Deck 8: The Structure, Replication, and Chromosomal Organization of Dna

Question 1

Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years.
After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didn't give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruce's back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate.
At the study clinic, Bruce learned that he would be in a Phase III trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.
What are Bruce's options at this point

Answer 1

Mr. B has two options at this point. They are either to go for chemotherapy or for DNA (deoxyribonucleic acid) vaccination.
DNA vaccination is a process of injecting genetically engineered DNA, which triggers immunological response against the diseased condition. The triggered immune system produces huge number of antibodies that destroy damaged cells in particular. DNA vaccines have more advantages over conventional vaccines.
Chemotherapy is a process of treating cancer by using chemical substances. Anti-cancer drugs are used in this process against different types of cancers. Those drugs can also be used against multiple sclerosis, psoriasis, systemic lupus erythematosus, etc.
The main action of chemotherapeutic drugs is to kill cells that divide at rapid rate. Therefore, there are wide chances of killing the cells that divide rapidly even under normal circumstances. For example, bone marrow, hair follicles, digestive tract.
Therefore, among the two options Mr. B has wished for DNA vaccination rather than for chemotherapy.

Question 2

Until 1944, which cellular component was thought to carry genetic information

A) carbohydrate
B) nucleic acid
C) protein
D) chromatin
E) lipid

Answer 2

A. Carbohydrates are chemical compounds that make up sugars and starches. Most scientists before 1944 were aware carbohydrates were used by cells as food not genetic information.
b. Nucleic acid most scientist before the 1944 DNA experiments had little idea the actual role of DNA.
c. Protein scientist suspected protein carried genetic information because protein makes up all the cell and ultimately biological function. Furthermore, similar species carry similar protein, so it would be suspected that proteins were inherited. This is the answer.
d. Chromatin chromatin is DNA wrapped up in histone proteins; their function was unknown at the time.
e. Lipid scientist was aware that lipid made up a cell's membrane structure and organelle membrane but not thought as genetic information.

Question 3

Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years.
After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didn't give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruce's back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate.
At the study clinic, Bruce learned that he would be in a Phase III trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.
Should he reconsider and try chemotherapy instead

Answer 3

Phase III trials are the trials that compare the currently available standard treatment with a new treatment. The standard treatment for cancer is chemotherapy and the new treatment available is DNA (deoxyribonucleic acid) vaccination. Chemotherapy is the process in which chemical drugs are used to treat cancer, whereas in DNA vaccination genetically engineered DNA will be injected into the patient.
The injected DNA allows synthesis of a protein that triggers immune system to yield large number of antibodies against the diseased cells. These antibodies will destroy the cancerous cells wherever they occur in the body. Thus, this treatment has long lasting effect once the engineered DNA is injected.
Chemotherapy has wide chances of getting side effects, whereas DNA vaccination does not have such effects. Therefore, Mr. B need not reconsider about the treatment. DNA vaccination is much better, as it removes all the damaged or diseased cells from the body using body's own immune system.

Question 4

Why do you think nucleic acids were originally not considered to be carriers of genetic information

Question 5

Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years.
After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didn't give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruce's back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate.
At the study clinic, Bruce learned that he would be in a Phase III trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.
Should he go ahead and enroll on the chance that he would receive the DNA vaccine and that it would be more effective than chemotherapy

Question 6

The experiments of Avery and his coworkers led to the conclusion that:
a. bacterial transformation occurs only in the laboratory
b. capsule proteins can attach to uncoated cells
c. DNA is the transforming agent and is the genetic material
d. transformation is an isolated phenomenon in E. coli
e. DNA must be complexed with protein in bacterial chromosomes

Question 7

In the experiments of Avery, MacLeod, and McCarty, what was the purpose of treating the transforming extract with enzymes

Question 8

Read the following experiment and interpret the results to form your conclusion. Experimental data: S bacteria were heat killed and cell extracts were isolated. The extracts contained cellular components, including lipids, proteins, DNA, and RNA. The extracts were mixed with live R bacteria and then injected together into mice along with various enzymes (proteases, RNAses, and DNAses). Proteases degrade proteins, RNAses degrade RNA, and DNAses degrade DNA. Based on these results, what is the transforming principle

Question 9

Recently, scientists discovered that a rare disorder called polkadotism is caused by a bacterial strain, polkadotiae. Mice injected with this strain (P) develop polka dots on their skin. Heat-killed P bacteria and live D bacteria, a nonvirulent strain, do not produce polka dots when injected separately into mice. However, when a mixture of heat-killed P cells and live D cells were injected together, the mice developed polka dots. What process explains this result Describe what is happening in the mouse to cause this outcome.

Question 10

List the pyrimidine bases, the purine bases, and the base-pairing rules for DNA.

Question 11

In analyzing the base composition of a DNA sample, a student loses the information on pyrimidine content. The purine content is A 5 27% and G 5 23%. Using Chargaff's rule, reconstruct the missing data and list the base composition of the DNA sample.

Question 12

The basic building blocks of nucleic acids are:

A) phosphate groups
B) nucleotides
C) ribose sugars
D) amino acids
E) purine bases

Question 13

Adenine is a:

A) nucleoside
B) purine
C) pyrimidine
D) nucleotide
E) base

Question 14

Polynucleotide chains have a 5' and a 3' end. Which groups are found at each of these ends

A) 5' sugars, 3' phosphates
B) 3' OH, 5' phosphates
C) 3' base, 5' phosphates
D) 5' base, 3' OH
E) 5' phosphates, 3' bases

Question 15

DNA contains many hydrogen bonds. Are hydrogen bonds stronger or weaker than covalent bonds What are the consequences of this difference in strength

Question 16

Watson and Crick received the Nobel Prize for:

A) generating X-ray crystallographic data of DNA structure
B) establishing that DNA replication is semiconservative
C) solving the structure of DNA
D) proving that DNA is the genetic material
E) showing that the amount of A equals the amount of T

Question 17

State the properties of the Watson-Crick model of DNA in the following categories:
a. number of polynucleotide chains
b. polarity (running in same direction or opposite directions)
c. bases on interior or exterior of molecule
d. sugar/phosphate on interior or exterior of molecule
e. which bases pair with which
f. right- or left-handed helix

Question 18

Using Figures 1 and 2 as a guide, draw a dinucleotide composed of C and A. Next to this, draw the complementary dinucleotide in an antiparallel fashion. Connect the dinucleotides with the appropriate hydrogen bonds.
FIGURE 1 Nucleotides can be joined together to form chains called polynucleotides. Polynucleotides are polar molecules with a 59 end (at the phosphate group) and a 39 end (at the sugar group). An RNA polynucleotide is shown at the left , and a DNA polynucleotide is shown at the right.
FIGURE 2 The two polynucleotide chains in DNA run in opposite directions. The left strand runs 59 to 39, and the right strand runs 39 to 59. The base sequences in each strand are complementary. An A in one strand pairs with a T in the other strand, and a C in one strand is paired with a G in the opposite strand.

Question 19

A beginning genetics student is attempting to complete an assignment to draw a base pair from a DNA molecule. The drawing is incomplete, and the student does not know how to finish. He asks for your advice. The assignment sheet shows that the drawing is to contain three hydrogen bonds, a purine, and a pyrimidine. From your knowledge of the pairing rules and the number of hydrogen bonds in A/T and G/C base pairs, what base pair do you help the student draw

Question 20

Chemical analysis shows that a nucleic acid sample contains A, U, C, and G. Is this DNA or RNA Why

Question 21

How does DNA differ from RNA with respect to the following characteristics
a. number of chains
b. bases used
c. sugar used

Question 22

RNA is ribonucleic acid, and DNA is deoxyribonucleic acid. What exactly is deoxygenated about DNA

Question 23

What is the function of DNA polymerase

A) It degrades DNA in cells.
B) It adds RNA nucleotides to a new strand.
C) It coils DNA around histones to form chromosomes.
D) It adds DNA nucleotides to a replicating strand.
E) None of these.

Question 24

Which of the following statements is not true about DNA replication

A) It occurs during the M phase of the cell cycle.
B) It makes a sister chromatid.
C) It denatures DNA strands.
D) It occurs semiconservatively.
E) It follows base-pairing rules.

Question 25

Make the complementary strand for the following DNA template and label both strands as 59 to 39 or 39 to 59 (P 5 phosphate in the diagram). Draw an arrow showing the direction of synthesis of the new strand. How many hydrogen bonds are in this double strand of DNA template: P-AGGCTCG-OH new strand:

Question 26

How does DNA replication occur in a precise manner to ensure that identical genetic information is put into the new chromatid See Figures 3 and 4.
FIGURE 3 In DNA replication, the two polynucleotide strands uncoil, and each is a template for synthesizing a new strand. A replicated DNA molecule contains one new strand and one old strand. This mechanism is called semiconservative replication.
FIGURE 4 A close-up look at the process of DNA replication. (a) As the strands uncoil, bases are added to the newly synthesized strand by complementary base pairing with bases in the template strand. The new bases are linked together by DNA polymerase. (b) DNA synthesis can proceed only in the 5' 3' direction; newly synthesized DNA on one template strand is made in short segments and linked together by the enzyme DNA ligase.
a) Each DNA strand has two ends: one with a 59 carbon, and one with a 39 carbon. DNA polymerase can add nucleotides only at the 39 carbon. In other words, DNA synthesis proceeds only in the 59 to 39 direction.
b) Because DNA synthesis proceeds only in the 5' to 3' direction, only one of the DNA strands can be assembled in a single piece. The other new DNA strand forms in short segments, which are called Okazaki fragments after the two scientists who discovered them. DNA ligase joins the fragments into a continuous strand of DNA.

Question 27

Nucleosomes are complexes of:

A) RNA and DNA
B) RNA and histone
C) histones and DNA
D) DNA, RNA, and protein
E) amino acids and DNA

Question 28

Discuss the levels of chromosomal organization with reference to the following terms:
a. nucleotide
b. DNA double helix
c. histones
d. nucleosomes
e. chromatin