Chapter 18 Flashcards
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Why are mutations important?
- sustains life and causes challenges
- genetic variation
- raw material for evolution
- creates diseases and disorders
- to help understand the fundamental biological processes
Adaptive mutation
Genetic variation occurs —> environment determines what is the best fit
Stressful conditions, adaptation necessary to survive through mutation, induced in bacteria
What causes mutations?
- spontaneous replication errors
- spontaneous chemical changes
- chemically induced mutations
- radiation
What are the two major types of mutations?
Somatic mutations
Germ-line mutations
Somatic mutations
Within body cells (i.e. non reproductive cells)
Not passed on to the next generation of offspring
Passed on through mitosis
Germ-line mutations
Cells that make the gametes
Can be passed onto your progeny
Genome shock hypothesis
Types of gene mutations based on their molecular nature
base substitutions
Insertion and deletions
Expanding nucleotide repeats
Base substitution
Transition (purine to purine, pyrimidine to pyrimidine)
Transversion (purine to pyrimidine or vise versa) —> distorts the shape of the helix, therefore the function
Changes a single codon
Insertions and deletions
Frameshift mutations
In-frame mutations
Change protein created for that gene
How different alleles are produced
Can affect STOP codons
Expanding nucleotide repeats
Increase in the number of copies of a set of nucleotides
Fragile X-chromosomes, a characteristic constriction on the long site —> lose that section
Nucleotides
Phenotypic effects of mutations
Forward mutation
Reverse mutation
Missense mutation
Nonsense mutation
Silent mutation
Neutral mutation
Forward mutation
Changes wild type to mutant
Reverse mutation
Change mutation to wild type
Missense mutation
Amino acid to different amino acid
Nonsense mutation
Sense codon (coding for an amino acid) —> stop codon
Neutral mutations
No change in functio
Silent mutations
Codon —> synonymous codon
Synonymous mutation
Change the base but don’t change the amino acid
Phenotypic effects of mutations
Loss-of-function mutation
Gain of function mutation
Lethal mutation
Loss-of-function mutation
Functional protein, mutate sequence, protein no longer works
Gain of function mutation
Rarer
On evolutionary scale, produces more advantageous phenotypes
Lethal mutation
Kills off the organism
Start codons
Methionine, m formal
NOT AMINIO ACIDS
Attract release factors
Stop codons
Central Dogma
DNA —> mRNA —> protein
Suppressor mutation
Hides or suppresses the effect of another mutation
Interagency
Intergenic
Intragenic
Within the same gene containing the mutation that’s suppressed
Intergenic
THINK: international
Across different genes
Mutation in the second gene that hides the mutation in the first gene
What factors affect mutation rates?
Frequency that changes take place in DNA
Probability that if a change occurs, it will be repaired
Probability that the mutation will be detected
Wobble base pairing
- Prokaryotes cannot correct this, eukaryotes can
- Leads to replicated error
- Gets passed on if not corrected, how alleles are formed, through mutations
- Base substitutions in general, not paired perfectly, physically wobble around because the base pairs are mismatched
- does NOT occur after the first replication
- ANOTHER EXAMPLE: tRNA does not match mRNA
Strand slippage
- when a bunch of repeats occur, strand slips
- if it slips on a newly synthesized strand, additional bases occur and bubble out
- in the next replication, there will be an increased number of As andTs
- in the template replication, there will be reduced number on the newly formed strand
Unequal crossing over impact?
Insertions and deletions
What happens if DNA is introduced to chemicals?
DNA bases could be modified/altered look, i.e. radiation
What are the impacts of RADIATION?
- increased mutation rates
- thymine dimer: two thymine bases dimerized and block replication
- SOS system in bacteria: SOS system allows bacterial cells to bypass the replication to block with a mutation prone pathway
Thymine dimer
Two thymines back to back, if radiation occurs, covalent bonds between the two thymine bases, forming the thymine dimer (a bulge)
DNA polymerase can’t tell what base it is
What were the impacts of Hiroshima?
- radiation caused mutations, even after bombs were dropped
How do you repair changes in DNA?
Mismatch repair
Direct repair
Base-exicision repair
Nucleotide-excision repair
Mismatch repair
- mismatched bases and DNA lesions corrected by this
- enzymes cut out a section of the newly synthesized strand of DNA, replacing it with new nucleotides
- Methylation determines
which strand is new - sealed with DNA ligase
Direct repair
Restores the correct structures of altered nucleotides, is exactly how it sounds
Methylation
Base-excision repair (JUST THE BASE NOT THE WHOLE NUCLEOTIDE)
– Glycosylase enzymes recognize and remove
specific types of modified bases FIRST STEP
– The entire nucleotide is then removed, and a section of the polynucleotide strand is replaced SECOND STEP
AP site
Nucleotide without its base
Nucleotide excision repair
– Removes and replaces many types of damaged
DNA that distort the DNA structure.
– The two strands of DNA are separated, held apart by SSBP (single stranded binding proteins), a section of the DNA containing the distortion is removed, DNA polymerase fills in the gap, and DNA ligase seals the filled-in gap.
What repairs changes in DNA?
- can only happen after S phase
- G1 stage mutation —> cell will bring together chromosomes
Homologous directed
Nonhomologous directed
Translesion DNA polymerases
Homologous directed
Nonhomologous directed repair
Tranlesion DNA polymerases
Types of TEs
- retrotransposons CLASS 1
- DNA transposon CLASS 2
Chromatin
Supercoiled DNA
Acetylation
Uncoiling of the chromatin structure, allowing it to be accessed by the transcriptional machinery for the expression of genes
Deacetylation
condensed or closed structure of the chromatin, less transcription occurs
Heterochromatin
Hibernating
Densely packed, transcriptionally INACTIVE DNA
Euchromatin
Less dense, transcriptionally ACTIVE DNA
Carsinogenesis
DEVELOPment of cancer
