Lecture 7

Question 1

Mechanisms of intercellular communication

Answer 1

• Direct communication
  (gap junctions, membrane (tunelling) nanotubes, mechanosignals)
• indirect communication
  (chemical messengers)

Question 2

Connexons

Answer 2

• The subunits that form a channel (gap junction)
• Pore size is very small: Permits passage of sugars, amino acids, ions between cells
• Found in virtually all cells except mature skeletal muscles

Question 3

Intercalated disks

Answer 3

-Type of gap junction in cardiac muscle - allows for rapid and coodinated propagation of action potentials for rhythmic contractions

• Smaller than connexons; can be acutely regulated (activated/deactivated) by phosphorylation/dephosphorylation

Question 4

Nanotubes

Answer 4

• Formed from the plasma membrane
• They are longer than gap junctions and have a larger pore diameter

-Transfer of nucleic acids, even small organelles, between cells
- Might be a way to transfer cellular components from stressed to healthy cells (contribute to spreading disease)

Question 5

Mechanosignal tansduction

Answer 5

-Conversion of mechanical stimuli into a cellular response

-Direct physical stress to cells, eliciting a chemical or metabolic response

Question 6

Indirect intercellular communication (paracrine)

Answer 6

Chemical messengers

Paracrine (acts on a nearby cell)
- Indirect no physical link
- Cell that’s signaling to a nearby cell but not through a physical connection

Question 7

Indirect intercellular communication (neurotransmitters)

Answer 7

1. synapse is a short distance
2. Neurotransmitter signals must be tightly controlled

• Not too many molecules released
  -Need an auto shutoff (reuptake or degradation)

Question 8

Indirect intercellular communication (hormones)

Answer 8

• Can be water or lipid soluble
• Must cross boundaries (membranes)
• Have target specificity (receptors)

Question 9

Indirect intercellular communication (hormones) hydrophilic

Answer 9

• Typically stored in secretory cells

-Dissolved in plasma, no need for a carrier

-Crossing a lipid barrier - so generally secreted by fusing secretory vesicles to membrane and releasing (exocytosis)

Question 10

Indirect intercellular communication (hormones) hydrophobic

Answer 10

• Storage is typically more limited (i.e made on demand)
• Cannot dissolve in plasma; needs a carrier

-Crossing a lipid membrane shouldn’t present a barrier