Second Messenger

Calmodulin is a small (148 amino acids, 17 kDa) ubiquitous protein in eukaryotes.

It is considered as the primary intracellular calcium sensor, making it a key regulator of intracellular signal transduction.

Ref: Harper’s Biochemistry 26th Edition Page 463 ; E. coli Gene Expression Protocols By Peter E. Vaillancourt, 2003, Page 69

D i.e. ATP

A i.e. Ca²⁺ dependent; B i.e. Through calmodulin dependent kinase

Calmodulin

• It has 148 amino acid residues & 4 Ca++ binding domains. It’s 115^th aa. is trimethylated. It is extensively conserved & found in plants & animals both. Calmodulin is involved in contraction of smooth muscle .Q It helps in initiation of contraction, not by, uncovering active site on actin molecule but by activating the myosin cross bridges.
• Is a Ca²⁺ binding proteinQ present in many cells notably in smooth muscles and brain cellsQ.
• Is a counterpart of Troponin. (Troponin is present in skeletal muscles)
• Calmodulin binds with Ca^t* & capable of activating 5 different calmodulin­dependent kinases Q. They are:

(i)         Myosine high chain kinaseQ – it phosphorylates myosin head conferring with the capability of binding with actin filament. This brings about contraction in smooth muscle.

(ii)        Phosphorylase kinaseQ

(iii)      Ca²V Calmodulin kinase I & II: concerned with synaptic function

(iv)      Ca²* / Calmodulin kinase III: concerned with protein synthesis

A i.e. c-AMP; B i.e. IP3; C i.e. Diacylglycerol

A i.e. Guanylyl cyclase

Ans. is ‘a’ i.e., cAMP

Muscarinic receptors (cholinergic receptors) in heart are M₂ type. These are responsible for vagus mediated bradycardia.

M₂ mediated actions are through cAMP.

TYPES OF RECEPTORS

Drug action on receptors is a two step process ‑

Step 1 → Binding of drug to receptors that leads to conformational change in receptors (in case of agonist) or prevention of conformational change by competing with agonist (in case of antagonist).

Step 2 → This conformational change induces changes in systems within the cell through a series of intermediate steps (transduction) that in turn brings about the response to the drug.

Ans. is ‘a’ i.e., Nitric acid

Activation of GC (Guanylyl cyclase) results in increased synthesis and intracellular accumulation of cGMP.

cGMP acts through cGMP dependent protein kinase.

Hormone acting through cGMP are atrial natriuretic peptide and nitric oxide.