Unit 4.1 DNA
In Figure 12-12, what percentage of thymine would you expect in yeast?
32.9%
Based on Chargaff's rule, the percentage of cytosine in the DNA of the bacterium, S. Lutea in Figure 12-3, should be around
36.6%
Figure 12-2 shows the structure of:
A DNA molecule
What is a bacteriophage?
A bacteriophage is a kind of virus that infects and kills bacteria.
What does DNA do with information?
DNA stores, copies, and transmits information.
What did Avery conclude caused transformation?
DNA was the transforming factor.
Two strands of nucleotide sequences are wound around each other.
Double Helix
The Watson and Crick model of DNA is a(an) ______________ , in which two strands are wound around each other.
Double helix
True/False: A DNA strand that had the sequence TACGTT would have a complimentary strand ATCGAT.
False
True/False: A bacteriophage is larger than a bacterium.
False
True/False: Bacteriophages inject protein into bacteria, altering the bacteria's genetic information.
False
True/False: DNA is a nucleic acid made up of nucleosomes joined into long strands or chains by covalent bonds.
False
True/False: DNA is tightly wrapped around nucleosomes.
False
True/False: In Figure 12-4, the percentages of all four columns should add up to 90.
False
True/False: In eukaryotes, DNA replication proceeds in one direction along the DNA molecule.
False
True/False: The replication of a DNA molecule results in four copies of the same gene.
False
True/False: Watson and Crick discovered that covalent bonds hold base pairs together at the center of a strand of DNA.
False
Which scientist made x-ray diffraction photos of DNA?
Franklin
Identify one difference between prokaryotic and eukaryotic DNA replication.
In prokaryotes, DNA replication starts in one place, and in eukaryotes DNA replication starts in many places.
When is DNA's role in transmitting information most important and why?
It is most important during the formation of reproductive cells, because the loss of any genetic material then means the loss of valuable information for offspring.
Approached the problem of DNA structure by building three-dimensional models to explain the specific structure and properties of DNA. The twisted double-helix model explains Chargaff's rule of base pairing and how the two strands of DNA are held together. DNA is a double helix, in which two strands of nucleotide sequences are wound around each other.
James Watson and Francis Crick
Studied nucleic acids and proteins via X-ray imaging. Was very successful in isolating single fibers of DNA and gathered some data about nucleic acid structure.
Maurice Wilkins
Which of the following best describes Rosalind Franklin's contribution to our understanding of the structure of DNA?
She purified large amounts of DNA, stretched the fibers so the strands were parallel, and used an X-ray beam to produce an image of the molecule.
Enzyme that adds short, repeated DNA sequences to telomeres as the chromosomes are replicated.
Telomerase
What enzyme works to add DNA to ends of chromosomes in rapidly dividing cells such as those found in an embryo, to prevent genes from being lost during replication?
Telomerase
The tips of eukaryotic chromosomes.
Telomere
The tips of chromosomes are known as ______________
Telomeres
Since both the protein and the DNA in Figure 12-13 were both radioactively labeled, how did the scientists determine that DNA was the material that infects the cell?
The DNA was labeled with 32P, and the protein was labeled with 35S. The two labels can be distinguished in the lab.
If the percentage of guanine in the DNA of a certain species decreased by 5 percent over time, what would you expect to have happened to the percentage of adenine in that DNA?
The percentage of adenine would have increased by about 5 percent.
Eukaryotic DNA has more replication forks than prokaryotic DNA, because it has more starting places, or ______________
origins of replication
Rosalind Franklin contributed to the understanding of DNA by...
producing images of DNA molecules using X-rays.
What binds to the prokaryotic chromosome to start DNA replication?
regulatory proteins
Griffith called the process he observed transformation because
the harmless bacteria had been transformed.
In eukaryotes, DNA is located in...
the nucleus.
Griffith's experiments advanced the study of genetics by proving that
there is a chemical that contains genetic information that can be passed from one organism to another.
Because of base pairing in DNA, the percentage of
thymine molecules in DNA is about equal to the percentage of adenine molecules
Which would be greater in a eukaryote than in a prokaryote?
The number of replication forks on a strand of DNA.
In Figure 12-5, what is adding base pairs to the strand?
DNA polymerase
In both prokaryotes and eukaryotes, how many copies of the chromosome are left after replication?
2
In figure 12-8, the percentage of guanine would be ______________.
20%
Based on Chargaff's rule, the percentages of guanine bases in chicken DNA should be around
21.5%
The table in Figure 12-4 shows the percentages of bases in a DNA sample. How much Thymine should you expect to find in the sample?
22%
Approximately what percentage of adenine would you expect to find in herring in Figure 12-12?
27.4%
The matching strand to the one in Figure 12-7, reading from the bottom up, would be ______________ .
AGCT
In Figure 12-5, what nucleotide is going to be added at point 1, opposite from thymine?
Adenine
Showed that when bacteriophages, which are composed of DNA and protein, infect bacteria, their DNA enters the host bacterial cell, but most of their protein does not.
Alfred Hershey and Martha Chase
Two strands in a DNA molecule run in opposite directions.
Antiparallel
How did Avery build on Griffith's work?
Avery repeated Griffith's experiment, and identified the component of the cell that caused transformation.
Which part of the bacteriophage in Figure 12-1 contains genetic material?
B
What do bacteriophages infect?
Bacteria
What property of DNA does bacterial transformation illustrate?
Bacterial DNA can move into another bacteria and function.
What process did Griffith identify in the series of experiments in Figure 12-11?
Bacterial transformation
a kind of virus that infects bacteria
Bacteriophage
What is the chronological order of the important discoveries in the structure of DNA?
Chargaff's ratios of nucleotides --> Franklin makes an X-ray diffraction photo of DNA --> Watson and Crick identify the double helix
Either of the two chains that make up a double helix of DNA, with corresponding positions on the two chains being composed of a pair of complementary bases (A-T and C-G).
Complementary
A prokaryotic cell replicates its ______________ before it splits to form new cells, so that each new cell can have genetic material.
DNA
Deoxyribonucleic acid. Hereditary material.
DNA
In Griffith's experiment, _____________ from the harmful bacteria transferred to the harmless bacteria, and transformed them.
DNA
What stores information in a cell
DNA
Enzyme that separates double-stranded DNA into single strands by breaking hydrogen bonds to allow each strand to be copied.
DNA Helicase
Enzyme that Joins individual nucleotides to synthesize a new, complementary strand of DNA. "Proofreads" each new DNA strand so that each molecule is a near-perfect copy of the original.
DNA Polymerase
The process by which a molecule of DNA is duplicated.
DNA Replication
Why did Hershey and Chase label the viral DNA with radioactive phosphorous and not radioactive sulfur?
DNA contains phosphorus and no sulfur.
In what way is DNA like a book?
DNA has stored information, that can be copied and passed on.
DNA replication is carried out by a series of ______________
Enzymes
Discovered that the percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. The same thing is true for the other two nucleotides, guanine [G] and cytosine [C].
Erwin Chargaff
Bacteria from the S strain were killed by heat, and their remains were added to R strain bacteria. While neither alone harmed the mice, the combination was able to kill its host. Able to isolate both live R and live S strains of pneumococcus from the blood of these dead mice. Concluded that the type R had been "transformed" into the lethal S strain by a "transforming principle" that was somehow part of the dead S strain bacteria. Tested to see whether the bacteria recovered from the sick mice in the experiment would produce smooth or rough colonies in a Petri dish to determine whether the substance transferred from the heat-killed bacteria to the R strain was heritable. Concluded that the transforming factor had to be a gene, because the factor was inherited by offspring of the transformed bacteria.
Frederick Griffith
What would happen to the percentage of G in Figure 12-4 if the percentage of A rose to 25%?
G would drop to 25%
During DNA replication, a DNA strand that has the bases CTAGGT produces a strand with the bases...
GATCCA.
What happens when a piece of DNA is missing?
Genetic information is lost
What did Griffith conclude transformed the harmless bacteria in his experiment?
He concluded that a chemical factor, a gene, had transformed the bacteria.
How did Avery determine that DNA was the molecule that carried the genes for transformation?
He systematically destroyed all the other kinds of molecules besides DNA in the dead-cell mixture before using the mixture to successfully transform harmless bacteria into helpful bacteria.
How did Hershey and Chase know that it was the DNA that had infected the bacterial cells in their experiment?
Hershey and Chase labeled the DNA of a bacteriophage with 32P, and found that after the bacteria were infected with the bacteriophage, the 32P was in the bacteria.
Chromatin contains proteins called ______________
Histones
______________ are weak bonds that hold the two strands of DNA together, but also allow the DNA to separate and replicate.
Hydrogen bonds
adenine, guanine, cytosine, and thymine
Nitrogenous Bases
In Griffith's transformation experiments, the DNA from one organism had to function in another. Did the DNA in the experiments in Figure 12-13 have to make new bacteriophages in the bacteria for the scientists to draw their conclusion? Explain your answer.
No, the DNA did not have to function and make new bacteria for Hershey and Chase to draw their conclusion. The DNA was radioactively labeled, so they could detect it inside the bacteria, even if the DNA did not function.
Built from subunits called nucleotides.
Nucleic Acid
Made up of a nitrogenous base, a deoxyribose sugar, and a phosphate group.
Nucleotide
The structure labeled X in Figure 12-2 is a...
Nucleotide
A sequence of DNA at which replication is initiated on a chromosome, plasmid or virus.
Origin of Replication
Showed that DNA was the "transforming principle." When isolated from one strain of bacteria, DNA was able to transform another strain and confer characteristics onto that second strain. DNA was carrying hereditary information. With DNA as the hereditary molecule, the stage was set for one of the most exciting periods in DNA science: understanding DNA structure and function.
Oswald Avery
The virus in Figure 12-6 is made of two parts the ______________ outside, and the genetic material inside.
Protein coat
Two ring nitrogenous base. Adenine and guanine.
Purine
One ring nitrogenous base. Thymine and cytosine.
Pyrimidine
If covalent bonds held the two strands of nucleotides together, the two strands could not easily separate and ______________.
Replicate
The point at which the two strands of DNA are separated to allow replication of each strand.
Replication Fork
Eukaryotic DNA molecules need to be carefully copied and sorted, especially in the formation of ______________ cells during meiosis.
Reproductive
Used a technique called X-ray diffraction to study the structure of DNA. The X-shaped pattern in the DNA X-ray that the strands in DNA are twisted around each other like the coils of a spring, a shape known as a helix. The angle of the "X" suggested that there were two strands to the molecule. Other clues suggested that the nitrogenous bases of the nucleotides were on the inside of the molecule.
Rosalind Franklin
How did X-ray technology enable scientists to better understand the structure of DNA?
Rosalind Franklin used powerful X-ray beams to make diffraction photographs that gave Watson and Crick the clues they needed to determine DNA's structure.
In which cells is the accurate transmission of information most important?
Sex cells
In the Hershey-Chase experiment, what happened to the bacteria that had been infected by viruses that had radioactive DNA, and to the bacteria that had been infected with viruses that had been marked with radioactive proteins?
The bacteria infected with viruses that had radioactive DNA had become radioactive. The bacteria that had been infected with viruses marked with radioactive proteins were not radioactive.
What can you infer about DNA and the bacterial cell membrane from Griffith's experiments in Figure 12-11?
The bacterial cell membrane can somehow permit very large molecules like DNA to enter the cell.
What structural problem prevents adenine from pairing with guanine?
The bases are both long.
Identify the three main components in the nucleotides shown in Figure 12-9.
The circles are the phosphate group, the pentagons are deoxyribose, and the A and T (adenosine and thymine) are the bases.
Who first did the experiments in Figure 12-13 and what did they confirm?
The experiments were done by Hershey and Chase, and they confirmed that DNA was the genetic material found in genes.
What happened to the bacteria and the mice in experiment 4, in Figure 12-11?
The harmless bacteria were transformed by the heat-killed bacteria, making the harmless bacteria deadly. The mice that were injected with the mixture died.
What would happen if Griffith took some of the bacteria from Experiment 4 in Figure 12-11, grew them on culture plates, killed them with heat, and mixed them with harmless bacteria? How could he test this hypothesis?
The harmless bacteria would be transformed into disease-causing bacteria. To test this hypothesis, he could inject the bacteria in to mice and see if the mice develop pneumonia, or he could grow them on plates and observe the colonies that grow.
What would have happened if Avery had added an enzyme that digested all the nucleic acids to the mixture of heat-killed bacteria, added the mixture to harmless bacteria, and injected the mixture into mice?
The harmless bacteria would not have been transformed, and the mice would have lived.
How were the bacteria in Griffith's experiment transformed?
The harmless living bacteria took in pneumonia-causing DNA (genes) from the heat-killed, pneumonia-causing bacteria, as a result of which the harmless bacteria changed into bacteria that cause pneumonia.
During DNA replication, what two processes must occur before the two strands of a DNA molecule can separate?
The hydrogen bonds between the base pairs must be broken, and the molecule must unwind.
In which experiments in Figure 12-11 do the mice live?
The mice live in experiments 2 and 3.
Identify and explain the role of the molecule, represented by the spheres in Figure 12-10.
The molecule is DNA polymerase, an enzyme that joins individual nucleotides to make a strand of DNA.
What happened when Griffith injected mice with the harmless, R-strain bacteria alone?
The mouse lived.
What are the roles of covalent bonds and hydrogen bonds in the structure of DNA?
The nucleotides in a strand of DNA are joined by covalent bonds between their sugar and phosphate groups, and by hydrogen bonds between the complimentary bases.
If the level of thymine in humans were 34 percent instead of 29.4, would you expect the levels of guanine and cytosine to rise or fall, compared to the values in the table in Figure 12-12?
The values would both fall.
What is the benefit gained if the experiments in Figure 12-13 point to the same conclusions that other scientists already established in other experiments?
These experiments confirm the result that Avery found: that genes are made of DNA. The conclusion is made much stronger because it is reached through two very different sets of experiments.
What would the scientists have found if protein in Figure 12-13 had been the carrier of genetic information?
They would have found that the bacteria contained 35S.
When one type of bacteria is changed permanently into another type.
Transformation
True / False: Chargaff showed that adenine and thymine were found in equal percentages in DNA, but he did not know this was because of base-pairing.
True
True/False: Chargaff contributed to the understanding of DNA by figuring out that the percentages of adenine and thymine were almost equal in any sample of DNA.
True
True/False: If protein had been responsible for carrying genetic information, Hershey and Chase would have observed that their bacteria were marked with radioactive sulfur.
True
True/False: The nucleotides within a DNA strand may have different nitrogenous bases, but all have identical sugar molecules.
True
True/False: Watson and Crick used the image of DNA taken by Franklin in their work to figure out the structure of DNA.
True
True/False: When Griffith mixed heat-killed, harmful bacteria with live, harmless bacteria and injected the mixture into mice, the mice died.
True
True/False: When scientists say that DNA transmits information, they mean that it passes information from one generation to the next.
True
Which scientist(s) figured out that the shape of a DNA molecule is a double helix?
Watson and Crick
In the last row of Figure 12-12, notice that the values adenine and cytosine are very different. If the value for adenine is high, does the value of cytosine have to be low? Explain your answer.
Yes if A is high, C will be low. Adenine pairs with thymine. So, there will be as much thymine as there is adenine. Together, A and T make up about 62 percent of the bases. That means only 38 percent of the bases can be a combination of G and C. So, G and C are each only about 19 percent of the total.
Which of the following forms a base pair with thymine?
adenine
In Figure 12-12, what do the A, T, G and C stand for?
adenine, thymine, guanine, and cytosine
In both prokaryotes and eukaryotes, DNA replication happens...
before cell division.
Which of the following include all the others?
chromosomes
Which of the following is a nucleotide found in DNA?
deoxyribose + phosphate group + cytosine
In Griffith's experiment, he mixed heat-killed S-strain bacteria with live, harmless bacteria from the R-strain. When this mixture was injected into mice, the mice...
developed pneumonia.
DNA makes a good molecule for storing information because...
its bases can be joined together in any order, like the letters of the alphabet can be strung to form different words.
Which bacteria killed the mice in Griffith's transformation experiment?
live, harmless bacteria and heat-killed, harmful bacteria
What is inside a bacteriophage?
nucleic acid
What did Rosalind Franklin contribute to the effort to identify the structure of DNA?
x-ray diffraction photos of the DNA molecule
