Secondary messengers are all the following EXCEPT
Correct Answer: Plasmalogen
Description: Ans. c (Plasmalogen) (Ref. Ganong physiology 22nd ed., 37-42; Harper's Biochemistry 27th/pg.ll6, 211)SECOND MESSENGERS# Nerve impulses--and binding of hormones to cell surface receptors--elicit changes in the rate of enzyme catalyzed reactions within target cells by inducing the release or synthesis of specialized allosteric effectors called second messengers.- 3', 5'-cAMP- cGMP- DAG- IP3- Ca~- Ceramide# cGMP serves as a second messenger in response to nitric oxide (NO) during relaxation of smooth muscle.# Cyclic AMP (cAMP) is formed from ATP by adenylyl cyclase at the inner surface of cell membranes and acts as an intracellular second messenger in response to hormones such as epinephrine, norepinephrine, and glucagon. cAMP is hydrolyzed by phosphodiesterase, so terminating hormone action. In liver, insulin increases the activity of phosphodiesterase.# Phosphatidylinositol is a precursor of second messengers. Phosphatidylinositol 4,5-bisphosphate is an important constituent of cell membrane phospholipids; upon stimulation by a suitable hormone agonist, it is cleaved into diacylglycerol (DAG) and inositol trisphosphate (IP3), both of which act as internal signals or second messengers.# Ceramide is an important signaling molecule (second messenger) regulating pathways including apoptosis (processes leading to cell death), cell senescence, and differentiation, and opposes some of the actions of diacylglycerol.PLASMALOGENS# Plasmalogens occur in brain & muscle.# Plasmalogens and platelet-activating factor (PAF) are either phospholipids formed from dihydroxyacetone phosphate.# These compounds constitute as much as 10% of the phospholipids of brain and muscle.# In multiple sclerosis, which is a demyelinating disease, there is loss of both phospholipids (particularly ethanolamine plasmalogen) and of sphingolipids from white matter. Thus, the lipid composition of white matter resembles that of gray matter. The cerebrospinal fluid shows raised phospholipid levels.
Category:
Biochemistry
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