Term
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Definition
o Spontaneous mutations occur every 1x109 bases
o One every 1 million replications for 1000 base pair gene
o Beneficial because generates diversity and drives evolution
o More common with mutagens |
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Term
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Definition
o Substances that increase mutation rate
§ Increase rate 10 to 1000 fold in DNA
§ 1 mutation for every 1000 to 100,000 replication of 1000 base pare gene
o Chemicals and some types of radiation are mutagens
§ Ionizing radiation
§ Low wavelength ultraviolet light |
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Term
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Definition
o X-rays, gamma rays, and high speed subatomic particles
§ X rays and gamma rays – high energy electromagnetic waves 1nm or less in length
· Produced from decomposing atoms and stars like sun
§ High speed subatomic particles like electrons are released by some natural elements and cathode ray tubes AKA particulate radiation
o Ionizing radiation causes OH- in cytoplasm to lose electrons
§ Form hydroxyl free radicals
§ Cause mutations in DNA by altering nucleotide bases
§ Also causes breaks in backbone |
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Term
Mutagenic Low Wavelength Ultraviolet Light |
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Definition
o Electromagnetic energy with wavelengths between 40 and 310 nm
§ 260nm most efficient
§ Adjacent pyrimidine bases in DNA bond together covalently
· Eg Thymine Dimer
§ Pyrmidine dimmers interfere with DNA replication and cause cell death and mutations |
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Term
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Definition
o 3 groups
§ Nucleotide-altering chemicals
§ Frameshift mutagens
§ Nucleotide analogs |
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Term
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Definition
o Structurally similar to nucleotide bases
o 5-bromouracil similar to thymine
§ Incorporated into replicating DNA instead of thymine
§ Pairs with guanin not adenine
§ When replicated, causes base pair mutation in daughter DNA |
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Term
Nucleotide altering Chemicals
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Definition
o Alter nucleotide bases
o Nitrous acid
§ Reacts with amino group of adenine and converts it to carbonyl group
§ Altered adenine (hypoxanthine) pairs with cytosine when replicated
§ Base pair change in daughter |
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Term
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Definition
o Chemicals that insert themselves between bases and cause insertions or deletions when DNA replicated
§ Benzopyrene, coal tars, acridine |
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Term
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Definition
o Light repair enzymes repair pyrimidine dimers
o Dark repair enzymes repair pyrimidine dimers
o Base excision repair enzymes
o Mismatch repair enzymes
o SOS Response
§ Drastic repair mechanism only used when DNA damage is so severe |
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Term
Light and Dark enzyme repair of pyrimidine dimmers
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Definition
o Light repair use light energy to break bond
o Dark repair enzymes excise and replace dimer nucleotides
§ Can be use for any damaged base |
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Term
Base excision repair enzymes
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Definition
o Mutated DNA cut out, polymerase repairs the gap with ligase
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Term
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Definition
| just removes individual nucleotide by recognizing methylated bases |
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Term
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Definition
o Wild types - Commonly found phenotypes
o Mutants can be detected by testing for altered phenotypes
§ Positive selection
§ Negative (indirect) selection |
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Term
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Definition
o Selects mutant cells and rejects non mutants
§ Growing cells on penicillin to find resistance mutants |
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Term
Negative (indirect) selection
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Definition
· Replicate plating
· More tedious
· Often used to isolate auxotroph, mutant has a new nutritional requirement not seen in wild type
o Eg. Isolate mutant that cannot synthesize tryptophan
o Use two medias, one with and without tryptophan
o Grow on tryptophan containing media
o Replicate plate with a membrane on both two new agars, one with and one without tryptophan
Compare |
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Term
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Definition
o Rapid inexpensive test that utilized histidine auxotroph of Salmonella typhimurium to identify mutagens and possible carcinogens
o Expose Salmonella histidine auxotroph to
§ Test chemical and liver enzymes
§ Liver enzymes
o Liver enzymes replicate changes of chemicals our body will produce
o If mutagen it will increase number of mutated bacteria that can synthesize histidine when grown on a histidine deplete plate
o 90% of mutagens are carcinogens
o Mutagens then tested for carcinogenic properties in animals |
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Term
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Definition
o Exchange of genes between two DNA molecules
o Eukaryotes use crossing over of two homologous chromosomes
o Beneficial to eukaryotes because it produces diversity in gametes |
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Term
Gene transfer and recombination in Prokaryotes
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Definition
o Horizontal Gene Transfer - Transfer of DNA between two different cells
o 3 mechanisms
§ Transformation
§ Conjugation
§ Transduction
o All methods have a donor cell giving part of genome to recipient cell
o Recombinant cell – cell that incorporates part of another’s DNA into own chromosome
o Create genetic diversity but also spread antibiotic resistance |
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Term
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Definition
· Transfer of genes from 1 cell to another as naked DNA in solution
· Discovered in 1928 by Frederick Griffith
· Live non-encapsulated S. pneumoniae do not infect, encapsulated do, heat treated encapsulated don’t, however heat treated encapsulated and live non-encapsulated do kill
o Non encapsulated take up dead encapsulated DNA
· 1944 Avery, Macleod, and McCarty showed DNA was transformative agent
o key experiment in showing DNA carried genetic information
· Competent cells – cells that take up DNA in solution
o Not all cells are
Most of DNA taken up is degraded, some is recombined |
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Term
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Definition
o Transfer of genes from one cell to another by virus
o 2 mechanisms in bacteria
§ Generalized transduction – DNA from degraded chromosome of bacteriophage infected bacterial cell is packaged into new phages. Any gene can transfer
§ Specialized transduction – specific bacterial genes are packaged in new phages
o Mechanism
§ Bacteriophages infect
§ Breakdown DNA
§ Repackage some Donor DNA
§ Repackaged DNA used in new phage |
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Term
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Definition
o Transfer of DNA from donor cell to recipient by direct contact
o E coli and other gram-neg bacteria use conjugation with sex pili
§ Sex pili genes on Fertility plasmid
§ F+ cells contain F factor
§ F- cells do not. They are recipients
o Mechanism
§ Sex pili reels another cell in
§ Cells contact
§ Plasmid replicates a strand
§ Transfers daughter strand to recipient
§ New cell is F+
o HFR cells have F factor in chromosome
§ During conjugation, only part of chromosome replicates and is transferred
§ New cell is not F+ but has recombinant DNA |
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Term
Clinical correlation. Conjugation and transformation can spread antibiotic resistant genes
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Definition
o Staphylococcus aureus used to be penicillin sensitive
o Causes 11% of nosocomial infections
o 95% now resistant due to plasmid coding for penicillinase which hydrolyzes penicillin
o 40% methicillin resistant
o MRSA strains usually have several plasmids and are resistant to many antibiotics
o Costly and hard to treat
o Vancomycin treats them now
§ Also used to treat Enterococcus infections responsible for about 8% of nosocomial infections
§ 30% of enterococcus isolates vancomycin resistant due to a plasmid
o Enterococci and Staphylococci can transmit plasmids
Some vancomycin resistant MRSA found |
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Term
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Definition
· Small pieces of DNA 70-40,00 BP) that can move from one location in DNA to another
· Cause frameshift mutations
· Present in genome of all cells but usually inactive
· Ends contain palindrome
o Ex. GAATTC and CTTAAG
· Simplest are called insertion sequences
o Contain transposase enzyme and palindromes at each end
o Recognizes its own repeat sequence
o Duplicates target site
o Inserts a copy of IS1 between target site and copy
· Complex transposons have genes in between two IS1 transposons
· Can cut itself out and bring gene with it
· Another possible way of transferring antibiotic resistance
· 50% of human genome composed of transposons
· Normally inactive due to methylation
· If activated for some reason (like viral infection) can insert itself
Insertions can cause frameshifts, and inactivate an essential gene like a protooncogene and cause cancer |
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