A difference between a DNA and an RNA molecule?
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.
Nucleotides are composed of
a pentose sugar, a nitrogenous base, and a phosphate group
Phosphate groups contain
phosphorus
You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.
sugar with two, and not three, oxygen atoms
Which of these nitrogenous bases is found in DNA but not in RNA?
thymine
DNA contains thymine; RNA does not.
Which letters are purines?
AG
Which letters are pyrimidines?
CUT
In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.
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.
Nucleic acids are assembled in the _____ direction.
5' to 3'
New nucleotides are added to the 3' end of a growing polynucleotide.
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
This is referred to as specific base pairing.
In an analysis of the nucleotide composition of DNA, which of the following will be found?
A + C = G + T
In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?
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.
Which of the following can be determined directly from X-ray diffraction photographs of crystallized DNA?
the diameter of the helix
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
This is referred to as specific base pairing.
After DNA replication is completed, _____.
each new DNA double helix consists of one old DNA strand and one new DNA strand
The first step in the replication of DNA is catalyzed by _____.
helicase
The action of helicase creates _____.
replication forks and replication bubbles
A replication fork is the transition region between paired and unpaired DNA strands.
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
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.
The synthesis of a new strand begins with the synthesis of a(n) _____.
RNA primer complementary to a preexisting DNA strand
The synthesis of a DNA strand begins with the formation of an RNA primer.
An old DNA strand is used as a _____ for the assembly of a new DNA strand.
template
An old DNA strand is used as a template for the synthesis of a complementary new strand.
What catalyzes DNA synthesis?
DNA polymerase
This enzyme catalyzes DNA synthesis.
Which of the following statements about DNA synthesis is true?
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.
Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?
Phosphate groups
The potential energy stored in the bonds of the phosphates provides the energy for DNA synthesis.
Which of the following enzymes creates a primer for DNA polymerase?
Primase
This RNA polymerase synthesizes an RNA primer antiparallel to the template DNA strand.
Which of the following statements about Okazaki fragments in E. coli is true?
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.
Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?
Topoisomerase
This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template.
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.
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.
What process repairs damage to a preexisting double helix?
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.
What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?
telomeres
Telomeres consist of many copies of a short DNA sequence that is bound by specific proteins.
Replication in prokaryotes differs from replication in eukaryotes for which of the following reasons?
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
Which enzyme catalyzes the elongation of a DNA strand in the 5' ? 3' direction?
DNA polymerase III
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 DNA of telomeres has been found to be highly conserved throughout the evolution of eukaryotes. What does this most probably reflect?
that the critical function of telomeres must be maintained
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 f
5' A C G U U A G G 3'
What is the function of topoisomerase?
relieving strain in the DNA ahead of the replication fork
What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?
It joins Okazaki fragments together.
Which of the following help(s) to hold the DNA strands apart while they are being replicated?
single-strand binding proteins
Which of the following would you expect of a eukaryote lacking telomerase?
a reduction in chromosome length in gametes
Which type of strand...
Only one primer needed
Made continuously
Daughter strand elongates toward replication fork
Leading strand
Which type of strand...
Multiple primers needed
Made in segments
Daughter strand elongates away from replication fork
Lagging strand
Which type of strand...
Synthesize 5' to 3'?
Leading and lagging strands
Where would RNA polymerase attach?
DNA
Which of the following is true of DNA during interphase?
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.
Why do histones bind tightly to DNA?
Histones are positively charged, and DNA is negatively charged.
In a nucleosome, the DNA is wrapped around
histones.
During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?
DNA synthesis can take place only in the 5' to 3' direction.
Define antiparallel elongation
subunits run in opposite directions
Nucleotides are added to a growing DNA strand as nucleoside triphosphates. What is the significance of this fact?
Hydrolysis of the two phosphate groups (P-Pi) and DNA polymerization are a coupled exergonic reaction.
Which of the enzymes covalently connects segments of DNA?
ligase
Which of the enzymes synthesizes short segments of RNA?
primase
Which of the following statements describes the eukaryotic chromosome?
It consists of a single linear molecule of double-stranded DNA plus proteins.
Which of the following represents the order of increasingly higher levels of organization of chromatin?
nucleosome, 30-nm chromatin fiber, looped domain
Research indicates that the best estimate of your age is from ______.
markers in your cells
The cells examined from the 2,400 people in this study were from ______.
blood
Which of the following damages cells and causes cell aging?
inflammation
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?
Longer telomeres indicate younger cells.
The researchers found that telomeres were ______.
longer in individuals who exercised regularly
The research showed that individuals who _______ had younger looking cells based on telomere measurements.
exercised for an average of 30 minutes per day
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
DNA polymerase can join new nucleotides only to the 3' end of a growing strand.
In analyzing the number of different bases in a DNA sample, which result would be consistent with the base-pairing rules?
A + G = C + T
The elongation of the leading strand during DNA synthesis
depends on the action of DNA polymerase.