Lecture 7 week 4?

Question 1

What are the two types of intercellular communication?

Answer 1

Direct and indirect communication

Question 2

What does direct communication include?

Answer 2

i. Gap junctions
ii. Membrane (tunnelling) nanotubes
iii. Mechanosignals

Question 3

What does indirect communication include?

Answer 3

i. Chemical messengers

Question 4

What are connexons? (direct)

Answer 4

The subunits that form a gap junction

Question 5

How big are connexons?

Answer 5

Pore size is very small

Question 6

What do connexons do? give an example.

Answer 6

Permits passage of sugars amino acids and ions between cells
ex. metabolic and electric exchange

Question 7

Where are connexons found?

Answer 7

Found in virtually all cells except mature skeletal muscle

Question 8

What are intercalated disks? (direct)

Answer 8

Type of gap junction in cardiac muscle

Question 9

What do intercalated disks do?

Answer 9

Allows propagation of action potentials for rhythmic contractions

Question 10

How big are intercalated disks?

Answer 10

Smaller than connexons

Question 11

How can intercalated disks be acutely regulated?

Answer 11

Can be acutely regulated (activated or deactivated) by phosphorylation or dephosphorylation

Question 12

Where are membrane nanotubes formed from?

Answer 12

Formed from the plasma membrane

Question 13

How big are membrane nanotubes ?

Answer 13

Longer than gap junctions and have a larger pore diameter

Question 14

What do membrane nanotubes do?

Answer 14

• Transfer of nucleic acids & even
  small organelles between cells
• Might be a way to transfer
  cellular components from
  stressed to healthy cells

Question 15

What does mechanosignal transduction do?

Answer 15

• Conversion of mechanical stimuli into a cellular response
• Direct physical stress to cells eliciting a chemical or metabolic response

Question 16

What are some examples of mechanosignal transduction

Answer 16

E.g. 1) Conversion of a soundwave into an electrical signal (hearing)
E.g. 2) Pulsatile & shearing stresses from blood flow on arterial endothelial cells
* Can induce formation of new blood vessels
* If excessive, mediates vascular inflammation & progression of atherosclerosis
E.g. 3) Mechanical stress to muscle fibers from weightlifting resulting in increased protein synthesis
E.g. 4) Remodeling of bone & cartilage through physical stresses (such as weight lifting)
E.g. 5) Conversion of pressure on skin into a neural (electrical) impulse

Question 17

What are the 4 chemical messengers? (indirect)

Answer 17

1. Paracrine signalling
2. Neurotransmitters
3. Hormones
4. Neuroendocrine signalling
   (autocrine when possible, considered more direct)

Question 18

Where does paracrine signalling act?

Answer 18

Acts on a nearby cell

Question 19

What does paracrine signalling do?

Answer 19

Clotting factors, growth factors e.g. estrogen
(promotes ovary maturation)

Question 20

What can secreted hormone from paracrine signalling act in?

Answer 20

Can act in both a paracrine and endocrine manner.

Question 21

Explain about neurotransmitters.

Answer 21

• Synapse is a short distance
• Neurotransmitter signal must be tightly controlled
• Not too many molecules released
• Need an auto shutoff (reuptake or
  degradation)

Question 22

What two things can hormones be?

Answer 22

Either water or lipid soluble

Question 23

What must hormones end up doing?

Answer 23

Must cross membranes

Question 24

Where are hormones intended to go?

Answer 24

Intended to go to target specificity (receptor

Question 25

What are some examples of hydrophilic hormones?

Answer 25

Insulin, epinephrine, serotonin

Question 26

Where are hydrophilic hormones typically stored?

Answer 26

Typically stored in secretory cell

Question 27

What does hydrophilic hormones dissolve in?

Answer 27

Dissolves in plasma

ex. no need for carrier

Question 28

How are hydrophilic hormones secreted?

Answer 28

Generally secreted by fusing secretory vesicles to membrane and releasing (oxytocin)

Question 29

What are some examples of hydrophobic hormones?

Answer 29

E.g. steroid & sex hormones
(estrogen, testosterone, cortisol)

Question 30

Are hydrophobic hormones stored?

Answer 30

Storage is typically more limited and made on demand

Question 31

Can hydrophobic hormones dissolve in plasma?

Answer 31

Cannot dissolve in plasma, needs a carrier

Question 32

Can hydrophobic molecules cross a lipid membrane

Answer 32

Yes

Question 33

How does receptor specificity work?

Answer 33

• Cells express many different types of receptors
• There may be hundreds or thousands of a given receptor type on a cell surface (i.e. amplification)
• Amount of a receptor is controllable i.e. can be up- or down- regulated Goal

Question 34

What is the goal of hormones?

Answer 34

To change overall profile of cellular protein/enzymatic activity

Question 35

How do hydrophilic hormones achieve their goal?

Answer 35

-Binds to cell surface (plasma membrane) receptor
-Alters activity of existing enzymes/ proteins directly or via second messengers

Question 36

How do hydrophobic hormones achieve their goal?

Answer 36

-Binds to cytosolic or nuclear receptors
-Turns on genes to make new proteins (i.e. enzymes)