Lecture 2

Question 1

signal molecule

Answer 1

• binds to receptor protein
• most receptor proteins are plasma membrane proteins
• signal molecule is ligand
• binding of signal and receptor is highly specific

Question 2

receptors

Answer 2

• most water-soluble ligands bind to specific sites on receptor proteins in plasma membrane
• small hydrophobic ligands bind to intracellular receptro proteins in cytoplasm/nucleus

Question 3

receptors in plasma membrane

Answer 3

• G protein-coupled receptors
• receptor tyrosin kinases
• ion channel receptors

Question 4

G protein-coupled receptors

Answer 4

• GPCR largest family (cell surface)
• similar in structure
• protein is on/off switch (GDP with G protein = off)
• ligand binding activates receptor (changes shape, binds inactive G protein: G protein activates, GDP displaced)
• actvated G protein (GTPase) dissociates from receptor, moves to bind an enzyme (changing shape of enzyme, enzyme activated)
• GTP hydrolysed to GDP (inactivates G protein, dissociated from enzyme, pathway shut down)

Question 5

receptor tyrosine kinases

Answer 5

• kinase = enzyme catalysing transfer of phosphate groups
• 1 RTK complex may activate multiple transduction pathways
• RTK’s are 2 monomers
• ligands bind (RTK’s form dimer)
• RTK dimer activated, each TK adds phosphate grp from ATP to Tyr
• RTK dimer fully activated (relay proteins bind to specific phosphorylated Tyr’s)

Question 6

ion channel receptors

Answer 6

• a ligand-gated ICR acts as gate when receptor changes shape
• receptor (gate closed)
• ligand binds (gate opens; ions in: [ion] inside cell change)
• ligand dissociates (gate closes)

Question 7

intracellular receptors

Answer 7

• eg. hydrophobic messengers are the steriod and thyroid hormones of animals (aldosterone)
• aldosteron receptor acts as transcription factor
• genes transcribes > mRNA > leave nucleus > translated into protein
• hormone-receptor complex (carries transduction of signal)