Chapter 8- Bacterial Genetics

natural selection

organisms more "fit" to survive and thrive in a new environmental setting

evolution

mutation and natural selection over time

genotype

sequence of nucleotides in the DNA

phenotype

organisms observable characteristics

mutation (vertical gene transfer)

change in the nucleotide sequence of a cells DNA which is passed on to daughter cells

horizontal gene transfer

A process in which an organism incorporates genetic material from another organism without being the offspring of that organism

what is another name for mutation?

vertical gene transfer

what three chemical mutagens produce mutation through horizontal gene transfer?

plasmids, DNA, and viruses

how do plasmids produce mutation?

through conjugation

how does DNA produce mutation?

through transformation

how do viruses produce mutation?

through transposition and transduction

prototroph

organism that has no other organic requirements for growth other than a source of carbon and energy

auxotroph

organism that requires an organic growth factor

wild type

the typical phenotype of strainds isolated from nature

“normal”

point mutation

mutation in the DNA sequence where one single nucleotide is altered

what are the types of point mutations?

insertion, deletion, base-substitution

base substitution

replication error where one base is substituted for another. DNA replication of that strand results in a point mutation

insertion

one nucleotide is added

deletion

one nucleotide is deleted

what mutations result in frameshift mutations?

insertion and deletion

silent mutation

base substitution has no impact on the amino acid encoded and therefore has no impact on the protein

missense mutation

when a base substitution changes the amino acid that is encoded

nonsense mutation

when a base substitution encodes for a stop codon, stopping translation

frameshift mutation

mutation where nucleotide addition/deletion causes a shift in the reading frame when transcribed and translated

what are the three chemical mutagens that induce mutation?

chemicals that modify nucleobases, base analogs, and intercalating agents

mutagen

something that induces mutations

how do alkylating agents work?

they add an alkyl group to guanine bases to cause mutation

how do base analogs work?

their structure mimics bases but can base pair differently than the right base, causing mutation

how do alkylating agents differ from base analogs?

alkylating agens add an alkyl group to a base, base analogs do not

why do intercalating agents mostly create frameshift mutations?

they insert themselves into the DNA, changing the reading frame

what is an example of a base analog?

AZT (HIV treatment), 5-bromouracil

what is an example of an intercalating agent?

ethidium bromide

what are the two types of radiation damage

UV light and x-rays

what are the three types of chemical mutagens?

chemicals that modify nucelobases (ex- alkylating agents), base analogs, and intercalating agents

how does UV light cause mutation?

it causes covalent bonds to form between adjacent thymine bases on the DNA, causing it to change shape, creating a thymine dimer

thymine dimer

two covalently bound thymines as a result of UV light

what are the two main types of DNA repair?

photoreactivation and excision repair

photoreactivation

enzyme uses the energy of light to break the covalent bond in thymine dimer, restoring DNA sequence back to its original

what is the vector for conjugation?

plasmids

what is the vector for transposition?

transposons

what is another name for transposons?

“jumping genes”

what is present on the borders of insertion sequences?

inverted repeats

how long are inverted repeats

15-20 nucleotides in length

transposase

an enzyme that facilitates the movement of transposable elements, allowing them to “jump” from one location to another within a genome

what is an insertion sequence?

a transposase gene bound to an inverted repeat on each end

what is a composite transposon?

a gene, usually antibiotic resistance or virulence factor, attached to an insertion sequence on each end

conjugation

transfer of genetic material (on plasmids) from donor cell to recipient cell through a pilus that connects the two cells

transposon

the segment of DNA that can “jump” from one location in the genome to another

(also called transposable element?)

what are the spontaneous mutations?

point mutation, frameshift mutation, transposition

what did barbara mcclintock do?

received a nobel prize for her work with zea mays (corn) and its genetics

what form of horizontal gene transfer is seen in the variegation of corns pigment?

transposition

what is the vector for transduction?

virus (phages)

competent

in a physiological state that allows the cell to take up exogenous DNA

intercalating agents generally cause what type of mutation?

frameshift

how does UV light cause damage to DNA

by creating thymine dimers

how do x-rays create DNA damage?

by creating nicks in the DNA backbone

what is the vector for transformation?

naked DNA

direct selection

cells with mutation (resistance gene) do grow on the selective media

replica plating

form of indirect replication where a growth plate is pressed onto velveteen and imprints are then pressed on plates with selective media. the mutants do not grow on the media

indirect selection

cells that are mutants (have resistance gene) do not grow on the selective media