Principle of cellular physiology 3 Flashcards
What does the first G protein discovered contain and what does is activate?
- Contained an alpha subunit
- Could activate adenyl cyclase (AC)
What are the different subunits of this G protein?
- Alpha s which stimulates AC
- Alpha i which inhibits AC
What do beta-adrenoreceptors couple to?
Gs
What do alpha 2 adrenoreceptors couple to?
Gi
G alpha q proteins allow hormones/neurotransmitters to activate which enzyme?
The amplifier enzyme phospholipase C (PLC)
Describe the stages leading to muscle contraction involving Gq proteins.
- Gq proteins stimulate PLC
- PLC splits PIP2 into IP3 and DAG
- IP3 is water soluble so travels through the cytosol and stimulates calcium release from ER
- DAG remains in the membrane where it recruits protein kinase c (PKC)
Describe the stages of calcium mediated intracellular responses.
- Each Calmodullin (CaM) binds to 4 Ca2+ ions
- Ca2+-CaM complex activates CaM kinases (CaMKs)
- CaMKs phosphorylates Serine and Threonine residues on substrate proteins
- alpha 1 adrenal-receptor mediates vascular smooth muscle contraction by increasing intracellular free Ca2+ activating CAMKs (vasoconstriction)
What are CaMKs involved in?
Smooth muscle contraction
What are the effects of DAG?
- DAG is hydrophobic and so remains in the plasma
membrane where it can increase the activity of Ca2+ dependent kinases - Evokes cellular responses by phosphorylating other
proteins. The most important one is proteins kinase C
(PKC) - PKCs can potentiate the effects of IP3
- Regulates cell shape, cell proliferation and
transcription factor activity
Describe the role of alpha 1 adrenoreceptors in blood pressure control.
- Causes vascular smooth muscle tone contraction
- Via Gq-PLC-IP3
- leads to increased blood pressure
Describe the role of beta 2 adrenoreceptors in blood pressure control.
- Causes relaxation of vascular smooth muscle
- Via Gs-cAMP-PKA
- leads to decreased blood pressure
What are muscarinic receptors?
Gq/Gi coupled receptors
What activates muscarinic receptors?
ACh
How many subtypes are there of muscarinic receptors?
- 5
- 1-3-5 Gq coupled stimulatory
- 2-4 Gi coupled inhibitory
What are the 4 enzyme linked receptors?
- Receptor guanylyl cyclases
- Receptor serine/threonine kinase
- Receptor tyrosine-kinase
- Receptor tyrosine phosphatase