Another example of direct reversal is the removal of the methyl group from the methylated base O6 –methylguanine  In this case, a methyltransferase removes the methyl group from the guanine residue by transferring it to one of its own cysteine residues. This is costly to the cell because the methyltransferase is not catalytic; having once accepted a methyl group, it cannot be used again.

TLS Online TPP Program

#Id: 9726

#Unit 6. System Physiology – Plant

Hemlock (Cicuta sp.) produces cicutoxin, a polyacetylene that prolongs the repolarization of neuronal action potentials.

TLS Online TPP Program

#Id: 9727

#Unit 6. System Physiology – Plant

The active principle in foxglove (Digitalis sp.) is cardinolide digitoxin, a cardiac glycoside that inhibits ATPase activity and can increase myocardial contraction.

TLS Online TPP Program

#Id: 9728

#Unit 6. System Physiology – Plant

Laticifers are made of individual cells and can occur either as articulated systems (single cells connected by a small tube) or non-articulated systems (one large syncytial cell).

TLS Online TPP Program

#Id: 9729

#Unit 6. System Physiology – Plant

Latex are resin terpenoids produced by laticifers is released upon damage and often contains cardiac glycosides which fend off herbivores.

TLS Online TPP Program

#Id: 9730

#Unit 6. System Physiology – Plant

Conifer resin ducts produces bicyclic monoterpenes such as a-pinene and b-pinene, monocyclic terpenes like limonene and terpinolene, and tricyclic sesquiterpenes, including longifolene, caryophyllene, and d-cadinene, as well as resin acids, which are released immediately upon damage by herbivores

TLS Online TPP Program

#Id: 9731

#Unit 6. System Physiology – Plant

The specialist caterpillars of the monarch butterfly

(Danaus plexippus) are insensitive to the terpenoid toxins. They feed on milkweed leaves and retain the cardenolides. As a result, most insectivorous birds quickly learn to avoid eating monarch caterpillars and adult monarch butterflies.