Biosignaling

Question 1

What are the two main types of gated ion channels located in a cell?

Answer 1

1. voltage-gated ion channel
2. ligand-gated ion channel

Question 2

Under resting conditions, what is the state of a voltage-gated ion channel?

Answer 2

It is closed, until depolarization occurs.

Question 3

How do ligand-gated ion channels function?

Answer 3

They open or close when bound to a specific ligand.

Example: neurotransmitters

Question 4

How is an enzyme-linked receptor activated?

Answer 4

When an extracellular ligand binds to the external portion of an enzyme, it becomes activated and initiates a second messenger cascade.

Example: receptor tyrosine kinase (RTK)

Question 5

If the α subunit of a G protein is bound to GDP, is it active or inactive?

Answer 5

INACTIVE

When the α subunit of a G protein is bound to GDP, the G protein is inactive.

Question 6

How many subunits does a heterotrimeric G protein have?

Answer 6

3

Question 7

What are the three main types of G proteins that can either stimulate or inhibit a signaling pathway?

Answer 7

1. G_{<strong>s</strong>} (stimulates adenylate cyclase, which increases cAMP levels)
2. G_{<strong>i</strong>} (inhibits adenylate cyclase, which decreases cAMP levels)
3. G_q (activates phospholipase C)

Question 8

What are the three subunits of a heterotrimeric G protein?

Answer 8

1. α (alpha)
2. β (beta)
3. γ (gamma)

The α and γ subunits both have lipid anchors (or tails) that anchor the G protein to the plasma membrane.

Question 9

If the α subunit of a G protein is bound to GTP, is it active or inactive?

Answer 9

ACTIVE

When the α subunit of a G protein binds to GTP, the G protein becomes active and the α subunit dissociates from the β and γ subunits.

Question 10

[Mnemonic]

TON DOFF = “turned off”

(how to remember the function of GTP and GDP when bound to a G protein)

Answer 10

TON DOFF = “turned off”

GTP: ON (active)

GDP: OFF (inactive)

Question 11

What is the difference between an inactive and active G protein?

Answer 11

Inactive: bound to GDP

Active: bound to GTP

Question 12

How many helices does a G protein-coupled receptor (GPCR) have?

Answer 12

7 transmembrane α-helices

Question 13

Which G protein subunit carries the binding site for the nucleotides (GDP or GTP)?

Answer 13

α subunit

Question 14

[Mnemonic]

G_s: stimulates

G_i: inhibits

“Mind your p’s” and q’s”

(how to remember the three different types of G proteins)

Answer 14

G_s: stimulates

G_i: inhibits

“Mind your p’s” and q’s”: G_q activates phospholipase C