Chapter 16 Questions Flashcards
During Griffith’s experiments with Streptococcus pneumoniae in mice, material from _____ bacteria transformed _____ bacteria.
heat-killed virulent … living nonvirulent
Avery and his colleagues’ 1944 experiment showed that DNA _____.
was the substance that transformed the bacteria in Griffith’s experiment
A scientist assembles a bacteriophage with the protein coat of phage T2 and the DNA of phage T4. If this composite phage were allowed to infect a bacterium, the phages produced in the host cell would have _____.
the protein and DNA of T4
In an important experiment, a radioactively labeled bacteriophage was allowed to infect bacteria. In a first trial, the phage contained radioactive DNA, and radioactivity was detected inside the bacteria. Next, phage containing radioactive protein was used, and the radioactivity was not detected inside the bacteria. These experiments led to the conclusion that _____.
the genetic material of the phage is DNA
Up until Hershey and Chase showed that DNA was the genetic molecule, what molecule was considered the best candidate for carrying genetic information and why?
proteins because they were thought to be the only molecule with both the variety and specificity of function to account for the array of heritable traits observed
-Many scientists believed that proteins must be the chemical carriers of genetic information.
Monomers for the synthesis of DNA are called _____.
nucleotides
Chargaff found that for DNA _____.
the ratio of A to T is close to 1:1 and the ratio of G to C is close to 1:1
-This is a result of specific base pairing and of DNA’s double-helical structure.
What technique was most helpful to Watson and Crick in developing their model for the structure of DNA?
X-ray crystallography
-Watson and Crick based their model of DNA on insights they were able to gain from Franklin’s X-ray diffraction photo.
In DNA, the two purines are _____, and the two pyrimidines are _____.
adenine and guanine … cytosine and thymine
Which of the following is correct?
Adenine forms two hydrogen bonds with thymine; guanine forms three hydrogen bonds with cytosine.
The two sugar-phosphate strands that form the rungs of a DNA double helix are joined to each other through _____.
hydrogen bonds between nucleotide bases
-The two sugar-phosphate strands of a DNA molecule are held together by hydrogen bonding between the nitrogenous bases, which are paired in the interior of the helix.
The information in DNA is contained in _____.
the sequence of nucleotides along the length of the two strands of the DNA molecule
Who is credited with explaining the structure of the DNA double helix?
Watson and Crick
Which of the following attributes of DNA is most crucial to its accurate duplication?
its specific base pairing and hydrogen bonding
During the replication of DNA, _____.
both strands of a molecule act as templates
The experiments of Meselson and Stahl showed that DNA _____.
replicates in a semiconservative fashion
-In the semiconservative model of DNA replication, the two strands of the parental molecule separate. Each functions as a template for the synthesis of a new complementary strand.
The DNA structures of prokaryotes and eukaryotes are different in several ways, but one way in which they are the same is that _____.
both have a sugar-phosphate backbone
Which of the following statements about replication origins is correct?
- In bacteria, the DNA sequence at the origin is recognized by specific proteins that then bind to the origin.
- Bacterial chromosomes have a single origin, but eukaryotic chromosomes have many origins.
- In both prokaryotes and eukaryotes, replication proceeds in both directions from each origin.
- The two strands of DNA at the origin are separated, allowing the formation of a replication bubble.
At each end of a DNA replication bubble is _____.
a replication fork
The role of DNA polymerases in DNA replication is to _____.
attach free nucleotides to the new DNA strand
The rate of elongation in prokaryotes is _____ the rate in eukaryotes.
much faster than
The two strands of a DNA double helix are antiparallel. This means that _____.
one strand runs in the 5’ to 3’ direction, and the other runs in the 3’ to 5’ direction
One strand of a DNA molecule has the base sequence 5′-ATAGGT-3′. The complementary base sequence on the other strand of DNA will be 3′-_____-5′.
TATCCA
-A always pairs with T, and G with C.
DNA polymerase adds nucleotides to the _____ of the leading strands, and to the _____ of the lagging strands (Okazaki fragments).
3′ end … 3′ end
What enzyme joins Okazaki fragments?
DNA ligase
After the formation of a replication bubble, which of the following is the correct sequence of enzymes used for the synthesis of the lagging DNA strand?
helicases, primase, DNA polymerases, ligase
Which of the following components is required for DNA replication?
RNA primer
The removal of the RNA primer and addition of DNA nucleotides to the 3’ end of Okazaki fragments in its place is carried out by _____.
DNA polymerase I
The unwinding of DNA at the replication fork causes twisting and strain in the DNA ahead of the fork, which is relieved by an enzyme called _____.
topoisomerase
Once the DNA at the replication fork is unwound by helicases, what prevents the two strands from coming back together to re-form a double helix?
Single-strand binding proteins bind the unwound DNA and prevent the double helix from re-forming.
Which description of DNA replication is correct?
Helicases separate the two strands of the double helix, and DNA polymerases then construct two new strands using each of the original strands as templates.
In what way(s) is our traditional representation of DNA polymerase molecules moving like locomotives along a track inaccurate?
- The proteins involved in replication do not move; instead, DNA is drawn through the complex.
- DNA polymerase acts as part of a large complex of proteins, not like a single locomotive.
The overall error rate in the completed DNA molecule is approximately _____.
1 error per 10,000,000,000 nucleotides
-The rate of initial pairing errors during replication is about 1 in 100,000. This level of accuracy is then dramatically enhanced by the different proofreading mechanisms discussed in the chapter.
The incorporation of an incorrect base into the DNA during replication _____.
can be repaired by the mismatch repair system
Which set of enzymes is involved in nucleotide excision repair?
nuclease, DNA polymerase, and ligase
Individuals with the disorder xeroderma pigmentosum _____.
- often have inherited defects in the nucleotide excision repair system
- have high rates of skin cancer
- have difficulty repairing thymine dimers
- are hypersensitive to sunlight
Unlike prokaryotic DNA replication, replication of eukaryotic chromosomes _____.
cannot be completed by DNA polymerase
-Prokaryotic DNA replication has a single origin; eukaryotic DNA replication has multiple origins.
Telomeres _____.
get shorter with continued cell division
Telomerase _____.
is an enzyme that lengthens telomeres
- In fact, telomerase appears to slow cell aging, and is present mostly only in germ cells and cancer cells.
Which of the following best illustrates the importance of altered DNA nucleotides in evolutionary processes?
In a temporally variable environment, a population of bacteria with an elevated rate in replication error can have a selective advantage over other populations with lower rates in replication error.
In a comparison between asexually reproducing bacteria and sexually reproducing multicellular eukaryotes, uncorrected errors in replication are more likely to be transmitted to subsequent generations in bacteria than in multicellular eukaryotes. Which of the following provides the best evidence-based explanation for this difference?
Being asexual and single-celled, all uncorrected errors of replication in bacteria are transmitted to subsequent generations. Multicellular eukaryotes typically reproduce sexually, so uncorrected errors are transmitted only if they occur in germ cells that meiotically divide to produce gametes.
What is the major difference between bacterial chromosomes and eukaryotic chromosomes?
Bacteria have a single circular chromosome whereas eukaryotes have several linear chromosomes.
Put the following DNA-containing entities in order according to the amount of DNA found in their genomes.
virus, bacteria, eukaryote
Why were many of the early experiments on DNA carried out on viruses and bacteria?
- Their chromosomes have a simpler structure.
- They can interact with each other.
- They have relatively small genomes.
- They have short generation times.
The “beads on a string” seen in interphase chromatin are _____.
nucleosomes
In his work with pneumonia-causing bacteria and mice, Griffith found that
some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic
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
In a nucleosome, the DNA is wrapped around
histones
E. Coli cells grown on ^15 N medium are transferred to ^14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?
one low-density and one intermediate-density band
A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?
DNA ligase
The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?
nuclease, DNA polymerase, DNA ligase
Helicase Function
unwinds parental double helix at replication forks
Single-strand binding protein Function
binds to and stabilizes single-stranded DNA until it can be used as a template
Topoisomerase Function
relieves “overwinding” strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands
Primase Function
synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand
DNA pol III Function
using parental DNA as a template, synthesizes new DNA strand by covalently adding nucleotides to 3’ end of a pre-existing DNA strand or RNA primer
DNA pol I Function
removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides
DNA ligase
joins 3’ end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand
