[sngm]

I think we need to discuss major ones below ones and conclude challenge on it and proceed for next.

Question Number :10  G-ve bacteria with saffraanin, G-ve have outer membrane with LPS,
Given answer :1 , but answer according to me is 2  as staining depends on peptidoglycan layer . and its thickness

Question numbeer 18 :
In eukaryotes cytokinesis is inhibited by :
again, according to some text books it is cytocalchisin B but not cytocalchisin D
and after googling out for colchicine though it is mitotic inhibitor but there is a paper that supports that it can be cytokinetic inhibitor in unicellular eukaryote so may be the answer is not preiscely defined in any of the options

Question number 21

an enzymatic reaction exhibits ,michaeles metnen constant ,
but as mentioned clearly [S]>>[E]
i think the CORRECT ANSWR HAS TO BE (C )
Km has to increase vmax stays same,
needs discussion..


Question number 45

pedigree analysis:
I have a doubt on option B , after working on it I got  only Y linked  .

Qno :51
E.corI restriction sites on 10kb dna
I didnt know how can 8kb fragment be generated?? pls explain..






CD IS PERFECT KEY...



[quote pid='11920' dateline='1488310932']
Mechanisms of Cytochalasin D

[quote pid='11920' dateline='1488310932']
Although similar in structure to the more commonly used cytochalasin B, there are noticeable differences in the functional groups of cytochalasin D. The congener is an isomeric metabolite of cytochalasin B, derived from Metarrhizium anisopliae and Zygosporium mansonii [31]. Although it retains the characteristic substituted perhydro-isoindolone attached to a macrocyclic ring, cytochalasin D has differences in the positioning of an ester group as well as the addition of a ketone group, and a contrast in the placement of double bonds (Fig. 55). While these differences may appear subtle, it has an enormous influence on efficacy, as cytochalasin D is much more efficient at disrupting actin polymerization [32]. It is so effective at disrupting microfilament formation, there are concerns as to whether cytochalasin D could act as a chemotherapeutic agent. A pharmacological agent that does not act specifically towards the intended target is not a therapeutic drug; it is a poison. Nevertheless, several studies have demonstrated the efficacy of cytochalasin D on a variety of neoplastic cell lines [20, 33-35], warranting further consideration for use as a viable chemotherapeutic agent.
[/quote]


[quote pid='11920' dateline='1488310932']
Fig. (5)
[/quote]
[quote pid='11920' dateline='1488310932']
Structure of cytochalasin D. Although its carbon skeleton is very similar to cytochalasin B, there are differences in positioning of an ester group as well as the addition of a ketone group, and a contrast in the placement of double bonds near the ester ...
[/quote]
[quote pid='11920' dateline='1488310932']
The remarkably high propensity cytochalasin D has for disrupting actin polymerization is enough by itself to warrant the understanding of its mechanism. As with cytochalasin B, cytochalasin D perturbs actin cytoskeleton dynamics by binding to the barbed end of actin filaments [36, 37]. When exposed to G-actin monomers, cytochalasin D induces G-actin dimer formation in the presence of Mg2+, thereby eliminating the polymerization lag phase due to accelerated nucleation by the dimers [38, 39]. ATP hydrolysis is also stimulated by cytochalasin D (Fig. 22), a feature that ultimately contributes to the efficacy of the agent, as perpetual ATP hydrolysis prevents the formation of viable microfilaments [40, 41]. Therefore, the mechanism can be summed up as follows: when cytochalasin D is introduced into a cellular environment, it sequesters Mg2+ which is essential for the formation of cytochalasin D-induced dimers [42]. In turn, the dimers act as nuclei to potentiate further dimer formation. Binding of Mg2+ to a low affinity site on the dimer induces a conformational change that enables enhanced ATP hydrolysis. Such action results in dissociation of the now numerous dimers, causing the release of G-actin monomers containing ADP. This considerably reduced rate of ATP exchange for bound ADP results in the aggregation of ADP-containing monomers. As these monomers have a high critical concentration, the final extent of polymerization is reduced dramatically, thereby preventing sufficient formation of microfilaments [42].
[/quote]

[quote pid='11920' dateline='1488310932']
Besides its ability to substantially limit actin polymerization, cytochalasin D is cell-permeable and has been shown to activate p53-dependent pathways, causing arrest of the cell cycle at the G1-S transition [43]. Activation of p53 is of monumental clinical importance as this well-known tumor suppressor gene is critical for inducing apoptosis in aberrant cells. While many cancers lose p53 activity through a series of mutations, there are other cancers that have functioning p53 protein products, indicating that such cells could be coerced into cell death via cytochalasin D treatment. *****************Akin to its isomeric relative cytochalasin B, cytochalsin D is also a potent cytokinesis inhibitor**********************, transforming cells into enlarged, multinucleated cells that have a significantly perturbed cytoskeleton and multiple targets for nucleic acid-directed agents. Taken together, cytochalasin D is an effective disruptor of actin polymerization, but has yet to be sufficiently examined
[/quote]

[/quote]