Bio Chapter 14

In a nucleosome, the DNA is wrapped around

histones.

If DNA of a particular species was analyzed and it was found that it contains 27 percent A, what would be the percentage of C?

23 percent.

Suppose a 100-base-pair, double-stranded DNA molecule consists of 15% thymine bases. How many total hydrogen bonds are holding the two strands together?

270

Suppose a double-stranded DNA molecule was shown to have 22% Guanine bases. What would be the expected percentage of Adenine bases in that molecule?

28 percent

If the sequence of the 5'-3' strand is AATGCTAC, then the complementary sequence has the following sequence:

3'-TTACGATG-5'

in analyzing the number of different bases in a DNA sample, which result would be consistent with base-pairing rules

A+G=C+T

In Meselson and Stahl's experiment proving semiconservative DNA replication, they started with bacteria grown in a heavy isotope of nitrogenand then switched them to a light isotope. They then observed the DNA density after one and two rounds of replication. What was the result after one round of replication?

All hybrid DNA

A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

DNA ligase

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized

DNA polymerase can join new nucleotides only to the 3' end of a pre-existing strand, and the strands are antiparallel.

The elongation of the leading strand during DNA synthesis

Depends on the action of DNA polymerase.

Imagine a bacterial replication fork. Synthesis of which new strands would be affected by mutations in the enzyme DNA ligase?

Lagging strand

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base opposite thymine. What combination of proteins could repair such damage.

Nuclease, DNA polymerase, DNA ligase

E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?

One low-density and one intermediate-density band.

What is the %T in wheat DNA?

approximately 28%

Imagine a bacterial replication fork. Synthesis of which new strands would be affected by mutations in the enzyme DNA polymerase III.

both leading and lagging strands.

In Meselson and Stahl's experiment proving semiconservative DNA replication, they started with bacteria grown in a heavy isotope of nitrogenand then switched them to a light isotope. They then observed the DNA density after one and two rounds of replication. What was the result after two rounds of replication?

equal amounts of light and hybrid DNA.

In his work with pneumonia-causing bacteria and mice, Griffith found that

some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic

Which of the following phenomena or processes does not contribute to the high fidelity of DNA replication?

telomerase.

Does the distribution of bases in sea urchin DNA and salmon DNA follow Chargaff's rules?

yes, because the %A approximately equals the %T and the %G approximately equals the %C in both species.