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Retroviruses bearing oncogenes will infect cells from their corresponding host animal but will usually not transform them to cancer cells. Yet these retroviruses will readily transform immortalized cells derived from the same organism. Explain.

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Hubert Koch
Hubert KochLv2
29 Sep 2019

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Related questions

1. Which of the following statements about antibiotic resistancein bacteria is NOT true?

Select one:

a. Antibiotic resistance often originates from the microbes thatproduce antibiotics for their own survival.

b. The antibiotic resistance gene can be transmitted to bacteriavia transformation or transduction.

c. Antibiotic resistance cannot be conferred by conjugation asconjugation only affects the fertility of bacteria.

d. Environments where antibiotics are frequently used such ashospitals are under the higher risk of developing antibioticresistance.

e. The plasmid containing the antibiotic resistance gene canpass the genes to genetically unrelated bacteria.

2. You perform interrupted-mating experiments on three Hfrstrains (A, B, and C). Genes are transferred (from last to first)in the following order from each strain: strain A,thi-his-gal-lac-pro; strain B, azi-leu-thr-thi-his; strain C,lac-gal-his-thi-thr. How are the F factors in these strainsoriented?

Select one:

a. A and B are oriented in the same direction.

b. B and C are oriented in the same direction.

c. All of them are oriented in the same direction.

d. A and C are oriented in the same direction.

e. It cannot be determined from the information given.

3.Which of the following statements about retroviruses isfalse?

Select one:

a. All retroviruses contain gag genes whose product forms theviral protein coat.

b. Not all RNA viruses are retroviruses.

c. All retroviruses contain oncogenes, which can induce theformation of tumors.

d. All retroviruses require pol genes, which are critical forretrotranscription.

e. All retroviral genomes have gag, pol, and env genes.

4. Which of the following facts would NOT be considered as anadvantage for using bacteria and viruses for genetic studies?

Select one:

a. Low cost to maintain and little storage space required

b. Rapid reproduction and high progeny number

c. Genomes being small and readily subjected to geneticmanipulation

d. Complete absence of recombination, which maintains theintegrity of genome

e. Haploid genome for expressing mutations

White blood cells called B cells produce proteins that can be used for the treatment of certain illnesses. However, these B cells do not live for very long on their own. To keep the B cells growing for a long time in laboratories, scientists fuse the B cells with cancer cells (fused B-cancer cells) that do grow for a very long time. The particular cancer cells used for the fusion are treated with chemicals that make them unable to produce the nitrogenous bases adenine and guanine, but the B cells with which they are fused do produce these nitrogenous bases. The scientists grow the large fused B-cancer cells in a growth medium that contains necessary nutrients for the cells and includes a source of carbon.
The membranes of both B cells and the cancer cells are largely composed of phospholipids.

Explain how, when the membranes are fused, the polar parts of the phospholipids from one cell will interact with the phospholipids from the other cell and how the nonpolar parts of the phospholipids from one cell will interact with the phospholipids from the other cell.


Class 6: Viruses (and Cells, continued)


Making connections: viruses and microbes Match the cell biology concept (on page 1) with an important application of that concept (on page 2). Then answer the follow-up questions at the bottom of page 2.


Cell Biology concepts
1. Bacteria that cannot construct new cell wall material become fragile and break down.
2. During influenza infection, the viral enzyme neuraminidase is required to release new viruses from the host cell in which they were made. Once released, the new viruses can infect many additional cells.
3. Thermus aquaticus is a bacterium found in hot springs and can live at temperatures up to ~80°C (175°F). It has adapted so that its enzymes are most functional at the elevated temperatures, compared with many organisms’ enzymes that function best ~37°C (98°F).
4. Until the isolation and investigation of retroviruses, scientists thought that RNA could be copied from DNA, but DNA could not be copied from RNA. Research on this class of viruses led to an update to this “Central Dogma” of biology.
5. Some bacteria have adapted, so that the enzymes involved in making cell wall materials have a slightly different shape and can no longer be bound by certain drugs.
6. Rhizobia are bacteria that colonize the roots of certain plants (legumes, including beans and peas). The host plant benefits from the prokaryotes’ ability to “fix” nitrogen, converting N2 from the atmosphere into a form that is usable by the plant.
7. Many species of bacteria contain the enzyme cellulase. More than 10 billion such bacteria and other symbiotic microbes may be found in a single milliliter of material from inside the digestive system of ruminant mammals.
8. Fungi, including those that cause athlete’s foot, use ergosterol to maintain healthy membranes. Animal cells do not make ergosterol, they use a similar lipid – cholesterol.
9. During retrovirus infection, a DNA copy is made of the virus’s RNA genome. A cut is made in the host cell’s DNA and the DNA copy of the viral genome is pasted into the host chromosome by a viral enzyme called integrase.
10. Prokaryotic cells contain smaller ribosomes (“70S” ribosomes) than eukaryotic cells (“80S” ribosomes). Both types of ribosomes synthesize proteins, but the macromolecules they use to do it are somewhat different.



2
Applications
_______ Oseltamivir, also called Tamiflu, binds and inhibits the viral protein neuraminidase.
_______ Clotrimazole is a drug that is used to treat certain infections. It interferes with synthesis of ergosterol, a lipid involved in phospholipid membranes.
_______ Penicillin is a drug that interferes with synthesis of peptidoglycans (these are biological molecules that are part protein and part carbohydrate) that are present in certain cell walls.
_______ HIV is often treated with several drugs that inhibit different parts of the viral replicative cycle. Raltegravir is an example of a drug that interferes with the integration of viral genes into the host cell’s chromosome.
_______ Cows, like other vertebrates, lack the ability to breakdown cellulose. Yet they are able to live on a diet of grass and other vegetation high in cellulose.
_______ Enzymes isolated from extremophiles have been very useful in laboratory research. For example, Taq polymerase facilitates PCR, a revolutionary technique for production of DNAs of particular sequences, which requires cycling reactions through high temperatures.
_______ Plants and animals require nitrogen to make biological macromolecules, however they’re unable to convert atmospheric nitrogen (N2) into a biologically useful form.
_______ Azithromycin is a drug that binds to 70S ribosomes and blocks synthesis of any new proteins.
_______ Methicillin-Resistant Staphylococcus aureus (MRSA) can cause life-threatening infections of the skin and bloodstream. One of the reasons MRSA infections are so serious is that they are resistant to treatment by many antibiotics, including methicillin and penicillin.
_______ The enzyme reverse transcriptase, isolated from retroviruses, is an important tool in molecular biology research. Scientists interested in learning what genes are turned on in particular cells use it to make DNA copies of RNAs they are studying (The DNA copies are useful because they are more stable).


When you have completed the matching activity, answer these follow-up questions:
• What types of infections can be treated with the following drugs?
o Penicillin
o Clotrimazole
o Azithromycin
o Tamiflu
o Raltegravir
• Why are these drugs (above) safe for you to take? That is, why don’t they kill your cells?
• Cancer cells are your own human cells that have become deregulated so that they divide and pile up in an uncontrolled way. Many chemotherapy drugs treat cancer by interfering with cell division and other cell processes.
o Why are there so many more side effects for individuals undergoing chemotherapy than for individuals taking antibiotics?

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