lec 6

Question 1

how do squid change colour? cod? in a race, who changes colours quicker?

Answer 1

squid use iridocytes, which work off contraction of muscles (FAST)

generally, chromatophores aggregate + disperse pigments
in cod, pigment granules are sequestered in cells using ATP hydrolysis (ie enzyme action moves along microtubules) (SLOW)

Question 2

how do ligand gated channels work? give me an example

Answer 2

in the ECF, a ligand (NOT SUBSTRATE) binds to the receptor protein, signaling the channel to open

ex. acetylcholine binds to let Na ions in

Question 3

how do G Protein Couple Receptors work? give me an example

Answer 3

ligand binds to GPCR, which activates a G protein. this G protein in turn activates another site (typically cAMP)

used in many sensory and monitoring duties, such as rhodopsin.

Question 4

how do enzyme linked receptors work? give example

Answer 4

ligand binds to an enzyme, which activates the site.

ex. atrial natriuretic peptide (ANP) receptor catalyzes synthesis of cGMP

Question 5

how do intracellular receptors work? give example

Answer 5

ligand comes in from the ECF and gets through the phospholipid bilayer (sometimes w help of chaperone), and then the nuclear envelope to bind onto something

ex. DNA response elements

SLOW PROCESS!

Question 6

how have cone snails adapted to fuck w receptors? what type of receptor is this?

Answer 6

normally, when acetylcholine (Ach) is released, it binds to muscle receptor cells (ligand activated). what conotoxin does is compete for these sites, but when it binds the channel does not open –> causes paralysis

Question 7

liver cells! how do we go from epinephrine to breakdown of glycogen to glucose? (hint: 4 steps, 4 enzymes)

Answer 7

1. epinephrine binds to a receptor, which activates a G prot which in turn activates adenyl cyclase by adding GTP (GPCR CHANNEL)
2. active adenyl cyclase causes ATP –> cAMP which binds to cAMP dependent protein kinase
3. activated cAMP dep prot kinase phosphorylates glycogen phosphorylase kinase, activating it
4. glycogen phosphorylase kinase activates glycogen phosphorylase, which breaks down glycogen into glucose

Question 8

how does protein kinase A (PKA) turn on/off?

Answer 8

when 4 cAMP bind to PKA, it releases phosphodiesterase which phosphorylates enzymes

at the same time, when PDE is released, it catalyzes a reaction that causes cAMP to AMP –> autoregulation

Question 9

how does the ECF compare to the ICF with respect to ion concentrations (esp Na+, K+, Cl- and other anions)? how have we adapted this?

Answer 9

ECF is dominated by Na+ and Cl- ions

ICF dominated by K+ ions and anionic [-] proteins

net effect is that cells are relatively [-] compared to their environ (roughly ~-70 mV)

we’ve adapted Na+ ions to be pulled in for action potentials. Cl- also wants to be pulled in, but cannot due to the cell’s negative charge

Question 10

what are two barriers to diffusion?

Answer 10

• lipid bilayer
• boundary layer: as diffusion occurs and we get closer to the cell, other ions etc also get closer –> a sort of competition for space to get close enough for diffusion
  (think of a clogged sink)

Question 11

how do freshwater fish gills work?

Answer 11

first u have to understand that sodium and chloride are at much higher conc in fish than outside water (fish is hyperosmotic)
–> water wants to move inside

fish have leaky junctions meaning they absorb lots of water –> need to constantly piss to balance out water

also use CO2 byproduct to form bicarbonate, which draws in salts to keep them in even better