Chapter 9 - DNA and Its Role in Heredity

If 30 percent of the bases in a double-stranded DNA molecule are T, _______ percent must be G.

20

What functional group at the end of the growing strand of DNA reacts with a nucleotide under the direction of DNA polymerase to elongate the strand?

3ʹ hydroxyl group

Which mechanism causes induced mutations to occur?

A mutagen causing a permanent change in DNA sequence

What feature of DNA most directly accounts for its replication mechanism?

Complementary base pairing

Which is a reason that explains why DNA replication occurs in a continuous fashion on one parental DNA strand and in a discontinuous fashion on the other parental DNA strand?

DNA polymerase only works to add nucleotides in one direction of the growing chain.

If the conservative model had been correct, how many generations of bacterial cell division would have had to pass before Meselson and Stahl would have observed evidence of a band in the CsCl gradient corresponding to a hybrid DNA molecule containing both 14N and 15N?

No generations; a hybrid would never form.

Ligases are enzymes that link two DNA fragments together. Suppose a bacterium develops a mutation in the ligase gene needed for DNA replication. This mutation results in an inactive form of the enzyme. What outcome can you expect for this bacterium and why?

The bacterium will not be able to replicate itself because only one DNA strand will result from the replication process instead of two.

Suppose thymidine labeled with carbon-14 was added to a culture of bacteria and allowed to incubate for 20 minutes (one generation time). The DNA molecules were then isolated from the bacterial cells. If DNA replication is semiconservative, what would you observe about these molecules?

The carbon-14 label would be found in all the DNA molecules but in only one strand of each helix.

DNA polymerase lengthens a polynucleotide strand by

covalently linking new nucleotides to a previously existing strand.

The base _______ is particularly prone to mutation from deamination.

cytosine

Double-stranded DNA looks like a ladder that has been twisted into a helix, or spiral. The rungs of the ladder are

pairs of bases.

The expression of the enzyme _______ is largely restricted to stem cells and gametes. However, it is expressed in 90 percent of human cancers and may be responsible for their ability to survive continuous division.

telomerase

During eukaryotic DNA replication,

the template strands must separate so that both can be copied.

DNA replication in eukaryotes differs from replication in bacteria because

there are many origins of replication in each eukaryotic chromosome and only one in bacterial DNA.

A silent mutation

would likely not affect the activity of a protein.