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Questions and Answers
In the accompanying image, a nucleotide is indicated by the letter _____
In the accompanying image, a nucleotide is indicated by the letter _____
B
Which of these is a difference between a DNA and an RNA molecule?
Which of these is a difference between a DNA and an RNA molecule?
DNA is usually double-stranded, whereas RNA is usually single-stranded
This is an image of a(n) _____
This is an image of a(n) _____
nucleotide
The letter A indicates a _____
The letter A indicates a _____
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A nitrogenous base is indicated by the letter _____
A nitrogenous base is indicated by the letter _____
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You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____
You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____
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Which of these nitrogenous bases is found in DNA but not in RNA?
Which of these nitrogenous bases is found in DNA but not in RNA?
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Which of these is(are) pyrimidines?
Which of these is(are) pyrimidines?
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In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.
In a nucleotide, the nitrogenous base is attached to the sugar's _____ carbon and the phosphate group is attached to the sugar's _____ carbon.
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Nucleic acids are assembled in the _____ direction.
Nucleic acids are assembled in the _____ direction.
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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.
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.
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This is an image of a _____.
This is an image of a _____.
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Who demonstrated that DNA is the genetic material of the T2 phage?
Who demonstrated that DNA is the genetic material of the T2 phage?
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The radioactive isotope 32P labels the T2 phage's _____
The radioactive isotope 32P labels the T2 phage's _____
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Hershey and Chase used _____ to radioactively label the T2 phage's proteins.
Hershey and Chase used _____ to radioactively label the T2 phage's proteins.
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After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.
After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.
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Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?
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It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?
It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information. Which of the following characteristics of DNA is responsible for this?
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For a science fair project, two students decided to repeat the Hershey and Chase experiment with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?
For a science fair project, two students decided to repeat the Hershey and Chase experiment with modifications. They decided to radioactively label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen atoms. Thus, labeling the nitrogen atoms would provide a stronger signal than labeling the phosphates. Why won't this experiment work?
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DNA replication is said to be semiconservative. What does this mean?
DNA replication is said to be semiconservative. What does this mean?
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What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?
What are the repetitive DNA sequences present at the ends of eukaryotic chromosomes called?
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In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?
In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?
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How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
How does the enzyme telomerase meet the challenge of replicating the ends of linear chromosomes?
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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?
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?
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Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?
Why does a new DNA strand elongate only in the 5' to 3' direction during DNA replication?
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Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?
Which of the following types of molecules help to hold the DNA strands apart while they are being replicated?
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Semiconservative replication involves a template. What is the template?
Semiconservative replication involves a template. What is the template?
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Which of the following statements accurately describes the structure of a eukaryotic chromosome?
Which of the following statements accurately describes the structure of a eukaryotic chromosome?
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If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?
If a cell were unable to produce histone proteins, which of the following results would be a likely effect on the cell?
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During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?
During DNA replication, the leading strand is synthesized continuously, whereas the lagging strand is synthesized as Okazaki fragments. Why is this so?
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Short segments of newly synthesized DNA are joined into a continuous strand by _____.
Short segments of newly synthesized DNA are joined into a continuous strand by _____.
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After DNA replication is completed, _____
After DNA replication is completed, _____
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The action of helicase creates _____.
The action of helicase creates _____.
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Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?
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An old DNA strand is used as a _____ for the assembly of a new DNA strand.
An old DNA strand is used as a _____ for the assembly of a new DNA strand.
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What catalyzes DNA synthesis?
What catalyzes DNA synthesis?
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Which of the following statements about DNA synthesis is true?
Which of the following statements about DNA synthesis is true?
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Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?
Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?
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Which of the following enzymes creates a primer for DNA polymerase?
Which of the following enzymes creates a primer for DNA polymerase?
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Which of the following statements about Okazaki fragments in E. coli is true?
Which of the following statements about Okazaki fragments in E. coli is true?
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Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?
Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?
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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 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.
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Study Notes
Nucleotides and Nucleic Acids
- Nucleotides consist of a phosphate group, a nitrogenous base, and a sugar.
- In RNA, the sugar has three oxygen atoms, while in DNA it has two.
- DNA is typically double-stranded, while RNA usually exists as a single strand.
- Nitrogenous bases in DNA include adenine, thymine, cytosine, and guanine; thymine is exclusive to DNA.
- Pyrimidines include cytosine, thymine, and uracil, differentiating these from purines like adenine and guanine.
DNA Structure and Function
- DNA strands are oriented in an antiparallel manner, with the nitrogenous base attached to the sugar's 1' carbon, and the phosphate on the 5' carbon.
- DNA is synthesized in the 5' to 3' direction due to the function of DNA polymerase.
- The sequence of nitrogenous bases in DNA encodes extensive hereditary information.
DNA Replication
- DNA replication is semiconservative; each new DNA double helix comprises one old strand and one new strand.
- Leading strands are synthesized continuously, while lagging strands are formed in short fragments known as Okazaki fragments.
- Telomeres protect the ends of chromosomes but shorten with each replication; telomerase lengthens these.
- Helicase unwinds DNA, creating replication forks, and topoisomerase relieves supercoiling tension.
Experimental Evidence
- Hershey and Chase demonstrated DNA as the genetic material in the T2 phage, using radioactive isotopes to label DNA and proteins.
- A primer forms at specific nucleotides to initiate DNA synthesis, created by primase.
- Nucleic acid synthesis requires energy, provided by the phosphate groups in deoxynucleoside triphosphates (dNTPs).
Implications of Mutations and Enzyme Functions
- Mutations in genes such as dnaB can prevent replication fork formation, halting DNA replication.
- Single-strand binding proteins help stabilize unwound DNA strands during replication.
- Mutations preventing histone production would hinder DNA packaging into nucleosomes, affecting cellular structure.
Summary of Key Enzymes
- DNA polymerase is crucial for DNA synthesis and requires primers to initiate.
- Ligase joins Okazaki fragments into continuous DNA strands post-replication.
- Primase synthesizes short RNA primers for DNA polymerase to extend.
General Concepts
- The abundance of cytosine in DNA relates to the percentage of thymine found, following Chargaff's rules.
- Understanding the role of each enzyme and molecular component is essential in molecular biology, particularly for DNA replication and repair mechanisms.
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