Signalling At The Cell Surface

Question 1

What are signaling molecules?

Answer 1

Chemical molecules released from a cell to transmit information to another cell via receptor interaction, triggering a response.

Question 2

What are the two types of signaling molecules based on solubility?

Answer 2

• Hydrophobic: Steroid hormones, thyroid hormones, vitamin D
• Hydrophilic: EGF, PDGF, NGF

Question 3

What is a receptor in cell signaling?

Answer 3

A protein embedded in the plasma membrane or cytoplasm that binds specific signaling molecules.

Question 4

What are the structural domains of a receptor?

Answer 4

• Ligand binding domain
• Transmembrane domain
• Signal transduction domain

Question 5

What are the 7 steps of cell-surface signaling?

Answer 5

1. Synthesis
   
   2. Release
   3. Transport
   4. Receptor binding
   5. Signal transduction initiation
   6. Cellular response
   7. Signal removal

Question 6

What are the types of signaling based on distance?

Answer 6

• Endocrine: Distant via blood
• Paracrine: Nearby cells
• Autocrine: Same cell

Question 7

What is the endocrine signaling mechanism?

Answer 7

Hormones are transported through the blood to distant target cells.

Question 8

What is autocrine signaling?

Answer 8

Cells respond to substances they themselves release; common in tumor cells.

Question 9

What is paracrine signaling?

Answer 9

Signals affect nearby target cells (e.g., neurotransmitters).

Question 10

What are second messengers?

Answer 10

Intracellular signaling molecules like cAMP, cGMP, DAG, IP3, Ca²⁺, phosphoinositides.

Question 11

What activates second messengers?

Answer 11

Binding of a ligand (“first messenger”) to a cell-surface receptor.

Question 11

What are GTPase switch proteins?

Answer 11

Intracellular proteins that toggle “on” (GTP-bound) or “off” (GDP-bound), regulated by GEFs and GAPs.

Question 12

What are the classes of GTPase switch proteins?

Answer 12

• Trimeric (large) G proteins
• Monomeric (small) G proteins

Question 13

What do protein kinases and phosphatases do?

Answer 13

• Kinase: Transfers phosphate from ATP to proteins
• Phosphatase: Removes phosphate groups

Question 14

What is a GPCR?

Answer 14

G protein-coupled receptor with 7 transmembrane regions; involved in many signaling pathways.

Question 15

What are the subunits of G proteins?

Answer 15

α, β, γ — β and γ stay bound as Gβγ.

Question 16

How does the Gα subunit function?

Answer 16

Cycles between active (GTP-bound) and inactive (GDP-bound) states; activates effectors.

Question 17

What is the function of PKA in cAMP signaling?

Answer 17

Inactive PKA (tetramer) becomes active when cAMP binds regulatory subunits, releasing catalytic subunits to act.

Question 18

What does CREB do in cAMP signaling?

Answer 18

Phosphorylated by PKA; binds to CRE on DNA to regulate gene expression.

Question 19

What are the key molecules in the IP3/DAG pathway?

Answer 19

PIP2 is cleaved into DAG (stays in membrane) and IP3 (diffuses in cytosol).

Question 20

How is Ca²⁺ regulated in the IP3/DAG pathway?

Answer 20

IP3 triggers Ca²⁺ release from ER; Ca²⁺ is then pumped out or back into ER.

Question 21

What are the components of the GPCR-triggered phospholipase C pathway?

Answer 21

• PIP2
• PLCβ
• DAG
• IP3
• Ca²⁺ signaling

Question 22

Fill in the blank: Signaling molecules are divided into _______ and _______ based on solubility.

Answer 22

Hydrophobic and hydrophilic

Question 23

Fill in the blank: The chemical property of a receptor is _______.

Answer 23

Specific binding to ligands

Question 24

Fill in the blank: Signaling in animals can be _______, _______, or _______ based on distance.

Answer 24

Endocrine, paracrine, autocrine

Question 24

How do GTPase switch proteins interact with their targets?

Answer 24

Via GTP binding (“on”) and GDP binding (“off”), regulated by GEFs and GAPs, altering protein conformation.

Question 25

Describe the cAMP/PKA pathway.

Answer 25

Ligand binds GPCR → activates adenylyl cyclase → increases cAMP → activates PKA → PKA phosphorylates CREB → gene transcription

Question 26

Describe the IP3/DAG pathway.

Answer 26

Hormone binds GPCR → activates PLCβ → PIP2 cleaved into IP3 and DAG → IP3 releases Ca²⁺ from ER → DAG and Ca²⁺ activate downstream signaling