Question

Question 4 0.5 pts Imagine that you are an astrobiologist charged with the task of figuring out how DNA replication works in a single celled organism found on a meteorite (yes, the alien organism had DNA!!!). You conduct an experiment where you allow the organisms to grow in a medium that has an altered form of nitrogen that glows green when it binds with carbon to form nitrogenous bases. So all the DNA in cells growing in this medium glow green. After the cells grow for a generation, you transfer them to a medium that has regular nitrogen. You allow the organisms to grow, then you take out a few cells and extract the DNA. You find that the DNA forms two clumps of equal size: one clump is regular whitish colored, and the other clump is a glowing green color. What do you figure out about the way DNA replicates in this organism? DNA replication is semi-conservative ODNA replication is dispersive O You would need the organisms to grow for one more generation in the regular medium to determine the answer. O DNA replication is conservative Question 5 0.5 pts 15 10

Answer 1

4.) the experiment shows that DNA is semi conservative in nature. As In the green medium with altered nitrogenous bases DNA replicates with each strand of double helix acting as a template for the synthesis of the new complymentry strand, one strand of the DNA remains normal and the other glow green. when it was grown again in the regular medium same process of DNA replication led the formation of equal amount of glowing green colored DNA and whitesh colored normal DNA.

9.) Meselson and stahl found that half the DNA was of low density (14N-14N) and half the DNA was of intermediate density (15N - 14N ). This result showed exactly what the semiconservative model predicts.

10.) The new DNA molecule is synthesised by maintaing one strand and building a new strand using the original as template.

11.) A covalent bond forms between the sugar of one Nucleotide and the phosphate of second.

12.) Phosphodiester bond : phosphate group attached to the 5' carbon of the sugar on one nucleotide forms an easter bond with the free hydroxyl on the 3' carbon of the next nucleotide. These bonds are called phosphodiester bonds.

13.) one end has an unlinked -OH group on the 3' carbon and the other end has an unlinked 5' phosphate group shows the definite polarity of the nucleic acid.

7.) A = Free phosphate end

B = sugar- phosphate backbone

C= free sugar end (-OH group on 3' carbon )

D = Nucleotide

E = Phosphodiester bond

F = Hydrogen bonds between base pairs.

G = Nitrogenous base