Polypeptides: Growth Hormones, Insulin, Glucagon Flashcards
What is the typical length of polypeptide signalling molecules?
30-200 amino acids
Are polypeptide signalling molecules hydrophobic or hydrophilic?
Hydrophilic
What receptors do polypeptide signalling molecules bind to?
Cell surface receptors
* do NOT cross plasma membrane
TRUE OR FALSE:
Polypeptide signalling molecule effects on target cells are immediate and generally short-lived
True
What is the lifespan of Polypeptide signalling molecules?
Short lifespan i.e. minutes
How are Polypeptide Signalling Molecules functionally subdivided?
- Polypeptide hormones
- Polypeptide growth / differentiation factors
What are some examples of Polypeptide Hormones?
- Insulin
- Glucagon
- Gastrin
- Vasopressin
- Adrenocorticotropic Hormone (ACTH)
- Follicle Stimulating Hormone (FSH)
- Luteinising Hormone (LH)
- Thyroid Stimulating Hormone (TSH)
- Parathyroid Hormone
What are some examples of Growth Factors?
- Epidermal Growth Factor (EGF)
- Insulin-like Growth Factor 1 (IGF-1)
- Interleukins (ILs)
- Nerve Growth Factor (NGF)
- Erythropoietin (Epo)
- Platelet Derived Growth Factor (PDGF)
- Somatotropin
What are the FIVE characteristics of Polypeptide Growth Factors/Hormones?
- Produced as a longer precursor form (on the RER)
- Have an N-terminal signal sequence
- Sometimes glycosylated and / or contain di-sulfide bridges
- Secreted via the secretory pathway
- Interact with cell surface receptors, which are typically tyrosine kinase receptors
How long is Epidermal Growth Factor (EGF)?
53 amino acids
How many intramolecular disulfide bonds are contained in EGF?
Three
What does EGF stimulate?
- Cell growth
- Differentiation
- Survival
What anti-cancer drug targets EGF?
Herceptin
How do Polypeptide Signalling Molecules respond to ligand binding?
Directly modify cellular proteins
What happens after ligand binding in the EGF receptor?
Autophosphorlyation of activated receptor and phosphorylation of other cellular proteins
What type of activity do EGF receptors display when activated?
Protein kinase activity (addition of phosphate groups)
What part of the protein is a phosphate group added to during phosphorylation?
Hydroxyl group (OH) of a Serine / Threonine or a Tyrosine
Where does Autophosphorylation occur after ligand binding to the EGF receptor?
Tyrosines
What is the function of the N-Terminal Signal Sequence on Polypeptide pre-hormones?
Targets them to the lumen of the Rough ER and to the secretory pathway
Where in the cell are mature hormones generated from pro-hormones?
Golgi apparatus
What is the mechanism of action for the Synthesis and Secretion of hormones?
- Pro-hormone translated on RER by ribosomes
- Enters ER lumen (signal sequence)
- Vesicles bud off the ER
- Vesicles go to Golgi and dock
- Enters Golgi
- Undergoes post-translational modification to form mature hormone (growth factor)
- Vesicles leave Golgi and go to Plasma Membrane (secretory pathway)
- Exocytosis from cell
How are Polypeptide Hormone Precursors post-translationally modified?
- Proteolytic cleavage
- Disulfide bridge formation
- Glycosylation
What does hormone / neurotransmitter stimulation cause?
Exocytosis of polypeptide hormone into the blood
How long do released polypeptides remain active in the blood?
Seconds to minutes
