mastering 16

How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?

It catalyzes the lengthening of telomeres, compensating for the shortening that could occur during replication without telomerase activity.

Which of the following is true of DNA during interphase?

It exists as chromatin and is less condensed than mitotic chromosomes.

What is the function of helicase in DNA replication?

It untwists the double helix and separates the two DNA strands.

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

gaps left at the 5' end of the lagging strand

The first step in the replication of DNA is catalyzed by _____.

helicase

Short segments of newly synthesized DNA are joined into a continuous strand by _____.

ligase

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

The action of helicase creates _____.

replication forks and replication bubbles

An old DNA strand is used as a _____ for the assembly of a new DNA strand.

template

What provides the energy for the polymerization reactions in DNA synthesis?

the deoxyribonucleotide triphosphate substrates

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

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

translocation

What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?

an inversion

Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?

aneuploidy

After DNA replication is completed, _____.

each new DNA double helix consists of one old DNA strand and one new DNA strand

If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?

1/4 of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.

What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

In E. coli, which enzyme catalyzes the elongation of a new DNA strand in the 5' → 3' direction?

DNA polymerase III

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?

DNA polymerase can assemble DNA only in the 5' to 3' direction

When can nondisjunction occur? Choose the best answer.

Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.

What is a major difference between eukaryotic DNA replication and prokaryotic DNA replication?

Prokaryotic chromosomes have a single origin of replication, while eukaryotic chromosomes have multiple origins of replication.

The synthesis of a new strand begins with the synthesis of a(n) _____.

RNA primer complementary to a preexisting DNA strand

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.

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.

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.