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Point mutation/Base substitution |
A change of one base pair to another in a DNA molecule |
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Missense mutation |
A change of one nucleotide of a triplet within a protein-coding portion of a gene that may result in the creation of a new triplet that codes for a different amino acid in the protein product |
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Nonsense mutation |
The triplet is changed into a stop codon, resulting in the termination of translation of the protein |
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Transition |
If a pyrimidine replaces a pyrimidine, or a purine replaces a purine |
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Transversion |
If a purine replaces a pyrimidine, or vice versa |
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One type of mutation involves the replacement of a purine with a purine, while another causes the replacement of a pyrimidine with a purine. What general terms are associated with these two mutational phenomena respectively? |
transition, transversion |
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True or False: Tautomers of nucleotide bases are isomers that differ from each other in the location of one hydrogen atom in the molecule. |
True |
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Which nucleotide will base‑pair with the enol form of 5‑bromouracil? |
The enol form of 5‑bromouracil forms a base pair with guanine. |
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Which events could result in a frameshift mutation? |
Insertion or deletion of a base (except when in multiples of three) |
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Base analogs |
Compounds that can substitute for purines or pyrimidines during nucleic acid biosynthesis |
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What are two examples of base analogs? |
5-bromouracil (5-BU) – behaves as a thymine analog (forms BrdU bromodeoxyuridine is chemically linked to deoxyribose) 2-amino purine (2-AP) – can act as an analog of adenine |
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Which of the following name two mutagens that would be classified as base analogs? |
5-bromouracil and 2-aminopurine |
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Apurinic sites (AP sites) involve a spontaneous loss of a(n)________ in an intact double-helix DNA molecule. |
purine |
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Depurination |
the loss of one of the nitrogenous bases in an intact double-helical DNA molecule; typically a purine (guanine or adenine) |
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Deamination |
An amino group in cytosine or adenine is converted to a keto group. In these cases, cytosine is converted to uracil, and adenine is changed to hypoxanthine. |
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A mutation that occurs naturally, without exposure to a known mutagen, is called a(n) ________ mutation. |
Spontaneous |
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Considering the electromagnetic spectrum, identify likely mutagens from the following list: radio waves, microwaves, infrared, ultraviolet, X-rays, gamma rays, cosmic rays. |
X-rays, gamma rays, cosmic rays, ultraviolet |
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True or False: The main effect of nitrous acid is to increase the rate of deamination. |
True |
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What are the consequences of having pyrimidine dimers in DNA? |
These dimers distort the DNA structure and result in errors during DNA replication. |
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True or False: Thymine dimers can be repaired by Photoreactivation Repair or Nucleotide Excision Repair. |
True |
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Nucleotide Excision Repair (NER) |
Damaged DNA is removed and new nucleotides are added using the opposite strand as a template. It is used to repair thymine dimers or any damaged segment of DNA. |
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Steps of NER: |
1. The distortion or error in the DNA is recognized. 2. The damaged area is removed by a nuclease. 3. DNA polymerase I fills the gap by inserting nucleotides complementary to the other strand. 4. Ligase seals the final nick in the backbone that remains at the 3′-OH end of the last base inserted. |
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Base Excision Repair (BER) |
Corrects damage to nitrogenous bases |
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Which of the following statements regarding Nucleotide Excision Repair (NER) and Base Excision Repair (BER) is true? |
Both NER and BER involve the removal of one or more damaged bases by a nuclease. |
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True or False: Strand discrimination during the process of DNA repair is based on DNA methylation in E. coli. |
True |
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The process of error correction of mismatched bases carried out by DNA polymerases is called ________. |
Proofreading |
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Recombinational repair is activated when damaged DNA has escaped repair and the distortion disrupts the process of replication. Which gene is responsible recombinational repair? |
recA |
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Which human condition is caused by unrepaired UV-induced lesions? |
xeroderma pigmentosum |
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Which enzyme is responsible for proofreading during replication? |
DNA Polymerase |
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True or False: Bacteria can distinguish between a newly replicated DNA strand and the original template strand because the newly replicated strand is methylated, whereas the original template strand is not. |
False: Methylation occurs shortly after replication, so the original template strand is methylated and the newly replicated DNA strand is not. |
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Which repair system uses the RecA and LexA proteins? |
SOS repair system |
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Transposons, or jumping genes, are DNA elements that move within the genome. In which organismic groups are transposons found? |
all organismic groups |
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True or False: Bacteria can distinguish between a newly replicated DNA strand and the original template strand because the newly replicated strand is methylated, whereas the original template strand is not. |
False: |
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Barbara McClintock discovered mobile elements in corn by analyzing the genetic behavior of two elements, Ds and Ac. The interplay between these two elements has become one of the most interesting stories of discovery in the field of genetics. How do Ds and Ac interact? |
While Ds moves only if Ac is present in the genome, Ac is capable of autonomous movement. |
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Some bacterial transposons, known as Tn elements, are larger than insertion sequences (IS elements) and contain protein-coding genes that have human health significance. What might such a bacterial transposon contain? |
Drug resistance |
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What is a spontaneous mutation? |
Mutations that occur as a result of natural biological and/or chemical processes are considered spontaneous. |
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Why are spontaneous mutations rare? |
They are relatively rare in comparison to induced mutations that are more directed to the physical or chemical properties of DNA. |
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Deaminating agents |
Change cytosine to uracial and adenine to hypoxanthine by converting an amino group to a keto group. |
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Alkylating agents |
Add a methyl or ethyl group to the amino or keto groups of nucleotides, changing base-pair affinities. |
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Base analogs |
Such as 5-bromouracil and 2 amino-purine, are incorporated as thymine and adenine, but base pair with guanine and cytosine respectively |
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Photoactivation repair |
dependent on a photon-activated enzyme that cleaves thymine dimers |
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Excision repair |
the process by which an endonuclease clips out UV-induced dimers, DNA polymerase III fills in the gap, and DNA ligase rejoins the phosphodiester backbone. |
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Recombinational repair |
uses the corresponding region on the undamaged parental strand of the same polarity |
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SOS repair |
a process in E. coli that induces error-prone DNA replication in an effort to fill gaps by inserting random nucleotides. |
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