Exam 2: The Structure of DNA

When two strands of DNA from different sources are hybridized in the lab, what provides the chemical stability for holding the two strands of DNA in a double helix structure?

Consider a linear DNA molecule of 20 complete turns (or twists, T=20) with 10.5 base pairs (bp) per turn in solution. If the double helix is underwound by one full turn to the left and then the ends are sealed together, the result is a strained circle with 11.67 bp per turn, where L (linking number) =19 and T=19. If one negative supercoil is spontaneously introduced, the DNA circle will have the following characteristics:

Which figure (I or II) shows the correct structure for a nucleic acid chain?

The abbreviation dNTP stands for

Topoisomerases are enzymes that

As DNA denatures its absorption of UV light increases, a phenomenon known as:

Which DNA pyrimidine forms three H bonds with its partner in the other DNA strand? Which forms two H bonds?

Discuss the significance of DNA supercoiling in vivo.

The polarity of doubled-stranded DNA arises from

The phosphodiester linkage between adjacent nucleotides to form a DNA or RNA chain occurs by a _______________ reaction involving the removal of _____________ and pyrophosphate.

The predominant form of DNA in vivo is

The melting temperature (T_m) of DNA is:

When the base composition of DNA from a grasshopper was determined, 29% of the bases were found to be adenine. (a) What is the percentage of cytosine? (b) What is the % composition of each of the four nucleotides in the DNA sequence? (c) What is the [G] + [C] content?

One DNA molecule varies from another by the

Starting with the dNTP shown below, draw a clearly labeled diagram showing where the linking bond is between two nucleotides in the same DNA chain. Name the bond. Label the 5′ and 3′ ends of the DNA chain. ‪

Explain to a patient with Friedreich's ataxia the underlying cause of his disease.

Explain why positively supercoiling of genomic DNA might be advantageous for themophilic organisms.

Which DNA purine forms three H bonds with its partner in the other DNA strand? Which forms two H bonds?

Distinguish between the terms "nucleoside" and "nucleotide."

You determine that a sequence of DNA contains numerous tandem repeats. What unusual DNA secondary structure would this sequence be most likely to form?