Chapter 11: Regulating Gene Expression Flashcards
(31 cards)
What is the actual mutation?
the total damage done to the genome minus the amount of damage that has been repaired by the cellular machinery
Mutations in the germline cells
is passed on to subsequent generations and is heritable
Mutations in the somatic cells
only affects the singular individual
What is a nucleotide sequence mutation
relatively small change to a localized area of the genome. includes the following: Point mutations (base substitutions), insertions/deletions, and duplications
What is a point mutation?
when a single nucleotide in a genome changes at a particular homologous site also known as base substitutions
What is a transition
occurs when a purine is substituted for another purine or a pyrimidine is substituted for another pyrimidine. Therefore there are four possible trasnitions: adenine is substituted for guanine
What is a transversion?
occurs when a purine is substituted for a pyrimidine, or a pyrimidine is substituted for a purine. Therefore, there are eight possible transversions
Note that for any existing base, a total of three base substitutions are possible: one transition and two transversions
What is more common, transversions or transitions?
Transitions are more common than transversions because transversions have a more disruptive effect on the structure of DNA
What is silent or synonymous substitutions?
occurs when a substitution of one nucleotide for another does not result in the formation of a different amino acid because the original codon and the mutant codon code for the same amino acid
What are missense replacement substitutions?
occurs when a substitution of one nucleotide for another results in the formation of a different amino acid but it doesn’t affect any of the other codons. May have no affect or may have a significant effect
What are nonsense replacement substitutions?
occurs when a substitution of one nucleotide for another causes DNA translation to stop prematurely because the mutation codes for a stop codon.
What is a frameshift mutation?
occurs when one or two bases (or multiples thereof) are inserted in a protein-coding sequence and therefore alter the reading frame, affecting all codons downstream from the change
Frameshift mutations can result from both insertions and deletions
Insertion - the addition of extra bases to the DNA sequence
Deletion - the loss of bases from the DNA sequence
What is frameshift causing extensive missense?
This occurs when the deletion or insertion of a nucleotide ruins the codon sequence such that all the downstream codons code for inappropriate amino acids
What is frameshift causing immediate nonsense ?
when the insertion of deletion of a nucleotide ruins the codon sequence and causes translation to stop prematurely
Insertion or deletion of three nucleotides also known as in frame indels
will not cause a frameshift because it will simply add or delete an amino acid from the polypeptide chain. adding and subtracting an amino acid is more deleterious than replacement substitutions because you are adding or subtracting an amino acid rather than just changing one amino acid in the sequence
Mutations can either be spontaneous or induced
Spontaneous -> due to errors in DNA replication
Induced -> due to exposure to chemical or physical mutagens that affect replicating or nonreplicating DNA
What are the causes of spontaneous mutations?
Polymerase base misincorporation -> DNA polymerase has the ability to cut out DNA base sequences that are misplaced in the 3’ to 5’ direction and add back the right base in the 5’ to 3’ direction
Tautomerization -> occurs when two alternative molecular versions of a molecule can readily interconvert. Like adenine bonding to guanine instead of thymine
Spontaneous deamination -> cytosine loses its amine group and converts into uracil
What are the causes of induced mutations?
Base analogs -> They fit into the DNA molecule like regular nucleotides, but they do not have same function
Direct damage to the DNA -> by exposure to UV light
Indirect damage to the DNA -> some metabolic agents can produce oxygen free radicals
What are DNA repair mechanisms
Mismatch repair -> sets of enzymes look back at the DNA that was replicated for any mismatched nucleotides. Mismatch enzymes only want to repair the bases on the daughter strand
Excision repair -> takes out a whole chunk of DNA and replaces it with the correct version
Direct repair -> directly fixes problems in the DNA such as dimers caused by UV
Recombination repair -> homologous recombination used
Transcription-coupled repair -> genes that are transcribed to help resolve problems that occur during transcription
What are the causes of insertions and deletions?
Replication slippage? repetitive nucleotide sequences at the site of replication
Non-homologous recombination -> crossing over at non-homologous chromosomes during Meiosis 1
Nondisjunction
chromosomes fail to separate in either Meiosis 1 or Meiosis 2 which leads to too many chromosomes in gametes (abnormal amount of chromosomes)
Aneuploidy
when an organism gains or loses an entire chromosome
Two types:
Trisomy: three homologous chromosomes of one type . Think down syndrome.
Monosomy: loses one chromosomes. Only has one chromosome of one type
