3.1 Proteins & Biosignaling

Question 2

Biosignalling

Answer 2

process in which cells receive and act on signals

Question 3

Ion channels

Answer 3

transmembrane proteins that provide a pathway for ions to enter the cell

facilitated diffusion of molecules down a concentration gradient

Question 4

3 main groups of ion channels

Answer 4

ungated
voltage gated
ligand-gated

Question 5

Ungated ion channels

Answer 5

ion channels that are always open

Question 6

Voltage-gated channels

Answer 6

open or close based on membrane potential charge near the channel

Question 7

Ligand-gated Channels

Answer 7

binding of a specific ligand to the channel causes it to open or close

ex. neurotransmitters bind to post-synaptic channels (ex. GABA opens chloride channels)

Question 8

Enzyme-linked receptors

Answer 8

membrane receptors that also display catalytic activity in response to ligand binding

often participate in cell signaling through initiation of second messenger cascades

Question 9

3 primary protein domains of enzyme-linked receptors

Answer 9

membrane-spanning domain
ligand-binding domain
catalytic domain

Question 10

Membrane-spanning domain of enzyme-linked receptors

Answer 10

anchors the receptor in the cell membrane

Question 11

Ligand-binding domain of enzyme-linked receptors

Answer 11

stimulated by the appropriate ligand and induces a conformational change that activates the catalytic domain

Question 12

Catalytic domain of enzyme-linked receptors

Answer 12

activates cellular enzymes; initiates second messenger cascade

Question 13

One of the most common enzyme-linked (catalytic) receptors

Answer 13

receptor tyrosine kinases (RTKs)

composed of a monomer that dimerizes upon ligand binding

the dimer is the active form that phosphorylates additional cellular enzymes (included the receptor itself)

Question 14

G protein-coupled receptors (GPCRs)

Answer 14

3transmemebrane integral proteins that interact with G proteins to transmit signals to effector cells

Question 15

how do GPCR’s work?

Answer 15

a ligand binds to the extracellular portion of the receptor and triggers and intercellular signalling cascade

Question 16

G protein 3 subunits

Answer 16

alpha, beta, and gamma

Question 17

3 main types of G proteins:

Answer 17

Gs - stimulates adenylate cyclase which i_ncreases levels of cAMP_ in the cell

Gi - inhibits adenylate cyclase which decreases levels of cAMP in the cell

Gq - activates phospholipase C which cleaves a phospholipid from the membrane to form PIP2; PIP2 is cleaved to DAG and IP3; IP3 opens calcium channels in the ER to increase calcium levels in the cell

Question 18

“resting state” of G protein

Answer 18

all three subunits are attached (alpha, beta, gamma)

GDP is bound to alpha subunit

Question 19

what happens to G protein followin ligand binding to GPCR?

Answer 19

GDP dissociates and GTP binds to alpha subunit

the alpha subunits separates from the beta-gamma dimer

Question 20

what happens after ATP binds to the alpha subunit of G protein?

Answer 20

the alpha-GTP subunit and beta-gamma subunits bind to target proteins to initiate the signalling cascade

once the target protein is activated, it can relay a signal