Prokaryotic Genetics in Nature

Question 1

how do prokaryotes reproduce

Answer 1

binary fission to produce geentically identical offspring

Question 2

how are prokaryotes the masters of adaptation

Answer 2

-prokaryotes are not genetically stagnant
-they mutate, exchange genes etc

Question 3

mutation

Answer 3

-a heritable change in the DNA sequence of a genome
-includes substituions mutations insertions deletions - any change

Question 4

mutant

Answer 4

-organism whose genome carriea a mutation

Question 5

wild type strain

Answer 5

-strain isolates from nature and or one being used as the parental strain i a genetic study
-the term wildtype can also be applied to a single

Question 6

genotype

Answer 6

the complete genetic makeup of an organism

Question 7

phenotype

Answer 7

an observale characteristic of an organism
-there can be many different sorts of phenotypes, metabolic virulence or morphology

Question 8

mutants in prokaryotic genetics

Answer 8

-in prokaryotic genetics we seek to make mutations
-resulting mutant strains have a different genotype compared to the WT
-it is then common to test to see if the wild type mutant strains have different pehnotypes

Question 9

natural mutation rate

Answer 9

10^-6–>10^-7 per 100bp per round of replication for prokaryotes
-average gene is around 100bp so each round of replication will introduce a mutation to a given gene in one of every 1-10million cells
-large enough numbers of bacteria in a population you will likely have some genetic diversity in each gene

Question 10

horizontal gene transfer

Answer 10

-acquiring new genetic material from the environment plays a bugger role than mutations in prokaryotic evolution

Question 11

3 major ways foreign DNA can enter a prokaryotic cell

Answer 11

-transformation, trasnduction, conjugation

Question 12

once inside the cell DNA can

Answer 12

be degreaded or lost, replicate as a seperate entity like phages or plasmids
-be integrates into the chromosome through recombination or transpoition

Question 13

transformation

Answer 13

-free floatinf DNA is incorportes into a recipeient cell and brings about genetic changge
-comes from variety of sources
-often comes from lysed cells within their environment

Question 14

competent

Answer 14

-cell capable of taking up free DNA
-some bacteria and archaea are naturally comptent others are not
-competence is often tightly regulated
-many bacteria can be made competitent in the lab

Question 15

how is DNA captured and cross the membrane in transformation

Answer 15

-DNA from environmnet is captured by pili which retract through outer membrane and cell wall
-one strand of DNA typically degraded and other strand passed through cytoplasmic membrane and into cell via multi protein competance system

Question 16

transduction

Answer 16

-bacteriphage infections
-virus that infects bacterium
-virus DNA is packaged into virions which feature protein coats that protect DNA
-virion binds cell and injects DNA

Question 17

Lytic and lysogenic pathway of transduction

Answer 17

-lytic - phage DNA replicated and new particles produced using host resources. Viruses then lyse host cell released to infect new cell
-lysogenic pathway - viral DNA integrated into host DNA-prophaage. Can be induced triggering the lytic cycle

Question 18

temperate

Answer 18

can operate the lytic or lysogenic pathway

Question 19

two types of transduction

Answer 19

-generalized
-specialized

Question 20

generalized transduction

Answer 20

-during the lytic cycle some hsot cell DNA is accidentally packaged into a viral particle
-this DNa injected into new cell in place of phage DNA

Question 21

specialized transduction

Answer 21

-when prophage is induced its DNA is excised from genome and packaged into phage particles
-sometimes some neighboring DNA is also packaged by mistake
-this DNA can then be injected into new cell by that phage particle

Question 22

conjugation

Answer 22

-horizontal gene tranfer requires cell to cell contact
-typically conjugation is mediated by plasmids called conjugative plasmids, F plamid has served as a host model
-Donor cell used conjugative pilus to grab a reciepnt cell
-type 4 secretion system replicated and tranfers from donor to recipient
-reciepnet strain now carries the F plasmid and can serve as a donor
-this system can be used to transfer genomic DNA from one bacterium to another

Question 23

how can foreign DNA be integrated into the host genome

Answer 23

-genetic recombination
-transposition

Question 24

genetic recombination

Answer 24

-physical exchange of DNA between genetic elements- one important type is homologous recombination

Question 25

homologous recombination

Answer 25

-important for DNA repair mechanism used to repair double strand breaks
-important for horizontal gene transfer
-In a nutshell, similar sequences can get shuffled around using this machiner
-foreign DNA with homology to a region of host chromosome can be insertd into genome in place of or in addition to the native DNA sequence
-important for genpme rearaangemnt such as deletions, duplication, inversion, of segments of DNA

Question 26

transposable elemtns

Answer 26

mobile genetic elements found in almost all species
-contain transposase genes flanked by inverted repeats

Question 27

transposase enzymes are able to

Answer 27

-recognize inverted repeates of DNA sequences
-cleave that DNA to free transpoable element
-cleave another dna (e.g chromosmal DNA)
-insert the transposable elemnt into that DNA
-this process is called transposition

Question 28

conservative vs replicative mechanism

Answer 28

-conservative - move from one place to another
-replicative - transposon remains and a copy is produced and inserted elsewehre

Question 29

transpoable elements figure

Answer 29

Question 30

evolution via horizontal gene transfer

Answer 30

-alot of acquired dna is lost as its not evolutionary useful
-genes that provide a selective advantage will be maintained and can outcompete parental strains that lack this new DNA
-mricobial genomes contain a greta deal of horizontally acquired DNA
-can tell horizontally acuqired DNA by %GC content
-has huge impacts on infectious disease factors like virulence mechanisma nd AMR