BIO105 Ch.15

Which enzyme catalyzes the elongation of a DNA strand in the 5' --> 3' direction?

DNA polymerase III

A new DNA strand elongates only in the 5' to 3' direction because

DNA polymerase can only add nucleotides to the free 3' end.

Researchers found E. coli that had mutation rates 100 times higher than normal. Which of the following is the most likely cause of these results?

The proofreading mechanism of DNA polymerase was not working properly.

What separates the DNA strands during replication?

helicase

Semiconservative replication involves a template. What is the template?

one strand of the DNA molecule

Which of the following synthesizes short segments of RNA?

primase

What is a telomere?

the ends of linear chromosomes

The leading and the lagging strands differ in that ________.

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction

What is the function of DNA polymerase III?

to add nucleotides to the end of a growing DNA strand

Identify the lagging strand during duplication of DNA starting from a double helix in the accompanying figure. d b a c

c

To repair a thymine dimmer by nucleotide excision repair, in which order do the necessary enzymes act?

endonuclease, DNA polymerase I, DNA ligase

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent

leading strands and Okazaki fragments.

Which of the following covalently connects segments of DNA? primase DNA polymerase III DNA polymerase I ligase helicase

ligase

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

DNA is synthesized through a process known as ________.

semiconservative replication

Which of the following help(s) to hold the DNA strands apart while they are being replicated?

single-strand DNA binding proteins

What helps to hold the DNA strands apart while they are being replicated?

single-strand binding proteins

What determines the nucleotide sequence of the newly synthesized strand during DNA replication?

the nucleotide sequence of the template strand

Mendel and Morgan did not know about the structure of DNA; however, which of the following of their contributions was (were) necessary to Watson and Crick?

the particulate nature of the hereditary material

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

A + C = G + T

For a science fair project, two students decided to repeat the Hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won't this experiment work?

Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins

In humans, xeroderma pigmentosum (XP) is a disorder of the nucleotide excision repair mechanism. These individuals are unable to repair DNA damage caused by ultraviolet light. Which of the following are the most prominent types of DNA lesions in individuals suffering from xeroderma pigmentosum? A) methylation of purines B) thymine dimers C) telomere shortening D) mismatch errors

B) thymine dimers

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts? A) DNA contains nitrogen, whereas protein does not. B) RNA includes ribose, whereas DNA includes deoxyribose sugars. C) DNA contains purines, whereas protein includes pyrimidines. D) DNA contains phosphorus, whereas protein does not. E) DNA contains sulfur, whereas protein does not.

D) DNA contains phosphorus, whereas protein does not

Which of the following statements describes the eukaryotic chromosome? A) It is composed of DNA alone. B) The nucleosome is its most basic functional subunit. C) The number of genes on each chromosome is different in different cell types of an organism. D) It consists of a single linear molecule of double-stranded DNA. E) Active transcription occurs on heterochromatin.

D) It consists of a single linear molecule of double-stranded DNA.

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?

DNA in both daughter cells would be radioactive

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

It joins Okazaki fragments together

Who performed classic experiments that supported the semiconservative model of DNA replication?

Meselson and Stahl

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

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

Use Figure 16.1 to answer the following question. 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 Figure 16.1 would be expected after one round of DNA replication in the presence of 14N?

14N-15N hybrid DNA

Put the following steps of DNA replication in chronological order. 1. Single-stranded binding proteins attach to DNA strands. 2. Hydrogen bonds between base pairs of antiparallel strands are broken. 3. Primase binds to the site of origin. 4. DNA polymerase binds to the template strand. 5. An RNA primer is created.

2, 1, 3, 5, 4

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium. Which pattern in Figure 16.1 would you expect if the DNA was replicated in a conservative manner?

Tube B

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 Figure 16.1 would be expected after one round of DNA replication in the presence of 14N?

Tube C