Receptor also acts as an intracellular enzyme
“enzyme that functions inside the cell”
Response: activates enzyme
G protein-linked Receptor
Receptor is linked to a group of proteins (G group) in membrane
Response: activates G protein (“moves laterally in membrane, away from receptor”) → activates another membrane bound protein (“could be a channel or enzyme, etc.”)
*Can activate multiple enzymes from one messenger because lots of G groups can be attached to receptor “amplifying the signal”
Reference picture on Slide 37 of Chemical Messengers Lecture
Second Messengers
Intracellular molecule produced (“made inside cell”) / entered (“entered inside the cell”) as a response to an extracellular messenger (1st chemical messenger)
CAN AMPLIFY SIGNAL
Examples of Second Messengers
Ca2+
Cyclic AMP (cAMP)
Long Distance Communication
Required to regulate all body activities
Regulated by:
Endocrine system
Nervous system
Endocrine System Regulation of Long Distance Communication
Releases hormones into blood
Effects moderately slow
“limited by speed of blood circulation”
Nervous System Regulation of Long Distance Communication
Signal target cells through NT
Effects fast (1/100 of a second)
Amines…
A) are only NT
“aa’s”
B) are only hormones
“steroids”
C) are only paracrines
“eicosanoids”
D) can be all of the above
“also peptides and proteins”
Which of the following is a paracrine?
A) Thromboxanes
“type of eicosanoid, helps w/blood clotting”
B) Glutamate
“NT b/c aa”
C) Cortisol
“stress hormone, example of steroid”
D) GABA
“NT b/c aa”
Which of the following chemical messengers will bind to an intracellular receptor?
A) Glycine
“aa = lipophobic”
B) Norepinephrine
“amines = lipophobic except thyroid hormones”
C) Testosterone
“steroid = lipophilic, derived from cholesterol”
D) Seratonin
“amines = lipophobic except thyroid hormones"
*looking at chemical property for this question, looking for lipophilic (can pass thru membrane)
A membrane receptor mediated response…
A) directly results in transcription of a gene
“intracellular mediated response”
B) can result in G protein activation
C) is generally slow to take into effect
“intracellular mediated response b/c creating protein, transcription/translation”
D) would occur with prostacyclins
“example of eicosanoids = lipophilic”
Which of the following is not true of G proteins?
A) are associated with membrane bound receptors
B) will act on a cytoplasmic protein when activated
“will actually act on another membrane bound protein”
C) can trigger a second messenger cascade
D) All of the above