Question 1

How big are the sites recognized by most restriction enzymes?

Accepted Answer

Most restriction enzymes recognize and cut DNA sequences that are 4 to 6 nucleotides in length. This specificity allows for precise cutting at specific sites within the DNA molecule.

Question 2

How sensitive is gel electrophoresis when it is used to separate DNA?

Accepted Answer

Gel electrophoresis is very sensitive and can separate DNA molecules that differ in length by only a single nucleotide. This is because the gel matrix acts as a molecular sieve, allowing smaller molecules to move more easily through the gel and separate from larger molecules. This can be especially useful in genetic testing and analysis, where even small variations in DNA sequence can have significant implications.

Question 3

How can a researcher visualize the DNA fragments separated in an electrophoresis gel?

Accepted Answer

Staining with ethidium bromide is the most common method used to visualize DNA fragments in an electrophoresis gel. Ethidium bromide intercalates between the bases of the DNA molecule and fluoresces under UV light, allowing the researcher to see the fragments.

Question 4

A small, circular, double-stranded DNA molecule that is separate from the main bacterial chromosome is called a ___________.

Accepted Answer

The term plasmid refers to a small, circular, double-stranded DNA molecule that is separate from the main bacterial chromosome. The other options are not correct terms for this definition.

Question 5

Under what circumstances will a component in a solution or a suspension sediment through a centrifugal field?

Accepted Answer

A component will sediment through a centrifugal field if it has a greater density than the surrounding medium. This is because the more dense component will experience a greater force than the surrounding medium, causing it to move towards the bottom of the container.

Question 6

During the gene cloning procedure, what is the purpose of inserting genes into a bacterium that give it resistance to antibiotics?

Accepted Answer

Antibiotic resistance allows researchers to select for those cells that contain a plasmid. By inserting genes that give the bacterium resistance to a particular antibiotic, only those cells that have successfully integrated the recombinant plasmid will be able to survive in the presence of the antibiotic. This allows researchers to easily select and identify cells that have successfully taken up the desired recombinant plasmid.

Question 7

Nowadays, what is the most common method for synthesizing double-stranded molecules of DNA for use in experimental procedures?

Accepted Answer

The most common method for synthesizing double-stranded molecules of DNA for use in experimental procedures is by automated synthesis of two single-stranded DNAs, followed by hybridization. This method is efficient, cost-effective, and allows for customization of the DNA sequence. Options A, B, D, and E do not accurately reflect current methods of DNA synthesis.

Question 8

Nucleic acid hybridization techniques are based on the observation that ______________.

Accepted Answer

Nucleic acid hybridization techniques are based on the observation that two single-stranded nucleic acid molecules of complementary base sequence can form a double-stranded hybrid. This process relies on the complementary base pairing of A-T and G-C, which contributes to the stability of the hybridization. By utilizing this principle, scientists can use hybridization techniques to identify and isolate specific nucleic acid sequences.

Question 9

Which of the following is a technique used to encourage bacteria to take up DNA from the surrounding culture medium?

Accepted Answer

Pretreatment of bacteria with Ca²⁺ ions, followed by a brief heat shock, is a common technique used to encourage bacteria to take up DNA from the surrounding culture medium. The Ca2+ ions neutralize the negatively charged cell membrane, allowing the DNA to pass through, while the brief heat shock creates pores in the membrane, further facilitating DNA uptake.

Question 10

What is the term used to describe a piece of DNA containing sequences derived from more than one organism?

Accepted Answer

Recombinant DNA is the term used to describe a piece of DNA containing sequences derived from more than one organism. This is achieved through techniques such as genetic engineering and gene splicing. The resulting DNA molecule can have desirable traits from both organisms, making it useful for various applications in fields such as biotechnology and medicine.

Question 11

What is the name of the procedure in which single-stranded DNA molecules are separated by electrophoresis, immobilized on a nitrocellulose filter and then hybridized with labeled, single-stranded DNA probes?

Accepted Answer

This procedure is called a Southern blot. The technique is named after Dr. Edwin Southern, who first developed it.

Question 12

Why does the S value alone not provide a measure of molecular mass?

Accepted Answer

The velocity at which a particle moves through a liquid column depends on a number of factors, including shape. Therefore, the s value alone cannot provide a measure of molecular mass as it does not take into account other factors that can influence velocity.

Question 13

What does the change in field direction in pulsed field electrophoresis accomplish?

Accepted Answer

The change in field direction in pulsed field electrophoresis causes the DNA molecules to reorient themselves during their migration, which allows for better separation and resolution of large DNA fragments.

Question 14

In what medium are small RNAs or DNAs of a few hundred nucleotides typically separated through electrophoresis?

Accepted Answer

Small RNAs or DNAs are typically separated through electrophoresis in a polyacrylamide gel. Polyacrylamide gels are able to resolve smaller nucleic acids more effectively than agarose gels due to their tighter pore sizes. Cellulose and paper are not suitable for separating small nucleic acids, and dextran gels are not commonly used in electrophoresis.

Question 15

How are probes labeled with a radioactive isotope detected?

Accepted Answer

Probes labeled with a radioactive isotope can be detected using autoradiography, a technique where the radioactive emissions from the isotope can be visualized on a photographic film or imaging plate. Fluorescence, color changes, SEM, and TEM are not typically used for detecting radioactive probes.

Question 16

When DNA molecules from two different organisms are incubated together, some duplexes are formed by DNA strands from the two species. What indicates that such duplexes are less stable than those between strands from the same organism?

Accepted Answer

The melting temperature (Tm) is the temperature at which half of the DNA duplexes have denatured into single strands. Heterogeneous duplexes, formed by DNA strands from two different organisms, have less stable base pairing due to differences in nucleotide sequence. Therefore, the Tm of heterogeneous duplexes is lower than that of homogeneous duplexes formed by DNA strands from the same organism. Choice A correctly indicates that heterogeneous duplexes melt at lower temperatures than homogeneous duplexes.

Question 17

How are double-stranded hybrids released from hydroxylapatite columns?

Accepted Answer

Double-stranded hybrids can be released from hydroxylapatite columns by increasing the elution buffer concentration. This helps to disrupt the interaction between the hybrid and the column matrix.

Question 18

A term to describe short, single-stranded nucleic acid molecules is _________.

Accepted Answer

Oligonucleotides are short, single-stranded nucleic acid molecules consisting of a few nucleotides, usually less than 50. Mininucleotides and micronucleotides are not commonly used terms in molecular biology, and polynucleotides usually refer to long chains of nucleotides, such as DNA or RNA.

Question 19

What is the technique for producing millions of copies of recombinant DNA with a specific DNA sequence in a short period of time from one or a few initial copies?

Accepted Answer

DNA cloning involves inserting a specific DNA sequence into a vector (such as a plasmid), which can then be introduced into bacteria for replication. This allows for the production of millions of copies of the recombinant DNA in a short period of time. DNA reproduction, replication, transcription, and copying are all general terms that do not specifically refer to the process of creating recombinant DNA.

Question 20

How do DNA molecules place themselves in a CsCl equilibrium gradient?

Accepted Answer

DNA molecules stop permanently at the point in the gradient that equals their buoyant density during centrifugation in a CsCl gradient. This is because each molecule moves until it reaches a position where the density of the gradient matches its own density, and then it no longer experiences a net movement.

Quiz 18: Techniques in Cell and Molecular Biology