Antibiotic Resistance II

Question 1

Transformation

Answer 1

Bacterial uptake of naked DNA from the environment

Question 2

Competence

Answer 2

The ability to take up DNA from the environment

Question 3

What are the 3 fates for uptake DNA in the cell?

Answer 3

1. Degradation
2. Circularization
3. Recombination

Question 4

Exogenote

Answer 4

The molecule of DNA introduced into the recipient

Question 5

Endogenote

Answer 5

Cell’s original chromosome

Question 6

Conjugation

Answer 6

Conjugation involves cell-cell contact, therefore it is sometimes called mating.

The donor cell contains a plasmid. Because all the genes required for conjugation reside on this plasmid, it is called a conjugal plasmid. The recipient does not carry the conjugal plasmid.

Question 7

How does conjugation occur?

Answer 7

The donor cell harbors an R plasmid; the recipient cell does not. Genes carried by the R plasmid encode a sex pilus, which facilitates capture of the recipient cell to form a mating pair.

Now, a conjugation bridge forms between these two cells through which DNA passes. Transfer of DNA occurs through a special form of replication, called transfer replication. Replication initiates at the origin of transfer (oriT) located on the R plasmid and proceeds by the rolling circle mechanism.

Question 8

Transduction

Answer 8

Transduction is form of gene transfer that is mediated by bacterial viruses

Question 9

Adsorbing

Answer 9

Phage binding to a specific receptor on the cell surface

Question 10

Lytic Phage

Answer 10

Lytic (virulent) phage cause lysis of the host cell. The phage genome replicates, proteins are synthesized and assembled into capsids, the replicated genomes are packaged within those capsids, the host cell lyses and the progeny escape into the environment to reiterate the process.

Question 11

Lysogenic Phage

Answer 11

Lysogenic (temperate) phage may initiate a lytic growth process or alternatively enter a quiescent form called a prophage. The host cell goes about its business as usual except that it harbors a latent prophage that it passes harmlessly onto its descendents. The cell is capable of becoming lytic at any time though.

Question 12

What are the two mechanisms where phages can become lysogenic?

Answer 12

• The prophage of certain temperate phage becomes latent by circularizing as an autonomously replicating plasmid.
• The prophage of other temperate phage becomes latent by physically integrating into the host chromosome.

Question 13

Does conjugation require cell to cell contact?

Answer 13

Yes

Question 14

Does transduction require cell to cell contact?

Answer 14

No

Question 15

Can nucleases disrupt transformation?

Answer 15

Yes

Question 16

Can nucleases disrupt transduction?

Answer 16

No as the phage head protects the DNA

Question 17

What are some of the clinical problems that arise with gene exchange?

Answer 17

Antibiotic preparations themselves are often contaminated with DNA that encodes resistance genes. This contamination thus increases the chance of genetic exchange via transformation between antibiotic-producing organisms and the pathogens they are being used to control.

Question 18

Factors that may affect efficient transformation 
A. Nucleases
B. Detergents
C. Cell competence 
D. None of the above 
E. All of the above

Answer 18

E. All of the above

Question 19

Lysogenization of phage can involve:

A. Contact by two bacteria
B. Integration into the bacterial chromosome
C. Nucleases
D. The R plasmid
E. None of the above

Answer 19

B. Integration into the bacterial chromosome