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.)
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 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: In eukaryotes, what is the DNA wrapped around?
- polymerase (Incorrect. A polymerase is an enzyme involved in copying nucleic acids.)
- single-stranded binding proteins (Incorrect. DNA does not wrap around single-stranded binding proteins.)
- histones (Correct. DNA wraps around histones in eukaryotes.)
A: histones

Q: DNA is packed into ________ cells by supercoiling.
- eukaryotic (Incorrect. Eukaryotic DNA is not packed by supercoiling.)
- both prokaryotic and eukaryotic (Incorrect. Eukaryotic DNA is not packed by supercoiling.)
- prokaryotic (Correct. Prokaryotic DNA is supercoiled.)
A: prokaryotic

Q: In eukaryotic cells, the ________ region of DNA is usually expressed, while the ________ region is not.
- copied; uncopied (Incorrect. Copying DNA does not have anything to do with expression.)
- nucleosomes; supercoiled (Incorrect. These terms are associated with DNA packaging in eukaryotes vs. prokaryotes.)
- euchromatin; heterochromatin (Correct. Heterochromatin is generally not expressed, and is packed tighter, while euchromatin is expressed.)
A: euchromatin; heterochromatin

Q: Chargaff’s rule tell us that the amount of ________.
- A = C and G = T (Incorrect. This is not the distribution of nucleotides that Chargaff discovered.)
- A = G and C = T (Incorrect. This is not the distribution of nucleotides that Chargaff discovered.)
- A = T and C =G (Correct. Chargaff discovered that the amount of A equals T and G equals C.)
A: A = T and C =G

Q: Chargaff was able to determine that the relative abundance of nucleotides differs between ________.
- individuals (Incorrect. Individuals of the same type will have the same relative abundance of nucleotides.)
- populations (Incorrect. Organisms of the same type will have the same relative abundance of nucleotides, even if they are in different populations.)
- species (Correct. Chargaff’s discovery indicated that species differ in the relative abundance of nucleotides.)
A: species

Q: ________ was the first to discover nucleic acids.
- Griffith (Incorrect. Griffith did contribute to our understanding of DNA, but not in this way.)
- Jeffreys (Incorrect. Jeffreys is credited with the start of modern DNA forensics.)
- Miescher (Correct. Miescher isolated phosphate-rich chemicals from the nuclei of white blood cells. These chemicals were eventually known to be RNA and DNA.)
A: Miescher

Q: Chase and Hershey provided the final evidence that ________.
- hereditary information could be transferred horizontally rather than by descent (Incorrect. This was the work of Griffith.)
- nucleic acids exist (Incorrect. Miescher isolated phosphate-rich chemicals from the nuclei of white blood cells. These chemicals were eventually known to be RNA and DNA.)
- DNA is the genetic material (Correct. Chase and Hershey’s work with a bacteriophage provided the final evidence that DNA, not protein, is the genetic material.)
A: DNA is the genetic material

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: The ends of a chromosome are protected by the presence of ________.
- endcaps (Incorrect. Each end of a chromosome is protected, but not by an ‘endcap’.)
- poly-A tails (Incorrect. Poly-A tails are associated with mRNA strands, not DNA strands.)
- telomeres (Correct. The ends of linear chromosomes are known as telomeres; these sequences appear to have a protective effect on the coding portion of the DNA chromosome.)
A: telomeres

Q: As an organism ages, its telomerase loses activity and the ________ begin to shorten.
- DNA strands (Incorrect. While this is technically correct, telomerase activity has a more specific result than just shorter DNA strands.)
- RNA strands (Incorrect. RNA strands do not shorten with age.)
- telomeres (Correct. Telomerase is the enzyme that specifically adds nucleotides to the 3’ end of DNA, protecting these ends from gradual shortening.)
A: telomeres

Q: Telomerase activity has been detected in ________ cells in spite of considerably shortened telomeres.
- damaged liver (Incorrect. No particular telomerase activity has been detected in damaged liver cells.)
- intestinal (Incorrect. Telomerase reactivation studies in mice have shown improvement in function of the intestine, but this does not relate to shortened telomeres.)
- cancerous (Correct. After telomeres become shortened in cancer cells, telomerase appears to reactivate. Therefore, this enzyme may be a future target of anticancer therapies.)
A: cancerous

Q: Mutations will ________ be inherited.
- always (Incorrect. Mutations that occur in body cells of an adult will not be inherited.)
- never (Incorrect. Mutations that occur in germ cells before reproduction occurs could be inherited.)
- sometimes (Correct. It all depends on when and where a mutation occurs: mutations in somatic cells will not be passed on but mutations in germ cells can be.)
A: sometimes

Q: Mutations that are ________ are considered to be fixed.
- silent (Incorrect. The fact that a mutation does not cause an obvious effect does not make it fixed.)
- detrimental (Incorrect. The fact that a mutation does not cause an ill effect does not make it fixed.)
- not repaired (Correct. Mutations that are not repaired will become the ‘new’ DNA sequence and will be copied each time the mutated sequence replicates.)
A: not repaired

Q: Mutations ________.
- are always bad (Incorrect. Some mutations can cause beneficial impacts, such as conveying a resistance to malaria.)
- are usually beneficial (Incorrect. Mutations can disrupt normal gene activity and result in diseases like cancer or sickle cell anemia.)
- have variable impacts (Correct. Mutations may have a positive, negative, or neutral effect. It all depends on where the mutation is, when it occurs, and what the actual sequence change is.)
A: have variable impacts

Q: Mutations in ________ cells will be passed along to offspring.
- somatic (Incorrect. Mutations in somatic (body) cells will not be passed to offspring.)
- gonadal (Incorrect. While gonadal cells are involved in reproduction, they are still body cells. Mutations in body cells will not be passed to offspring.)
- germ (Correct. Mutations in either egg or sperm (germ) cells will be passed along to the offspring.)
A: germ

Q: Somatic mutations develop ________.
- in a person’s germ cells at a young age (Incorrect. Not all somatic mutations develop at a young age.)
- in various specialized cells at an old age (Incorrect. Not all somatic mutations develop at an old age.)
- over an individual’s life and are present in different cells (Correct. Somatic mutations occur in body cells while an organism is alive.)
A: over an individual’s life and are present in different cells

Q: If there is no family history of a particular disease but a child has the disease as well as the responsible genetic mutation in every cell, then it may have arisen due to a(n) ________ mutation early during development.
- acquired (Incorrect. Acquired mutations do occur in an individual during his/her life but they are not present in every cell.)
- hereditary (Incorrect. If there is no family history of a disease, then it is unlikely to be a hereditary mutation that caused it.)
- de novo (Correct. A de novo (new) mutation that occurs early in development would be present in nearly every cell in a child’s body.)
A: de novo

Q: Somatic mutations during embryonic development lead to ________.
- cancer (Incorrect. Not all mutations lead to cancer.)
- polymorphism (Incorrect. A polymorphism refers to the presence of a mutation in a population, not an individual.)
- mosaicism (Correct. Mosaicism occurs when cells in a single individual have different DNA sequences; a mutation during the later stages of embryonic development would not be present in every cell of the individual.)
A: mosaicism

Q: ________ mutations result from exposure to a hazard such as a chemical.
- Spontaneous (Incorrect. Spontaneous mutations have no known cause.)
- De novo (Incorrect. De novo is not the term used to describe mutations caused by environmental agents.)
- Induced (Correct. The hazardous chemical causes (induces) the mutation.)
A: Induced

Q: Silent mutations have ________.
- limited, but noticeable, effect on an organism (Incorrect. Silent mutations do not have limited effects.)
- extensive effects on an organism (Incorrect. Silent mutations do not have extensive effects.)
- no effect on an organism (Correct. Mutations with no effect on an organism are called ‘silent’.)
A: no effect on an organism

Q: The body will naturally generate ________ mutations.
- induced (Incorrect. Induced mutations arise after exposure to an environmental agent.)
- de novo (Incorrect. De novo just means a mutation is a new one; it does not indicate the cause of a mutation.)
- spontaneous (Correct. Spontaneous mutations have no known cause.)
A: spontaneous

Q: In a transversion mutation, ________.
- adenine may be replaced with a guanine. (Incorrect. This would be a transition mutation.)
- an additional guanine may be inserted before a thymine (Incorrect. This would be an insertion.)
- thymine may be replaced with a guanine (Correct. A transversion replaces a purine with a pyrimidine (or vice versa).)
A: thymine may be replaced with a guanine