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Give two examples of cellular functions hormonal signalling is essential for
- Cell proliferation
- Glucose homeostasis
- Growth and development
- Stress response
What type of glands are hormones produced from?
Does endocrine signalling occur over long or short distances?
Why are receptors essential for endocrine signalling?
Endocrine signalling requires transport of signalling molecules through the blood over long distances. If the target cell has a receptor for a particular hormone then it will initiate a response. If the cell doesn't have a receptor for the hormone then it cannot respond to that particular hormone.
What are the two types of cell receptors?
Cell surface (embedded within the cell membrane) or intracellular receptors (within the cytoplasm or the nucleus)
How do signalling molecules interact with cell surface receptors?
- Lipophobic molecules bind to receptor
- Receptor transfers signal to the inside of the cell
- Triggers a signal transduction cascade
- There is a physiological response
How do signalling molecules interact with intracellular receptors?
- Chemical messengers are lipophilic
- They bind to cytosolic receptors or nuclear receptors
- Their effect is to affect gene activity (+ or -)
What is phosphorylation?
The transfer of the terminal phosphate of ATP to a hydroxyl group on specific amino acids
What are the three key features of signalling pathways?
- Cascade reactions - there are many intermediate proteins involved. The reaction occurs like a 'relay system' i.e. the signal is passed from one protein to the next, then the next, and so on.
- Single amplification - at each step you get a bigger response. This ensures low levels of hormones will get a big/rapid response.
- Hormones are present at very low concentrations
What are the three main classes of hormones? Give an example of each
- Polypeptide derived eg insulin, glucagon
- Cholesterol derived eg aldosterone, cortisol, oestrogen, testosterone, progesterone
- Aminoacid derived eg thyroid hormones T4 and T3, adrenaline and noradrenaline (catecholamines)
Which hormones are water soluble/lipid soluble?
- Water soluble: Protein/peptide hormones, catecholamines
- Lipid soluble: Steroid and thyroid hormones
What are the three main signal pathways in extracellular (cell surface) receptors?
- Ion channel linked receptors
- Enzyme linked receptors
- G-protein linked receptors
How do ion channel linked receptors work?
- The signalling molecule interacts with the channel protein
- This creates an electrical signal
- Which elicits a cellular response
- (And can also activate G-protein coupled receptors)
How do enzyme linked receptors work?
- The hormone binds to the receptor
- This activates tyrosine kinase on the cytoplasmic side of the membrane
- Which triggers the phosphorylation of intracellular proteins
How do G-protein linked receptors work?
G proteins have three subunits - α, β, and γ. When there is no hormone associated with the receptor the protein is inactive; in its inactive state the α subunit carries a molecule of GDP. When a hormone binds with the receptor this molecule undergoes a phosphorylation event to for GTP - an active subunit. GTP can open ion channels or activate amplifier enzymes.
Intracellular receptors function as _______ ________ by regulating gene expression?
Which type of hormones use cytosolic / nuclear intracellular receptors?
- Thyroid hormones use nuclear receptors
- Steroid hormones use cytosolic receptors apart from oestrogen which uses a nuclear receptor
Describe the mechanism of a steroid hormone
- Steroid hormones diffuse through the plasma membrane
- Hormone binds to the receptor
- Receptor is complexed with heat shock proteins
- The receptor-hormone complex forms dimers
- Dimer complex functions as a transcription factor
Which hormones are involved in calcium homeostasis?
- Parathyroid hormone
- Vitamin D