In his transformation experiments, what did Griffith observe?
Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
How do we describe transformation in bacteria?
Assimilation of external DNA into a cell
After mixing a heat-killed, phosphorescent strain of bacteria with a living nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observations would provide the best evidence that the ability to fluoresce is a heritable trait?
Descendants of the living cells are also phosphorescent.
In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?
DNA contains phosphorus, whereas protein does not.
Which of the following investigators was/were responsible for the following discovery? In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine.
Alfred Hershey and Martha Chase
Cytosine makes up 40% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in the sample will be thymine?
10%
it became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in what?
Sequence of bases
In an analysis of the nucleotide composition of DNA, what equation is always found?
A + C = T + G
Replication in prokaryotes differs from replication in eukaryotes for which reason?
Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.
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.
Suppose that you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?
DNA in both daughter cells would be radioactive.
An Okazaki fragment has what arrangement?
5′ RNA nucleotides, DNA nucleotides 3′
In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. What would you expect as a result of this mutation?
No replication fork will be formed.
Which enzyme catalyzes the elongation of a DNA strand in the 5′ to 3′ direction?
DNA polymerase III
Eukaryotic telomeres replicate differently than the rest of the chromosome. This is a consequence of what?
Gaps left at the 5′ end of the lagging strand.
The enzyme telomerase solves the problem of replication at the ends of linear chromosome how?
Adding numerous short DNA sequences such as TTAGGG, which form a hairpin turn.
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 functions 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 starred T of the template. What is the primer sequence?
5′ A G C T T A G G 3′
What is a thymine dimer?
A pair of abnormally chemically bonded adjacent thymine bases in DNA, resulting from damage by ultra-violet irradiation. The cellular processes that repair this lesion often make errors that create mutations.
To repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?
Endonuclease, DNA polymerase I, DNA ligase
What is the function of DNA polymerase III?
To add nucleotides to the 3′ end of a growing strand
The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that?
The nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.
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
A new DNA strand elongates only in the 5′ to 3′ direction because
DNA polymerase can only add nucleotides to the free 3′ end
What is the function of topoisomerase?
relieving the strain in the DNA as it unwinds 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 helps to hold the DNA strands apart while they are being replicated?
Single-strand binding proteins
Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells are impaired in what way?
They cannot repair thymine dimers.
Which of the following would you expect of a eukaryote lacking telomerase?
A reduction in chromosome length in gametes.
Which enzyme removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3′ end of Okazaki fragments?
DNA polymerase I
Which enzyme separates the DNA strands during replication?
Helicase
Which enzyme covalently connects segments of DNA
ligase
Which enzyme synthesizes short segments of RNA
primase
What materials are required by both eukaryotes and prokaryotes for replication?
double-stranded DNA, four kinds of nNTPs, primers, origins
Studies of nucleosomes have shown that histones exist in each nucleosome as two kinds of tetramers: one of 2H2A molecules and 2 H2B molecules, and the other as 2 H3 and 2 H4 molecules. What supports this data?
The two types of tetramers associate to form an octamer.
How would you describe a eukaryotic chromosome?
It consists of a single linear molecule of double stranded DNA plus proteins.
If a cell were unable to produce histone proteins, what would be a likely effect?
The cell’s DNA couldn’t be packed into its nucleus
Why do histones bind tightly to DNA?
Histones are positively charged and DNA is negatively charged
For a science fair project, two students decided to repeat the Hershey and Chase experiment with modifications. They decided to label the nitrogen of the DNA rather than the phosphate. They reasoned each nucleotide has only one phosphate and two to five nitrogens. Thus, labeling the nitrogens would provide a stronger signal than labeling the phosphates. Why won’t this work?
Amino acids (and thus proteins) also have nitrogen atoms; thus, the radioactivity would not distinguish between DNA and proteins.
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