AP Bio Chapter 16

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

Answer: 8% 31% 8% 16% 42% It cannot be determined from the information provided.

In an analysis of the nucleotide composition of DNA, which of the following will be found?

Answer: A + C = G + T A + C = G + T A = G and C = T A = C G + C = T + A

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in the figure above would be expected after one round of DNA replication in the presence of 14N?

Answer: D (test tube with the line at 14N-15N hybrid DNA ONLY) A B C D E

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

Answer: DNA contains phosphorus, whereas protein does not. DNA contains sulfur, whereas protein does not. DNA contains nitrogen, whereas protein does not. DNA contains purines, whereas protein includes pyrimidines. DNA contains phosphorus, whereas protein does not. RNA includes ribose, whereas DNA includes deoxyribose sugars.

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

Answer: DNA in both daughter cells would be radioactive. 1. Neither of the two daughter cells would be radioactive. 2. All four bases of the DNA would be radioactive. 3. Radioactive thymine would pair with nonradioactive guanine. 4. One of the daughter cells, but not the other, would have radioactive DNA. 5. DNA in both daughter cells would be radioactive.

Select the most accurate statement describing DNA replication complexes.

Answer: DNA replication complexes are grouped into factories, which are anchored to the nuclear matrix. 1. DNA replication complexes are grouped into factories, which are anchored to the nuclear matrix. 2. DNA replication complexes move along a DNA railway track. 3. DNA and the DNA replication complexes fit together like a lock and key.

Meselson and Stahl cultured E. coli for several generations in a medium with a heavy isotope of nitrogen, 15N. They transferred the bacteria to a medium with a light isotope of nitrogen, 14 N. After two rounds of DNA replication, half the DNA molecules were light (both strands had 14N) and half were hybrids (15N-14N). What did the researchers conclude from these results?

Answer: DNA replication is semiconservative. 1. DNA replication is semiconservative. 2. The nitrogenous bases in DNA molecules incorporate both 15N and 14N. 3. Opposite DNA strands are complementary to each other.

During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?

Answer: DNA synthesis can take place only in the 5' to 3' direction. 1.DNA polymerases can bind to only one strand at a time. 2. DNA synthesis can take place only in the 5' to 3' direction. 3. There are thousands of origins of replication on the lagging strand but only one on the leading strand.

Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of which of the following?

Answer: Gaps left at the 5' end of the lagging strand gaps left at the 3' end of the lagging strand because of the need for a primer the "no ends" of a circular chromosome gaps left at the 5' end of the lagging strand the evolution of telomerase enzyme DNA polymerase that cannot replicate the leading strand template to its 5' end

Nucleotides are added to a growing DNA strand as nucleoside triphosphates. What is the significance of this fact?

Answer: Hydrolysis of the two phosphate groups (P-Pi) and DNA polymerization are a coupled exergonic reaction. 1. Nucleoside triphosphates are more abundant in the cell than nucleotides. 2. Hydrolysis of the two phosphate groups (P-Pi) and DNA polymerization are a coupled exergonic reaction. 3. Nucleoside triphosphates are more easily transported in the cell than are nucleotides.

Use the following list of choices for the following question: I. helicase II. DNA polymerase III III. ligase IV. DNA polymerase I V. primase Which of the enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of Okazaki fragments?

Answer: IV I II III IV V

Which of the following statements describes the eukaryotic chromosome?

Answer: It consists of a single linear molecule of double-stranded DNA plus proteins. 1. It is composed of DNA alone. 2. The nucleosome is its most basic functional subunit. 3. It consists of a single linear molecule of double-stranded DNA plus proteins. 4. Active transcription occurs on heterochromatin but not euchromatin. 5. The number of genes on each chromosome is different in different cell types of an organism.

The DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes. What does this most probably reflect?

Answer: That the critical function of telomeres must be maintained 1. that new evolution of telomeres continues 2. the inactivity of this DNA 3. that mutations in telomeres are relatively advantageous 4. the low frequency of mutations occurring in this DNA 5. that the critical function of telomeres must be maintained

What is meant by the description "antiparallel" regarding the strands that make up DNA?

Answer: The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. 1. Base pairings create unequal spacing between the two DNA strands. 2. One strand is positively charged and the other is negatively charged. 3. The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand. 4. The twisting nature of DNA creates nonparallel strands. 5. One strand contains only purines and the other contains only pyrimidines.

DNA is a self-replicating molecule. What accounts for this important property of DNA?

Answer: The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C. Because of the specificity of the pairing of the nitrogenous bases, each strand of the double helix specifies the matching sequence of bases on the other strand. During replication, when the strands separate, each strand serves as a template for the replication of other strand. Read about base pairing in DNA. 1. The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C. 2. Its two strands are held together by easily broken covalent bonds. 3. Replication is thermodynamically spontaneous and requires no enzymes.