Question 1

What is the purpose of RNase in a DNA extraction procedure?

Accepted Answer

RNase is used in DNA extraction procedures to remove RNA from the preparation, ensuring that the final product is enriched for DNA.

Question 2

How does eukaryotic DNA differ from prokaryotic DNA?

Accepted Answer

All of the options correctly describe differences between eukaryotic and prokaryotic DNA. Eukaryotic DNA contains introns within mRNA, is wound around histones, has more regulatory sequences, and is more highly coiled compared to prokaryotic DNA.

Question 3

How is RNA different from DNA?

Accepted Answer

All of the options listed are correct differences between RNA and DNA. RNA contains uracil instead of thymine, has ribose sugar instead of deoxyribose, and is typically single-stranded, unlike DNA which is double-stranded.

Question 4

Which procedural step in DNA purification below is required for eukaryotic cells but not prokaryotic cells?

Accepted Answer

Eukaryotic cells have a nucleus that contains their DNA, while prokaryotic cells do not. The step of centrifugation to pellet the nucleus is necessary to separate the nuclear DNA from the rest of the cell components in eukaryotic cells, a step that is not applicable to prokaryotic cells which lack a nucleus.

Question 5

How does chemical degradation DNA sequencing (Maxam- Gilbert)differ from the dideoxy chain termination (Sanger)method?

Accepted Answer

Maxam-Gilbert sequencing, also known as chemical degradation sequencing, involves chemically modifying and then cleaving DNA at specific bases, whereas Sanger sequencing relies on the incorporation of dideoxynucleotides to terminate DNA synthesis at specific bases. The key difference is the method of base identification: chemical modification in Maxam-Gilbert vs. chain termination in Sanger.

Question 6

Which enzyme below links the discontinuous strands being synthesized in the 3' to 5' direction?

Accepted Answer

DNA ligase is responsible for linking (ligating) the discontinuous strands, known as Okazaki fragments, synthesized in the 5' to 3' direction on the lagging strand during DNA replication. This process effectively creates a continuous strand in the 3' to 5' direction complementary to the template.

Question 7

How can DNA be removed from an agarose gel?

Accepted Answer

All the methods listed are techniques used to recover DNA from an agarose gel. Cutting out the band directly removes the DNA segment of interest. Low melting agarose facilitates easier DNA extraction due to its ability to melt at lower temperatures without damaging the DNA. Electroelution is a method where an electric field is used to elute DNA out of the gel. Sephacryl S-300 columns can be used for size-exclusion chromatography to separate DNA fragments from smaller molecules.

Question 8

All of the following can be used to lyse cells except

Accepted Answer

Diethylpyrocarbonate (DEPC) is not used to lyse cells; it is primarily used to inactivate RNases in the preparation of RNA from cells or tissues. The other options (sarkosyl, lysozyme, Triton-X, and guanidium isothiocyanate) are all used in various protocols to lyse cells.

Question 9

How can double- stranded DNA be converted to single stranded DNA?

Accepted Answer

Double-stranded DNA can be converted to single-stranded DNA through all the mentioned methods: formaldehyde can denature proteins and nucleic acids, high temperatures (in excess of 90°C) can break the hydrogen bonds between the DNA strands, and highly alkaline conditions (pH greater than 10.5) can also denature DNA by disrupting hydrogen bonding.

Question 10

When restriction enzymes cut a large strand of DNA, the resulting mixture is called a(n)

Accepted Answer

Restriction enzymes cut DNA into smaller fragments, and the mixture of these fragments is referred to as a digest.

Question 11

Which of the following is true regarding the structure of deoxyribonucleic acid (DNA)?

Accepted Answer

The structure of DNA is indeed a double helix, as discovered by James Watson and Francis Crick in 1953. The sides of the helix are composed of alternating sugar (deoxyribose) and phosphate groups, not sulfate. Regarding the nitrogenous bases, adenine pairs with thymine, and cytosine pairs with guanine, not as described in option C.

Question 12

Each of the following is TRUE regarding mRNA except

Accepted Answer

A single strand of mRNA can be translated by ribosomes multiple times, not just once. This allows for the production of many copies of a protein from a single mRNA molecule.

Question 13

What is the first step in DNA purification from whole cells?

Accepted Answer

The first step in DNA purification from whole cells is cell lysis, which breaks open the cells to release their contents, including DNA.

Question 14

What is the purpose of EDTA in a DNA extraction procedure?

Accepted Answer

EDTA is used in DNA extraction to chelate divalent metal ions like Mg2+ and Ca2+, which are cofactors for DNase enzymes. By binding these ions, EDTA inhibits DNase activity, preventing the degradation of DNA.

Question 15

Each word below is paired correctly with its definition below except

Accepted Answer

Introns are actually portions of mRNA that are not translated into protein; they are removed before translation occurs.

Question 16

In a DNA extraction procedure, what will a mixture of phenol and chloroform extract?

Accepted Answer

Phenol-chloroform extraction is a method used to purify DNA, but it also extracts RNA and proteins by separating them into different phases, allowing for the isolation of DNA from the other molecules.

Question 17

Large size RNA can be precipitated using

Accepted Answer

Lithium chloride is commonly used for the precipitation of large RNA molecules. It effectively separates RNA from DNA and proteins by precipitating RNA at high concentrations, making it a standard method in molecular biology for RNA purification.

Question 18

Why is intact mRNA difficult to purify?

Accepted Answer

All of the options listed contribute to the difficulty in purifying intact mRNA. RNases, which degrade RNA, are ubiquitous: they are naturally present in cells, on human skin, and in the environment. Additionally, structural RNA and tRNA can contaminate preparations, making it challenging to isolate intact mRNA.

Question 19

Which enzyme(s)below is (are)paired correctly with function?

Accepted Answer

The answer of Which enzyme(s)below is (are)paired correctly with function?
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Question 20

Which reagent below is necessary to construct chimeric DNA?

Accepted Answer

Restriction enzymes are necessary to cut DNA at specific sequences, allowing for the construction of chimeric DNA by joining DNA fragments from different sources.

Quiz 12: Hybridization Techniques