Lecture 46 Flashcards
Some of the key differences between bacterial and eukaryotic cells are that bacterial cells do not have _____ (the protein around which eukaryotic DNA is wrapped/condensed), and bacterial cells simultaneously carry out transcription and translation (should make sense since there is no nucleus to isolate transcription process).
Histones
Bacterial genes are typically organized into ______, a transcriptional unit with multiple genes. This is not true for eukaryotic genes which are organized into singletons. Also, bacterial genes do not typically contain ______, so the transcript requires little or no processing before translantion –> another reason these processes can occur simultaneously in bacterial cells.
Operons
Introns
Most bacterial have a single circular dsDNA molecule and plasmids. However, this is not always the case. For example, ______ ______ (causes Lyme disease) has a single _____ dsDNA chromosome, and _____ _____ (causes cholera) has TWO circular dsDNA chromosomes.
Borrelia burgdoferi
Vibrio cholerae
Bacterial DNA (B-DNA) typically has about ____ bp per turn in the relaxed (minimal energy) state. However, the stress of under or over-winding causes supercoiling. Is positively or negatively supercoiled DNA required for transcription?
about 10 bp/turn (10.6)
Negatively (underwound) supercoiled is required for transcription.
Topoisomerase ___ (aka gyrase) is the enzyme responsible for negatively supercoiling B-DNA, while Topoisomerase ___ is responsible for positively supercoiling. An indication that a balance between these two is necessary in bacteria is if you introduce a point mutation in one of the enzymes, the other will acquire a compensatory mutation.
Topoisomerase II
Topoisomerase I
______ is the class of antibiotics that acts on Topoisomerase II –> positive supercoiling cannot be undone –> B-DNA replication cannot continue
Quinolones
The main DNA polymerase in B-DNA replication is DNA Pol ___. The one that fills in the gaps in the lagging strand and is involved in DNA damage repair is DNA Pol __.
Pol III
Pol I
What kind of supercoiling does the action of helicase induce, and what enzyme must act upstream to compensate?
Positive supercoiling is induced, so Topoisomerase II must act upstream to compensate.
Bacterial DNA can acquire genetic variations through both homologous and non-homologous recombination. E. coli require a minimum _____ bp sequence of homology for homologous recombination.
300bp
There are two types of bacterial transposable gene elements (TGEs). the first, an _____ _____, is a single 15-40bp reading frame that codes for transposase and is flanked by inverted repeat sequences (IR-left and IR-right). The second, a ______, is typically larger, about 40bp, and contains basically the same structure but with multiple reading frames that typically include a gene conferring antibiotic resistance.
Insertion Sequence
Transposon
Bacterial cells will always have only one type of flagellar filament. Salmonella flagellar phase variation is a good example of how TGEs cause knock out of gene expression, and thus a variation in phenotype. Normally, the flj__ reading frame (Phase 2/type B flagella) is transcribed along with the flj___ reading frame (translational repressor of flj__). However, the ___ segement of the operon contains the promoter for the flj__ and flj__ genes, and this segment can be inverted –> if it is, the flj__ gene does not produce the Phase 2 flagella, and he flj__ gene does not produce the repressor for the flj__ gene, which codes for the Phase 1/Type C flagella. This flagella phase variation provides a mechanism for evading the host immune response that had initially recognized the Phase 2/Type B flagella.
fljB
fljA
fljC
H segment (hin gene)
fljB and fljA
fljB
fljA
fljC
Griffith’s classic experiment in 1928, using mice and Pneumococcal smooth (S) and rough (R) strains, showed horizontal gene transfer. How did this experiment work?
Mouse was injected with R-strain –> mouse lived
Mouse injected with S-strain –> mouse died
Mouse injected with heat-killed S-strain –> mouse lived
Mouse injected with heat-killed S-strain + live R-strain –> mouse died.
So it must be the case that the R-strain acquired virulence from the heat-killed S-strain.
