sOLuTIOns- (i) Both CP and Bt-toxin target the midgut lumen. CP
is known to damage the peritrophic protein matrix of
midgut lumen in the larvae, a structure that protects
the midgut from microbial infection. The mechanism
of damage by Bt-toxin is different as compared to
that of CP. Bt-toxin is converted to its active form
in the alkaline midgut environment. This then binds
to the specific midgut receptors on the brush border
membrane of midgut cells with very high affinity,
forming lytic pores, that result in cell death.
(ii) Over many generations, laboratory populations of
Lepidopteran larvae have evolved resistance against
Bt-toxins. This resistance could have developed by the
following ways:
(a) The alteration of Bt-toxin binding site on the mid-
gut receptors e.g., decreased affinity or reduction in
the number of binding sites.
(b) Changes in midgut environment such that Bt-
toxin is not converted to its active form.
(c) Rapid regeneration of the damaged midgut
epithelium.
(d) Genotypic/phenotypic variation in resistance
and selection pressure due to Bt-toxin, resulting in
differential reproductive success/fitness, and change
in allele frequency, over time.- (i) From the 12th week to 6th year (since primary
infection), the HIV RNA copies remain constant at 3/
less than 10/-0 copies per mL plasma, which is called
clinical latency.
Replication of HIV occurs, as reverse transcriptase
catalyzes the synthesis of a complementary DNA
strand (cDNA) from viral RNA.
This is followed by synthesis of a second DNA strand,
which is complementary to cDNA, resulting in a double
Oxytocin (OT) is a neuropeptide secreted from the posterior pituitary gland in the brain and is best
known for its role in mammalian birth and lactation.
In response to a variety of stimuli such as sucking, parturition, or certain kinds of stress, the
processed OT peptide is released from the posterior pituitary into the systemic circulation.
The OT receptor's activity is mediated by G proteins which activate a phosphatidylinositol-calcium
second messenger system.
i. The blood brain barriers is set by the endothelial cells lining the vessels in the brain. Suggest why
these cells can prevent oxytocin secreted from the gland to re-enter the brain.
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ii. With reference to the given figure explain how a molecule of oxytocin can lead to signal amplification
leading to cellular responses?
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