3) Hormone Action Flashcards
What often occurs during the transmission of a signal? What does that result in?
- The signal is exponentially amplified
- Results in an on or off stage
Why must we possess specific receptors?
- Because there is a multitude of hormone signalling
- There cannot be interference among different receptors
What are target proteins?
Key regulatory proteins that determine the properties of a cell
Based on the signal receptor, what are the two main classes of pathways?
1) Pathways with cell-surface receptors
2) Pathways with intracellular receptors
What are the characteristics of cell-surface receptor ligands?
- Receive hydrophilic molecules (soluble in the extracellular fluid)
- Molecules bind to the outside of the cell (cell-surface receptor)
What are the characteristics of intracellular receptor ligands?
Receive lipophilic molecules, which partition themselves into the plasma membrane
What must hydrophobic molecules possess to travel in the blood? What allows them to interact with intracellular receptors?
- Must possess a carrier protein
- Dissociation from the carrier protein allows them to diffuse into the cell
What are the three structures that form a cell-surface receptor?
- Ectodomain
- Hydrophobic transmembrane domain
- Cytoplasmic domain (endodomain)
What is the ectodomain associated with?
- Amino terminus
- Area where the hormone binds
What is the hydrophobic transmembrane domain composed of?
- Domain that crosses the lipid bilayer
- Alpha helix
- Stretch of hydrophobic amino acids that are soluble in the lipid membrane
What is the function of the cytoplasmic domain of the cell-surface receptor?
- The endodomain activates the signal transduction mechanism
- The “lock and key” mechanism of the receptor and hormone results in the change in the transmembrane domain, activating a change in the cytoplasmic domain
How many amino acids are needed to cross the lipid bilayer membrane?
25 amino acids
Which end of the cell-surface receptor is associated with the amino end of the peptide? Which end of the cell-surface receptor is associated with the carboxyl end of the peptide?
- Amino (NH2): Ectodomain
- Carboxyl (COOH): Endodomain
Are the three domains of the cell-surface receptor functionally dependent or independent?
- Independent
- They are interchangeable
What are structural characteristics of the ectodomain of cell-surface receptors?
- Amino end of the peptide
- Rich in cysteine residues (S-S bonds for folding)
- Often glycosylated
What is the function of a free ectodomain?
May circulate as a hormone binding protein
What equilibrium exists in terms of circulating GH?
Equilibrium between GH bound to the ectodomain, and GH in the aqueous phase
How are ectodomains implicated in Grave’s disease?
- The ectodomain cleaved from the TSH receptor may induce antibodies
- Antibodies bind to the receptor and mimic TSH action
- Causes hyperthyroidism
What are conformational changes during a signalling cascade induced by?
- Phosphorylation of proteins
- Binding between proteins
Many signalling proteins are activated by phosphorylation at which amino acids?
- Serine
- Threonine
- Tyrosine
Which amino acid may be phosphorylated, and serves as a docking site for other proteins to interact?
Tyrosine (aromatic)
Which group is replaced by a phosphate group during phosphorylation?
A polar hydroxyl group is replaced by a phosphate group
What is the phosphate donor for protein phosphorylation?
ATP
Many signalling proteins are _____ that are activated (or inactivated) by phosphorylation.
kinases