9.1

Question 1

Define ligand

Answer 1

signaling molecule

Question 2

Define receptor

Answer 2

molecule to which the ligand binds

Question 3

Discriminate between methods of signaling based on distance from source to reception.

Answer 3

o Direct contact
o Endocrine signaling
 Long range
o Paracrine signaling
 Short range
o Synaptic signaling

Question 4

Describe how phosphorylation and dephosphorylation can affect protein function.

Answer 4

o Phosphorylation
 Addition of phosphate group to a protein
 Usually causes activation of proteins
 Done by protein kinases
o Dephosphorylation
 Removal of phosphate group from a protein
 Usually causes inactivation of proteins
 Done by protein phosphatases

Question 5

Contrast between cell surface receptors (membrane receptors) and intracellular receptors

Answer 5

o Cell surface receptor or membrane receptors
 Located on the plasma membrane to bind a ligand outside the cell
• Transmembrane protein in contact with both the cytoplasm and the extracellular environment
o Intracellular receptor
 Located within the cell

Question 6

List and describe the different types of membrane receptors

Answer 6

o Chemically gated ion channels
 Channel-linked receptors that open to let a specific ion pass in response to a ligand
o Enzymatic receptors
 Receptor is an enzyme that is activated by the ligand
• Almost all are protein kinases
o G protein-coupled receptor
 A g-protein (bound to GTP) assists in transmitting the signal from receptor to enzyme (effector)

Question 7

Describe the chemical nature of ligands for intracellular receptors.

Answer 7

o Small & hydrophobic so they can freely cross the plasma membrane
o Act as regulators of gene expression
o Binding of the hormone to the receptor causes the complex to shift from the cytoplasm to the nucleus

Question 8

Describe how intracellular receptors can regulate gene expression

Answer 8

o Hormone-binding domain
 Hormones cross plasma membrane and bind to cytoplasmic receptors
 Hormone binding alters receptor conformation, so it no longer binds inhibitors
 Hormone-receptor complex translocates to nucleus
o DNA-binding domain
 Hormone-receptor complex binds to DNA
 This usually turns on transcription, but can also turn it off
o Domain that interacts with co-activators
 Determine what the cellular response will be
• It’s a change in gene expression
o Can act as enzymes