24. Horizontal Gene Transfer: Transformatino Flashcards
How does bacteria reproduce?
- asexually
- a single parent cell divides to produce two daughter cells.
- the daughter cell generation receives a copy of the genetic instructions (DNA) found in the parental generation
Define vertical gene transfer
- when one generation of organisms passes its genetic info to the next generation
- applies to both asexual reproduction and sexual reproduction
What is a mutation?
- a change in DNA sequence
- most occur randomly: the base sequence of an organisms genome changes in a random fashion
- effects can be neutral, harmful, or beneficial for the survival of the organism.
-often inherited by succeeding generations of an organism
Why do asexually reproducing species shows a higher rate of mutations?
- have limited ways to create genetically diverse offspring
What happens during horizontal gene transfers?
- parts of the genetic information in one bacterial cell is transferred to a second bacterial cell
- the two cells do not have a parent-daughter relationship
- can occur between completely unrelated bacterial species
- contributes to the spread of medically important genes; endotoxin genes and antibiotic resistance genes
What are the 3 mechanisms of horizontal gene transfer?
- transformation
- conjugation
- transduction
What occurs during the transformation mechanism of horizontal gene transfer?
- a bacterial cell takes in DNA molecule from its surroundings
- once naked cell is taken up by bacterial, the instructions in the DNA are used by the bacterial cell
How are bacteria classified if they cannot perform transformation?
- naturally competent
- most bacteria cannot perform transformation
- Ex. Haemophilus Influenzae, Neisseria gonorrhoeae
What are plasmids?
- extra molecules of DNA that some bacteria possess
- double-stranded
What is the structure of a plasmid?
- circular; it loops back to connect to itself
- tend to be smaller than bacterial chromosomes= they carry a small number of genes ( <10)
What occurs during the conjugation mechanism of horizontal gene transfer?
-bacterial cell transfers a plasmid to another bacterial cell
What happens during the transduction mechanism of horizontal gene transfer?
- involves viruses (bacteriophages/phages) that infect bacterial cells
- the phage reproduction cycle is called the lytic cycle
Explain the process of the phage lytic cycle
- the lytic cycle starts when a phage particle attaches to a host bacterial cell and injects its DNA into the cell
- the host cell makes numerous copies of the phage DNA and builds many phage proteins
- the new components then assemble into 50 new phage particles which are released when the host bacterial cell lyses.
- the newly built (progeny) phage particles then diffuse through the environment until they encounter more host cells to repeat the cycle
What makes up the plasmid pGLO
- Ori: origin DNA sequence, without it the plasmid DNA could not be replicate by the bacterial cell
- AmpR gene
- GFP (green fluorescent protein)
- araBAD promoter
- AraC gene
What is the function of the AmpR gene of the pGLO plasmid?
- encodes the enzyme beta lactamase; digests ampicillin and other antibiotics in the penicillin family
- bacteria that possess this gene is resistant to ampicillin and related antibiotics
What is the function of the GFP (green fluorescent protein) of the pGLO plasmid
- emits a green light when shined upon by UV light
- acts as a marker protein
What is the function of the araBAD promoter on the pGLO plasmid?
-before a cell with the pGLO plasmid can make the protein GFP, RNA polymerase must attach to the araBAD promoter and transcribe the GFP gene into mRNA
What is the function of the AraC gene of the pGLO plasmid?
- encodes a regulatory protein that by default blocks RNA polymerase and turn off transcription of the GFP gene.
- if the bacterial cells are exposed to the sugar arabinose, this sugar binds to the AraC protein.
- will then change its function to attracting the RNA polymerase
What is the medical significance of horizontal gene transfer?
- It’s primary mechanism for the spread of antibiotic resistance in bacteria, and plays an important role in the evolution of bacteria
- ex. Exotoxin genes, antibiotic resistance genes
What is a promoter? Function?
-A DNA sequence where RNA polymerase attaches to a DNA molecule and then transcribes a portion of the DNA sequence into RNA
E.Coli are not naturally competent…How did we make them competent during our in class lab?
- Heat shocking (ice > 42 degrees C/45 sec > back to ice)
- suspend E.coli cells in a solution containing high concentration of Ca ions
(Allows E. Coli to take in naked DNA from their surroundings)
