question

A difference between a DNA and an RNA molecule?

answer

DNA is double-stranded, whereas RNA is single-stranded. (With some exceptions) DNA is a double-stranded molecule and RNA is a single-stranded molecule.

question

Nucleotides are composed of

answer

a pentose sugar, a nitrogenous base, and a phosphate group

question

Phosphate groups contain

answer

phosphorus

question

You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.

answer

sugar with two, and not three, oxygen atoms

question

Which of these nitrogenous bases is found in DNA but not in RNA?

answer

thymine DNA contains thymine; RNA does not.

question

Which letters are purines?

answer

AG

question

Which letters are pyrimidines?

answer

CUT

question

In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.

answer

1' ... 5' The nitrogenous base is attached to the sugar's 1' carbon and the phosphate group is attached to the sugar's 5' carbon.

question

Nucleic acids are assembled in the _____ direction.

answer

5' to 3' New nucleotides are added to the 3' end of a growing polynucleotide.

question

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.

answer

thymine ... cytosine This is referred to as specific base pairing.

question

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

answer

A + C = G + T

question

In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?

answer

Radioactively labeled phosphorus was present inside the infected bacteria. When the bacteria had been infected with T2 phage whose DNA was tagged with radioactive phosphorus, the pellet of mainly bacterial material contained most of the radioactivity, indicating that the labeled phage DNA had entered the cells.

question

Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA?

answer

the diameter of the helix

question

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.

answer

thymine ... cytosine This is referred to as specific base pairing.

question

After DNA replication is completed, _____.

answer

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

question

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

answer

helicase

question

The action of helicase creates _____.

answer

replication forks and replication bubbles A replication fork is the transition region between paired and unpaired DNA strands.

question

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

answer

DNA polymerase can assemble DNA only in the 5' to 3' direction Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled in short 5' to 3' segments, which are later joined together by ligase.

question

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

answer

RNA primer complementary to a preexisting DNA strand The synthesis of a DNA strand begins with the formation of an RNA primer.

question

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

answer

template An old DNA strand is used as a template for the synthesis of a complementary new strand.

question

What catalyzes DNA synthesis?

answer

DNA polymerase This enzyme catalyzes DNA synthesis.

question

Which of the following statements about DNA synthesis is true?

answer

Primers are short sequences that allow the initiation of DNA synthesis. When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.

question

Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?

answer

Phosphate groups The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis.

question

Which of the following enzymes creates a primer for DNA polymerase?

answer

Primase This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.

question

Which of the following statements about Okazaki fragments in E. coli is true?

answer

They are formed on the lagging strand of DNA. While DNA is synthesized continuously on the leading strand, Okazaki fragments are formed on the lagging strand because DNA synthesis always proceeds in the 5' to 3' direction.

question

Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?

answer

Topoisomerase This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template.

question

True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.

answer

True When the 3' end of one DNA strand points in the same direction as the 5' end of the other DNA strand, the strands are said to be antiparallel.

question

What process repairs damage to a preexisting double helix?

answer

nucleotide excision repair In nucleotide excision repair, a section of DNA containing the damage is removed, and the gap is then filled in and completed by DNA polymerase and DNA ligase.

question

What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?

answer

telomeres Telomeres consist of many copies of a short DNA sequence that is bound by specific proteins.

question

Replication in prokaryotes differs from replication in eukaryotes for which of the following reasons?

answer

Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

question

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

answer

DNA polymerase III

question

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

question

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

question

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork: 3' C C T A G G C T G C A A T C C 5' An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

answer

5' A C G U U A G G 3'

question

What is the function of topoisomerase?

answer

relieving strain in the DNA ahead of the replication fork

question

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

answer

It joins Okazaki fragments together.

question

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

answer

single-strand binding proteins

question

Which of the following would you expect of a eukaryote lacking telomerase?

answer

a reduction in chromosome length in gametes

question

Which type of strand... Only one primer needed Made continuously Daughter strand elongates toward replication fork

answer

Leading strand

question

Which type of strand... Multiple primers needed Made in segments Daughter strand elongates away from replication fork

answer

Lagging strand

question

Which type of strand... Synthesize 5' to 3'?

answer

Leading and lagging strands

question

Where would RNA polymerase attach?

answer

DNA

question

Which of the following is true of DNA during interphase?

answer

It exists as chromatin and is less condensed than mitotic chromosomes. Chromatin is the term for the loosely coiled DNA observed in cells during interphase. Even during interphase, however, parts of the chromosome may still be rather tightly coiled and packed.

question

Why do histones bind tightly to DNA?

answer

Histones are positively charged, and DNA is negatively charged.

question

In a nucleosome, the DNA is wrapped around

answer

histones.

question

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.

question

Define antiparallel elongation

answer

subunits run in opposite directions

question

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.

question

Which of the enzymes covalently connects segments of DNA?

answer

ligase

question

Which of the enzymes synthesizes short segments of RNA?

answer

primase

question

Which of the following statements describes the eukaryotic chromosome?

answer

It consists of a single linear molecule of double-stranded DNA plus proteins.

question

Which of the following represents the order of increasingly higher levels of organization of chromatin?

answer

nucleosome, 30-nm chromatin fiber, looped domain

question

Research indicates that the best estimate of your age is from ______.

answer

markers in your cells

question

The cells examined from the 2,400 people in this study were from ______.

answer

blood

question

Which of the following damages cells and causes cell aging?

answer

inflammation

question

The researchers used strands of DNA located at the ends of chromosomes (called telomeres) to classify the cells they studied. What assumption did they make about telomeres?

answer

Longer telomeres indicate younger cells.

question

The researchers found that telomeres were ______.

answer

longer in individuals who exercised regularly

question

The research showed that individuals who _______ had younger looking cells based on telomere measurements.

answer

exercised for an average of 30 minutes per day

question

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

answer

DNA polymerase can join new nucleotides only to the 3' end of a growing strand.

question

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

answer

A + G = C + T

question

The elongation of the leading strand during DNA synthesis

answer

depends on the action of DNA polymerase.

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