DNA Mutation and Repair Flashcards
(39 cards)
N-Terminus nonsense mutation
The very first amino acids translated are those at the N-terminus of the sequence. Therefore, a nonsense mutation there will terminate translation at its beginning and drastically truncate the protein. This presents the most extreme disruption to protein function.
C-Terminus nonsense mutation
A C-terminal nonsense mutation would remove one amino acid at the very C-terminus of the protein, which could result in a minor alteration to protein function.
Conservative Mutation
A conservative mutation results in a new amino acid with similar properties to the original amino acid which it replaced. This type of mutation likely will not disrupt protein folding, and so the majority of protein function is retained.
Non Conservative Mutation
A missense mutation that results in a new amino acid with dissimilar properties to the original amino acid is a non-conservative mutation. The function of a protein is determined by the structure which it folds into, which in turn is determined by the structural properties conferred by each amino acid in its primary sequence. When amino acid characteristics are altered, protein folding is altered, which would likely disrupt protein function.
Silent Mutation
A silent mutation results in no change to primary structure. Therefore, it confers no effect at all on protein function.
A glycine is mutated to an alanine. What would this be classified as?
Conservative mutation
In a nascent protein being translated, what is the first terminus to exit the ribosome?
N-terminus. The protein is translated from N to C. Remember the backbone N-C-C.
Place the following in order of most disruptive to least: Conservative mutation Non-conservative mutation Silent mutation C-terminal nonsense mutation N-terminal nonsense mutation
N-terminal nonsense mutation Non-conservative mutation C-terminal nonsense mutation Conservative mutation Silent mutation
What damage can UV radiation cause to DNA?
Pyrimidine dimers
How are Pyrimidine dimers repaired
Nucleotide excision is the process by which pyrimidine dimers, caused by UV radiation, are excised from DNA and the DNA is subsequently repaired.
How is damage caused by free radicals repaired?
Free radicals can cause damage to DNA, which can be repaired on the level of individual nucleotides. This occurs through a process known as base excision.
How are errors in DNA polymerase repaired?
3-5 exonuclease activity by DNA polymerase. DNA polymerase is responsible for replicating DNA, but also repairing DNA through 3’-to-5’ proofreading activity when it accidentally inserts an incorrect nucleotide.
What are the Stop codons?
TAA, TAG, TGA UAA, UAG, UGA
What are transposons?
Transposons are generally non-coding sequences of DNA which, through enzymatic action, can jump from location to location within the genome. When this jumping activity occurs from one chromosome to another, the resulting transposition is simply transposon genetic material being added to another chromosome with no other genetic material being exchanged. Thus, transposition can be described as unidirectional.
True or false: A normal human cell contains 23 pairs of chromosomes, while a trisomic cell contains 24 pairs.
This statement is false. A normal human cell does have 23 pairs of homologous chromosomes. A trisomic cell also has 23 homologous chromosomes pairs; however, one of those pairs has an extra chromosome copy.
A scientist exposes a cell line to mutagens. He then observes their phenotype to determine if any changes to the cells’ genetic material have occurred. He notices no change to protein expression, activity, or localization. If mutagenesis occurs would DNA polymerase be able to repair it?
DNA polymerase only repairs spontaneous mutations during DNA replication. Other processes, such as nucleotide and base excision, are responsible for repairs following mutagen-induced mutations.
A scientist exposes a cell line to mutagens. He then observes their phenotype to determine if any changes to the cells’ genetic material have occurred. He notices no change to protein expression, activity, or localization. What would be able to repair the mutagenesis if it occured?
Nucelotide and Base excision would be able to repair this
True or false: The cell membrane receptor for insulin is still likely to bind its ligand after a conservative mutation alters an amino acid which codes for part of the insulin receptor’s active site.
This statement is true. Conservative and non-conservative mutations are two types of missense mutations – DNA mutations which alter the amino acid that a 3-letter sequence of DNA codes for. A conservative mutation is a missense mutation which results in the production of a new amino acid bearing similar properties to the original amino acid (e.g. valine to leucine). Non-conservative mutations are missense mutations which result in the production of a new amino acid bearing very different properties to the original amino acid (e.g. valine to aspartic acid). The active site of a protein receptor is highly specific to the charge distribution and shape of its corresponding ligand. Because the mutation to the insulin receptor is conservative, the shape of its active site is likely conserved, and thus its ability to bind to its ligand stays intact.
A scientist exposes a cell line to mutagens. He then observes their phenotype to determine if any changes to the cells’ genetic material have occurred. He notices no change to protein expression, activity, or localization. What could explain these findings?
For protein expression, activity, and localization to remain unchanged, the only possibility is that no amino acids were mutagenized or only conservative mutations occurred. Silent mutations by definition do not change protein structure. Missense mutations, on the other hand, do not necessarily conserve protein structure and activity. However, if only conservative missense mutations occurred, then protein expression, activity, and localization could remain unchanged.
A couple gives birth to a child who has monosomy of chromosome 22, as well as having some genetic material translocated from chromosome 3 to chromosome 4. How would this impact gene expression?
Monosomy is an abnormal condition where one chromosome (of a pair of homologous chromosomes) has gone missing. Having only one copy of chromosome 22, the child will likely express only half as much gene product. As for the genetic material which has undergone translocation, a chromosomal aberration resulting in the location of genes switching from one chromosome to another, the gene copy count remains the same. Therefore, expressivity of genes on chromosomes 3 and 4 will likely remain unaltered.
True or false: If individual DNA bases become oxidized, the appropriate repair process to fix them will be base excision repair.
This statement is true. If DNA damage needs to be repaired on the level of individual nucleotides, then this occurs through a process known as base excision repair.
Scientists create an inactive version of the allele coding for Green Fluorescent Protein (GFP). The inactive allele differs from the wild type allele by only one nucleotide base pair. Scientists obtained a colony of cells which only contained copies of the inactive variant. What methods could scientists could potentially use to create a cell, from their colony of cells, containing a copy of the wild type GFP allele.
DNA mutations can occur as a result of damage to the chemical structure of DNA by environmental agents such as ionizing radiation or UV light, free radical attack, or excessive heating. So you could titrate the cells with a free radical species, If the cells described in the passage are exposed to high energy emissions from radioisotopes (e.g. beta, alpha, or gamma emissions), then the DNA containing an inactive allele may undergo a substitution mutation . Or If the cells described in the passage are exposed to high energy ultraviolet light, then the DNA acted on by the UV rays will likely form pyrimidine dimers, which is not a sufficient condition to reverse a point mutation as described in the passage. However, radicalization of oxygen will create free radicals that can damage DNA and cause point mutations.
How can you induce DNA mutations?
DNA mutations can occur as a result of damage to the chemical structure of DNA by environmental agents such as ionizing radiation or UV light, free radical attack, or excessive heating.
Mutagen induced vs spontaneous DNA mutations
Mutagens are generally environmental agents that can damage our DNA and induce mutations. For example, exposing a person to UV light will induce DNA mutations. However, there is no reason to believe that a person is exposed to more mutagens as they age. However, spontaneous DNA mutations are mutations that result from natural biological processes such as errors in DNA repair. Spontaneous mutations increase as we age, because errors in processes such as DNA repair increase as we age.
