1 | Page
mgy377 Questions and Answers
what is transfer DNA essential for
Ans: 1. driving bacterial evolution
2. spreading adaptive traits
3. generating new gene variant combinations
L21
ways that bacteria acquire new genes
Ans: 1. transformation - uptake from environment
2. conjugation - plasmid transfer from one bacteria to another
3. transduction - spread via bacteriophage
L21
what is griffith expt
Ans: showed that bacteria are able to transfer things to each other.
mouse inoculated with heat killed S strain and live R strain died. shows
that perhaps the S strain transfering something to transform the live R
strain to be able to be virulent
L21
What is the Avery-MacLeod-McCarty experiment?
© 2025 All rights reserved
, 2 | Page
Ans: The Griffith led to the Arthur McClout McCarthy experiment, and it
discovered the transformaing principle of DNA.
-Mixing live R cells with S cell DNA leads to virulent S cells
L21
What is competence?
Ans: a bacteria's ability to take up DNA from the environment and be
transformed (have a genetic change)
Note: in the lab, a phenotypic change is usually needed to detect
successful transfection
L21
what is natural competence? examples?
Ans: Physiological, genetically programmed state permitting efficient
uptake of DNA
gram+:staphylococcus, bacillus
gram-:neisseria gonorrhea, haemophilus influenzae
L21
what is artifically induced competence
Ans: when bacteria are made to be competent via chemical or physical
alteration
L21
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, 3 | Page
describe competence in gram+ bacteria. give example of how it is
CONTROLLED in a bacteria.
Ans: -controlled by Quorem sensing like mechanism. gram+ bacteria
only become competent when there are sufficient other similar bacteria
in the environment to ensure safe uptake of DNA.
In staphylococcus:
-comC produces pre-CSP which is processed and secreted by comAB
transporter as CSP. this occurs at a basal rate in all staph.
-when sufficient staph in environment, CSP in environment will be high
and will reach threshold of comD histidine kinase. This leads to
autophosphorylation and then phosphorylation of comE intracellularly.
-comE-P activates early competence proteins like comAB and comCDE. It
also activates comX, a minor sigma factor for the synthesis of late
competence machinery, RecA, and negative feedback inhibition
L21
describe gram+ competence machinery
Ans: 1. membrane spanning pseudopilis reels in DNA to help attach it to
comEA, a DNA binding protein
2. nuclease induce ds breaks in DNA.
3. comEA brings DNA to comEC, a pore on cytoplasmic membrane
4. comFA, an ATPase attached to comEC, uses proton gradient/ATP
hydrolysis to pull in DNA from 3' end into the cell. comFA also acts as
helicase to unwind and pull in DNA.
5. DNA enters cytoplasm 3' end first through comEC and binds to ssDNA
binding proteins. (5' end is chopped into nucleotides in the cell wall)
6. DNA can be added to genome using RecA homologous recombination,
or can be used as a food source.
L21
Describe transformation in gram- cells
© 2025 All rights reserved
, 4 | Page
Ans: 1. Use DNA uptake Sequence
2. DUS binds to unknown receptor DR
DNA is passed through PilQ secretin complex**
3. DR feeds the DNA to comE in the periplasm
4. comE delivers DNA to comA, cytoplasmic membrane protein
5. DNA is pushed into cell via force similar to gram+
L21
What are the 2 ways to artificially induce competence?
Ans: 1. Calcium Induced
2. Electroporation
L21
describe Calcium Induced competence
Ans: add high concentration calcium ion and then heat shock in cold
temp to induce low efficiency competence
>10% cells become competent
works for dsDNA and plasmids.
good because doesn't require special equipment
exact mechanism not known
L21
describe Electroporation
© 2025 All rights reserved
mgy377 Questions and Answers
what is transfer DNA essential for
Ans: 1. driving bacterial evolution
2. spreading adaptive traits
3. generating new gene variant combinations
L21
ways that bacteria acquire new genes
Ans: 1. transformation - uptake from environment
2. conjugation - plasmid transfer from one bacteria to another
3. transduction - spread via bacteriophage
L21
what is griffith expt
Ans: showed that bacteria are able to transfer things to each other.
mouse inoculated with heat killed S strain and live R strain died. shows
that perhaps the S strain transfering something to transform the live R
strain to be able to be virulent
L21
What is the Avery-MacLeod-McCarty experiment?
© 2025 All rights reserved
, 2 | Page
Ans: The Griffith led to the Arthur McClout McCarthy experiment, and it
discovered the transformaing principle of DNA.
-Mixing live R cells with S cell DNA leads to virulent S cells
L21
What is competence?
Ans: a bacteria's ability to take up DNA from the environment and be
transformed (have a genetic change)
Note: in the lab, a phenotypic change is usually needed to detect
successful transfection
L21
what is natural competence? examples?
Ans: Physiological, genetically programmed state permitting efficient
uptake of DNA
gram+:staphylococcus, bacillus
gram-:neisseria gonorrhea, haemophilus influenzae
L21
what is artifically induced competence
Ans: when bacteria are made to be competent via chemical or physical
alteration
L21
© 2025 All rights reserved
, 3 | Page
describe competence in gram+ bacteria. give example of how it is
CONTROLLED in a bacteria.
Ans: -controlled by Quorem sensing like mechanism. gram+ bacteria
only become competent when there are sufficient other similar bacteria
in the environment to ensure safe uptake of DNA.
In staphylococcus:
-comC produces pre-CSP which is processed and secreted by comAB
transporter as CSP. this occurs at a basal rate in all staph.
-when sufficient staph in environment, CSP in environment will be high
and will reach threshold of comD histidine kinase. This leads to
autophosphorylation and then phosphorylation of comE intracellularly.
-comE-P activates early competence proteins like comAB and comCDE. It
also activates comX, a minor sigma factor for the synthesis of late
competence machinery, RecA, and negative feedback inhibition
L21
describe gram+ competence machinery
Ans: 1. membrane spanning pseudopilis reels in DNA to help attach it to
comEA, a DNA binding protein
2. nuclease induce ds breaks in DNA.
3. comEA brings DNA to comEC, a pore on cytoplasmic membrane
4. comFA, an ATPase attached to comEC, uses proton gradient/ATP
hydrolysis to pull in DNA from 3' end into the cell. comFA also acts as
helicase to unwind and pull in DNA.
5. DNA enters cytoplasm 3' end first through comEC and binds to ssDNA
binding proteins. (5' end is chopped into nucleotides in the cell wall)
6. DNA can be added to genome using RecA homologous recombination,
or can be used as a food source.
L21
Describe transformation in gram- cells
© 2025 All rights reserved
, 4 | Page
Ans: 1. Use DNA uptake Sequence
2. DUS binds to unknown receptor DR
DNA is passed through PilQ secretin complex**
3. DR feeds the DNA to comE in the periplasm
4. comE delivers DNA to comA, cytoplasmic membrane protein
5. DNA is pushed into cell via force similar to gram+
L21
What are the 2 ways to artificially induce competence?
Ans: 1. Calcium Induced
2. Electroporation
L21
describe Calcium Induced competence
Ans: add high concentration calcium ion and then heat shock in cold
temp to induce low efficiency competence
>10% cells become competent
works for dsDNA and plasmids.
good because doesn't require special equipment
exact mechanism not known
L21
describe Electroporation
© 2025 All rights reserved
