Meselson and Stahlʹs experiments involved growing E. coli on a medium containing 15N (heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only 14N. DNA samples were obtained for analysis after one, two and three rounds of replication (generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the 14N medium?

#Question id: 28742

#Unit 2. Cellular Organization

Peroxisomes carry out which type of reaction?

a) oxidation reactions

b) oxidation-reduction reactions

c) Hydrolysis reactions

d) peroxidation reaction

#Question id: 5652

#Unit 5. Developmental Biology

What generalization can be applied to the pole plasm of Drosophila, the P-granules of C. elegans, the yolk-free vegetal cytoplasm of Xenopus, and the localized mRNA for vasa in zebrafish?

#Question id: 1406

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a consequence of p53 stabilization?

a. stabilization of Cdc25A      b. activation of ATM                c. blocked apoptosis

d. transcription of p21                        e. DNA repair

#Question id: 1030

#Unit 4. Cell Communication and Cell Signaling

The membranes of eukaryotes and mycoplasma

#Question id: 7212

#Unit 5. Developmental Biology

The regeneration blastema forms from pluripotent stem cells called clonogenic neoblast. If cNeoblasts are essential for regeneration, their total loss should prevent regeneration. Following statements are made in respect to planaria regeneration are given below.

(A) The gene sigma/zeta is expressed by all neoblasts and has become the most common marker for their identification across planarian species.

(B)   In planaria, Wnt/β-catenin functions to establish dorsal ventral polarity of the regenerating flatworm.

(C)   Inhibition of Wnt/β-catenin signaling in regeneration-deficient species yields fully functional regenerated heads.

(D)   If β-catenin is eliminated from the posterior (tail-forming) blastema by RNA interference, that blastema will form a tail.

Which of the above statements are true?