Title: DNA Structure and Replication
Course: Question Banks

Q: If DNA of a particular species was analyzed and it was found that it contains 23 percent A, what would be the percentage of G?
- 23% (Incorrect. Remember that A base pairs with T (not G), so this would be the amount of T present.)
- 37% (Incorrect. Check your math on this one.)
- 27% (Correct. G base pairs with C so together they must make up 54%, with each contributing half that amount.)
A: 27%

Q: For the DNA sequence of the 5′-3′ strand ATGGAATT, choose the complementary sequence.
- 3′-CGAACCGG-5′ (Incorrect. The base pairing is wrong in this sequence.)
- 3′-TTAAGGTA-5′ (Incorrect. This is the reverse of the strand above, not the complement.)
- 3′-TACCTTAA-5′ (Correct. This is the mirror image (complement) of the strand above and follows the base pairing rules.)
A: 3′-TACCTTAA-5′

Q: The pairing of ________ is responsible for the diameter of a DNA double helix.
- pentose to purine (Incorrect. A purine is a nucleotide that is based off a pentose sugar. But this does not specify the diameter of the DNA double helix.)
- pentose to pyrimidine (Incorrect. A pyrimidine is a nucleotide that is based off a pentose sugar. But this does not specify the diameter of the DNA double helix.)
- purine to pyrimidine (Correct. Only the pairing between a purine and pyrimidine explains the uniform 2nm diameter.)
A: purine to pyrimidine

Q: The sugar-phosphate backbone of a DNA double helix is joined together by ________ bonds.
- hydrogen (Incorrect. Hydrogen bonds join the complementary base pairs.)
- hydroxyl (Incorrect. The phosphate of one residue is linked to the hydroxyl of the next, but it is not by a hydroxyl bond.)
- phosphodiester (Correct. Phosphodiester bonds link the nucleotides that make up the backbone of DNA.)
A: phosphodiester

Q: Genetic information is stored in the ________ of a DNA molecule.
- base pairing (Incorrect. Base pairing provides a structural and protective function to a DNA molecule.)
- length (Incorrect. The length of DNA does not store the genetic information.)
- sequence of nucleotides (Correct. The sequence of A, T, G, and C provides all the information needed to build a living organism.)
A: sequence of nucleotides

Q: Accurate copying of the DNA molecule with each replication and reliable expression of the stored information in a DNA strand are required in order for ________ to function as a storage molecule for genetic information.
- RNA (Incorrect. RNA is not a storage molecule for genetic information.)
- nuclei (Incorrect. Nuclei are not storage molecules.)
- DNA (Correct. DNA must be copied faithfully and expressed as functional protein or it is no use as a storage molecule for genetic information.)
A: DNA

Q: In order to change ________ of an organism, one would only need to change the DNA sequence.
- the karyotype (Incorrect. Small changes in the DNA sequence would have no impact on the karyotype.)
- nucleotides (Incorrect. Changing the DNA sequence = changing the nucleotides.)
- an observable characteristic (Correct. Nucleotides must be changed to have an impact on observable characteristics of an organism.)
A: an observable characteristic

Q: Information stored in DNA must be ________ into specific functional products.
- copied (Incorrect. DNA is copied but just into more DNA (storage) molecules.)
- converted (Incorrect. This is not the terminology used to describe how DNA is turned into a functional product.)
- translated (Correct. DNA is translated into proteins.)
A: translated

Q: Meselson and Stahl's experiments proved that DNA replicates by which mode?
- conservative (Incorrect. This is not the mode of DNA replication indicated by the experimental results.)
- dispersive (Incorrect. This is not the mode of DNA replication indicated by the experimental results.)
- semi-conservative (Correct. Based on the distribution of DNA containing a "heavy" isotope of nitrogen, Meselson and Stahl determined DNA replication is semi-conservative.)
A: semi-conservative

Q: Meselson and Stahl used "heavy" ________ in their replication studies because ________.
- phosphate; it is present in the sugar-phosphate backbone (Incorrect. While this logic is correct, phosphate is also present in a lot of other molecules in cells (including proteins). This would have complicated the experimental data.)
- sulfur; it makes up amino acids (Incorrect. Sulfur is present in amino acids, but not in DNA. Therefore it would not help in a DNA study.)
- nitrogen; it is present in nucleotides (Correct. The majority of the nitrogen in cells is in the DNA. This makes nitrogen most useful for a DNA study.)
A: nitrogen; it is present in nucleotides

Q: In which direction does DNA replication take place?
- both 5′–3′ and 3′–5′ at once (Incorrect. DNA replication is unidirectional.)
- 3′–5′ (Incorrect. DNA replication does not move in a 3’ to 5’ direction.)
- 5′–3′ (Correct. DNA replication proceeds 5’ to 3’.)
A: 5′–3′

Q: The enzyme helicase ________.
- rejoins DNA strands (Incorrect. This is the function of ligase.)
- synthesizes the new DNA strand (Incorrect. This is the function of polymerase.)
- separates the 2 DNA strands of the double helix (Correct. Helicase is responsible for unwinding the DNA helix.)
A: separates the 2 DNA strands of the double helix

Q: The enzyme ________ adds of new bases to a growing DNA strand.
- ligase (Incorrect. Ligase rejoins DNA strands.)
- helicase (Incorrect. Helicase is responsible for unwinding the DNA helix.)
- polymerase (Correct. Polymerase synthesizes the new DNA strand.)
A: polymerase

Q: The anchor used to start a new DNA strand is called a ________.
- starter (Incorrect. There is no starter in DNA replication.)
- trigger (Incorrect. There is no trigger in DNA replication.)
- primer (Correct. A new DNA strand is primed by a short sequence called a primer.)
A: primer

Q: In DNA ________, the newest base is reread before another is added to ensure the DNA strand is being copied accurately.
- verification (Incorrect. This is not the term for rereading newly added bases in a growing DNA strand.)
- copy-editing (Incorrect. This is not the term for rereading newly added bases in a growing DNA strand.)
- proofreading (Correct. DNA polymerase reads the newly added base before adding the next one in a growing DNA strand.)
A: proofreading

Q: Mismatch repair occurs when ________.
- enzymes cut a DNA strand on each side of an incorrect base (Incorrect. This is nucleotide excision repair.)
- two nucleotides switch places in the middle of DNA replication (Incorrect. Nucleotides do not switch places after they have been added to the DNA strand.)
- a single nucleotide is replaced after DNA replication is complete (Correct. DNA mismatch repair occurs after DNA replication is complete when incorrect nucleotides are removed and replaced in the newly synthesized DNA strand.)
A: a single nucleotide is replaced after DNA replication is complete

Q: Nucleotide excision repair occurs when ________.
- a single nucleotide is replaced after DNA replication is complete (Incorrect. Nucleotide excision repair does not replace just a single nucleotide.)
- two nucleotides switch places in the middle of DNA replication (Incorrect. Nucleotides do not switch places after they have been added to the DNA strand.)
- enzymes cut a DNA strand on each side of an incorrect base (Correct. Nucleotide excision repair results in several bases of DNA being removed, so that an entire segment must be replaced after excision occurs.)
A: enzymes cut a DNA strand on each side of an incorrect base

Q: Viruses utilize ________ as their genetic material.
- proteins (Incorrect. Viruses are not infectious proteins.)
- carbohydrates (Incorrect. Viruses do not use carbohydrates for their genetic material.)
- nucleic acids (Correct. Viruses use either DNA or RNA as their genetic material.)
A: nucleic acids

Q: During the ________ phase, a bacteriophage is incorporated into the host genome.
- lytic (Incorrect. During the lytic phase, the host cell ruptures, releasing the bacteriophages.)
- prophage (Incorrect. When the phage DNA is incorporated into the host, it is called a prophage. But this is not a phase of the lifecycle.)
- lysogenic (Correct. During the lysogenic phase, phage DNA exists in the host genome as a prophage.)
A: lysogenic

Q: During the lysogenic phase, a bacteriophage ________.
- ruptures the host cell (Incorrect. This occurs during the lytic phase.)
- is retroviral (Incorrect. A retrovirus is a type of virus, not a phase of the bacteriophage lifecycle.)
- incorporates into the host genome (Correct. During the lysogenic phase, phage DNA exists in the host genome as a prophage.)
A: incorporates into the host genome

Q: ________ infections cause no symptoms.
- Acute (Incorrect. Acute diseases/infections get increasingly worse for a short period before being eliminated from the body.)
- Chronic (Incorrect. Chronic infections are long-term but this does not indicate the level of symptoms.)
- Asymptomatic (Correct. Asymptomatic infections cause no symptoms even though the virus is being produced by the host.)
A: Asymptomatic

Q: Prions are unique in that they contain ________.
- no proteins (Incorrect. Prions are made of proteins.)
- triple stranded DNA (Incorrect. Prions do not have triple stranded DNA.)
- no nucleic acids (Correct. Prions are infectious protein particles with no nucleic acids.)
A: no nucleic acids

Q: ________ are responsible for kuru.
- Viroids (Incorrect. Viroids infect plants, not animals. Kuru is a human (animal) disease.)
- Viruses (Incorrect. Viruses do not cause kuru.)
- Prions (Correct. Kuru is a prion disease in some humans of Papua New Guinea)
A: Prions

Q: Prion infections cause ________.
- misfolds in brain tissue (Incorrect. This is not the result of a prion infection.)
- abnormal division of brain cells (Incorrect. This is not the result of a prion infection.)
- lesions in brains (Correct. These holes give rise to spongiform encephalopathies, because the brain takes on a “spongy” appearance.)
A: lesions in brains

Q: ________ are spread by eating infected tissue.
- Viroids (Incorrect. Viroids infect plants only, so eating infected plants would have no impact.)
- Viruses (Incorrect. Some viruses can be spread through infected tissue but not all.)
- Prions (Correct. Prions can be transmitted by eating infected animal tissue.)
A: Prions

Q: Viroids infect ________.
- nervous tissue (Incorrect. Prions infect nervous tissue.)
- bacteria (Incorrect. Viroids do not infect bacteria.)
- plant cells (Correct. Viroids are simpler than viruses but are capable of infecting plant cells.)
A: plant cells

Q: Viroids differ from viruses in that they ________.
- can reproduce independently (Incorrect. Viroids must be reproduced by a host cell.)
- contain both DNA and RNA (Incorrect. Viroids do not contain DNA.)
- do not produce proteins (Correct. Viroids appear to just be infectious RNA particles.)
A: do not produce proteins

Q: ________ have the largest impact on the agriculture industry.
- Prions (Incorrect. To date prions have had a limited impact on livestock; since they only infect animals, they have no impact on the plant side of agriculture.)
- Viruses (Incorrect. Viruses have their largest impact directly on human health.)
- Viroids (Correct. The plants that most viroids infect are agriculture crops like potatoes, cucumbers, and avocados. Some do infect floral plants but not many.)
A: Viroids