Exam 11: DNA Replication and Recombination

What term is used to describe genetic exchange at equivalent positions along two chromosomes with substantial DNA sequence homology?

The complex of proteins that is involved in the replication of DNA is called a(n)________.

Chromatin assembly factors (CAFs)move along with the replication fork and assemble new nucleosomes.

Assume that you grew a culture of E.coli for many generations in medium containing ¹⁵N (from the ammonium ion),a heavy isotope of nitrogen.You extract DNA from a portion of the culture and determine its density to be 1.723 gm/cm³ (call this sampleA).You then wash the remaining E.coli cells and grow them for one generation in ¹⁴N,extract the DNA from a portion of the culture,and determine its density to be 1.715 gm/cm³ (call this sampleB).You let the culture grow for one more generation in ¹⁴N,and extract the DNA (call this sampleC)is then heated to completely denature the double-stranded structures,cooled quickly (to keep the strands separate),and subjected to ultracentrifugation.Present the centrifugation profiles for heat-denatured DNA (samples A,B,andC)that you would expect.Use the graph below.(Note: Although not the case,assume that single-stranded DNA has the same density as double-stranded DNA.).Each sample of DNA (A,B,andC)

Assume that a culture of E.coli was grown for approximately 50 generations in ¹⁵N (provided in the medium in the ammonium ion),which is a heavy isotope of nitrogen (¹⁴N).You extract the DNA from the culture,and it has a density of 1.723 gm/cm³ (water = 1.00 gm/cm³).From the literature,you determine that DNA containing only the common form of nitrogen,¹⁴N,has a density of 1.700 gm/cm³.Bacteria from the ¹⁵N culture were washed in buffer and transferred to ¹⁴N medium for one generation immediately after which the DNA was extracted and its density determined. (a) What would be the expected density of the extracted DNA? (b) After you heat the extracted DNA until it completely denatures (95°C for 15 minutes),what would you expect the density of the DNA in the denatured extract to be? For the purposes of this question,assume that DNA has the same density regardless of whether it is single- or double-stranded. (c) Assuming that the molar percentage of adenine in the extracted DNA was 20%,what would be the expected molar percentages of the other nitrogenous bases in this DNA? (d) Assume that a fraction of the extracted DNA was digested to completion with the enzyme snake venom diesterase.This enzyme cleaves between the phosphate and the 3′ carbon.Present a "simplified" diagram that would illustrate the structure of the predominant resulting molecule.

Which structural circumstance in DNA sets up the requirement for its semidiscontinuous nature of replication?

Bacteria are dependent on telomerase to complete synthesis of their chromosome ends.

Briefly describe what is meant by the term autoradiography and identify a classic experiment that used autoradiography to determine the replicative nature of DNA in eukaryotes.

What three possible models were suggested to originally describe the nature of DNA replication?

A characteristic of aging cells is that their telomeres become shorter.