chapter 8: microbial genetics Flashcards
gene
segments of DNA (usually proteins)
chromosome
structures with DNA that contain genes & carry hereditary info; string of DNA wrapped around proteins that give the nucleic acid bases structure
DNA
deoxyribose nucleic acid; macromolecule that carries genetic information; typically double stranded
how are genes encoded?
by three codons which code as a specific amino acid
what do genes encode?
the synthesis of a gene product, either RNA or protein
gene expression
controlled by operons; process by which the information encoded in a gene is used to direct the assembly of a protein molecule
constitutive gene expression
gene transcribed at a constant level; expressed at a fixed rate
regulated gene expression
some switch to turn gene on or off (repressor / transcription factors)
central dogma
DNA transcribed → RNA translated→ protein
what makes retroviruses different?
they reverse transcribe RNA → DNA
“semiconservative nature of DNA replication”
DNA is half old and half new when it is replicated
vertical gene transfer
genes from parents; flow of genetic info from one generation to the next
horizontal gene transfer
organisms can pick up genetic traits from sources other than parents
ex) virus picks up your genes and gives it to another host “transduction”; tree “tumors”; important for evolution
bacterial operon
group of genes turned on by single promoter
promoter
binds RNA polymerase + DNA
operator
genetic sequences recognized by oppressor; allows proteins responsible for transcription (operons) to attach to the DNA sequence
repressible operon
sticks to DNA and prevents gene from being expressed; blocks transcription; default position is on
inducible operon
requires an inducer; default position is off
phenotype
“physical” expression of genes
genotype
genetic makeup of an organism
base substitution / point mutation
change in one base in DNA; single DNA base pair is altered
frameshift mutation
insertion / deletion of one or more nucleotide pairs; shifts the translational “reading frame”
missense mutation
base substitution results in change in an amino acid; the meaning of the genetic material gets changed
nonsense mutation
base substitution results in nonsense (stop) codon
nucleotide excision repair
cut out the nonmethylated strand where there is damage and then use the methylated strand to write in a complementary copy
photolyases
DNA repair enzyme that uses visible light to break thymine dimers (abnormal chemical bond of thymine bases in DNA) apart; mostly used for repairing damage from ultraviolet radiation
non-homologous end joining (NHEJ)
mechanism for repairing double-strand breaks in the sugar-phosphate backbone of DNA; “non-homologous” =does not use a template to place broken piece back on
homologous recombination (HR)
mechanism for repairing double-strand breaks in the sugar-phosphate backbone of DNA which uses a homologous / sister chromosome as a template to know where to piece the broken pieces of the DNA back together
positive (direct) selection
killing off everything that does not match what you want to keep; mutant cells grow / appear different that unmutated cells
negative (indirect) selection
killing off cells that you want; mutant cells that cannot grow or perform a certain function
selective media
allows certain organisms to grow while inhibiting the growth of other organisms
replica plating
technique in which one or more secondary petri dishes containing different selective growth media are inoculated with the same colonies of microorganisms from a primary plate by stamping
ex) in selective, colony will die; in nonselective, colony will live
ames test
tests for carcinogenicity by growing bacteria that require histidine without histidine
transformation (horizontal gene transfer)
genes transferred from one bacterium to another as “naked” DNA
transduction (horizontal gene transfer)
DNA is transferred from a donor cell to a recipient via a bacteriophage (virus)
conjugation (horizontal gene transfer)
plasmids transferred from one bacterium to another; requires cell-to-cell contact via pili
plasmid
circle of DNA that have an origin of replication; code for proteins that enhance pathogenicity of a bacterium
transposon
section of DNA that can cut and paste itself from one region to another; “jumping genes”; contains insertion sequences (IS) that codes for transposae that cuts and reseals DNA
