Horizontal gene transfer

Question 1

What are the horizontal gene transfer steps?

Answer 1

1. Transformation
2. Conjugation
3. Transduction

Question 2

What is horizontal gene transfer transformation?

Answer 2

natural transformation
* depends on if the cell is gram positive or gram negative
* exogenous DNA may be consumed for carbon and energy
* DNA is just laying around and it would do this because it needs to eat and it will consume whatever it can since it is starving and it is all it can eat
* exogenous DNA may be used to repair a cell’s own DNA by recombination (DNA from compatible species)

Question 3

What is horizontal gene transfer transformation in gram positive cells?

Answer 3

• cells secrete competence factor (CF) peptides (species specific), which accumulate and bind onto cell surface sensor protein
• the cell has to respond to the competence factor first that has been secreted via quorum sensing
• since CF binds to a sensor protein on the surface of the cell and it can sense how much CF is in the environment

if it does not sense alot of CF then it is probably alone and sensing its own CF

• they are called CF because when the cell is ready and able to take stuff from the environment then it is competent and in order for it to be competent it needs to secrete CF and get the signal

Once CF binds to the sensor protein then a response regulator (sigma factor) comes in and with this signal genes are encoded and they activate encoding proteins that form transformasome

Question 4

What is horizontal gene transfer transformation in gram negative cells?

Answer 4

• does not depend on cell-cell communication (they have different stimuli that tell them)
• always competent
• competent upon starvation
• exogenous DNA is dragged into the cell by the dynamic expansion and contraction of type IV pili on the cell surface

Question 5

What is quorum sensing

Answer 5

when sufficient signal is detected, an intracellular signal activates a sigma factor

Question 6

What is horizontal gene transfer artificial transformation?

Answer 6

• happens in a lab
• different ways to make it competent
• CaCl2 –> competent cells
• may be followed by heat shock
• electroporation
• DNA is negative and the surface of the cell is also negative
• But that is why we give it CaCl2 treatment

Question 7

What is conjugation

Answer 7

• only some plasmids are self-transferable
• some plasmid cant control the cell because they don’t have the genes

F factor: This forms two origins of replication
OriV (vegetative) used to replicate
OriT (the transfer) used to faciliate rolling circle and it is what is used when conjugation takes place

1. The sex pilus brings the cells together until they are together
2. A protein complex forms called the relaxosome
3. there is a nick at the oriT
4. then rolling circle replication and then the DNA polymerase III makes new DNA strands
5. The two membranes are brought together with a pathway between them
6. The relaxosome cuts the plasmid and relaxes the plasmid, has both a helicase

Question 8

What is transduction

Answer 8

Bacteriophage may carry bacterial DNA from one cell to another

theres two types
1. generalized transduction
2. specialized transduction

Question 9

What is generalized transduction?

Answer 9

• host DNA is accidentally packaged into phage capsids instead of phage DNA (“transducing particles”)
• particle could be infectious
• can move any host gene

steps
1. phage infects cell
2. phage DNA is packaged into some capsids and host DNA is packaged into other capsids
3. phage assembly is complete
4. new DNA may recombine with exisiting chromosome via homologous recombination
5. bacterium lyses and transducing phage containing host DNA, infects another cell

Question 10

what is specalized transduction

Answer 10

• Some phage (phage lambda) integrate into the bacterial chromosome as normal part of the phage life cycle, and remain there, dormant
• They integrate at one specific location in the host chromosome
• Because of the sequence similarities in one spot of the genome
• Later, when the dormant phage is reactivated, it excises its genome from the chromosome
• Aberrant excision can produce a chimeric transducing phage, that carries bacterial genes adjacent to the chromosomal site of integration

Question 11

what is transformasome

Answer 11

it is in the gram positive transformation part and it is made via encoding proteins and its job is to suck up the DNA from the environment