Ch 9 hw

Which of the following best describes a clone in the context of genetic modification procedures?

A culture of genetically identical cells -The word clone has a variety of meanings. In the context of genetic modification, clone (as a noun) refers to a culture of identical cells. For example, a clone might refer to a culture of bacterial cells that contain a particular recombinant DNA plasmid, as in, "This is our clone of human insulin." Perhaps confusingly, the word clone is also used as a verb to describe the overall process of using recombinant DNA techniques to create numerous copies of a gene—for example, "The gene for human growth hormone has been cloned."

Which of the following statements about recombinant DNA technology is FALSE? A. It has limited application because genes of interest cannot be moved from one type of cell to another. B. It allows researchers to make many copies of a gene of interest. C. It allows researchers to make protein products of a gene. D. It can be used to screen individuals for many different types of genetic diseases.

A. It has limited application because genes of interest cannot be moved from one type of cell to another. -Recombinant DNA technology is commonly used to move DNA from one type of cell to another.

Which of the following attaches the target gene to a desired location?

DNA ligase

Suppose the thermocycler is INCORRECTLY programmed to omit the 72∘C step in each cycle of an otherwise normal PCR run. Which of the following would most likely occur?

DNA polymerase would synthesize DNA more slowly. -The 72∘C step is the "extension" step, where the thermocycler maximizes DNA polymerase activity. At 55∘C, the polymerase used is significantly slower. Thus, omitting the 72∘C extension step would limit the polymerase to working solely (and slowly) during the 55∘C annealing step. The polymerase has essentially no activity at the 94∘C "denaturation" step because the primers have too much kinetic energy at that temperature to bind to the template strands.

Why is PCR a valuable technique?

PCR creates large amounts of DNA from minute source quantities. -PCR amplifies specific DNA sequences from minute starting concentrations. Thus, PCR is a sensitive technique that can detect the presence of small concentrations of specific DNA. The technique is also useful for creating large quantities of a target DNA sequence for research purposes.

Which statement best describes restriction enzymes?

They are important for cloning applications because they can be used to cut DNA at specific nucleotide sequences.

In general, how might recombinant DNA technology be used to prevent a genetic disorder caused by a mutation in a single gene?

To insert a desirable gene, remove an undesirable gene, or replace a defective gene with a functioning gene.

In PCR, it is important to use Taq DNA polymerase, as opposed to other DNA polymerases. This is because Taq is capable of synthesizing DNA _________.

After exposure to 94∘C -Since PCR protocols necessarily include a 94∘C denaturation step, all of the biomolecules need to remain stable after exposure to this temperature. Most enzymes are damaged at 94∘C, whereas the Taq polymerase is heat-tolerant and stable.

Which of the following best describes how recombinant DNA technology currently helps patients who do NOT produce adequate amounts of growth hormone (hGH)—a condition that otherwise leads to stunted growth?

Bacteria now produce hGH. -To achieve normal growth, these patients need regular injections of hGH (a protein). Before rDNA technology was developed, hGH could be obtained only from the brains of human cadavers, which was both expensive and unsafe. But once the gene for hGH was inserted into bacteria, all of that changed. These bacteria now produce hGH protein that is harvested and purified by pharmaceutical companies. This represents a safe and (relatively) inexpensive source of hGH that has helped thousands of patients.

Which of the following best describes why a vector is used in genetic modification procedures?

Cells usually won't copy an isolated gene sequence. -Vectors, sometimes called gene-cloning vectors, are necessary vehicles for inserting genes of interest into bacteria. A DNA sequence from a human, by itself, won't do much if taken up by a bacterium. DNA molecules with exposed ends (i.e., noncircular) are degraded by bacterial enzymes. Even if the sequence persists long enough to be translated, it still won't be copied because it lacks the necessary sequence to initiate replication. Incorporating the human sequence into a vector provides a means for that sequence to be copied within the bacterium. The recombinant vector copies are then passed on to subsequent daughter cells that make up the clone.

Which of the following pairings of recombinant DNA techniques and applications does NOT match? A. Genetic modification of yeast; production of purified insulin B. Gene editing; using CRISPR to correct a genetic mutation at precise locations C. PCR; making many copies of a segment of DNA D. Gene silencing; production of subunit vaccines

D. Gene silencing; production of subunit vaccines -Gene silencing uses small interfering RNAs to silence the expression of a gene.

Which of the following best describes why PCR protocols contain numerous cycles of the denaturation/annealing/extension steps?

Each cycle of PCR doubles the amount of DNA synthesized, but the number of copies starts out small. Numerous cycles are required to produce a sufficient number of copies -The goal of PCR is to create many copies (amplicons) from a target DNA sequence. Yet PCR is typically used when the amount of source DNA is small. Even though the number of amplicons increases exponentially with each cycle, numerous cycles are necessary to produce a sufficient amount. These late cycles in the protocol are extremely important: Each subsequent PCR cycle ideally creates as many amplicons as were created in all previous cycles combined.

Foreign DNA can be inserted into cells using a variety of different methods. Which method involves the formation of microscopic pores in the cell's membrane?

Electroporation -Microscopic pores in the cell membrane are formed by applying an electrical current. DNA can enter cells through these pores.

Why would a recombinant DNA molecule be inserted into a host cell?

It can be copied, transcribed, and translated into a desired protein.

Recombinant DNA techniques typically involve generating a clone. Why?

Producing a clone generates many copies of the gene of interest -In a strict sense, recombinant DNA (rDNA) is simply a DNA molecule that combines two or more sequences from different sources—for example, a plasmid from a bacterium, and the gene coding for insulin from a human. However, recombinant DNA techniques are typically used to produce more than just a single rDNA molecule. Usually the goal is to produce many copies of the gene—either to harvest those DNA copies, or to produce (and harvest) large amounts of the gene's protein product. In either case, once the vector is taken up by a bacterium, that bacterium is allowed to reproduce naturally. This produces a large number of identical cells—a clone—with each cell containing a copy of the gene of interest.

What does a thermocycler do?

Subjects samples to temperature changes -The thermocycler is responsible for adjusting the reaction tube's temperature. By changing the temperature of the reaction mixture, the various steps of a PCR cycle are accomplished: DNA denaturation, primer annealing, and DNA extension.

How do restriction enzymes cut DNA sequences?

They cut DNA at sites, called recognition sites, that have specific nucleotide sequences.

After the 94∘C step, why must the thermocycler reduce the temperature to 55∘C?

To allow primers to bind to the DNA template strands -After DNA strand separation at 94∘C, the reaction tube temperature is lowered to 55∘C. This allows primers to bind to the DNA template strands. The primers are present in high concentrations, so when the temperature is lowered, the template strands are much more likely to bind to a primer than to re-combine with another template strand

What is the purpose of the polymerase chain reaction (PCR)?

To produce mRNA from a DNA template -The polymerase chain reaction (PCR) is used to amplify small amounts of DNA present in a sample. The resulting DNA may be analyzed in a variety of ways, including separation by gel electrophoresis. PCR is used to diagnose genetic diseases, identify bacteria and viruses, study human evolution, and to solve crimes.

Which of the following best describes the purpose of primers in PCR?

To provide a structure from which DNA can be synthesized -A good DNA structure for promoting replication by DNA polymerase is a single-stranded DNA molecule that is bound to a primer. DNA replication proceeds from the 3'OH of the primer