Lecture 12 Flashcards
What is a temperature-sensitive mutation?
A conditional mutation that produces the mutant phenotype in one (restrictive or non-permissive) temperature range and the wild-type phenotype in another (permissive) temperature range
What is a missense mutation?
A point mutation in which a single nucleotide change results in a codon that codes for a different amino acid
What is a nonsense mutation?
A point mutation in a sequence of DNA that results in a premature stop codon, or a nonsense codon in the transcribed mRNA, and in a truncated, incomplete, and usually nonfunctional protein product
What is a silent mutation?
DNA mutations that do not significantly alter the phenotype of the organism in which they occur. Silent mutations can occur in non-coding regions, or they may occur within exons
What are the four types of base substitution mutations?
Missense, nonsense, silent, and temperature-sensitive mutations
What are the types of small addition/deletion mutations?
Frameshift and in-frame mutations
What is a frameshift mutation?
An addition or deletion of a single or multiple nucleotides (not a multiple of 3) that causes a shift in the codons produced by genetic material
What is an in-frame mutation?
Addition or deletion mutations that result in no change in the codons produced by the genetic material, except for the affect area
What problems can arise from having a mutation in the promoter region of DNA?
1) If the region that binds transcription initiation factors is mutated, the factors (such as TFIIA, TFIID and IFIIB) will not bind and transcription will not take place
2) If the activator region upstream from the promoter region is mutated, the activating factors will not bind and transcription may take place at a slower rate or not at all
3) If the inhibitor region is mutated, the inhibitor factors will not bind and constitutive transcription will occur
What is constitutive transcription?
A gene that is transcribed continually compared to a facultative gene which is only transcribed as needed. Occurs when inhibitors are not present or a mutation disallows the inhibitors from acting during transcription
What is a splicing mutation?
A splice site mutation is a genetic mutation that inserts, deletes or changes a number of nucleotides in the specific site at which splicing of an intron takes place during the processing of precursor messenger RNA into mature messenger RNA. The abolishment of the splicing site results in one or more introns remaining in mature mRNA and may lead to the production of aberrant proteins. For example, mutations that cause the incorrect splicing of β-globin mRNA are responsible of some cases of β-thalassemia
What is genotypic reversion?
A point mutation can be reversed by another point mutation, in which the nucleotide is changed back to its original state (true reversion) or by second-site reversion (a complementary mutation elsewhere that results in regained gene functionality)
What is genotypic suppression?
A suppressor mutation is a second mutation that alleviates or reverts the phenotypic effects of an already existing mutation. Genetic suppression therefore restores the phenotype seen prior to the original background mutation
What is the difference between intragenic and intergenic suppression?
Intragenic occurs on the same gene as in the initial mutation did, while intergenic occurs on a different gene than the initial mutation did
What is polymerase fidelity?
The fidelity of a DNA polymerase is the result of accurate replication of a desired template. Specifically, this involves multiple steps, including the ability to read a template strand, select the appropriate nucleoside triphosphate and insert the correct nucleotide at the 3´ primer terminus, such that Watson-Crick base pairing is maintained. In addition to effective discrimination of correct versus incorrect nucleotide incorporation, some DNA polymerases possess a 3´→5´ exonuclease activity. This activity, known as “proofreading”, is used to excise incorrectly incorporated mononucleotides that are then replaced with the correct nucleotide. High-fidelity PCR utilizes DNA polymerases that couple low misincorporation rates with proofreading activity to give faithful replication of the target DNA of interest.
What is deamination and what is its function?
Deamination is the removal of an amine group from a molecule. Enzymes that catalyse this reaction are called deaminases. In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are broken down if there is an excess of protein intake. The amino group is removed from the amino acid and converted to ammonia.
What is depurination?
Depurination is a chemical reaction of purine deoxyribonucleosides, deoxyadenosine and deoxyguanosine, and ribonucleosides, adenosine or guanosine, in which the β-N-glycosidic bond is hydrolytically cleaved releasing a nucleic base, adenine or guanine, respectively. The second product of depurination of deoxyribonucleosides and ribonucleosides is sugar, 2’-deoxyribose and ribose, respectively. When depurination occurs with DNA, it leads to the formation of apurinic site and results in an alteration of the structure. Depurination is known to play a major role in cancer initiation.
