Lecture 7 Flashcards
What are the 2 types of intercellular communication?
1) direct communication
2) indirect communication
What are the three forms of direct communication?
1) Gap junctions
2)Membrane (tunneling) nanotubes
3) Mechano signals
What is the form of indirect communication
Chemical messengers
What are cell-cell junctions
When cells link to eachother to regulate homeostasis and critical cell processes
Where do cell-cell junctions occur
Large multiprotien complexs
What are the three types of cell-cell junctions
- Tight junctions
- Anchoring junctions
- Gap junctions
Where are gap junctions found
Dispersed in the plasma membrane
What are the roles of gap junctions
- Act as communication channels between adjacent cells in animal cells
- Allow molecules and ions ot pass through
What is the structure of gap junctions
Made of transmembrane protein connexin’s
- 6 connexin = 1 connexon
- 6 connexon = 1 protien connexon
Explain homemeric vs hetromeric connexon
- Homemeric connexon = 6 copies of the same connexin protiens
- Hetromeric connexon = 6 copies of different connexin protiens
Gap junctions - how are protein channels made
When a connexon in one cell membrane meets with a connexon in another cell membrane, they pair to make a protein channel
What do gap junctions allow to pass through
Ions, sugars, secondary messengers, other small molecules between molecules
What regulates the opening and closing of gap junctions
1) Voltage
2) Ion concentration
3) pH
What are the 2 main parts of gap junctions
1) Connexons
2) Intercalated disks
Which is smaller; connexons or intercalated disks
Intercalated disks
What are intercalated disks
Type of gap junction found in cardiac muslce
What is the role of intercalated disks
Allow rapid and coordinated propagation of action potentials into rhythmic contractions
How are intercalated disks regulated
Phosphorylation and dephosphorlyation
Where are connexons NOT found
Mature skeletal cells
What are membrane nanotubes formed from
Plasma membranes
How big are membrane nanotubes in comparison to gap junctions
Longer and larger pore diameter then gap junctions
What do membrane nanotubes transfer
Nucleic acids, and small organelles between cells
What are the purpose of membrane nanotubes
To transfer cell components from stressed to healthy cells
What is mechano signal transduction
- A direst physical stress on cells, electing a chemical or metabolic response
- Conversion of mechanical stimuli to cellular response
What are examples of mechano signal transduction (name 1)
- Mechanical stress to muscle fibres from weight lifting resulting in increased protein synthesis
- Remodelling of bone and cartilage through physical stress (such as weightlifting)
- Conversion of pressure on skin into neural (electrical) impulse
What are the 4 main types of chemical messangers
1) Paracrines
2) Neurotransmitters
3) Hormones
4) Neuroendocrines
what do paracrines do
Allow cells to communicate with each other by releasing signalling molecules that bind to and activate surronding cells
Whats an example of paracrines
Clotting factors, growth factors (eg. estrogen)
How can secreted hormones act
In paracrine and endocrine matters
How does endocrine signalling work
Uses circulatory system to transport ions or molecules
What is the purpose of neurotransmitters
Neurons relayed by neurotransmitters from presynaptic to postsynaptic neuron to propagate electrical impulses
What size are the synapse in neurotransmitters
Short distances
In which direction do neurotransmitters allow information
Unidirectional information transfer
What are the 3 conditions for hormones
1) Must be water or lipid soluble
2) Must cross cell boundaries or membranes
3) Must have target specificity (receptors - targets they have to connect with and act on for a chemical signal to move forward)
How are neurotransmitter signals controlled
1) Must not release too many molecules
2) Needs auto shutoff (reuptake or degradation)
Examples of hydrophillic messengers
Insulin, epinephrine, seritonin
What are the 2 types of hormone messangers
1) Hydrophilic messangers
2) Hydrophobic messangers
Where are hydrophilic messengers stored
Secretory cells
Do hydrophilic cells need a carrier
No, dissolve in plasma
Can hydrophilic cells easily pass lipid membranes
Crossing a lipid membrane presents a barrier - so generally secreted by fusing secretory vesicles to membrane and releasing (exocytosis)
Examples of hydrophobic messengers
Steroids, sex hormones
Where are hydrophobic messengers stored
Storage limited, made on dement
Do hydrophobic messengers need messengers
Cannot dissolve in plasma, need messengers
Can hydrophobic cells easily pass lipid membranes
Yes, crossing membrane doesn’t cause barrior
What is autocrine communication
Cell signalling where cell secretes autocrine signals that bond to receptors in same cell, leading to changes in said cell
When is autocrine communication possible
When messenger acts back on the cell that produced the chemical messenger, but would be considered direct communication
Do cells only have one time of receptor
No, cells express many different types of receptors. May be 100s or 1000s of receptors on cells surface (ie. amplification)
Can the amount of receptors in a cell be controlled
Yes, it can be:
1) Can be up or down regulated
3) Gene regulation
What is the goal of chemical signal transduction
Goal to change overall profile of cellular protein/enzymatic activity
What is an example of issues with chemical signal transduction
Lactose intolerance - chemical signals do not communicate with body to produce enough of lactase enzyme to digest with the lactose consumed
